1
|
Biller JR, McPeak JE. EPR Everywhere. APPLIED MAGNETIC RESONANCE 2021; 52:1113-1139. [PMID: 33519097 PMCID: PMC7826499 DOI: 10.1007/s00723-020-01304-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Revised: 10/16/2020] [Accepted: 12/06/2020] [Indexed: 06/12/2023]
Abstract
This review is inspired by the contributions from the University of Denver group to low-field EPR, in honor of Professor Gareth Eaton's 80th birthday. The goal is to capture the spirit of innovation behind the body of work, especially as it pertains to development of new EPR techniques. The spirit of the DU EPR laboratory is one that never sought to limit what an EPR experiment could be, or how it could be applied. The most well-known example of this is the development and recent commercialization of rapid-scan EPR. Both of the Eatons have made it a point to remain knowledgeable on the newest developments in electronics and instrument design. To that end, our review touches on the use of miniaturized electronics and applications of single-board spectrometers based on software-defined radio (SDR) implementations and single-chip voltage-controlled oscillator (VCO) arrays. We also highlight several non-traditional approaches to the EPR experiment such as an EPR spectrometer with a "wand" form factor for analysis of the OxyChip, the EPR-MOUSE which enables non-destructive in situ analysis of many non-conforming samples, and interferometric EPR and frequency swept EPR as alternatives to classical high Q resonant structures.
Collapse
Affiliation(s)
| | - Joseph E. McPeak
- University of Denver, Denver, CO 80210 USA
- Berlin Joint EPR Laboratory and EPR4Energy, Department Spins in Energy Conversion and Quantum Information Science (ASPINS), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| |
Collapse
|
2
|
Shi Y, Eaton SS, Eaton GR. Rapid-scan EPR imaging of a phantom comprised of species with different linewidths and relaxation times. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 308:106593. [PMID: 31520789 PMCID: PMC6829054 DOI: 10.1016/j.jmr.2019.106593] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 09/05/2019] [Accepted: 09/06/2019] [Indexed: 06/10/2023]
Abstract
As a demonstration of the application of rapid-scan EPR to imaging at low frequency and magnetic field, a multi-compartment phantom containing six different samples was imaged. The samples were nitroxide radicals, trityl (substituted triarylmethyl) radicals, and the oxygen-sensitive solid lithium phthalocyanine (LiPc), all of which are useful for in vivo imaging. The 2D spectral-spatial image demonstration was performed at 250 MHz, with samples in sealed tubes of various sizes arranged in a 3D-printed plastic holder. Maximum gradients of 10 G/cm gave a spatial resolution of about 0.1 mm for the narrow trityl and LiPc signals and about 1 mm for the nitroxide. The importance of proper selection of resonator bandwidth and scan rate for obtaining accurate linewidth information is demonstrated for a case in which the phantom is composed of species with signal linewidths and relaxation times that differ by more than a factor of 10.
Collapse
Affiliation(s)
- Yilin Shi
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
| |
Collapse
|
3
|
Buchanan LA, Woodcock LB, Rinard GA, Quine RW, Shi Y, Eaton SS, Eaton GR. 250 MHz Rapid Scan Cross Loop Resonator. APPLIED MAGNETIC RESONANCE 2019; 50:333-345. [PMID: 30799909 PMCID: PMC6380496 DOI: 10.1007/s00723-018-1078-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
A 25 mm diameter 250 MHz crossed-loop resonator was designed for rapid scan electron paramagnetic resonance imaging. It has a saddle coil for the driven resonator and a fine wire, loop gap resonator for the sample resonator. There is good separation of E and B fields and high isolation between the two resonators, permitting a wide range of sample types to be measured. Applications to imaging of nitroxide, trityl, and LiPc samples illustrate the utility of the resonator. Using this resonator and a trityl sample the signal-to-noise of a rapid scan absorption spectrum is about 20 times higher than for a first-derivative CW spectrum.
