Electronically Tunable Surface-Coil-Type Resonator for L-Band EPR Spectroscopy

Hirata, Hiroshi; Walczak, Tadeusz; Swartz, Harold M.

doi:10.1006/jmre.1999.1927

Cited by 93 publications

(85 citation statements)

References 20 publications

(11 reference statements)

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“…An electronically tunable SCR with a loop of 10 mm in diameter had an efficiency of 77 µT/W 1/2 [29,39]. While the loop of the resonator in this study was 5.5-fold larger than that of an SCR at 1.1 GHz, the resonator was almost half as efficient as the SCR.…”

Section: Discussionmentioning

confidence: 57%

“…Even if a trimmer capacitor C M is adjustable, critical coupling of the resonator could only be achieved when the other capacitors were appropriately adjusted. For several EPR resonators, remote tuning and matching circuits with varactor diodes have been reported [28][29][30][31]. Since the varactor diodes are usually used in applications with small signals, e.g., tuning of RF oscillators and radio/television receivers, non-linearity of the varactor diodes will appear in high-power applications.…”

Section: Resonator Designmentioning

confidence: 99%

“…Since AFC was operating in this measurement, a dominant cause of this periodic noise could be related to impedance mismatching of the resonator. This could be further suppressed with automatic matching control, also called automatic coupling control [28][29][30][31]. Figure 6B shows an EPR image of the bottle phantom in the ZY-plane (Fig.…”

Section: Sensitivity Distribution In the Loopmentioning

confidence: 99%

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A loop resonator for slice-selective in vivo EPR imaging in rats

Hirata

Deng

et al. 2008

Journal of Magnetic Resonance

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A loop resonator was developed for 300-MHz continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy and imaging in live rats. A single-turn loop (55 mm in diameter) was used to provide sufficient space for the rat body. Efficiency for generating a radiofrequency magnetic field of 38 µT/W 1/2 was achieved at the center of the loop. For the resonator itself, an unloaded quality factor of 430 was obtained. When a 350 g rat was placed in the resonator at the level of the lower abdomen, the quality factor decreased to 18. The sensitive volume in the loop was visualized with a bottle filled with an aqueous solution of the nitroxide spin probe 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (3-CP). The resonator was shown to enable EPR imaging in live rats. Imaging was performed for 3-CP that had been infused intravenously into the rat and its distribution was visualized within the lower abdomen.

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Section: Discussionmentioning

confidence: 57%

Section: Resonator Designmentioning

confidence: 99%

Section: Sensitivity Distribution In the Loopmentioning

confidence: 99%

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A loop resonator for slice-selective in vivo EPR imaging in rats

Hirata

Deng

et al. 2008

Journal of Magnetic Resonance

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“…For efficient coupling, the circumference of the coupling loop can not be longer than λ/2 of the wavelength in the conductor. So, in order to provide homogeneous coupling for L-band frequencies (29,30), it should be no more than 63 mm (or 20 mm in diameter). To overcome these limitations, a parallel double loop design was implemented.…”

Section: Electrical Design Of the Resonator And Its Coupling Mechanismmentioning

confidence: 99%

Single loop multi-gap resonator for whole body EPR imaging of mice at 1.2GHz

Petryakov

Samouilov

Kesselring

et al. 2007

Journal of Magnetic Resonance

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For whole body EPR imaging of small animals, typically low frequencies of 250-750 MHz have been used due to the microwave losses at higher frequencies and the challenges in designing suitable resonators to accommodate these large lossy samples. However, low microwave frequency limits the obtainable sensitivity. L-band frequencies can provide higher sensitivity, and have been commonly used for localized in vivo EPR spectroscopy. Therefore, it would be highly desirable to develop an L-band microwave resonator suitable for in vivo whole body EPR imaging of small animals such as living mice. A 1.2 GHz 16 gap resonator with inner diameter of 43 mm and 48 mm length was designed and constructed for whole body EPR imaging of small animals. The resonator has good field homogeneity and stability to animal induced motional noise. Resonator stability was achieved with electrical and mechanical design utilizing a fixed position double coupling loop of novel geometry, thus minimizing the number of moving parts. Using this resonator, high quality EPR images of lossy phantoms and living mice were obtained. This design provides good sensitivity, ease of sample access, excellent stability and uniform B 1 field homogeneity for in vivo whole body EPR imaging of mice at 1.2 GHz.

