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Boucher MC, Sun P, Keresztes I, Harrell LE, Marohn JA. The Landau-Zener-Stückelberg-Majorana transition in the T 2 ≪ T 1 limit. J Magn Reson 2023; 354:107523. [PMID: 37625202 DOI: 10.1016/j.jmr.2023.107523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 07/08/2023] [Accepted: 07/09/2023] [Indexed: 08/27/2023]
Abstract
Landau-Zener-Stückelberg-Majorana (LZSM) transitions occur between quantum states when parameters in the system's Hamiltonian are varied continuously and rapidly. In magnetic resonance, losses in adiabatic rapid passage can be understood using the physics of LZSM transitions. Most treatments of LZSM transitions ignore the T2 dephasing of coherences, however. Motivated by ongoing work in magnetic resonance force microscopy, we employ the Bloch equations, coordinate transformation, and the Magnus expansion to derive expressions for the final magnetization following a rapid field sweep at fixed irradiation intensity that include T2 losses. Our derivation introduces an inversion-function, Fourier transform method for numerically evaluating highly oscillatory integrals. Expressions for the final magnetization are given for low and high irradiation intensity, valid in the T2≪T1 limit. Analytical results are compared to numerical simulations and nuclear magnetic resonance experiments. Our relatively straightforward calculation reproduces semiquantitatively the well known LZSM result in the T2→0 limit.
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Affiliation(s)
- Michael C Boucher
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Peter Sun
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Ivan Keresztes
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Lee E Harrell
- Department of Physics and Nuclear Engineering, U.S. Military Academy, West Point, NY 10996, USA
| | - John A Marohn
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
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2
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Ivanov KL, Snadin AV, Kiryutin AS, Lukzen NN. Analytical solution for the inverting pulses with constant adiabaticity. J Magn Reson 2022; 343:107298. [PMID: 36116162 DOI: 10.1016/j.jmr.2022.107298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Revised: 09/01/2022] [Accepted: 09/02/2022] [Indexed: 06/15/2023]
Abstract
The exact solution was found for inverting pulses with constant adiabaticity for spin ½. The analytical relationship between the time-varying frequency of the microwave resonant field (or RF field in the case of NMR) and its amplitude time dependence such that the adiabaticity parameter remains constant for the single isochromat throughout the pulse is found. Comparison with EPR (hyperbolic tangent)-(hyperbolic secant) pulse method was carried out. On the basis of the analytical solution the pulses with different dependences of the microwave field amplitude conserving the constant adiabaticity have been constructed. The pulses exhibit rather sharp inversion selectivity that can be used in the field of EPR, NMR and MRI.
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Affiliation(s)
- Konstantin L Ivanov
- International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia
| | - Alexander V Snadin
- International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia
| | - Alexei S Kiryutin
- International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia
| | - Nikita N Lukzen
- International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia.
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3
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Verstraete JB, Foroozandeh M. Improved design of frequency-swept pulse sequences. J Magn Reson 2022; 336:107146. [PMID: 35144158 DOI: 10.1016/j.jmr.2022.107146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Revised: 01/11/2022] [Accepted: 01/12/2022] [Indexed: 06/14/2023]
Abstract
Frequency-swept pulses are extensively used in magnetic resonance spectroscopic techniques for the robust manipulation of spins across wide ranges of offset frequencies in the presence of B1 field variations. Nevertheless, designing pulse sequences consisting of multiple frequency-swept pulses can be challenging, as they often require specific timings and parameter tweaking. In the present work we discuss a simple and general approach for constructing such sequences. We present new and improved pulse sequences for applications including broadband B1-tolerant CPMG (CHORUS-CPMG), broadband chirped excitation with suppression of homonuclear J-modulation (PROCHORUS), and the further compression of frequency-swept pulse sequences by superposition of pulses which reduces pulse sequence durations by 25-40%. All sequence design strategies are accompanied by mathematical presentations, experimental results, and supporting simulations.
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Graf C, Rund A, Aigner CS, Stollberger R. Accuracy and performance analysis for Bloch and Bloch-McConnell simulation methods. J Magn Reson 2021; 329:107011. [PMID: 34147025 DOI: 10.1016/j.jmr.2021.107011] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 05/12/2021] [Accepted: 05/26/2021] [Indexed: 06/12/2023]
Abstract
PURPOSE To introduce new solution methods for the Bloch and Bloch-McConnell equations and compare them quantitatively to different known approaches. THEORY AND METHODS A new exact solution per time step is derived by means of eigenvalues and generalized eigenvectors. Fast numerical solution methods based on asymmetric and symmetric operator splitting, which are already known for the Bloch equations, are extended to the Bloch-McConnell equations. Those methods are compared to other numerical methods including spin domain, one-step and multi-step methods, and matrix exponential. Error metrics are introduced based on the exact solution method, which allows to assess the accuracy of each solution method quantitatively for arbitrary example data. RESULTS Accuracy and performance properties for nine different solution methods are analyzed and compared in extensive numerical experiments including various examples for non-selective and slice-selective MR imaging applications. The accuracy of the methods heavily varies, in particular for short relaxation times and long pulse durations. CONCLUSION In absence of relaxation effects, the numerical results confirm the rotation matrices approach as accurate and computationally efficient Bloch solution method. Otherwise, as well as for the Bloch-McConnell equations, symmetric operator splitting methods are recommended due to their excellent numerical accuracy paired with efficient run time.
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Affiliation(s)
- Christina Graf
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | - Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria
| | | | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria.
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Crawley T, Palmer III A. Approximate Representations of Shaped Pulses Using the Homotopy Analysis Method. Magn Reson (Gott) 2021; 2:175-186. [PMID: 34414395 PMCID: PMC8372782 DOI: 10.5194/mr-2-175-2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 03/23/2021] [Indexed: 06/13/2023]
Abstract
The evolution of nuclear spin magnetization during a radiofrequency pulse in the absence of relaxation or coupling interactions can be described by three Euler angles. The Euler angles in turn can be obtained from the solution of a Riccati differential equation; however, analytic solutions exist only for rectangular and chirp pulses. The Homotopy Analysis Method is used to obtain new approximate solutions to the Riccati equation for shaped radiofrequency pulses in NMR spectroscopy. The results of even relatively low orders of approximation are highly accurate and can be calculated very efficiently. The results are extended in a second application of the Homotopy Analysis Method to represent relaxation as a perturbation of the magnetization trajectory calculated in the absence of relaxation. The Homotopy Analysis Method is powerful and flexible and is likely to have other applications in magnetic resonance.
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Affiliation(s)
- Timothy Crawley
- Department of Biochemistry and Molecular Biophysics, Columbia
University, 630 West 168th Street, New York, NY 10032, United States
| | - Arthur G. Palmer III
- Department of Biochemistry and Molecular Biophysics, Columbia
University, 630 West 168th Street, New York, NY 10032, United States
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Paul S, Shankar Ray D. Vibrational resonance in a driven two-level quantum system, linear and nonlinear response. Philos Trans A Math Phys Eng Sci 2021; 379:20200231. [PMID: 33455551 DOI: 10.1098/rsta.2020.0231] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/17/2020] [Indexed: 05/22/2023]
Abstract
We consider a two-level quantum system interacting with two classical time-periodic electromagnetic fields. The frequency of one of the fields far exceeds that of the other. The effect of the high-frequency field can be averaged out of the dynamics to realize an effective transition frequency of the field-dressed two-level system. We examine the linear response, second harmonic response and Stokes and anti-Stokes Raman response of the dressed two-level system, to the weak frequency field. The vibrational resonance enhancement in each case is demonstrated for optimal strength of the high-frequency field. Our theoretical scheme is corroborated by full numerical simulation of the two-level, two-field dynamics governed by loss-free Bloch equations. We suggest that quantum optics can offer an interesting arena for the study of the vibrational resonance. This article is part of the theme issue 'Vibrational and stochastic resonance in driven nonlinear systems (part 1)'.
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Affiliation(s)
- Shibashis Paul
- Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Deb Shankar Ray
- Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
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Hibe Y, Noda Y, Takegoshi K, Takeda K. Rapid survey of nuclear quadrupole resonance by broadband excitation with comb modulation and dual-mode acquisition. Phys Chem Chem Phys 2020; 22:25584-25592. [PMID: 33146658 DOI: 10.1039/d0cp05309k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Nuclear Quadrupole Resonance (NQR) provides spectra carrying information as to the electric-field gradient around nuclei with a spin quantum number I > 1/2 and offers helpful clues toward characterizing the electronic structure of materials of chemical interest. A major challenge in NQR is finding hitherto unknown resonance frequencies, which can scatter over a wide range, requiring time consuming repetitive measurements with stepwise frequency increments. Here, we report on an efficient, two-step NQR protocol by bringing rapid-scan and frequency-comb together. In the first step, wideband excitation and simultaneous signal acquisition, both realized by a non-adiabatic, frequency-swept hyperbolic secant (HS) pulse with comb modulation, offers a clue for the existence/absence of the resonance within the frequency region under investigation. When and only when the sign of the resonance has been detected, the second step is implemented to compensate the limited detection bandwidth of the first and to unambiguously determine the NQR frequency. We also study the spin dynamics under the comb-modulated HS pulse by numerical simulations, and experimentally demonstrate the feasibility of the proposed scheme, which is referred to as RApid-Scan with GApped excitation with Dual-mode Operation (RASGADO) NQR.
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Affiliation(s)
- Yuta Hibe
- Division of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan.
