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Wallstein N, Müller R, Pampel A, Möller HE. Radiation damping at clinical field strength: Characterization and compensation in quantitative measurements. Magn Reson Med 2024; 91:1239-1253. [PMID: 38010072 DOI: 10.1002/mrm.29934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 10/03/2023] [Accepted: 10/24/2023] [Indexed: 11/29/2023]
Abstract
PURPOSE In any MR experiment, the bulk magnetization acts on itself, caused by the induced current in the RF receiver circuit that generates an oscillating damping field. This effect, known as "radiation damping" (RD), is usually weak and, therefore, unconsidered in MRI, but can affect quantitative studies performed with dedicated coils that provide a high SNR. The current work examined RD in a setup for investigations of small tissue specimens including a quantitative characterization of the spin-coil system. THEORY AND METHODS A custom-made Helmholtz coil (radius and spacing 16 mm) was interfaced to a transmit-receive (Tx/Rx) switch with integrated passive feedback for modulation or suppression of RD similar to preamplifier decoupling. Pulse sequences included pulse-width arrays to demonstrate the absence/ presence of RD and difference techniques employing gradient pulses or composite RF pulses to quantify RD effects during free precession and transmission, respectively. Experiments were performed at 3T in small samples of MnCl2 solution. RESULTS Significant RD effects may impact RF pulse application and evolution periods. Effective damping time constants were comparable to typical T2 * times or echo spacings in multi-echo sequences. Measurements of the phase relation showed that deviations from the commonly assumed 90° angle between the damping field and the transverse magnetization may occur. CONCLUSION Radiation damping may affect the accuracy of quantitative MR measurements performed with dedicated RF coils. Efficient mitigation can be achieved hardware-based or by appropriate consideration in the pulse sequence.
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Affiliation(s)
- Niklas Wallstein
- Nuclear Magnetic Resonance Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Roland Müller
- Nuclear Magnetic Resonance Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - André Pampel
- Nuclear Magnetic Resonance Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Harald E Möller
- Nuclear Magnetic Resonance Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
- Faculty of Physics and Earth Sciences, Felix Bloch Institute for Solid State Physics, Leipzig University, Leipzig, Germany
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Pelupessy P. Radiation damping strongly perturbs remote resonances in the presence of homonuclear mixing. MAGNETIC RESONANCE (GOTTINGEN, GERMANY) 2022; 3:43-51. [PMID: 37905177 PMCID: PMC10539763 DOI: 10.5194/mr-3-43-2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 02/12/2022] [Indexed: 11/02/2023]
Abstract
In this work, it is experimentally shown that the weak oscillating magnetic field (known as the "radiation damping" field) caused by the inductive coupling between the transverse magnetization of nuclei and the radio frequency circuit perturbs remote resonances when homonuclear total correlation mixing is applied. Numerical simulations are used to rationalize this effect.
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Affiliation(s)
- Philippe Pelupessy
- Laboratoire des Biomolécules (LBM), Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
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Jena A, Taneja S, Rana P, Goyal N, Vaish A, Botchu R, Vaishya R. Emerging role of integrated PET-MRI in osteoarthritis. Skeletal Radiol 2021; 50:2349-2363. [PMID: 34185124 DOI: 10.1007/s00256-021-03847-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 06/16/2021] [Accepted: 06/16/2021] [Indexed: 02/02/2023]
Abstract
Osteoarthritis (OA) is a common degenerative disorder of the articular cartilage, which is associated with hypertrophic changes in the bone, synovial inflammation, subchondral sclerosis, and joint space narrowing (JSN). Radiography remains the first line of imaging till now. Due to the lack of soft-tissue depiction in radiography, researchers are exploring various imaging techniques to detect OA at an early stage and understand its pathophysiology to restrict its progression and discover disease-modifying agents in OA. As the OA relates to the degradation of articular cartilage and remodeling of the underlying bone, an optimal imaging tool must be sensitive to the bone and soft tissue health. In that line, many non-invasive imaging and minimally invasive techniques have been explored. Out of these, the non-invasive compositional magnetic resonance imaging (MRI) for evaluation of the integrity of articular cartilage and positron emission tomography (PET) scan with fluorodeoxyglucose (FDG) and more specific bone-seeking tracer like sodium fluoride (18F-NaF) for bone cartilage interface are some of the leading areas of ongoing work. Integrated PET-MRI system, a new hybrid modality that combines the virtues of the above two individual modalities, allows detailed imaging of the entire joint, including soft tissue cartilage and bone, and holds great potential to research complex disease processes of OA. This narrative review attempts to signify individual characteristics of MRI, PET, the fusion of these characteristics in PET-MRI, and the ongoing research on PET-MRI as a potential tool to understand the pathophysiology of OA.