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“…In the past decade, advances in hardware (12)(13)(14), such as lumped circuit resonator designs and optimized automatic frequency control systems, have led to more stable and efficient EPRI systems, but system stability (15,16) still remains a serious issue that may limit the reproducibility and quality of the acquired data. In addition, electromagnetic interference, microphonics, temperature fluctuations, and animal motion may introduce unwanted noise or distortions to the data, which may leave the entire data set unusable even if only a small fraction of the data are affected.…”

mentioning

confidence: 99%

Automated on‐the‐fly detection and correction procedure for EPR imaging data acquisition

Ahmad

Vikram

Petryakov

et al. 2006

Magnetic Resonance in Med

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Fast and reliable data acquisition is a major requirement for successful and useful biological electron paramagnetic resonance imaging (EPRI) experiments. Even a technologically advanced and professionally supervised EPRI system can exhibit instabilities initiated by perturbations such as animal motion, microphonics, and temperature changes. As a result, part of an acquired data set may become corrupted with excessive noise and distortions, which in turn may degrade the quality of the reconstructed image. In this work an automated scheme to monitor the system performance and stability over the course of an experiment is demonstrated. This method ensures that the quality of the acquired data is maintained during the experiment. For this purpose, four parameters including noise content and integration of each acquired projection are quantified and measured against those of the zero-gradient (ZG) projection, which is set as a quality benchmark. Key words: noise; system stability; microphonics; motion artifacts Electron paramagnetic resonance imaging (EPRI) is a noninvasive technique that is capable of mapping the distribution of unpaired electrons (1,2). It has a distinct advantage for many medical applications (3-5) in which it can be used to directly measure both endogenous and introduced free radicals that carry unpaired electrons. In the past few years, the potential applications of EPRI to studies of living biological systems have been recognized (6 -9). However, despite all of the progress made in the last two decades, the acquisition of high-quality images of biological samples has been limited by several technical factors, including gradient strength and accuracy, sensitivity, reliability, and speed of data acquisition (10,11).In the past decade, advances in hardware (12-14), such as lumped circuit resonator designs and optimized automatic frequency control systems, have led to more stable and efficient EPRI systems, but system stability (15,16) still remains a serious issue that may limit the reproducibility and quality of the acquired data. In addition, electromagnetic interference, microphonics, temperature fluctuations, and animal motion may introduce unwanted noise or distortions to the data, which may leave the entire data set unusable even if only a small fraction of the data are affected. Testing the performance of the system hardware in advance does improve the chances of attaining sustained performance during the acquisition, but because of the complex nature of the system, there is no guarantee that it would behave as expected over the course of an experiment. Therefore, it would be extremely useful to constantly monitor the performance of a system to ensure the quality of data acquired during the experiment. In this work we present a procedure to identify any damaged projections. For this purpose we first quantify four parameters: the noise intensity, spike amplitude, and first and second integrations of the acquired projections. We then compare the monitored parameters (MPs) of each projection ...

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Electronically Tunable Surface-Coil-Type Resonator for L-Band EPR Spectroscopy

Cited by 93 publications

References 20 publications

A loop resonator for slice-selective in vivo EPR imaging in rats

A loop resonator for slice-selective in vivo EPR imaging in rats

Single loop multi-gap resonator for whole body EPR imaging of mice at 1.2GHz

Automated on‐the‐fly detection and correction procedure for EPR imaging data acquisition

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