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Dacko M, Lange T. Flexible MEGA editing scheme with asymmetric adiabatic pulses applied for T 2 measurement of lactate in human brain. Magn Reson Med 2020; 85:1160-1174. [PMID: 32975334 DOI: 10.1002/mrm.28500] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Revised: 08/03/2020] [Accepted: 08/05/2020] [Indexed: 11/09/2022]
Abstract
PURPOSE A flexible MEGA editing scheme which decouples the editing efficiency from TE is proposed and the utility of asymmetric adiabatic pulses for this new technique is explored. It is demonstrated that the method enables robust T 2 measurement of lactate in healthy human brain. METHODS The proposed variation of the MEGA scheme applies editing pulses in both acquired spectra, ensuring that the difference in J-evolution of the target resonance leads to maximal signal yield in the difference spectrum for arbitrary TE. A MEGA-sLASER sequence is augmented with asymmetric adiabatic editing pulses for enhanced flexibility and immunity to B 1 + miscalibration and inhomogeneities. The technique is validated and optimized for flexible lactate editing via a simple analytical model, numerical simulations and in vitro experiments. The T 2 relaxation constant of lactate is determined in vivo via multiple-TE measurements with the proposed method and a dedicated postprocessing and quantification approach. RESULTS Asymmetric adiabatic editing pulses improve robustness and facilitate efficient J-editing in sequences or protocols with strong timing constraints. Single voxel measurements using the proposed MEGA scheme in the occipital cortex of six healthy subjects yield a relaxation constant of T 2 = 171 ± 19 ms for the methyl resonance of lactate at a field strength of 3T. CONCLUSIONS The proposed MEGA editing scheme allows for novel kinds of J-editing experiments and promises to be an asset to robust T 2 measurement of lactate and potentially other J-coupled metabolites in vivo.
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Affiliation(s)
- Michael Dacko
- Center for Diagnostic and Therapeutic Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Thomas Lange
- Center for Diagnostic and Therapeutic Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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9
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Abstract
It is shown that adiabatic decoupling is extremely flexible and achieves very high figure of merit (decoupling bandwidth to RF amplitude ratio) exceeding that of the conventional composite pulse decoupling (CPD) methods by more than an order of magnitude. This comes at a price of increasingly intrusive cycling sidebands when the decoupling bandwidth exceeds that of the CPD methods. Following a brief review of the decoupling theory and modes of adiabatic sweeps a particular attention is focused on decoupling sideband suppression techniques. The close to perfect inversion profiles of adiabatic pulses ensure by far fewer cyclic sidebands as compared to the typically complex sideband patterns observed in CPD applications. The coherent sideband suppression techniques eliminate the cycling sidebands by altering their phase in successive scans thus achieving sideband reduction levels by up to four orders of magnitude and leaving a clean baseline. We show that adiabatic decoupling is highly adaptive offering significant power savings in spin systems with smaller J-couplings while in the other extreme enabling 13C decoupling of up to a 1 MHz wide bandwidth potentially satisfying the needs of ultra-high-field NMR for the foreseeable future.
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Affiliation(s)
- Ēriks Kupče
- Bruker UK Ltd., Banner Lane, Coventry CV4 9GH, United Kingdom.
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10
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Businger M, Tiranov A, Kaczmarek KT, Welinski S, Zhang Z, Ferrier A, Goldner P, Afzelius M. Optical Spin-Wave Storage in a Solid-State Hybridized Electron-Nuclear Spin Ensemble. Phys Rev Lett 2020; 124:053606. [PMID: 32083938 DOI: 10.1103/physrevlett.124.053606] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 01/09/2020] [Indexed: 06/10/2023]
Abstract
Solid-state impurity spins with optical control are currently investigated for quantum networks and repeaters. Among these, rare-earth-ion doped crystals are promising as quantum memories for light, with potentially long storage time, high multimode capacity, and high bandwidth. However, with spins there is often a tradeoff between bandwidth, which favors electronic spin, and memory time, which favors nuclear spins. Here, we present optical storage experiments using highly hybridized electron-nuclear hyperfine states in ^{171}Yb^{3+}:Y_{2}SiO_{5}, where the hybridization can potentially offer both long storage time and high bandwidth. We reach a storage time of 1.2 ms and an optical storage bandwidth of 10 MHz that is currently only limited by the Rabi frequency of the optical control pulses. The memory efficiency in this proof-of-principle demonstration was about 3%. The experiment constitutes the first optical storage using spin states in any rare-earth ion with electronic spin. These results pave the way for rare-earth based quantum memories with high bandwidth, long storage time, and high multimode capacity, a key resource for quantum repeaters.
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Affiliation(s)
- M Businger
- Department of Applied Physics, University of Geneva, CH-1211 Genève, Switzerland
| | - A Tiranov
- Department of Applied Physics, University of Geneva, CH-1211 Genève, Switzerland
| | - K T Kaczmarek
- Department of Applied Physics, University of Geneva, CH-1211 Genève, Switzerland
| | - S Welinski
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France
| | - Z Zhang
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France
| | - A Ferrier
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France
- Faculté des Sciences et Ingnierie, Sorbonne Université, UFR 933, 75005 Paris, France
| | - P Goldner
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France
| | - M Afzelius
- Department of Applied Physics, University of Geneva, CH-1211 Genève, Switzerland
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11
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Grob U, Krass MD, Héritier M, Pachlatko R, Rhensius J, Košata J, Moores BA, Takahashi H, Eichler A, Degen CL. Magnetic Resonance Force Microscopy with a One-Dimensional Resolution of 0.9 Nanometers. Nano Lett 2019; 19:7935-7940. [PMID: 31647666 DOI: 10.1021/acs.nanolett.9b03048] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Magnetic resonance force microscopy (MRFM) is a scanning probe technique capable of detecting MRI signals from nanoscale sample volumes, providing a paradigm-changing potential for structural biology and medical research. Thus far, however, experiments have not reached sufficient spatial resolution for retrieving meaningful structural information from samples. In this work, we report MRFM imaging scans demonstrating a resolution of 0.9 nm and a localization precision of 0.6 nm in one dimension. Our progress is enabled by an improved spin excitation protocol furnishing us with sharp spatial control on the MRFM imaging slice, combined with overall advances in instrument stability. From a modeling of the slice function, we expect that our arrangement supports spatial resolutions down to 0.3 nm given sufficient signal-to-noise ratio. Our experiment demonstrates the feasibility of subnanometer MRI and realizes an important milestone toward the three-dimensional imaging of macromolecular structures.
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Affiliation(s)
- U Grob
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - M D Krass
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - M Héritier
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - R Pachlatko
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - J Rhensius
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - J Košata
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - B A Moores
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - H Takahashi
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - A Eichler
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
| | - C L Degen
- Department of Physics , ETH Zurich , Otto Stern Weg 1 , 8093 Zurich , Switzerland
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Assländer J, Lattanzi R, Sodickson DK, Cloos MA. Optimized quantification of spin relaxation times in the hybrid state. Magn Reson Med 2019; 82:1385-1397. [PMID: 31189025 DOI: 10.1002/mrm.27819] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2018] [Revised: 04/01/2019] [Accepted: 04/29/2019] [Indexed: 01/08/2023]
Abstract
PURPOSE The optimization and analysis of spin ensemble trajectories in the hybrid state-a state in which the direction of the magnetization adiabatically follows the steady state while the magnitude remains in a transient state. METHODS Numerical optimizations were performed to find spin ensemble trajectories that minimize the Cramér-Rao bound for T 1 -encoding, T 2 -encoding, and their weighted sum, respectively, followed by a comparison between the Cramér-Rao bounds obtained with our optimized spin-trajectories, Look-Locker sequences, and multi-spin-echo methods. Finally, we experimentally tested our optimized spin trajectories with in vivo scans of the human brain. RESULTS After a nonrecurring inversion segment on the southern half of the Bloch sphere, all optimized spin trajectories pursue repetitive loops on the northern hemisphere in which the beginning of the first and the end of the last loop deviate from the others. The numerical results obtained in this work align well with intuitive insights gleaned directly from the governing equation. Our results suggest that hybrid-state sequences outperform traditional methods. Moreover, hybrid-state sequences that balance T 1 - and T 2 -encoding still result in near optimal signal-to-noise efficiency for each relaxation time. Thus, the second parameter can be encoded at virtually no extra cost. CONCLUSIONS We provided new insights into the optimal encoding processes of spin relaxation times in order to guide the design of robust and efficient pulse sequences. We found that joint acquisitions of T 1 and T 2 in the hybrid state are substantially more efficient than sequential encoding techniques.
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Affiliation(s)
- Jakob Assländer
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York
| | - Riccardo Lattanzi
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York
| | - Daniel K Sodickson
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York
| | - Martijn A Cloos
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York
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13
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Suzuki Y, Okell TW, Chappell MA, van Osch MJ. A framework for motion correction of background suppressed arterial spin labeling perfusion images acquired with simultaneous multi-slice EPI. Magn Reson Med 2019; 81:1553-1565. [PMID: 30311694 PMCID: PMC6492089 DOI: 10.1002/mrm.27499] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 07/10/2018] [Accepted: 08/01/2018] [Indexed: 11/23/2022]
Abstract
PURPOSE When using simultaneous multi-slice (SMS) EPI for background suppressed (BGS) arterial spin labeling (ASL), correction of through-plane motion could introduce artefacts, because the slices with most effective BGS are adjacent to slices with the least BGS. In this study, a new framework is presented to correct for such artefacts. METHODS The proposed framework consists of 3 steps: (1) homogenization of the static tissue signal over the different slices to eliminate most inter-slice differences because of different levels of BGS, (2) application of motion correction, and (3) extraction of a perfusion-weighted signal using a general linear model. The proposed framework was evaluated by simulations and a functional ASL study with intentional head motion. RESULTS Simulation studies demonstrated that the strong signal differences between slices with the most and least effective BGS caused sub-optimal estimation of motion parameters when through-plane motion was present. Although use of the M0 image as the reference for registration allowed 82% improvement of motion estimation for through-plane motion, it still led to residual subtraction errors caused by different static tissue signal between control and label because of different BGS levels. By using our proposed framework, those problems were minimized, and the accuracy of CBF estimation was improved. Moreover, the functional ASL study showed improved detection of visual and motor activation when applying the framework as compared to conventional motion correction, as well as when motion correction was completely omitted. CONCLUSION When combining BGS-ASL with SMS-EPI, particular attention is needed to avoid artefacts introduced by motion correction. With the proposed framework, these issues are minimized.