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Affiliation(s)
- Amarnath Jena
- PET SUITE (Indraprastha Apollo Hospitals and House of Diagnostics), Department of Molecular Imaging and Nuclear Medicine, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
| | - Sangeeta Taneja
- PET SUITE (Indraprastha Apollo Hospitals and House of Diagnostics), Department of Molecular Imaging and Nuclear Medicine, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
| | - Prerana Rana
- PET SUITE (Indraprastha Apollo Hospitals and House of Diagnostics), Department of Molecular Imaging and Nuclear Medicine, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India.,Apollo Hospitals Education & Research Foundation, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
| | - Nidhi Goyal
- Department of Radiodiagnosis and Imaging, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
| | - Abhishek Vaish
- Department of Orthopaedics and Joint Replacement Surgery, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
| | - Rajesh Botchu
- Department of Musculoskeletal Radiology, Royal Orthopedic Hospital, Birmingham, UK.
| | - Raju Vaishya
- Department of Orthopaedics and Joint Replacement Surgery, Indraprastha Apollo Hospitals, Sarita Vihar, Delhi-Mathura Road, New Delhi, 110076, India
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Detection of early cartilage degeneration in the tibiotalar joint using 3 T gagCEST imaging: a feasibility study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2020; 34:249-260. [PMID: 32725359 PMCID: PMC8018923 DOI: 10.1007/s10334-020-00868-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 07/10/2020] [Accepted: 07/14/2020] [Indexed: 02/07/2023]
Abstract
OBJECTIVE To establish and optimize a stable 3 Tesla (T) glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging protocol for assessing the articular cartilage of the tibiotalar joint in healthy volunteers and patients after a sustained injury to the ankle. METHODS Using Bloch-McConnell simulations, we optimized the sequence protocol for a 3 T MRI scanner for maximum gagCEST effect size within a clinically feasible time frame of less than 07:30 min. This protocol was then used to analyze the gagCEST effect of the articular cartilage of the tibiotalar joint of 17 healthy volunteers and five patients with osteochondral lesions of the talus following ankle trauma. Reproducibility was tested with the intraclass correlation coefficient. RESULTS The mean magnetization transfer ratio asymmetry (MTRasym), i.e., the gagCEST effect size, was significantly lower in patients than in healthy volunteers (0.34 ± 1.9% vs. 1.49 ± 0.11%; p < 0.001 [linear mixed model]). Intra- and inter-rater reproducibility was excellent with an average measure intraclass correlation coefficient (ICC) of 0.97 and a single measure ICC of 0.91 (p < 0.01). DISCUSSION In this feasibility study, pre-morphological tibiotalar joint cartilage damage was quantitatively assessable on the basis of the optimized 3 T gagCEST imaging protocol that allowed stable quantification gagCEST effect sizes across a wide range of health and disease in clinically feasible acquisition times.
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Shishmarev D, Chapman BE, Naumann C, Mamone S, Kuchel PW. (1)H NMR z-spectra of acetate methyl in stretched hydrogels: quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 250:29-36. [PMID: 25486634 DOI: 10.1016/j.jmr.2014.11.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 10/28/2014] [Accepted: 11/03/2014] [Indexed: 06/04/2023]
Abstract
The (1)H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm.
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Affiliation(s)
- Dmitry Shishmarev
- School of Molecular Bioscience, University of Sydney, NSW 2006, Australia
| | - Bogdan E Chapman
- School of Molecular Bioscience, University of Sydney, NSW 2006, Australia
| | - Christoph Naumann
- School of Molecular Bioscience, University of Sydney, NSW 2006, Australia
| | - Salvatore Mamone
- School of Chemistry, Southampton University, SO17 1BJ, United Kingdom
| | - Philip W Kuchel
- School of Molecular Bioscience, University of Sydney, NSW 2006, Australia.