Collapse
Affiliation(s)
- Laura A. Buchanan
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210
| | - Lukas B. Woodcock
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210
| | - George A. Rinard
- School of Engineering and Computer Science, University of Denver, Denver, CO 80210
| | - Richard W. Quine
- School of Engineering and Computer Science, University of Denver, Denver, CO 80210
| | - Yilin Shi
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210
| |
Collapse
|
4
|
Rinard GA, Quine RW, Buchanan LA, Eaton SS, Eaton GR, Epel B, Sundramoorthy SV, Halpern HJ. Resonators for In Vivo Imaging: Practical Experience. APPLIED MAGNETIC RESONANCE 2017; 48:1227-1247. [PMID: 29391664 PMCID: PMC5788320 DOI: 10.1007/s00723-017-0947-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Resonators for preclinical electron paramagnetic resonance imaging have been designed primarily for rodents and rabbits and have internal diameters between 16 and 51 mm. Lumped circuit resonators include loop-gap, Alderman-Grant, and saddle coil topologies and surface coils. Bimodal resonators are useful for isolating the detected signal from incident power and reducing dead time in pulse experiments. Resonators for continuous wave, rapid scan, and pulse experiments are described. Experience at the University of Chicago and University of Denver in design of resonators for in vivo imaging is summarized.
Collapse
Affiliation(s)
- George A Rinard
- Center for EPR Imaging In Vivo Physiology, Department of Chemistry and Biochemistry and School of Engineering and Computer Science, University of Denver, Denver, CO 80210, USA
| | - Richard W Quine
- Center for EPR Imaging In Vivo Physiology, Department of Chemistry and Biochemistry and School of Engineering and Computer Science, University of Denver, Denver, CO 80210, USA
| | - Laura A Buchanan
- Center for EPR Imaging In Vivo Physiology, Department of Chemistry and Biochemistry and School of Engineering and Computer Science, University of Denver, Denver, CO 80210, USA
| | - Sandra S Eaton
- Center for EPR Imaging In Vivo Physiology, Department of Chemistry and Biochemistry and School of Engineering and Computer Science, University of Denver, Denver, CO 80210, USA
| | - Gareth R Eaton
- Center for EPR Imaging In Vivo Physiology, Department of Chemistry and Biochemistry and School of Engineering and Computer Science, University of Denver, Denver, CO 80210, USA
| | - Boris Epel
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, IL, USA
| | - Subramanian V Sundramoorthy
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, IL, USA
| | - Howard J Halpern
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, IL, USA
| |
Collapse
|
5
|
Rinard GA, Quine RW, McPeak J, Buchanan L, Eaton SS, Eaton GR. An X-Band Crossed-Loop EPR Resonator. APPLIED MAGNETIC RESONANCE 2017; 48:1219-1226. [PMID: 29276341 PMCID: PMC5739319 DOI: 10.1007/s00723-017-0945-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
A copper X-band (9.22 GHz) cross loop resonator has been constructed for use with 4 mm sample tubes. The Q for the two resonators are 380 and 350, respectively. The resonator efficiency is about 1 G per square root of watt. Operation has been demonstrated with measurement of T1 by saturation recovery for samples of coal and an immobilized nitroxide radical.
Collapse
Affiliation(s)
- George A Rinard
- School of Engineering and Computer Science and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Richard W Quine
- School of Engineering and Computer Science and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Joseph McPeak
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Laura Buchanan
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry and Center for EPR Imaging In Vivo Physiology, University of Denver, Denver, CO 80208
| |
Collapse
|
6
|
Boris E, Sundramoorthy SV, Halpern HJ. 250 MHz passive Q-modulator for reflection resonators. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2017; 47B:e21356. [PMID: 29576754 PMCID: PMC5863916 DOI: 10.1002/cmr.b.21356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A simple scheme for dynamically switching the quality factor, Q, of a Loop-Gap Resonator (LGR); working at 250 MHz is presented. The addition of this Q-modulator resulted in 30% improvement in Electron Paramagnetic Resonance imager signal-to-noise ratio. During pulse excitation, this scheme lowered the Q, while higher Q was obtained during signal detection. These conditions favored the image acquisition. The Q-modulator is passive; the transition between different states was actuated by the radio frequency power itself.