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Affiliation(s)
- Yuriko Suzuki
- C.J. Gorter Center for High Field MRIDepartment of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| | - Thomas W. Okell
- Wellcome Centre for Integrative NeuroimagingFMRIBNuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUnited Kingdom
| | - Michael A. Chappell
- Wellcome Centre for Integrative NeuroimagingFMRIBNuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUnited Kingdom
- Institute of Biomedical EngineeringUniversity of OxfordOxfordUnited Kingdom
| | - Matthias J.P. van Osch
- C.J. Gorter Center for High Field MRIDepartment of RadiologyLeiden University Medical CenterLeidenThe Netherlands
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14
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Yu Z, Zhao T, Assländer J, Lattanzi R, Sodickson DK, Cloos MA. Exploring the sensitivity of magnetic resonance fingerprinting to motion. Magn Reson Imaging 2018; 54:241-248. [PMID: 30193953 PMCID: PMC6215476 DOI: 10.1016/j.mri.2018.09.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 09/01/2018] [Accepted: 09/04/2018] [Indexed: 11/19/2022]
Abstract
PURPOSE To explore the motion sensitivity of magnetic resonance fingerprinting (MRF), we performed experiments with different types of motion at various time intervals during multiple scans. Additionally, we investigated the possibility to correct the motion artifacts based on redundancy in MRF data. METHODS A radial version of the FISP-MRF sequence was used to acquire one transverse slice through the brain. Three subjects were instructed to move in different patterns (in-plane rotation, through-plane wiggle, complex movements, adjust head position, and pretend itch) during different time intervals. The potential to correct motion artifacts in MRF by removing motion-corrupted data points from the fingerprints and dictionary was evaluated. RESULTS Morphological structures were well preserved in multi-parametric maps despite subject motion. Although the bulk T1 values were not significantly affected by motion, fine structures were blurred when in-plane motion was present during the first part of the scan. On the other hand, T2 values showed a considerable deviation from the motion-free results, especially when through-plane motion was present in the middle of the scan (-44% on average). Explicitly removing the motion-corrupted data from the scan partially restored the T2 values (-10% on average). CONCLUSION Our experimental results showed that different kinds of motion have distinct effects on the precision and effective resolution of the parametric maps measured with MRF. Although MRF-based acquisitions can be relatively robust to motion effects occurring at the beginning or end of the sequence, relying on redundancy in the data alone is not sufficient to assure the accuracy of the multi-parametric maps in all cases.
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Affiliation(s)
- Zidan Yu
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, USA.
| | - Tiejun Zhao
- Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA; Siemens Medical Solutions USA Inc., 40 Liberty Boulevard, Malvern, PA 19355, USA
| | - Jakob Assländer
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA
| | - Riccardo Lattanzi
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, USA
| | - Daniel K Sodickson
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, USA
| | - Martijn A Cloos
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI(2)R), Department of Radiology, New York University School of Medicine, New York, NY, USA; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, USA
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15
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Teucher M, Bordignon E. Improved signal fidelity in 4-pulse DEER with Gaussian pulses. J Magn Reson 2018; 296:103-111. [PMID: 30241017 DOI: 10.1016/j.jmr.2018.09.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 09/07/2018] [Accepted: 09/08/2018] [Indexed: 05/24/2023]
Abstract
The introduction of arbitrary waveform generator (AWG) technology and the availability of high power microwave amplifiers mark a "new era" in pulse EPR due to significant sensitivity improvements and the possibility to perform novel types of experiments. We present an optimized 4-pulse DEER setup that uses Gaussian observer pulses (GaussDEER) in connection with a Gaussian/shaped pump pulse. Gaussian pulses allow to experimentally remove the "2+1" pulse train ESE signal which is intrinsically present in any DEER experiment performed with rectangular pulses. Further signal improvements are obtained with shaped pump pulses, which can significantly increase the modulation depth of the DEER experiment due to their tailored excitation bandwidth. Although sequences like CP (Carr-Purcell) DEER offer advantages such as a prolongation of the dipolar evolution time, they suffer from post-processing of the time-domain data to remove artifacts. Therefore, it is worth having a 4-pulse DEER experiment free of residual "2+1" signal since this is still the main dipolar spectroscopic technique used in structural biology. In this work we focus on nitroxides, which are the spin probes primarily used in site-directed spin labeling studies of biomolecules, however, the advantages introduced by Gaussian pulses can be extended to any spin type.
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Affiliation(s)
- Markus Teucher
- Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Universitaetsstr. 150, 44801 Bochum, Germany
| | - Enrica Bordignon
- Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Universitaetsstr. 150, 44801 Bochum, Germany.
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16
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Wi S, Schurko RW, Frydman L. Broadband adiabatic inversion cross-polarization phenomena in the NMR of rotating solids. Solid State Nucl Magn Reson 2018; 94:31-53. [PMID: 30125798 DOI: 10.1016/j.ssnmr.2018.08.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 08/08/2018] [Indexed: 06/08/2023]
Abstract
We explore the use of cross-polarization magic-angle spinning (CPMAS) methods incorporating an adiabatic frequency sweep in a standard Hartman-Hahn CPMAS pulse scheme, to achieve signal enhancements in solid-state NMR spectra of rare spins under fast MAS spinning rates, including spin-1/2, integer spin, and half-integer spin nuclides. These experiments, dubbed Broadband Adiabatic INversion Cross-Polarization Magic-Angle Spinning (BRAIN-CPMAS) experiments, involve an adiabatic inversion pulse on the S-channel of a rare spin nuclide while simultaneously applying a conventional spin-locking pulse on the I-channel (1H). The signal enhancement imparted by this CP scheme on the S-spin is broadbanded, while employing low RF field strengths on both I- and S-channels. A feature demanded by these BRAIN-CPMAS methods is to impose a selective adiabatic frequency sweep over a single MAS spinning centerband or sideband, to avoid interference between the MAS modulation and sweeps over multiple sidebands. Upon implementing this swept-CP method, a number of MAS-driven processes happen, including broadband zero- and double-quantum CP transfers, and MAS-driven rotary-resonance phenomena. When this CP method is applied to integer and half-integer quadrupolar nuclei at very fast MAS spinning rates, a favorable double-quantum CP condition is found that can be easily achieved, and avoids the level-crossings among various ms energy levels that complicate quadrupolar CPMAS NMR experiments along lines first shown by Alex Vega. An additional CP mechanism was found in the 1H-2H case, involving static-like zero-quantum CP modes driven by a quadrupole-modulated RF-dipolar zero-order recoupling under MAS. All these phenomena were examined using average Hamiltonian theory, numerical simulations, and experiments on model compounds. Sensitivity-enhanced, distortion-free CP over wide bandwidths were predicted and observed for S = 1/2 and for S = 1 (2H) under fast MAS rates. BRAIN-CPMAS also delivered undistorted central transition NMR spectra of half-integer quadrupolar nuclei, while utilizing low RF field strengths that avoid complex level-crossing effects under high MAS rates.
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Affiliation(s)
- Sungsool Wi
- National High Magnetic Field Laboratory, Tallahassee, FL, 32304, USA.
| | - Robert W Schurko
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, NPB 3P4, Canada
| | - Lucio Frydman
- National High Magnetic Field Laboratory, Tallahassee, FL, 32304, USA; Department of Chemical and Biological Physics, Weizmann Institute of Sciences, Rehovot, 76100, Israel.
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17
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Wang X, Greer JS, Dimitrov IE, Pezeshk P, Chhabra A, Madhuranthakam AJ. Frequency Offset Corrected Inversion Pulse for B 0 and B 1 Insensitive Fat Suppression at 3T: Application to MR Neurography of Brachial Plexus. J Magn Reson Imaging 2018; 48:1104-1111. [PMID: 30218576 DOI: 10.1002/jmri.26021] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 03/07/2018] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The 3D short tau inversion recovery (STIR) sequence is routinely used in clinical MRI to achieve robust fat suppression. However, the performance of the commonly used adiabatic inversion pulse, hyperbolic secant (HS), is compromised in challenging areas with increased B0 and B1 inhomogeneities, such as brachial plexus at 3T. PURPOSE To demonstrate the frequency offset corrected inversion (FOCI) pulse as an efficient fat suppression STIR pulse with increased robustness to B0 and B1 inhomogeneities at 3T, compared to the HS pulse. STUDY TYPE Prospective. SUBJECTS/PHANTOM Initial evaluation was performed in phantoms and one healthy volunteer by varying the B1 field, while subsequent comparison was performed in three healthy volunteers and five patients without varying the B1 . FIELD STRENGTH/SEQUENCE 3T; 3D TSE-STIR with HS and FOCI pulses. ASSESSMENT Brachial plexus images were qualitatively evaluated by two musculoskeletal radiologists independently using a four-point grading scale for fat suppression, shading artifacts, and nerve visualization. STATISTICAL TEST The Wilcoxon signed-rank test with P < 0.05 was considered statistically significant. RESULTS Simulations and phantom experiments demonstrated broader bandwidth (2.5 kHz vs. 0.83 kHz, increased B0 robustness) at the same adiabatic threshold and lower adiabatic threshold (5 μT vs. 7 μT at 3.5 ppm, increased B1 robustness) at the same bandwidth with the FOCI pulse compared to the HS pulse With increased bandwidth, the FOCI pulse achieved robust fat suppression even at 50% of maximum B1 strength, while the HS pulse required >75% of maximum B1 strength. Compared to the standard 3D TSE-STIR with HS pulse, the FOCI pulse achieved uniform fat suppression (P < 0.05), better nerve visualization (P < 0.05), and minimal shading artifacts (P < 0.01) in brachial plexus at 3T. DATA CONCLUSION The FOCI pulse has increased robustness to B0 and B1 inhomogeneities, compared to the HS pulse, and enables uniform fat suppression in brachial plexus at 3T. LEVEL OF EVIDENCE 1 Techinical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1104-1111.