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Kauppinen RA. Multiparametric magnetic resonance imaging of acute experimental brain ischaemia. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 80:12-25. [PMID: 24924265 DOI: 10.1016/j.pnmrs.2014.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 05/07/2014] [Accepted: 05/07/2014] [Indexed: 06/03/2023]
Abstract
Ischaemia is a condition in which blood flow either drops to zero or proceeds at severely decreased levels that cannot supply sufficient oxidizable substrates to maintain energy metabolism in vivo. Brain, a highly oxidative organ, is particularly susceptible to ischaemia. Ischaemia leads to loss of consciousness in seconds and, if prolonged, permanent tissue damage is inevitable. Ischaemia primarily results in a collapse of cerebral energy state, followed by a series of subtle changes in anaerobic metabolism, ion and water homeostasis that eventually initiate destructive internal and external processes in brain tissue. (31)P and (1)H NMR spectroscopy were initially used to evaluate anaerobic metabolism in brain. However, since the early 1990s (1)H Magnetic Resonance Imaging (MRI), exploiting the nuclear magnetism of tissue water, has become the key method for assessment of ischaemic brain tissue. This article summarises multi-parametric (1)H MRI work that has exploited diffusion, relaxation and magnetisation transfer as 'contrasts' to image ischaemic brain in preclinical models for the first few hours, with a view to assessing evolution of ischaemia and tissue viability in a non-invasive manner.
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Affiliation(s)
- Risto A Kauppinen
- School of Experimental Psychology and Clinical Research and Imaging Centre, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
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Xu X, Lee JS, Jerschow A. Ultrafast Scanning of Exchangeable Sites by NMR Spectroscopy. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303255] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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8
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Xu X, Lee JS, Jerschow A. Ultrafast scanning of exchangeable sites by NMR spectroscopy. Angew Chem Int Ed Engl 2013; 52:8281-4. [PMID: 23813633 DOI: 10.1002/anie.201303255] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Indexed: 01/09/2023]
Affiliation(s)
- Xiang Xu
- Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY 10003, USA
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Krishnan VV, Murali N. Radiation damping in modern NMR experiments: progress and challenges. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2013; 68:41-57. [PMID: 23398972 PMCID: PMC3644564 DOI: 10.1016/j.pnmrs.2012.06.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 06/07/2012] [Indexed: 05/12/2023]
Affiliation(s)
- V V Krishnan
- Department of Chemistry, California State University, Fresno, CA 93740, USA.
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Scheidegger R, Vinogradov E, Alsop DC. Amide proton transfer imaging with improved robustness to magnetic field inhomogeneity and magnetization transfer asymmetry using saturation with frequency alternating RF irradiation. Magn Reson Med 2011; 66:1275-85. [PMID: 21608029 DOI: 10.1002/mrm.22912] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Revised: 02/01/2011] [Accepted: 02/15/2011] [Indexed: 01/21/2023]
Abstract
Amide proton transfer (APT) imaging has shown promise as an indicator of tissue pH and as a marker for brain tumors. Sources of error in APT measurements include direct water saturation, and magnetization transfer (MT) from membranes and macromolecules. These are typically suppressed by postprocessing asymmetry analysis. However, this approach is strongly dependent on B(0) homogeneity and can introduce additional errors due to intrinsic MT asymmetry, aliphatic proton features opposite the amide peak and radiation damping-induced asymmetry. Although several methods exist to correct for B(0) inhomogeneity, they tremendously increase scan times and do not address errors induced by asymmetry of the z-spectrum. In this article, a novel saturation scheme-saturation with frequency alternating RF irradiation (SAFARI)-is proposed in combination with a new magnetization transfer ratio (MTR) parameter designed to generate APT images insensitive to direct water saturation and MT, even in the presence of B(0) inhomogeneity. The feasibility of the SAFARI technique is demonstrated in phantoms and in the human brain. Experimental results show that SAFARI successfully removes direct water saturation and MT contamination from APT images. It is insensitive to B(0) offsets up to 180 Hz without using additional B(0) correction, thereby dramatically reducing scanning time.
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Affiliation(s)
- Rachel Scheidegger
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA.