Collapse
Affiliation(s)
- Epel Boris
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637
| | - Subramanian V Sundramoorthy
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637
| | - Howard J Halpern
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637
| |
Collapse
|
7
|
Quine RW, Rinard GA, Shi Y, Buchanan L, Biller JR, Eaton SS, Eaton GR. UHF EPR spectrometer operating at frequencies between 400 MHz and 1 GHz. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2016; 46B:123-133. [PMID: 28190987 PMCID: PMC5300075 DOI: 10.1002/cmr.b.21328] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A spectrometer was designed and constructed to facilitate measurements of T1, T2, spin echo signal-to-noise, and resonator quality factor, Q, between about 400 and 1000 MHz. Pulse patterns are generated at 250 MHz and mixed with the output from a second source to perform excitation and detection. A cross-loop resonator was constructed in which the same sample could be measured in the same resonator over the full range of frequencies. An air-core, 4-coil, water-cooled electromagnet with a large experimental volume was built.
Collapse
Affiliation(s)
- Richard W. Quine
- Ritchie School of Engineering and Computer Science, University of Denver, Denver, Colorado 80210 USA
| | - George A. Rinard
- Ritchie School of Engineering and Computer Science, University of Denver, Denver, Colorado 80210 USA
| | - Yilin Shi
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210 USA
| | - Laura Buchanan
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210 USA
| | - Joshua R. Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210 USA
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210 USA
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado, 80210 USA
| |
Collapse
|
8
|
Biller JR, Tseitlin M, Quine RW, Rinard GA, Weismiller HA, Elajaili H, Rosen GM, Kao JPY, Eaton SS, Eaton GR. Imaging of nitroxides at 250MHz using rapid-scan electron paramagnetic resonance. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 242:162-8. [PMID: 24650729 PMCID: PMC4081024 DOI: 10.1016/j.jmr.2014.02.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 02/15/2014] [Accepted: 02/18/2014] [Indexed: 05/12/2023]
Abstract
Projections for 2D spectral-spatial images were obtained by continuous wave and rapid-scan electron paramagnetic resonance using a bimodal cross-loop resonator at 251MHz. The phantom consisted of three 4mm tubes containing different (15)N,(2)H-substituted nitroxides. Rapid-scan and continuous wave images were obtained with 5min total acquisition times. For comparison, images also were obtained with 29s acquisition time for rapid scan and 15min for continuous wave. Relative to continuous wave projections obtained for the same data acquisition time, rapid-scan projections had significantly less low-frequency noise and substantially higher signal-to-noise at higher gradients. Because of the improved image quality for the same data acquisition time, linewidths could be determined more accurately from the rapid-scan images than from the continuous wave images.
Collapse
Affiliation(s)
- Joshua R Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States
| | - Mark Tseitlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States
| | - Richard W Quine
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States; School of Engineering and Computer Science, University of Denver, Denver, CO 80208, United States
| | - George A Rinard
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States; School of Engineering and Computer Science, University of Denver, Denver, CO 80208, United States
| | - Hilary A Weismiller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States
| | - Gerald M Rosen
- Center for Biomedical Engineering and Technology, University of Maryland, School of Medicine, Baltimore, MD 21201, United States; Department of Pharmaceutical Sciences, University of Maryland, Baltimore, MD 21201, United States
| | - Joseph P Y Kao
- Center for Biomedical Engineering and Technology, University of Maryland, School of Medicine, Baltimore, MD 21201, United States; Department of Physiology, University of Maryland, School of Medicine, Baltimore, MD 21201, United States
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States; Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208, United States.
| |
Collapse
|
9
|
Sundramoorthy SV, Epel B, Halpern HJ. Orthogonal resonators for pulse in vivo electron paramagnetic imaging at 250 MHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 240:45-51. [PMID: 24530507 PMCID: PMC3974126 DOI: 10.1016/j.jmr.2013.12.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 12/03/2013] [Accepted: 12/27/2013] [Indexed: 05/13/2023]
Abstract
A 250 MHz bimodal resonator with a 19 mm internal diameter for in vivo pulse electron paramagnetic resonance (EPR) imaging is presented. Two separate coaxial cylindrical resonators inserted one into another were used for excitation and detection. The Alderman-Grant excitation resonator (AGR) showed the highest efficiency among all the excitation resonators tested. The magnetic field of AGR is confined to the volume of the detection resonator, which results in highly efficient use of the radio frequency power. A slotted inner single loop single gap resonator (SLSG LGR), coaxial to the AGR, was used for signal detection. The resulting bimodal resonator (AG/LGR) has two mutually orthogonal magnetic field modes; one of them has the magnetic field in the axial direction. The resonator built in our laboratory achieved 40 dB isolation over 20 MHz bandwidth with quality factors of detection and excitation resonators of 36 and 11 respectively. Considerable improvement of the B1 homogeneity and EPR image quality in comparison with reflection loop-gap resonator of similar size and volume was observed.