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Affiliation(s)
- Xinzeng Wang
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Joshua S Greer
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Bioengineering, University of Texas at Dallas, Richardson, Texas, USA
| | - Ivan E Dimitrov
- Philips Medical Systems, Gainesville, Florida, USA.,Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Parham Pezeshk
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Avneesh Chhabra
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Orthopedic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Ananth J Madhuranthakam
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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18
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Abstract
Radiofrequency (RF) coils are an essential MRI hardware component. They directly impact the spatial and temporal resolution, sensitivity, and uniformity in MRI. Advances in RF hardware have resulted in a variety of designs optimized for specific clinical applications. RF coils are the "antennas" of the MRI system and have two functions: first, to excite the magnetization by broadcasting the RF power (Tx-Coil) and second to receive the signal from the excited spins (Rx-Coil). Transmit RF Coils emit magnetic field pulses ( B1+) to rotate the net magnetization away from its alignment with the main magnetic field (B0 ), resulting in a transverse precessing magnetization. Due to the precession around the static main magnetic field, the magnetic flux in the receive RF Coil ( B1-) changes, which generates a current I. This signal is "picked-up" by an antenna and preamplified, usually mixed down to a lower frequency, digitized, and processed by a computer to finally reconstruct an image or a spectrum. Transmit and receive functionality can be combined in one RF Coil (Tx/Rx Coils). This review looks at the fundamental principles of an MRI RF coil from the perspective of clinicians and MR technicians and summarizes the current advances and developments in technology. LEVEL OF EVIDENCE 1 Technical Efficacy: Stage 6.
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Affiliation(s)
- Bernhard Gruber
- A.A. Martinos Center for Biomedical Imaging, Harvard‐MIT Division of Health Sciences & Technology, Massachusetts General HospitalCharlestownMassachusettsUSA
- Department of Radiology, Harvard Medical SchoolMassachusetts General HospitalBostonMassachusettsUSA
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Martijn Froeling
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Tim Leiner
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Dennis W.J. Klomp
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
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19
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Breitgoff FD, Soetbeer J, Doll A, Jeschke G, Polyhach YO. Artefact suppression in 5-pulse double electron electron resonance for distance distribution measurements. Phys Chem Chem Phys 2018; 19:15766-15779. [PMID: 28590496 DOI: 10.1039/c7cp01488k] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A 5-pulse version of the Double Electron Electron Resonance (DEER) experiment with Carr-Purcell delays and an additional pump pulse has been shown to significantly extend the experimentally accessible distance range in cases where nuclear spin diffusion dominates electron spin phase memory loss [Borbat et al., J. Phys. Chem. Lett., 2013, 4, 170]. We show that the sequence also prolongs coherence decay for spin labels in or near lipid bilayers, where this decay is mono-exponential. Compared to 4-pulse DEER, 5-pulse DEER suffers from additional artefacts that stem from pulse imperfection and excitation band overlap. Only some of these artefacts can be suppressed by phase cycling and the remaining ones have hindered widespread utilization of the method. Here, we report previously unknown additional artefact contributions stemming from overlap between the excitation bands of the microwave pulses that introduce additional dipolar evolution pathways. Experimental conditions are analyzed in detail that suppress these as well as the already known artefacts. Such suppression results in data that contain at most the partial excitation artefact, which can be deliberately shifted in time by a change in pulse timing without affecting the wanted contribution.
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Affiliation(s)
- Frauke D Breitgoff
- Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
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20
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Bahrenberg T, Rosenski Y, Carmieli R, Zibzener K, Qi M, Frydman V, Godt A, Goldfarb D, Feintuch A. Improved sensitivity for W-band Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements with shaped pulses. J Magn Reson 2017; 283:1-13. [PMID: 28834777 DOI: 10.1016/j.jmr.2017.08.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 08/08/2017] [Accepted: 08/09/2017] [Indexed: 06/07/2023]
Abstract
Chirp and shaped pulses have been recently shown to be highly advantageous for improving sensitivity in DEER (double electron-electron resonance, also called PELDOR) measurements due to their large excitation bandwidth. The implementation of such pulses for pulse EPR has become feasible due to the availability of arbitrary waveform generators (AWG) with high sampling rates to support pulse shaping for pulses with tens of nanoseconds duration. Here we present a setup for obtaining chirp pulses on our home-built W-band (95GHz) spectrometer and demonstrate its performance on Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements. We carried out an extensive optimization procedure on two model systems, Gd(III)-PyMTA-spacer-Gd(III)-PyMTA (Gd-PyMTA ruler; zero-field splitting parameter (ZFS) D∼1150MHz) as well as nitroxide-spacer-nitroxide (nitroxide ruler) to evaluate the applicability of shaped pulses to Gd(III) complexes and nitroxides, which are two important classes of spin labels used in modern DEER/EPR experiments. We applied our findings to ubiquitin, doubly labeled with Gd-DOTA-monoamide (D∼550MHz) asa model for a system with a small ZFS. Our experiments were focused on the questions (i) what are the best conditions for positioning of the detection frequency, (ii) which pump pulse parameters (bandwidth, positioning in the spectrum, length) yield the best signal-to-noise ratio (SNR) improvements when compared to classical DEER, and (iii) how do the sample's spectral parameters influence the experiment. For the nitroxide ruler, we report an improvement of up to 1.9 in total SNR, while for the Gd-PyMTA ruler the improvement was 3.1-3.4 and for Gd-DOTA-monoamide labeled ubiquitin it was a factor of 1.8. Whereas for the Gd-PyMTA ruler the two setups pump on maximum and observe on maximum gave about the same improvement, for Gd-DOTA-monoamide a significant difference was found. In general the choice of the best set of parameters depends on the D parameter of the Gd(III) complex.
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Affiliation(s)
- Thorsten Bahrenberg
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Yael Rosenski
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Raanan Carmieli
- Department of Chemical Research Support, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Koby Zibzener
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Mian Qi
- Faculty of Chemistry and Center for Molecular Materials (CM(2)), Bielefeld University, 33615 Bielefeld, Germany
| | - Veronica Frydman
- Department of Chemical Research Support, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Adelheid Godt
- Faculty of Chemistry and Center for Molecular Materials (CM(2)), Bielefeld University, 33615 Bielefeld, Germany
| | - Daniella Goldfarb
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Akiva Feintuch
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel.
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21
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Abstract
Designing accurate and high-fidelity broadband pulses is an essential component in conducting quantum experiments across fields from protein spectroscopy to quantum optics. However, constructing exact and analytic broadband pulses remains unsolved due to the nonlinearity and complexity of the underlying spin system dynamics. Here, we present a nontrivial dynamic connection between nonlinear spin and linear spring systems and show the surprising result that such nonlinear and complex pulse design problems are equivalent to designing controls to steer linear harmonic oscillators under optimal forcing. We derive analytic broadband π/2 and π pulses that perform exact, or asymptotically exact, excitation and inversion over a defined bandwidth, and also with bounded amplitude. This development opens up avenues for pulse sequence design and lays a foundation for understanding the control of two-level systems. Coherent control of two-level systems is crucial for achieving fidelity in spectroscopy and quantum computing, but inherent nonlinearities and parameter variation have, to date, required an approximate, numerical approach. Here, Li et al. show how to map a spin ensemble to a spring model so analytic pulses can be designed using linear methods.
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Affiliation(s)
- Jr-Shin Li
- Department of Electrical and Systems Engineering, Washington University in St Louis, St Louis, MO, 63130, USA.
| | - Justin Ruths
- Departments of Mechanical and Systems Engineering, University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Steffen J Glaser
- Department of Chemistry, Technical University of Munich, 85747, Garching, Germany
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22
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Spindler PE, Schöps P, Kallies W, Glaser SJ, Prisner TF. Perspectives of shaped pulses for EPR spectroscopy. J Magn Reson 2017; 280:30-45. [PMID: 28579101 DOI: 10.1016/j.jmr.2017.02.023] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2016] [Revised: 02/27/2017] [Accepted: 02/28/2017] [Indexed: 06/07/2023]
Abstract
This article describes current uses of shaped pulses, generated by an arbitrary waveform generator, in the field of EPR spectroscopy. We show applications of sech/tanh and WURST pulses to dipolar spectroscopy, including new pulse schemes and procedures, and discuss the more general concept of optimum-control-based pulses for applications in EPR spectroscopy. The article also describes a procedure to correct for experimental imperfections, mostly introduced by the microwave resonator, and discusses further potential applications and limitations of such pulses.
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Affiliation(s)
- Philipp E Spindler
- Institute of Physical and Theoretical Chemistry and Center of Biomolecular Magnetic Resonance, Goethe University Frankfurt, Germany
| | - Philipp Schöps
- Institute of Physical and Theoretical Chemistry and Center of Biomolecular Magnetic Resonance, Goethe University Frankfurt, Germany
| | - Wolfgang Kallies
- Department of Chemistry, Technical University of Munich, Germany
| | - Steffen J Glaser
- Department of Chemistry, Technical University of Munich, Germany
| | - Thomas F Prisner
- Institute of Physical and Theoretical Chemistry and Center of Biomolecular Magnetic Resonance, Goethe University Frankfurt, Germany.