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Närväinen J, Hubbard PL, Kauppinen RA, Morris GA. Z-spectroscopy with Alternating-Phase Irradiation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 207:242-250. [PMID: 20920868 DOI: 10.1016/j.jmr.2010.09.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Revised: 09/08/2010] [Accepted: 09/08/2010] [Indexed: 05/29/2023]
Abstract
Magnetization transfer (MT) MRI and Z-spectroscopy are tools to study both water-macromolecule interactions and pH-sensitive exchange dynamics between water and the protons of mobile chemical groups within these macromolecules. Both rely on saturation of frequencies offset from water and observation of the on-resonance water signal. In this work, an RF saturation method called Z-spectroscopy with Alternating-Phase Irradiation (ZAPI) is introduced. Based on the T(2)-selectivity of the irradiation pulse, ZAPI can be used to separate the different contributions to a Z-spectrum, as well as to study the T(2) distribution of the macromolecules contributing to the MT signal. ZAPI can be run at resonance for water and with low power, thus minimizing problems with specific absorption rate (SAR) limits in clinical applications. In this paper, physical and practical aspects of ZAPI are discussed and the sequence is applied in vitro to sample systems and in vivo to rat head to demonstrate the method.
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Affiliation(s)
- Johanna Närväinen
- A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Finland.
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Terreno E, Castelli DD, Viale A, Aime S. Challenges for molecular magnetic resonance imaging. Chem Rev 2010; 110:3019-42. [PMID: 20415475 DOI: 10.1021/cr100025t] [Citation(s) in RCA: 567] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Enzo Terreno
- Department of Chemistry IFM and Molecular Imaging Center, University of Torino, Torino, Italy
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Chapman BE, Naumann C, Philp DJ, Eliav U, Navon G, Kuchel PW. z-Spectra of 23Na+ in stretched gels: quantitative multiple quantum analysis. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 205:260-268. [PMID: 20638995 DOI: 10.1016/j.jmr.2010.05.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2010] [Revised: 05/12/2010] [Accepted: 05/12/2010] [Indexed: 05/29/2023]
Abstract
The (23)Na NMR spectrum of NaCl in various stretched hydrogels displays a well-resolved triplet with the theoretically predicted relative intensities of the components of 3:4:3. Families of such spectra were obtained using partially-saturating radio-frequency (RF) radiation over a range of off-set frequencies; the resulting steady-state irradiation envelopes, or 'z-spectra', have the notable feature that marked suppression of the three peaks occurs when the irradiation is applied on any of them or exactly in the middle between the central peak and either of the two satellites. We present a quantum mechanical analysis that describes this phenomenon and show that it depends on double and triple quantum transitions. The physical-mathematical analysis is an extension of our quadrupolar case for HDO with (2)H NMR. The experimental procedures and results have implications for enhancement of contrast in (23)Na magnetic resonance imaging of heterogeneous systems using quadrupolar interactions.
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Affiliation(s)
- Bogdan E Chapman
- School of Molecular Bioscience, University of Sydney, Building G08, NSW 2006, Australia
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Terreno E, Stancanello J, Longo D, Castelli DD, Milone L, Sanders HMHF, Kok MB, Uggeri F, Aime S. Methods for an improved detection of the MRI-CEST effect. CONTRAST MEDIA & MOLECULAR IMAGING 2010; 4:237-47. [PMID: 19839029 DOI: 10.1002/cmmi.290] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
CEST imaging is a recently introduced MRI contrast modality based on the use of endogenous or exogenous molecules whose exchangeable proton pools transfer saturated magnetization to bulk water, thus creating negative contrast. One of the critical issues for further development of these agents is represented by their limited sensitivity in vivo. The aim of this work is to improve the detection of CEST agents by exploring new approaches through which the saturation transfer (ST) effect can be enhanced. The performance of the proposed methods has been tested in vitro and in vivo using highly sensitive and highly shifted lipoCEST agents, and the results were compared with the standard ST evaluation mode. The acquired Z-spectra were interpolated locally and voxel-by-voxel by smoothing splines. Besides expressing the ST in the standard mode, we explore two methods, enhanced and integral ST, which better exploit all the information contained in the Z-spectrum. By combining different modes for ST assessment a significant improvement in the detection of the lipoCEST agents, both in vitro and in vivo, has been found. The results obtained from the application of the proposed methods outline the importance of post-processing analysis for highlighting the CEST-MRI contrast.