Collapse
Affiliation(s)
- Subramanian V Sundramoorthy
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA
| | - Boris Epel
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA.
| | - Howard J Halpern
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA.
| |
Collapse
|
10
|
Biller JR, Meyer VM, Elajaili H, Rosen GM, Eaton SS, Eaton GR. Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250 MHz and 34 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 225:52-7. [PMID: 23123770 PMCID: PMC3538045 DOI: 10.1016/j.jmr.2012.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2012] [Revised: 10/04/2012] [Accepted: 10/07/2012] [Indexed: 05/16/2023]
Abstract
Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide (2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T(2)) or 3-pulse inversion recovery (T(1)) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T(1) measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2,T(1)~T(2), as expected in the fast tumbling regime. At higher frequencies T(2) was shorter than T(1) due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T(1) is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, τ(R) are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ωτ(R) (ω is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1.
Collapse
Affiliation(s)
- Joshua R. Biller
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Virginia M. Meyer
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gerald M. Rosen
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
- Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Baltimore, MD, 21201
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
- Center for EPR Imaging in Vivo Physiology, University of Denver, Denver, CO 80208 and University of Maryland, Baltimore, Baltimore, MD, 21201
| |
Collapse
|
11
|
Eaton SS, Eaton GR. The world as viewed by and with unpaired electrons. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 223:151-63. [PMID: 22975244 PMCID: PMC3496796 DOI: 10.1016/j.jmr.2012.07.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Revised: 07/26/2012] [Accepted: 07/27/2012] [Indexed: 06/01/2023]
Abstract
Recent advances in electron paramagnetic resonance (EPR) include capabilities for applications to areas as diverse as archeology, beer shelf life, biological structure, dosimetry, in vivo imaging, molecular magnets, and quantum computing. Enabling technologies include multifrequency continuous wave, pulsed, and rapid scan EPR. Interpretation is enhanced by increasingly powerful computational models.
Collapse
Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | | |
Collapse
|
12
|
Spindler PE, Zhang Y, Endeward B, Gershernzon N, Skinner TE, Glaser SJ, Prisner TF. Shaped optimal control pulses for increased excitation bandwidth in EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 218:49-58. [PMID: 22578555 DOI: 10.1016/j.jmr.2012.02.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 02/16/2012] [Accepted: 02/18/2012] [Indexed: 05/12/2023]
Abstract
A 1 ns resolution pulse shaping unit has been developed for pulsed EPR spectroscopy to enable 14-bit amplitude and phase modulation. Shaped broadband excitation pulses designed using optimal control theory (OCT) have been tested with this device at X-band frequency (9 GHz). FT-EPR experiments on organic radicals in solution have been performed with the new pulses, designed for uniform excitation over a significantly increased bandwidth compared to a classical rectangular π/2 pulse of the same B(1) amplitude. The concept of a dead-time compensated prefocused pulse has been introduced to EPR with a self-refocusing of 200 ns after the end of the pulse. Echo-like refocused signals have been recorded and compared to the performance of a classical Hahn-echo sequence. The impulse response function of the microwave setup has been measured and incorporated into the algorithm for designing OCT pulses, resulting in further significant improvements in performance. Experimental limitations and potential new applications of OCT pulses in EPR spectroscopy will be discussed.
Collapse
Affiliation(s)
- Philipp E Spindler
- Institut für physikalische und theoretische Chemie, Goethe Universität Frankfurt, Max von Laue Strasse 7, 60438 Frankfurt am Main, Germany.
| | | | | | | | | | | | | |
Collapse
|
13
|
Tseitlin M, Rinard GA, Quine RW, Eaton SS, Eaton GR. Rapid frequency scan EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 211:156-61. [PMID: 21664848 PMCID: PMC3145835 DOI: 10.1016/j.jmr.2011.05.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2011] [Revised: 05/12/2011] [Accepted: 05/12/2011] [Indexed: 05/03/2023]
Abstract
In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x, y plane decays to baseline at the end of the scan, which typically is about 5T(2) after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5T(2). However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5T(2), even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B(1), periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation.