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23
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Vallatos A, Gilmour L, Chalmers AJ, Holmes WM. Multiple boli arterial spin labeling for high signal-to-noise rodent brain perfusion imaging. Magn Reson Med 2017; 79:1020-1030. [PMID: 28516482 DOI: 10.1002/mrm.26706] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 02/18/2017] [Accepted: 03/19/2017] [Indexed: 12/30/2022]
Abstract
PURPOSE A systematic method is proposed for optimizing a promising preclinical arterial spin labeling (ASL) sequence based on the use of a train of adiabatic radiofrequency pulses labeling successive boli of blood water. METHODS The sequence optimization is performed and evaluated using brain imaging experiments in mice and in rats. It involves the investigation of several parameters, ranging from the number of adiabatic pulses and labeling duration to the properties of the adiabatic hyperbolic secant pulses (ie, amplitude and frequency modulation). RESULTS Species-dependent parameters are identified, allowing for robust fast optimization protocols to be introduced. The resulting optimized multiple boli ASL (mbASL) sequence provides with significantly higher average signal-to-noise ratios (SNR) per voxel volume than currently encountered in ASL studies (278 mm-3 in mice and 172 mm-3 in rats). Comparing with the commonly used flow-sensitive alternating inversion recovery technique (FAIR), mbASL-to-FAIR SNR ratios reach 203% for mice and 725% for rats. CONCLUSION When properly optimized, mbASL can offer a robust, high SNR ASL alternative for rodent brain perfusion studies Magn Reson Med 79:1020-1030, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Antoine Vallatos
- Glasgow Experimental MRI Centre, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom
| | - Lesley Gilmour
- Wolfson Wohl Translational Cancer Research Center, Institute of Cancer Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Anthony J Chalmers
- Wolfson Wohl Translational Cancer Research Center, Institute of Cancer Sciences, University of Glasgow, Glasgow, United Kingdom
| | - William M Holmes
- Glasgow Experimental MRI Centre, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom
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24
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Winfield JM, Payne GS, Weller A, deSouza NM. DCE-MRI, DW-MRI, and MRS in Cancer: Challenges and Advantages of Implementing Qualitative and Quantitative Multi-parametric Imaging in the Clinic. Top Magn Reson Imaging 2016; 25:245-54. [PMID: 27748710 DOI: 10.1097/RMR.0000000000000103] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Multi-parametric magnetic resonance imaging (mpMRI) offers a unique insight into tumor biology by combining functional MRI techniques that inform on cellularity (diffusion-weighted MRI), vascular properties (dynamic contrast-enhanced MRI), and metabolites (magnetic resonance spectroscopy) and has scope to provide valuable information for prognostication and response assessment. Challenges in the application of mpMRI in the clinic include the technical considerations in acquiring good quality functional MRI data, development of robust techniques for analysis, and clinical interpretation of the results. This article summarizes the technical challenges in acquisition and analysis of multi-parametric MRI data before reviewing the key applications of multi-parametric MRI in clinical research and practice.
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25
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Abstract
Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.
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Affiliation(s)
- Claudia E Tait
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Stefan Stoll
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
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26
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Zhang J, Garwood M, Park JY. Full analytical solution of the bloch equation when using a hyperbolic-secant driving function. Magn Reson Med 2017; 77:1630-1638. [PMID: 27171915 PMCID: PMC5107179 DOI: 10.1002/mrm.26252] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 03/07/2016] [Accepted: 03/31/2016] [Indexed: 12/22/2022]
Abstract
PURPOSE The frequency-swept pulse known as the hyperbolic-secant (HS) pulse is popular in NMR for achieving adiabatic spin inversion. The HS pulse has also shown utility for achieving excitation and refocusing in gradient-echo and spin-echo sequences, including new ultrashort echo-time imaging (e.g., Sweep Imaging with Fourier Transform, SWIFT) and B1 mapping techniques. To facilitate the analysis of these techniques, the complete theoretical solution of the Bloch equation, as driven by the HS pulse, was derived for an arbitrary state of initial magnetization. METHODS The solution of the Bloch-Riccati equation for transverse and longitudinal magnetization for an arbitrary initial state was derived analytically in terms of HS pulse parameters. The analytical solution was compared with the solutions using both the Runge-Kutta method and the small-tip approximation. RESULTS The analytical solution was demonstrated on different initial states at different frequency offsets with/without a combination of HS pulses. Evolution of the transverse magnetization was influenced significantly by the choice of HS pulse parameters. The deviation of the magnitude of the transverse magnetization, as obtained by comparing the small-tip approximation to the analytical solution, was < 5% for flip angles < 30 °, but > 10% for the flip angles > 40 °. CONCLUSION The derived analytical solution provides insights into the influence of HS pulse parameters on the magnetization evolution. Magn Reson Med 77:1630-1638, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Jinjin Zhang
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Jang-yeon Park
- Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Gyeonggi-do, South Korea
- Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do, South Korea
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27
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Suzuki Y, Fujima N, Ogino T, Meakin JA, Suwa A, Sugimori H, Van Cauteren M, van Osch MJP. Acceleration of ASL-based time-resolved MR angiography by acquisition of control and labeled images in the same shot (ACTRESS). Magn Reson Med 2017; 79:224-233. [PMID: 28321915 PMCID: PMC5947673 DOI: 10.1002/mrm.26667] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 01/19/2017] [Accepted: 02/12/2017] [Indexed: 01/15/2023]
Abstract
PURPOSE Noncontrast 4D-MR-angiography (MRA) using arterial spin labeling (ASL) is beneficial because high spatial and temporal resolution can be achieved. However, ASL requires acquisition of labeled and control images for each phase. The purpose of this study is to present a new accelerated 4D-MRA approach that requires only a single control acquisition, achieving similar image quality in approximately half the scan time. METHODS In a multi-phase Look-Locker sequence, the first phase was used as the control image and the labeling pulse was applied before the second phase. By acquiring the control and labeled images within a single Look-Locker cycle, 4D-MRA was generated in nearly half the scan time of conventional ASL. However, this approach potentially could be more sensitive to off-resonance and magnetization transfer (MT) effects. To counter this, careful optimizations of the labeling pulse were performed by Bloch simulations. In in-vivo studies arterial visualization was compared between the new and conventional ASL approaches. RESULTS Optimization of the labeling pulse successfully minimized off-resonance effects. Qualitative assessment showed that residual MT effects did not degrade visualization of the peripheral arteries. CONCLUSION This study demonstrated that the proposed approach achieved similar image quality as conventional ASL-MRA approaches in just over half the scan time. Magn Reson Med 79:224-233, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Yuriko Suzuki
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.,Philips Electronics Japan, Ltd., Healthcare, Tokyo, Japan
| | - Noriyuki Fujima
- Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, Hokkaido, Japan
| | - Tetsuo Ogino
- Philips Electronics Japan, Ltd., Healthcare, Tokyo, Japan
| | - James Alastair Meakin
- Diagnostic Image Analysis Group, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Akira Suwa
- Philips Electronics Japan, Ltd., Healthcare, Tokyo, Japan
| | | | | | - Matthias J P van Osch
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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28
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Schuenke P, Paech D, Koehler C, Windschuh J, Bachert P, Ladd ME, Schlemmer HP, Radbruch A, Zaiss M. Fast and Quantitative T1ρ-weighted Dynamic Glucose Enhanced MRI. Sci Rep 2017; 7:42093. [PMID: 28169369 DOI: 10.1038/srep42093] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Accepted: 01/05/2017] [Indexed: 02/06/2023] Open
Abstract
Common medical imaging techniques usually employ contrast agents that are chemically labeled, e.g. with radioisotopes in the case of PET, iodine in the case of CT or paramagnetic metals in the case of MRI to visualize the heterogeneity of the tumor microenvironment. Recently, it was shown that natural unlabeled D-glucose can be used as a nontoxic biodegradable contrast agent in Chemical Exchange sensitive Spin-Lock (CESL) magnetic resonance imaging (MRI) to detect the glucose uptake and potentially the metabolism of tumors. As an important step to fulfill the clinical needs for practicability, reproducibility and imaging speed we present here a robust and quantitative T1ρ-weighted technique for dynamic glucose enhanced MRI (DGE-MRI) with a temporal resolution of less than 7 seconds. Applied to a brain tumor patient, the new technique provided a distinct DGE contrast between tumor and healthy brain tissue and showed the detailed dynamics of the glucose enhancement after intravenous injection. Development of this fast and quantitative DGE-MRI technique allows for a more detailed analysis of DGE correlations in the future and potentially enables non-invasive diagnosis, staging and monitoring of tumor response to therapy.
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Zhang Z, Shemesh N, Frydman L. Efficient spectroscopic imaging by an optimized encoding of pretargeted resonances. Magn Reson Med 2017; 77:511-519. [PMID: 26910285 PMCID: PMC5184843 DOI: 10.1002/mrm.26161] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 01/11/2016] [Accepted: 01/20/2016] [Indexed: 12/25/2022]
Abstract
PURPOSE A "relaxation-enhanced" (RE) approach to acquire in vivo localized spectra with flat baselines and good sensitivity has been recently proposed. As RE MR spectroscopy (MRS) targets a subset of a priori known resonances, new possibilities arise to acquire spectroscopic imaging data in faster, more efficient manners. This is hereby illustrated by Spectroscopically Encoded Chemical Shift Imaging (SECSI). METHODS SECSI delivers spectral/spatial correlations by collecting gradient echo trains whose timings are defined by the shifts of the resonances to be disentangled. Condition number considerations allow one to unravel these image contributions for various sites by a simple matrix inversion. The efficiency of the ensuing method is high enough to enable a sampling of additional spatial axes by means of their phase encoding in spin-echo trains. RESULTS The one-dimensional (1D) spectral / 2D spatial SECSI acquisitions were implemented on phantom, ex vivo, and in vivo models. In all cases, quality site-resolved images were obtained. The experimentally observed enhancements were consistent with theoretical signal-to-noise ratio derivations. CONCLUSION While still bound by MRSI's sensitivity limitations, a novel spectroscopic imaging protocol exploiting a priori information, selective excitations and multiple echo encodings, was proposed and demonstrated. The method is promising when dealing with high T2 / T2* ratios, sparse data, or hyperpolarization studies. Magn Reson Med 77:511-519, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Zhiyong Zhang
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian 361005, China
| | - Noam Shemesh
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
- Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Lisbon, Portugal
| | - Lucio Frydman
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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30
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Schuenke P, Koehler C, Korzowski A, Windschuh J, Bachert P, Ladd ME, Mundiyanapurath S, Paech D, Bickelhaupt S, Bonekamp D, Schlemmer HP, Radbruch A, Zaiss M. Adiabatically prepared spin-lock approach for T1ρ-based dynamic glucose enhanced MRI at ultrahigh fields. Magn Reson Med 2016; 78:215-225. [DOI: 10.1002/mrm.26370] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 07/12/2016] [Accepted: 07/14/2016] [Indexed: 12/23/2022]
Affiliation(s)
- Patrick Schuenke
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Christina Koehler
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | - Andreas Korzowski
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Johannes Windschuh
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Peter Bachert
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Mark E. Ladd
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | | | - Daniel Paech
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | | | - David Bonekamp
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | | | - Alexander Radbruch
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | - Moritz Zaiss
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
- Max-Planck-Institute for Biological Cybernetics; Tübingen Baden-Württemberg Germany
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31
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Sun Y, Brauckmann O, Nixdorf DR, Kentgens A, Garwood M, Idiyatullin D, Heerschap A. Imaging human teeth by phosphorus magnetic resonance with nuclear Overhauser enhancement. Sci Rep 2016; 6:30756. [PMID: 27498919 PMCID: PMC4976379 DOI: 10.1038/srep30756] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 07/06/2016] [Indexed: 01/04/2023] Open
Abstract
Three-dimensional phosphorus MR images ((31)P MRI) of teeth are obtained at a nominal resolution of 0.5 mm in less than 15 minutes using acquisition pulse sequences sensitive to ultra-short transversal relaxation times. The images directly reflect the spatially resolved phosphorus content of mineral tissue in dentin and enamel; they show a lack of signal from pulp tissue and reduced signal from de-mineralized carious lesions. We demonstrate for the first time that the signal in (31)P MR images of mineralized tissue is enhanced by a (1)H-(31)P nuclear Overhauser effect (NOE). Using teeth as a model for imaging mineralized human tissue, graded differences in signal enhancement are observed that correlate well with known mineral content. From solid-state NMR experiments we conclude that the NOE is facilitated by spin diffusion and that the NOE difference can be assigned to a higher water content and a different micro-structure of dentin. Thus, a novel method for imaging mineral content without ionizing radiation is proposed. This method has potential use in the assessment of de-mineralization states in humans, such as caries of teeth and osteoporosis of bones.
