<scp>UHF EPR</scp> spectrometer operating at frequencies between 400 MHz and 1 GHz

Quine, Richard W.; Rinard, George A.; Shi, Yilin; Buchanan, Laura; Biller, Joshua R.

doi:10.1002/cmr.b.21328

Cited by 8 publications

(7 citation statements)

References 16 publications

(26 reference statements)

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“…Experiments at 400–1000 MHz were performed at the University of Denver using the variable frequency UHF spectrometer described in [11]. The cross-loop resonator that was used for the multifrequency measurements was designed such that the frequency can be adjusted between about 400–1000 MHz with the same 16-mm OD sample and the same filling factor, thus maintaining all resonator characteristics, except resonance frequency and resonator Q, constant throughout the series of relaxation and S/N measurements.…”

Section: Experimental Methodsmentioning

confidence: 99%

Triarylmethyl Radical: EPR Signal to Noise at Frequencies between 250 MHz and 1.5 GHz and Dependence of Relaxation on Radical and Salt Concentration and on Frequency

Shi

Quine

Rinard

et al. 2016

Zeitschrift Für Physikalische Chemie

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In vivo oximetry by pulsed electron paramagnetic resonance is based on measurements of changes in electron spin relaxation rates of probe molecules, such as the triarylmethyl radicals. A series of experiments was performed at frequencies between 250 MHz and 1.5 GHz to assist in the selection of an optimum frequency for oximetry. Electron spin relaxation rates for the triarylmethyl radical OX063 as a function of radical concentration, salt concentration, and resonance frequency were measured by electron spin echo 2-pulse decay and 3-pulse inversion recovery in the frequency range of 250 MHz–1.5 GHz. At constant OX063 concentration, 1/T1 decreases with increasing frequency because the tumbling dependent processes that dominate relaxation at 250 MHz are less effective at higher frequency. 1/T2 also decreases with increasing frequency because 1/T1 is a significant contribution to 1/T2 for trityl radicals in fluid solution. 1/T2–1/T1, the incomplete motional averaging contribution to 1/T2, increases with increasing frequency. At constant frequency, relaxation rates increase with increasing radical concentration due to contributions from collisions that are more effective for 1/T2 than 1/T1. The collisional contribution to relaxation increases as the concentration of counter-ions in solution increases, which is attributed to interactions of cations with the negatively charged radicals that decrease repulsion between trityl radicals. The Signal-to-Noise ratio (S/N) of field-swept echo-detected spectra of OX063 were measured in the frequency range of 400 MHz–1 GHz. S/N values, normalized by √Q, increase as frequency increases. Adding salt to the radical solution decreased S/N because salt lowers the resonator Q. Changing the temperature from 19 to 37 °C caused little change in S/N at 700 MHz. Both slower relaxation rates and higher S/N at higher frequencies are advantageous for oximetry. The potential disadvantage of higher frequencies is the decreased depth of penetration into tissue.

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Section: Experimental Methodsmentioning

confidence: 99%

Triarylmethyl Radical: EPR Signal to Noise at Frequencies between 250 MHz and 1.5 GHz and Dependence of Relaxation on Radical and Salt Concentration and on Frequency

Shi

Quine

Rinard

et al. 2016

Zeitschrift Für Physikalische Chemie

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“…To study the frequency region up to about 1 GHz, we designed a resonator for which the sample and filling factor could remain constant as the frequency was changed from about 400 MHz to about 1 GHz by changing the capacitance. This resonator and its applications were described in [46–48]. A rapid scan and pulse resonator for 700 MHz is shown in Figure 10.…”

Section: Design and Construction Of Resonators For Epr Imagingmentioning

confidence: 99%

Resonators for In Vivo Imaging: Practical Experience

et al. 2017

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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.

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“…The maximum field based on full output of the power supply would be 37 mT, however, this magnet is currently only air‐cooled so it is not operated above 11 mT. A sister‐version of this magnet design which does employ a water‐jacket has recently been described for use with a pulsed L‐band EPR spectrometer …”

Section: Instrument Designmentioning

confidence: 99%

“…A sisterversion of this magnet design which does employ a waterjacket has recently been described for use with a pulsed Lband EPR spectrometer. 32 The design process for the magnet was as follows: A solution was found with a finite turns ratio between the two coil-pairs of 7/3. This solution for the infinitesimal coil case has nearly equal coil diameters.…”

Section: Magnet Description and Designmentioning

confidence: 99%

Characterization of a PXIe based low‐field digital NMR spectrometer

Biller

Stupic

Kos

et al. 2017

Concepts Magn Reson

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A low‐field nuclear magnetic resonance (NMR) instrument is an important tool for investigating a wide variety of samples under different conditions. In this paper, we describe a system constructed primarily with commercially available hardware and control software, capable of single‐pulse NMR experiments. Details of the construction of the main B0 magnet are also included. The operating frequency for demonstration is 460 kHz (10 mT), however, the range of the hardware spans 700 Hz (16 μT) to 25 MHz (0.6 T). Tip angle optimizations are used to find the most narrow usable pulse width for this configuration, and the T1 of water is measured by single‐pulse‐saturation‐recovery (SPSR) to demonstrate the potential for this system as a relaxometer. Discussions of resonator construction and efficiency, power requirements and programming strategies that would increase the utility of this system are also included. Construction of any low‐field NMR system will depend on experimental interests, budget and engineering resources. A survey of other low‐field NMR systems from the literature is included to aid the novice or experienced magnetic resonance scientist in consideration of how a low‐field spectrometer could be constructed and used in the lab.

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UHF EPR spectrometer operating at frequencies between 400 MHz and 1 GHz

Cited by 8 publications

References 16 publications

Triarylmethyl Radical: EPR Signal to Noise at Frequencies between 250 MHz and 1.5 GHz and Dependence of Relaxation on Radical and Salt Concentration and on Frequency

Triarylmethyl Radical: EPR Signal to Noise at Frequencies between 250 MHz and 1.5 GHz and Dependence of Relaxation on Radical and Salt Concentration and on Frequency

Resonators for In Vivo Imaging: Practical Experience

Characterization of a PXIe based low‐field digital NMR spectrometer

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