Collapse
Affiliation(s)
- Mark Tseitlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - George A. Rinard
- School of Engineering and Computer Science, University of Denver, Denver, CO 80208
| | - Richard W. Quine
- School of Engineering and Computer Science, University of Denver, Denver, CO 80208
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| |
Collapse
|
14
|
Tseitlin M, Quine RW, Eaton SS, Eaton GR. Use of polyphase continuous excitation based on the Frank sequence in EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 211:221-7. [PMID: 21737326 PMCID: PMC3148075 DOI: 10.1016/j.jmr.2011.06.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 05/14/2011] [Accepted: 06/06/2011] [Indexed: 05/12/2023]
Abstract
Polyphase continuous excitation based on the Frank sequence is suggested as an alternative to single pulse excitation in EPR. The method allows reduction of the source power, while preserving the excitation bandwidth of a single pulse. For practical EPR implementation the use of a cross-loop resonator is essential to provide isolation between the spin system and the resonator responses to the excitation. Provided that a line broadening of about 5% is acceptable, the cumulative turning angle of the magnetization vector generated by the excitation sequence can be quite large and can produce signal amplitudes that are comparable to that achieved with a higher power 90° pulse.
Collapse
Affiliation(s)
- Mark Tseitlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Richard W. Quine
- School of Engineering and Computer Science, University of Denver, Denver, CO 80208
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| |
Collapse
|
15
|
Quine RW, Rinard GA, Eaton SS, Eaton GR. Quantitative rapid scan EPR spectroscopy at 258 MHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 205:23-7. [PMID: 20382055 PMCID: PMC3097513 DOI: 10.1016/j.jmr.2010.03.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2009] [Revised: 03/17/2010] [Accepted: 03/18/2010] [Indexed: 05/05/2023]
Abstract
Experimental data obtained with an electron paramagnetic resonance (EPR) rapid scan spectrometer were translated through the reverse transfer functions of the spectrometer hardware to the sample position. Separately, theoretical calculations were performed to predict signal and noise amplitudes at the sample position for specified experimental conditions. A comparison was then made between the translated experimental values and the calculated values. Excellent agreement was obtained.
Collapse
Affiliation(s)
| | | | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| |
Collapse
|
16
|
Rinard GA, Quine RW, Biller JR, Eaton GR. A Wire Crossed-Loop-Resonator for Rapid Scan EPR. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2010; 37B:86-91. [PMID: 21603086 PMCID: PMC3098462 DOI: 10.1002/cmr.b.20161] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
A crossed-loop (orthogonal mode) resonator (CLR) was constructed of fine wire to achieve design goals for rapid scan in vivo EPR imaging at VHF frequencies (in practice, near 250 MHz). This application requires the resonator to have a very open design to facilitate access to the animal for physiological support during the image acquisition. The rapid scan experiment uses large amplitude magnetic field scans, and sufficiently large resonator and detection bandwidths to record the rapidly-changing signal response. Rapid-scan EPR is sensitive to RF/microwave source noise and to baseline changes that are coherent with the field scan. The sensitivity to source noise is a primary incentive for using a CLR to isolate the detected signal from the RF source noise. Isolation from source noise of 44 and 47 dB was achieved in two resonator designs. Prior results showed that eddy currents contribute to background problems in rapid scan EPR, so the CLR design had to minimize conducting metal components. Using fine (AWG 38) wire for the resonators decreased eddy currents and lowered the resonator Q, thus providing larger resonator bandwidth. Mechanical resonances at specific scan frequencies are a major contributor to rapid scan backgrounds.
Collapse
|
17
|
Tseitlin M, Quine RW, Rinard GA, Eaton SS, Eaton GR. Combining absorption and dispersion signals to improve signal-to-noise for rapid-scan EPR imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 203:305-10. [PMID: 20181505 PMCID: PMC2856439 DOI: 10.1016/j.jmr.2010.01.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Accepted: 01/29/2010] [Indexed: 05/12/2023]
Abstract
Direct detection of the rapid-scan EPR signal with quadrature detection and without automatic frequency control provides both the absorption and dispersion components of the signal. The use of a cross-loop resonator results in similar signal-to-noise in the two channels. The dispersion signal can be converted to an equivalent absorption signal by means of Kramers-Kronig relations. The converted signal is added to the directly measured absorption signal. Since the noise in the two channels is not correlated, this procedure increases the signal-to-noise ratio of the resultant absorption signal by up to a factor of square root 2. The utility of this method was demonstrated for 2D spectral-spatial imaging of a phantom containing three tubes of LiPc with different oxygen concentrations and therefore different linewidths.