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Affiliation(s)
- Yi Sun
- Radiology, Radboud University Nijmegen Medical Centre, Geert Grooteplein zuid 10, 6586 GA Nijmegen The Netherlands
| | - Ole Brauckmann
- Solid State NMR, Institute of Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands
| | - Donald R. Nixdorf
- Division of TMD and Orofacial Pain Department of Diagnostic and Biological Sciences, University of Minnesota, 515 Delaware St. SE, Minneapolis, MN 55455, United States
| | - Arno Kentgens
- Solid State NMR, Institute of Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands
| | - Michael Garwood
- Center for Magnetic Resonance Research, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, United States
| | - Djaudat Idiyatullin
- Center for Magnetic Resonance Research, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, United States
| | - Arend Heerschap
- Radiology, Radboud University Nijmegen Medical Centre, Geert Grooteplein zuid 10, 6586 GA Nijmegen The Netherlands
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Kim SE, Roberts JA, Eisenmenger LB, Aldred BW, Jamil O, Bolster BD, Bi X, Parker DL, Treiman GS, McNally JS. Motion-insensitive carotid intraplaque hemorrhage imaging using 3D inversion recovery preparation stack of stars (IR-prep SOS) technique. J Magn Reson Imaging 2016; 45:410-417. [PMID: 27383756 DOI: 10.1002/jmri.25365] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 06/15/2016] [Indexed: 11/11/2022] Open
Abstract
PURPOSE Carotid artery imaging is important in the clinical management of patients at risk for stroke. Carotid intraplaque hemorrhage (IPH) presents an important diagnostic challenge. 3D magnetization prepared rapid acquisition gradient echo (MPRAGE) has been shown to accurately image carotid IPH; however, this sequence can be limited due to motion- and flow-related artifact. The purpose of this work was to develop and evaluate an improved 3D carotid MPRAGE sequence for IPH detection. We hypothesized that a radial-based k-space trajectory sequence such as "Stack of Stars" (SOS) incorporated with inversion recovery preparation would offer reduced motion sensitivity and more robust flow suppression by oversampling of central k-space. MATERIALS AND METHODS A total of 31 patients with carotid disease (62 carotid arteries) were imaged at 3T magnetic resonance imaging (MRI) with 3D IR-prep Cartesian and SOS sequences. Image quality was determined between SOS and Cartesian MPRAGE in 62 carotid arteries using t-tests and multivariable linear regression. Kappa analysis was used to determine interrater reliability. RESULTS In all, 25 among 62 carotid plaques had carotid IPH by consensus from the reviewers on SOS compared to 24 on Cartesian sequence. Image quality was significantly higher with SOS compared to Cartesian (mean 3.74 vs. 3.11, P < 0.001). SOS acquisition yielded sharper image features with less motion (19.4% vs. 45.2%, P < 0.002) and flow artifact (27.4% vs. 41.9%, P < 0.089). There was also excellent interrater reliability with SOS (kappa = 0.89), higher than that of Cartesian (kappa = 0.84). CONCLUSION By minimizing flow and motion artifacts and retaining high interrater reliability, the SOS MPRAGE has important advantages over Cartesian MPRAGE in carotid IPH detection. LEVEL OF EVIDENCE 1 J. Magn. Reson. Imaging 2017;45:410-417.
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Affiliation(s)
- Seong-Eun Kim
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.,Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | - John A Roberts
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.,Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | | | - Booth W Aldred
- Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | - Osama Jamil
- Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | | | - Xiaoming Bi
- Siemens Healthcare, Salt Lake City, Utah, USA
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.,Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | - Gerald S Treiman
- Department of Surgery, University of Utah, Salt Lake City, Utah, USA.,Department of Veterans Affairs, VASLCHCS, Salt Lake City, Utah, USA
| | - J Scott McNally
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.,Department of Radiology, University of Utah, Salt Lake City, Utah, USA
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Tse DHY, Wiggins CJ, Ivanov D, Brenner D, Hoffmann J, Mirkes C, Shajan G, Scheffler K, Uludağ K, Poser BA. Volumetric imaging with homogenised excitation and static field at 9.4 T. MAGMA 2016; 29:333-45. [PMID: 26995492 PMCID: PMC4891373 DOI: 10.1007/s10334-016-0543-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 02/26/2016] [Accepted: 02/29/2016] [Indexed: 11/29/2022]
Abstract
OBJECTIVES To overcome the challenges of B0 and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B0 and flip-angle homogenisation was implemented on a human 9.4 T scanner. MATERIALS AND METHODS Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B0- and B1-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B0 shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T1- and T 2 (*) -weighted images with MPRAGE and 3D EPI, respectively. RESULTS Over six in vivo acquisitions, the B0-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10 ± 0.01 ppm (39 ± 2 Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode's 30.5 ± 0.9 to 9.2 ± 0.7 % with all B 1 (+) voids eliminated. The SNR inhomogeneities and contrast variations in the T1- and T 2 (*) -weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T1-weighted image. CONCLUSION A 15-minute B0- and flip-angle homogenisation workflow, including the B0- and B1-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images.
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Affiliation(s)
- Desmond H Y Tse
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
| | | | - Dimo Ivanov
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Daniel Brenner
- German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Jens Hoffmann
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
| | - Christian Mirkes
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
- Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany
| | - Gunamony Shajan
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
| | - Klaus Scheffler
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
- Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany
| | - Kâmil Uludağ
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
- Scannexus BV, Maastricht, The Netherlands
| | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
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Gras V, Vignaud A, Amadon A, Le Bihan D, Boulant N. Universal pulses: A new concept for calibration-free parallel transmission. Magn Reson Med 2016; 77:635-643. [PMID: 26888654 DOI: 10.1002/mrm.26148] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 01/11/2016] [Accepted: 01/13/2016] [Indexed: 11/12/2022]
Abstract
PURPOSE A calibration-free parallel transmission method is investigated to mitigate the radiofrequency (RF) field inhomogeneity problem in brain imaging at 7 Tesla (T). THEORY AND METHODS Six volunteers were scanned to build a representative database of RF and static field maps at 7T. Small-tip-angle and inversion pulses were designed with joint kT -points trajectory optimization to work robustly on all six subjects. The returned "universal" pulses were then inserted in an MPRAGE sequence implemented on six additional volunteers without further field measurements and pulse optimizations. Similar acquisitions were performed in the circularly polarized mode and with subject-based optimizations for comparison. Performance of the different approaches was evaluated by means of image analysis and computation of the flip angle normalized root mean square errors (NRMSE). RESULTS For both the excitation and inversion, the universal pulses (NRMSE∼11%) outperformed the circularly polarized (NRMSE∼28%) and RF shim modes (NRMSE∼20%) across all volunteers and returned slightly worse results than for subject-based optimized pulses (NRMSE∼7%). CONCLUSION RF pulses can be designed to robustly mitigate the RF field inhomogeneity problem over a population class. This appears as a first step toward another plug and play parallel transmission solution where the pulse design can be done offline and without measuring subject-specific field maps. Magn Reson Med 77:635-643, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Vincent Gras
- NeuroSpin, CEA, DSV, Gif sur Yvette, Cedex, France
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35
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Dupas L, Massire A, Amadon A, Vignaud A, Boulant N. Two-spoke placement optimization under explicit specific absorption rate and power constraints in parallel transmission at ultra-high field. J Magn Reson 2015; 255:59-67. [PMID: 25912342 DOI: 10.1016/j.jmr.2015.03.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Revised: 03/17/2015] [Accepted: 03/19/2015] [Indexed: 06/04/2023]
Abstract
The spokes method combined with parallel transmission is a promising technique to mitigate the B1(+) inhomogeneity at ultra-high field in 2D imaging. To date however, the spokes placement optimization combined with the magnitude least squares pulse design has never been done in direct conjunction with the explicit Specific Absorption Rate (SAR) and hardware constraints. In this work, the joint optimization of 2-spoke trajectories and RF subpulse weights is performed under these constraints explicitly and in the small tip angle regime. The problem is first considerably simplified by making the observation that only the vector between the 2 spokes is relevant in the magnitude least squares cost-function, thereby reducing the size of the parameter space and allowing a more exhaustive search. The algorithm starts from a set of initial k-space candidates and performs in parallel for all of them optimizations of the RF subpulse weights and the k-space locations simultaneously, under explicit SAR and power constraints, using an active-set algorithm. The dimensionality of the spoke placement parameter space being low, the RF pulse performance is computed for every location in k-space to study the robustness of the proposed approach with respect to initialization, by looking at the probability to converge towards a possible global minimum. Moreover, the optimization of the spoke placement is repeated with an increased pulse bandwidth in order to investigate the impact of the constraints on the result. Bloch simulations and in vivo T2(∗)-weighted images acquired at 7 T validate the approach. The algorithm returns simulated normalized root mean square errors systematically smaller than 5% in 10 s.