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Affiliation(s)
- Enzo Terreno
- Dipartimento di Chimica IFM and Molecular Imaging Center, University of Torino, Via P. Giuria 7, 10125 Torino, Italy
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Avni R, Mangoubi O, Bhattacharyya R, Degani H, Frydman L. Magnetization transfer magic-angle-spinning z-spectroscopy of excised tissues. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 199:1-9. [PMID: 19409825 DOI: 10.1016/j.jmr.2009.03.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Accepted: 03/11/2009] [Indexed: 05/27/2023]
Abstract
NMR experiments devised to aid in analyses of tissues include magnetization transfer (MT), which can highlight the signals of biological macromolecules through cross-relaxation and/or chemical exchange processes with the bulk (1)H water resonance, and high-resolution magic-angle-spinning (HRMAS) methods, akin to those used in solid-state NMR to introduce additional spectral resolution via the averaging of spin anisotropies. This paper explores the result of combining these methodologies, and reports on MT "z-spectroscopy" between water and cell components in excised tissues under a variety of HRMAS conditions. Main features arising from the resulting (1)H "MTMAS" experiments include strong spinning sideband manifolds centered at the liquid water shift, high-resolution isotropic features coinciding with aliphatic and amide proton resonances, and a second sideband manifold arising as spinning speeds are increased. Interpretations are given for the origin of these various features, including simulations shedding further light onto the nature of MT NMR signals observed for tissue samples. Concurrently, histological examinations are reported validating the limits of HRMAS NMR procedures to the analysis of tissue samples preserved in a number of different ways.
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Affiliation(s)
- Reut Avni
- Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel
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Stancanello J, Terreno E, Castelli DD, Cabella C, Uggeri F, Aime S. Development and validation of a smoothing-splines-based correction method for improving the analysis of CEST-MR images. CONTRAST MEDIA & MOLECULAR IMAGING 2008; 3:136-49. [DOI: 10.1002/cmmi.240] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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17
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Zhao JM, Har-el YE, McMahon MT, Zhou J, Sherry AD, Sgouros G, Bulte JWM, van Zijl PCM. Size-induced enhancement of chemical exchange saturation transfer (CEST) contrast in liposomes. J Am Chem Soc 2008; 130:5178-84. [PMID: 18361490 PMCID: PMC2759111 DOI: 10.1021/ja710159q] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Liposome-based chemical exchange saturation transfer (lipoCEST) agents have shown great sensitivity and potential for molecular magnetic resonance imaging (MRI). Here we demonstrate that the size of liposomes can be exploited to enhance the lipoCEST contrast. A concise analytical model is developed to describe the contrast dependence on size for an ensemble of liposomes. The model attributes the increased lipoCEST contrast in smaller liposomes to their larger surface-to-volume ratio, causing an increased membrane water exchange rate. Experimentally measured rates correlate with size, in agreement with the model. The water permeability of liposomal membrane is found to be 1.11 +/- 0.14 microm/s for the specific lipid composition at 22 degrees C. Availability of the model allows rational design of the size of liposomes and quantification of their properties. These new theoretical and experimental tools are expected to benefit applications of liposomes to sensing the cellular environment, targeting and imaging biological processes, and optimizing drug delivery properties.
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Jokivarsi KT, Gröhn HI, Gröhn OH, Kauppinen RA. Proton transfer ratio, lactate, and intracellular pH in acute cerebral ischemia. Magn Reson Med 2007; 57:647-53. [PMID: 17390356 DOI: 10.1002/mrm.21181] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The amide proton transfer ratio (APTR) from the asymmetry of the Z-spectrum was determined in rat brain tissue during and after unilateral middle cerebral artery occlusion (MCAo). Cerebral lactate (Lac) as determined by (1)H NMR spectroscopy, water diffusion, and T(1rho) were quantified as well. Lac concentrations were used to estimate intracellular pH (pH(i)) in the brain during the MCA occlusion. A decrease in APTR during occlusion indicated acidification from 7.1 to 6.79 +/- 0.19 (a drop by 0.3 +/- 0.2 pH units), whereas pH(i) computed from Lac concentration was 6.3 +/- 0.2 (a drop by 0.8 +/- 0.2 pH units). Despite the disagreement between the two methods in terms of the size of the change in the absolute pH(i) during ischemia, DeltaAPTR and pH(i) (and Lac concentration) displayed a strong correlation during the MCAo. Diffusion and T(1rho) indicated cytotoxic edema following MCA occlusion; however, APTR returned slowly toward the values determined in the contralateral hemisphere post-ischemia. These data argue that the APTR during ischemia is affected not only by pH(i) but by other physicochemical factors as well, and indicates different aspects of pathology in the post-ischemic brain compared to those that influence water diffusion and T(1rho).
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Affiliation(s)
- Kimmo T Jokivarsi
- Department of Neurobiology, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland
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