Collapse
Affiliation(s)
- Mark Tseitlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | | | | | | | | |
Collapse
|
18
|
Quine RW, Tseytlin M, Eaton SS, Eaton GR. A Very Fast Switched Attenuator Circuit for Microwave and R.F. Applications. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2010; 37B:39-44. [PMID: 21546999 PMCID: PMC3086740 DOI: 10.1002/cmr.b.20157] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
An electronic circuit was designed and constructed that can switch an r.f. signal between two amplitude levels at very fast speed (less than 10 ns). The circuit incorporates a TTL control for convenient interfacing to existing equipment. The attenuation of the more attenuated state can be adjusted to be up to 12 dB more than for the less attenuated state. The initial application was in Pulsed Electron Paramagnetic Resonance (EPR) spectroscopy to produce a π/2 - π pulse sequence with pulses of equal time duration and 6 dB difference in amplitude. A new method for measuring electron spin echoes for narrow, homogeneously-broadened lines is described.
Collapse
Affiliation(s)
- Richard W. Quine
- Department of Engineering, University of Denver, Denver, CO 80208
| | - Mark Tseytlin
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| |
Collapse
|
19
|
Subramanian VS, Epel B, Mailer C, Halpern HJ. A passive dual-circulator based transmit/receive switch for use with reflection resonators in pulse EPR. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2009; 35B:133-138. [PMID: 20052312 PMCID: PMC2801570 DOI: 10.1002/cmr.b.20141] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
In order to protect the low noise amplifier (LNA) in the receive arm of a pulsed 250 MHz EPR bridge, it is necessary to install as much isolation as possible between the power exciting the spin system and the LNA when high power is present in the receive arm of the bridge, while allowing the voltage induced by the magnetization in the spin sample to be passed undistorted and undiminished to the LNA once power is reduced below the level that can cause a LNA damage. We discuss a combination of techniques to accomplish this involving the power-routing circulator in the bridge, a second circulator acting as an isolator with passive shunt PIN diodes immediately following the second circulator. The low resistance of the forward biased PIN diode passively generates an impedance mismatch at the second circulator output port during the high power excitation pulse and resonator ring down. The mismatch reflects the high power to the remaining port of the second circulator, dumping it into a system impedance matched load. Only when the power diminishes below the diode conduction threshold will the resistance of the PIN diode rise to a value much higher than the system impedance. This brings the device into conduction mode. We find that the present design passively limits the output power to 14 dBm independent of the input power. For high input power levels the isolation may exceed 60 dB. This level of isolation is sufficient to fully protect the LNA of pulse EPR bridge.
Collapse
Affiliation(s)
- V S Subramanian
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637
| | | | | | | |
Collapse
|
20
|
Epel B, Sundramoorthy SV, Mailer C, Halpern HJ. A Versatile High Speed 250 MHz Pulse Imager for Biomedical Applications. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2008; 33B:163-176. [PMID: 19924261 PMCID: PMC2778030 DOI: 10.1002/cmr.b.20119] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
A versatile 250 MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article we demonstrate the ability of the instrument to obtain three dimensional images using the electron spin echo (ESE) and single point imaging (SPI) methods. In a phantom that contains a 1 mM solution of narrow line (16 μT, peak-to-peak) paramagnetic spin probe we achieved an acquisition time of 32 seconds per image with a fast 3D ESE imaging protocol. Using an 18 minute 3D phase relaxation (T(2e)) ESE imaging protocol in a homogeneous sample a spatial resolution of 1.4 mm and a standard deviation of T(2e) of 8.5% were achieved. When applied to in vivo imaging this precision of T(2e) determination would be equivalent to 2 torr resolution of oxygen partial pressure in animal tissues.