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Affiliation(s)
- Laura Dupas
- CEA, DSV, I2BM, NeuroSpin, UNIRS, 91191 Gif-sur-Yvette, France.
| | | | - Alexis Amadon
- CEA, DSV, I2BM, NeuroSpin, UNIRS, 91191 Gif-sur-Yvette, France
| | | | - Nicolas Boulant
- CEA, DSV, I2BM, NeuroSpin, UNIRS, 91191 Gif-sur-Yvette, France
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Zhang J, Idiyatullin D, Corum CA, Kobayashi N, Garwood M. Gradient-modulated SWIFT. Magn Reson Med 2015; 75:537-46. [PMID: 25800547 DOI: 10.1002/mrm.25595] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 11/17/2014] [Accepted: 12/08/2014] [Indexed: 01/20/2023]
Abstract
PURPOSE Methods designed to image fast-relaxing spins, such as sweep imaging with Fourier transformation (SWIFT), often utilize high excitation bandwidth and duty cycle, and in some applications the optimal flip angle cannot be used without exceeding safe specific absorption rate (SAR) levels. The aim is to reduce SAR and increase the flexibility of SWIFT by applying time-varying gradient-modulation (GM). The modified sequence is called GM-SWIFT. THEORY AND METHODS The method known as gradient-modulated offset independent adiabaticity was used to modulate the radiofrequency (RF) pulse and gradients. An expanded correlation algorithm was developed for GM-SWIFT to correct the phase and scale effects. Simulations and phantom and in vivo human experiments were performed to verify the correlation algorithm and to evaluate imaging performance. RESULTS GM-SWIFT reduces SAR, RF amplitude, and acquisition time by up to 90%, 70%, and 45%, respectively, while maintaining image quality. The choice of GM parameter influences the lower limit of short T2 (*) sensitivity, which can be exploited to suppress unwanted image haze from unresolvable ultrashort T2 (*) signals originating from plastic materials in the coil housing and fixatives. CONCLUSIONS GM-SWIFT reduces peak and total RF power requirements and provides additional flexibility for optimizing SAR, RF amplitude, scan time, and image quality.
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Affiliation(s)
- Jinjin Zhang
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.,School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota, USA
| | - Djaudat Idiyatullin
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Curtis A Corum
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Naoharu Kobayashi
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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Wi S, Gan Z, Schurko R, Frydman L. Cross-polarization phenomena in the NMR of fast spinning solids subject to adiabatic sweeps. J Chem Phys 2015; 142:064201. [DOI: 10.1063/1.4907206] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Sungsool Wi
- National High Magnetic Field Laboratory, Tallahassee, Florida 32304, USA
| | - Zhehong Gan
- National High Magnetic Field Laboratory, Tallahassee, Florida 32304, USA
| | - Robert Schurko
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor N9B 3P4, Ontario, Canada
| | - Lucio Frydman
- National High Magnetic Field Laboratory, Tallahassee, Florida 32304, USA
- Department of Chemical Physics, Weizmann Institute of Sciences, 76100 Rehovot, Israel
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Schöps P, Spindler PE, Marko A, Prisner TF. Broadband spin echoes and broadband SIFTER in EPR. J Magn Reson 2015; 250:55-62. [PMID: 25506814 DOI: 10.1016/j.jmr.2014.10.017] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Revised: 10/25/2014] [Accepted: 10/28/2014] [Indexed: 05/12/2023]
Abstract
Applications of broadband pulses for EPR have been reported for FID, echo detection and inversion pulses recently. Here we present a broadband Hahn, stimulated and refocused echo sequence derived from adiabatic pulses. The formation of echoes is accomplished by using variable chirp rates and pulse lengths. In all three broadband echo experiments the complete spectral shape of a nitroxide (about 70 Gauss at X-band frequency) could be recovered by Fourier transformation of the quadrature detected echo signals. Such broadband echoes provide an exciting opportunity to optimize pulse sequences where a full excitation of the spectrum is mandatory for an optimum performance. We applied our pulses to the SIFTER (single frequency technique for refocusing dipolar couplings) experiment, a solid echo based pulse sequence to measure the dipolar coupling between two unpaired electron spins. By employing our broadband Hahn echo sequence on a nitroxide biradical we could achieve an artifact free dipolar evolution time trace in the SIFTER experiment with 95% modulation depth at X-band frequency and of 10% modulation depth at Q-band frequency.
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Affiliation(s)
- Philipp Schöps
- Institut für physikalische und theoretische Chemie, Goethe Universität Frankfurt, Max von Laue Straße 7, 60438 Frankfurt am Main, Germany
| | - Philipp E Spindler
- Institut für physikalische und theoretische Chemie, Goethe Universität Frankfurt, Max von Laue Straße 7, 60438 Frankfurt am Main, Germany
| | - Andriy Marko
- Institut für physikalische und theoretische Chemie, Goethe Universität Frankfurt, Max von Laue Straße 7, 60438 Frankfurt am Main, Germany
| | - Thomas F Prisner
- Institut für physikalische und theoretische Chemie, Goethe Universität Frankfurt, Max von Laue Straße 7, 60438 Frankfurt am Main, Germany.
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Skinner TE. Further perspective on the theory of heteronuclear decoupling. J Magn Reson 2014; 248:146-152. [PMID: 25104565 DOI: 10.1016/j.jmr.2014.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 06/02/2014] [Accepted: 06/05/2014] [Indexed: 06/03/2023]
Abstract
An exact general theory of heteronuclear decoupling is presented for spin-1/2 IS systems. RF irradiation applied to the I spins both modifies and generates additional couplings between states of the system. The recently derived equivalence between the dynamics of any N-level quantum system and a system of classical coupled harmonic oscillators makes explicit the exact physical couplings between states. Decoupling is thus more properly viewed as a complex intercoupling. The sign of antiphase magnetization plays a fundamental role in decoupling. A one-to-one correspondence is demonstrated between ±2SyIz and the sense of the S-spin coupling evolution. Magnetization Sx is refocused to obtain the desired decoupled state when ∫2SyIzdt=0. The exact instantaneous coupling at any time during the decoupling sequence is readily obtained in terms of the system states, showing that the creation of two-spin coherence is crucial for reducing the effective scalar coupling, as required for refocusing to occur. Representative examples from new aperiodic sequences as well as standard cyclic, periodic composite-pulse and adiabatic decoupling sequences illustrate the decoupling mechanism. The more general aperiodic sequences, obtained using optimal control, realize the potential inherent in the theory for significantly improved decoupling.
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Affiliation(s)
- Thomas E Skinner
- Physics Department, Wright State University, Dayton, OH 45435, USA.
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40
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Donovan KJ. Synchronized and concurrent experiments in Moving Tube NMR: using separate sample volumes for different pulse sequences. J Magn Reson 2014; 247:104-109. [PMID: 25261744 DOI: 10.1016/j.jmr.2014.08.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 08/27/2014] [Accepted: 08/30/2014] [Indexed: 06/03/2023]
Abstract
This study presents a new application of sample shuttling with a long NMR tube (Moving Tube NMR, MT-NMR) as a method for collecting different experiments synchronously or even concurrently using separate sample regions. Synchronized experiments were performed using an automated shuttling apparatus to move different sample regions into the coil between transients such that each experiment was collected using a separate, specific sample segment. Additionally, a 2D NOESY spectrum and a double quantum filtered COSY (DQCOSY) spectrum were collected concurrently by shuttling between two different sample regions during the NOESY mixing time. These applications of the Moving Tube technique show that it is a useful platform for compounded data acquisition to optimize spectrometer time by minimizing measurement times and avoiding problems arising from instrument and sample instabilities. Furthermore, collecting a DQCOSY during a 2D NOESY mixing time opens a wide array of possibilities, as this principle can be applied to collect any experiment during a NOESY mixing time provided that the mixing period is longer than the sum of the sample shuttling time plus a complete scan of the intermittent experiment. While this methodology relies on the use of a long sample tube, it does not require excessive sample volumes, as two milliliters is enough to constitute multiple sample regions.
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Affiliation(s)
- Kevin J Donovan
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA.
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Jahng GH, Li KL, Ostergaard L, Calamante F. Perfusion magnetic resonance imaging: a comprehensive update on principles and techniques. Korean J Radiol 2014; 15:554-77. [PMID: 25246817 PMCID: PMC4170157 DOI: 10.3348/kjr.2014.15.5.554] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Accepted: 07/05/2014] [Indexed: 12/16/2022] Open
Abstract
Perfusion is a fundamental biological function that refers to the delivery of oxygen and nutrients to tissue by means of blood flow. Perfusion MRI is sensitive to microvasculature and has been applied in a wide variety of clinical applications, including the classification of tumors, identification of stroke regions, and characterization of other diseases. Perfusion MRI techniques are classified with or without using an exogenous contrast agent. Bolus methods, with injections of a contrast agent, provide better sensitivity with higher spatial resolution, and are therefore more widely used in clinical applications. However, arterial spin-labeling methods provide a unique opportunity to measure cerebral blood flow without requiring an exogenous contrast agent and have better accuracy for quantification. Importantly, MRI-based perfusion measurements are minimally invasive overall, and do not use any radiation and radioisotopes. In this review, we describe the principles and techniques of perfusion MRI. This review summarizes comprehensive updated knowledge on the physical principles and techniques of perfusion MRI.
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Affiliation(s)
- Geon-Ho Jahng
- Department of Radiology, Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul 134-727, Korea
| | - Ka-Loh Li
- Wolfson Molecular Imaging Center, The University of Manchester, Manchester M20 3LJ, UK
| | - Leif Ostergaard
- Center for Functionally Integrative Neuroscience, Department of Neuroradiology, Aarhus University Hospital, Aarhus C 8000, Denmark
| | - Fernando Calamante
- Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria 3084, Australia
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Wastling SJ, Barker GJ. Designing hyperbolic secant excitation pulses to reduce signal dropout in gradient-echo echo-planar imaging. Magn Reson Med 2014; 74:661-72. [PMID: 25203420 DOI: 10.1002/mrm.25444] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 08/14/2014] [Accepted: 08/14/2014] [Indexed: 12/24/2022]
Abstract
PURPOSE To design hyperbolic secant (HS) excitation pulses to reduce signal dropout in the orbitofrontal and inferior temporal regions in gradient-echo echo-planar imaging (GE-EPI) for functional MRI (fMRI) applications. METHODS An algorithm based on Bloch simulations optimizes the HS pulse parameters needed to give the desired signal response across the range of susceptibility gradients observed in the human head (approximately ±250 μT·m(-1) ). The impact of the HS pulse on the signal, temporal signal-to-noise ratio, blood oxygen level-dependent (BOLD) sensitivity, and ability to detect resting state BOLD signal changes was assessed in six healthy male volunteers at 3T. RESULTS The optimized HS pulse (μ = 4.25, β = 3040 Hz, A0 = 12.3 μT, Δf = 4598 Hz) had a near uniform signal response for through-plane susceptibility gradients in the range ±250 μT·m(-1) . Signal, temporal signal-to-noise ratio, BOLD sensitivity, and the detectability of resting state networks were all partially recovered in the orbitofrontal and inferior temporal regions; however, there were signal losses of up to 50% in regions of homogeneous field (and signal loss from in-plane susceptibility gradients remained). CONCLUSION The HS pulse reduced signal dropout and could be used to acquire task and resting state fMRI data without loss of spatial coverage or temporal resolution.
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Balchandani P, Qiu D. Semi-adiabatic Shinnar-Le Roux pulses and their application to diffusion tensor imaging of humans at 7T. Magn Reson Imaging 2014; 32:804-12. [PMID: 24928300 PMCID: PMC4099418 DOI: 10.1016/j.mri.2014.04.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 02/11/2014] [Accepted: 04/04/2014] [Indexed: 10/25/2022]
Abstract
The adiabatic Shinnar-Le Roux (SLR) algorithm for radiofrequency (RF) pulse design enables systematic control of pulse parameters such as bandwidth, RF energy distribution and duration. Some applications, such as diffusion-weighted imaging (DWI) at high magnetic fields, would benefit from RF pulses that can provide greater B1 insensitivity while adhering to echo time and specific absorption rate (SAR) limits. In this study, the adiabatic SLR algorithm was employed to generate 6-ms and 4-ms 180° semi-adiabatic RF pulses which were used to replace the refocusing pulses in a twice-refocused spin echo (TRSE) diffusion-weighted echo planar imaging (DW-EPI) sequence to create two versions of a twice-refocused adiabatic spin echo (TRASE) sequence. The two versions were designed for different trade-offs between adiabaticity and echo time. Since a pair of identical refocusing pulses is applied, the quadratic phase imposed by the first is unwound by the second, preserving the linear phase created by the excitation pulse. In vivo images of the human brain obtained at 7Testa (7T) demonstrate that both versions of the TRASE sequence developed in this study achieve more homogeneous signal in the diffusion-weighted images than the conventional TRSE sequence. Semi-adiabatic SLR pulses offer a more B1-insensitive solution for diffusion preparation at 7T, while operating within SAR constraints. This method may be coupled with any EPI readout trajectory and parallel imaging scheme to provide more uniform coverage for diffusion tensor imaging at 7T and 3T.
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Affiliation(s)
- Priti Balchandani
- Department of Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Department of Radiology, Stanford University, Stanford, CA, USA.
| | - Deqiang Qiu
- Department of Radiology, Stanford University, Stanford, CA, USA; Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, USA
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Brenner D, Stirnberg R, Pracht ED, Stöcker T. Two-dimensional accelerated MP-RAGE imaging with flexible linear reordering. Magn Reson Mater Phy 2014; 27:455-62. [DOI: 10.1007/s10334-014-0430-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 12/18/2013] [Accepted: 01/13/2014] [Indexed: 11/30/2022]
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Garbacz P, Terskikh VV, Ferguson MJ, Bernard GM, Kędziorek M, Wasylishen RE. Experimental characterization of the hydride 1H shielding tensors for HIrX2(PR3)2 and HRhCl2(PR3)2: extremely shielded hydride protons with unusually large magnetic shielding anisotropies. J Phys Chem A 2014; 118:1203-12. [PMID: 24460126 DOI: 10.1021/jp411378j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The hydride proton magnetic shielding tensors for a series of iridium(III) and rhodium(III) complexes are determined. Although it has long been known that hydridic protons for transition-metal hydrides are often extremely shielded, this is the first experimental determination of the shielding tensors for such complexes. Isolating the (1)H NMR signal for a hydride proton requires careful experimental strategies because the spectra are generally dominated by ligand (1)H signals. We show that this can be accomplished for complexes containing as many as 66 ligand protons by substituting the latter with deuterium and by using hyperbolic secant pulses to selectively irradiate the hydride proton signal. We also demonstrate that the quality of the results is improved by performing experiments at the highest practical magnetic field (21.14 T for the work presented here). The hydride protons for iridium hydride complexes HIrX2(PR3)2 (X = Cl, Br, or I; R = isopropyl, cyclohexyl) are highly shielded with isotropic chemical shifts of approximately -50 ppm and are also highly anisotropic, with spans (=δ11 - δ33) ranging from 85.1 to 110.7 ppm. The hydridic protons for related rhodium complexes HRhCl2(PR3)2 also have unusual magnetic shielding properties with chemical shifts and spans of approximately -32 and 85 ppm, respectively. Relativistic density functional theory computations were performed to determine the orientation of the principal components of the hydride proton shielding tensors and to provide insights into the origin of these highly anisotropic shielding tensors. The results of our computations agree well with experiment, and our conclusions concerning the importance of relativistic effects support those recently reported by Kaupp and co-workers.
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Affiliation(s)
- Piotr Garbacz
- Gunning/Lemieux Chemistry Centre, University of Alberta , Edmonton, Alberta T6G 2G2, Canada
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Lee Y, Han Y, Park H, Watanabe H, Garwood M, Park JY. New phase-based B1 mapping method using two-dimensional spin-echo imaging with hyperbolic secant pulses. Magn Reson Med 2014; 73:170-81. [PMID: 24459088 DOI: 10.1002/mrm.25110] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2013] [Revised: 12/07/2013] [Accepted: 12/11/2013] [Indexed: 11/09/2022]
Abstract
PURPOSE To propose a new phase-based B1-mapping method that exploits phase information created by hyperbolic secant (HS) pulses in conventional 2D spin-echo imaging. METHODS In this B1-mapping method, HS pulses are used to accomplish π/2 excitation and π refocusing in standard multislice spin-echo imaging. When setting the ratio of pulse lengths of the π/2 and π HS pulses to 2:1, the spin-echo phase is independent of offset frequency and varies as a function of B1 strength. To eliminate undesired phase accumulations induced by unknown factors other than the B1 strength, two spin-echo images are acquired using HS pulses applied with opposite frequency-sweep directions, and the resulting phase images are subtracted from each other. To demonstrate the performance of the proposed method, phantom and in vivo experiments were performed using a surface coil and a volume coil. RESULTS The B1 maps obtained by using the proposed method were in accordance with the B1 maps obtained using previous methods in both phantom and in vivo experiments. CONCLUSION The proposed method is easy to implement without any sequence modification, is insensitive to B0 inhomogeneity and chemical shift, and is robust in a reasonably wide range of B1 field strength.
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Affiliation(s)
- Yoojin Lee
- Department of Electrical Engineering, Korean Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Yeji Han
- Department of Electrical Engineering, Korean Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - HyunWook Park
- Department of Electrical Engineering, Korean Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Hidehiro Watanabe
- Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, Japan
| | - Michael Garwood
- The Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jang-Yeon Park
- School of Biomedical Engineering, College of Biomedical and Health Science, Research Institute of Biomedical Engineering, Konkuk University, Chungju, Korea (ROK)
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Theis T, Feng Y, Wu T, Warren WS. Composite and shaped pulses for efficient and robust pumping of disconnected eigenstates in magnetic resonance. J Chem Phys 2014; 140:014201. [DOI: 10.1063/1.4851337] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Kathiravan S, Kanakaraj J. A review on potential issues and challenges in MR imaging. ScientificWorldJournal 2013; 2013:783715. [PMID: 24381523 DOI: 10.1155/2013/783715] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 10/29/2013] [Indexed: 11/17/2022] Open
Abstract
Magnetic resonance imaging is a noninvasive technique that has been developed for its excellent depiction of soft tissue contrasts. Instruments capable of ultra-high field strengths, ≥7 Tesla, were recently engineered and have resulted in higher signal-to-noise and higher resolution images. This paper presents various subsystems of the MR imaging systems like the magnet subsystem, gradient subsystem, and also various issues which arise due to the magnet. Further, it also portrays finer details about the RF coils and transceiver and also various limitations of the RF coils and transceiver. Moreover, the concept behind the data processing system and the challenges related to it were also depicted. Finally, the various artifacts associated with the MR imaging were clearly pointed out. It also presents a brief overview about all the challenges related to MR imaging systems.
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Kaufmann T, Keller TJ, Franck JM, Barnes RP, Glaser SJ, Martinis JM, Han S. DAC-board based X-band EPR spectrometer with arbitrary waveform control. J Magn Reson 2013; 235:95-108. [PMID: 23999530 PMCID: PMC3863685 DOI: 10.1016/j.jmr.2013.07.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 07/28/2013] [Accepted: 07/30/2013] [Indexed: 05/07/2023]
Abstract
We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ≤ 250 ps resolution. The implications and potential applications of these capabilities will be discussed.
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Affiliation(s)
- Thomas Kaufmann
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Timothy J. Keller
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA
| | - John M. Franck
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Ryan P. Barnes
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA
| | | | - John M. Martinis
- Department of Physics, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Songi Han
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA
- Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA, USA
- Corresponding author. Address: Department of Chemistry and Biochemistry, 9510, University of California Santa Barbara, CA, USA. (S. Han)
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