Collapse
Affiliation(s)
- Boris Epel
- Center for EPR Imaging In Vivo Physiology, University of Chicago, Department of Radiology Oncology, MC1105, 5841 S. Maryland Avenue, Chicago, IL 60637, USA
| | | | | | | |
Collapse
|
21
|
Hyodo F, Subramanian S, Devasahayam N, Murugesan R, Matsumoto K, Mitchell JB, Krishna MC. Evaluation of sub-microsecond recovery resonators for in vivo electron paramagnetic resonance imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 190:248-254. [PMID: 18042414 PMCID: PMC2258207 DOI: 10.1016/j.jmr.2007.11.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Revised: 10/16/2007] [Accepted: 11/02/2007] [Indexed: 05/25/2023]
Abstract
Time-domain (TD) electron paramagnetic resonance (EPR) imaging at 300MHz for in vivo applications requires resonators with recovery times less than 1 micros after pulsed excitation to reliably capture the rapidly decaying free induction decay (FID). In this study, we tested the suitability of the Litz foil coil resonator (LCR), commonly used in MRI, for in vivo EPR/EPRI applications in the TD mode and compared with parallel coil resonator (PCR). In TD mode, the sensitivity of LCR was lower than that of the PCR. However, in continuous wave (CW) mode, the LCR showed better sensitivity. The RF homogeneity was similar in both the resonators. The axis of the RF magnetic field is transverse to the cylindrical axis of the LCR, making the resonator and the magnet co-axial. Therefore, the loading of animals, and placing of the anesthesia nose cone and temperature monitors was more convenient in the LCR compared to the PCR whose axis is perpendicular to the magnet axis.
Collapse
Affiliation(s)
- F Hyodo
- Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1002, USA
| | | | | | | | | | | | | |
Collapse
|
22
|
Mailer C, Sundramoorthy SV, Pelizzari CA, Halpern HJ. Spin echo spectroscopic electron paramagnetic resonance imaging. Magn Reson Med 2006; 55:904-12. [PMID: 16526015 DOI: 10.1002/mrm.20849] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The use of spin echoes to obtain spectroscopic EPR images (spectral-spatial images) at 250 MHz is described. The advantages of spin echoes-larger signals than the free induction decay, better phase characteristics for Fourier transformation, and decay shapes undistorted by instrumental dead time-are clearly shown. An advantage is gained from using a crossed loop resonator that isolates the 250-W pump power by greater than 50 dB from the observer arm preamplifiers. The echo decay rates can be used to determine the oxygen content in solutions containing 1 mM trityl concentrations. Two- and three-dimensional images of oxygen concentration are presented.
Collapse
Affiliation(s)
- Colin Mailer
- Center for EPR Imaging In Vivo Physiology, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, Illinois 60637, USA.
| | | | | | | |
Collapse
|
23
|
Owenius R, Eaton GR, Eaton SS. Frequency (250 MHz to 9.2 GHz) and viscosity dependence of electron spin relaxation of triarylmethyl radicals at room temperature. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2005; 172:168-175. [PMID: 15589420 DOI: 10.1016/j.jmr.2004.10.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Indexed: 05/24/2023]
Abstract
Electron spin relaxation times for four triarylmethyl (trityl) radicals at room temperature were measured by long-pulse saturation recovery, inversion recovery, and electron spin echo at 250 MHz, 1.5, 3.1, and 9.2 GHz in mixtures of water and glycerol. At 250 MHz T(1) is shorter than at X-band and more strongly dependent on viscosity. The enhanced relaxation at 250 MHz is attributed to modulation of electron-proton dipolar coupling by tumbling of the trityl radicals at rates that are comparable to the reciprocal of the resonance frequency. Deuteration of the solvent was used to distinguish relaxation due to solvent protons from the relaxation due to intra-molecular electron-proton interactions at 250 MHz. For trityl-CD(3), which contains no protons, modulation of dipolar interaction with solvent protons dominates T(1). For proton-containing radicals the relative importance of modulation of intra- and inter-molecular proton interactions varies with solution viscosity. The viscosity and frequency dependence of T(1) was modeled based on dipolar interaction with a defined number of protons at specified distances from the unpaired electron. At each of the frequencies examined T(2) decreases with increasing viscosity consistent with contributions from T(1) and from incomplete motional averaging of anisotropic hyperfine interaction.
Collapse
Affiliation(s)
- Rikard Owenius
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | | | | |
Collapse
|
24
|
Eaton GR, Eaton SS. EPR Spectrometers at Frequencies Below X-band. EPR: INSTRUMENTAL METHODS 2004. [DOI: 10.1007/978-1-4419-8951-2_2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
25
|
|