Nitroxide free radical clearance in the live rat monitored by radio-frequency CW-EPR and PEDRI

Alecci, Marcello; Seimenis, Ioannis; McCallum, S.; Lurie, David John; Foster, Margaret A.

doi:10.1088/0031-9155/43/7/011

Cited by 29 publications

(18 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, the knowledge of the B 1 spatial distribution at 3 T is of importance for a posteriori MRI correction techniques such as relaxation time measurements (34) and image segmentation (35). As an additional application, accurate RF B 1 mapping may also find use in low frequency (100 -300 MHz) EPR imaging and Overhauser MRI (36).…”

Section: Discussionmentioning

confidence: 99%

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

Alecci

Collins

Smith

et al. 2001

Magnetic Resonance in Med

Self Cite

121

View full text Add to dashboard Cite

The RF B 1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B 1 distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B 1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B 1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B 1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B 1 uniformity was 9 cm with phantoms and 7 cm in the head. The recent development of high-efficiency head gradient coils and ultrafast MRI pulse sequences has allowed an impressive number of functional MRI studies in human brain research to be realized. The need for higher sensitivity has pushed current MRI research towards the development of high field (Ͼ1.5 T) MRI systems (1). However, magnetic field inhomogeneity and susceptibility artifacts increase with field strength, requiring the development of methods to evaluate and, possibly, eliminate their effects (2). Even if the problems of B 0 magnetic field susceptibility were to be solved, the effect of RF magnetic field (B 1 ) inhomogeneity has long been recognized as a potential source of image artifacts in high field systems (3,4). In fact, for frequencies higher than 64 MHz the RF eddy currents induced in the human body cannot be neglected. Moreover, because the effective wavelength of the RF field is comparable to or smaller than the dimension of the human body, there is a significant variation of the B 1 phase along the sample (3). This gives B 1 standing wave effects and consequently the RF field homogeneity can be strongly degraded. As a further consideration, at high field the distribution of the power deposition caused by the RF irradiating field must be carefully considered for safety reasons and strict limits on the specific absorption rate (SAR) have been established (5,6).Because of the complex anatomical structure of the human head, it is impossible to analytically evaluate the RF B 1 spatial distribution. In the past few years, for RF coils operating between 64 MHz and 341 MHz, numerical electromagnetic (EM) computational techniques have been developed to evaluate the B 1 and the SAR in phantoms and in the human head (7-13). Although very powerful, these numerical techniques use a simplified model of the human head (typically, 2 mm voxel, up to 20 tissues, measured or interpolated/extrapolated dielectric properties of tissues). The effects of head size, position, and motion within the RF coil have not been considered. Additionally, they make many assumptions about the RF coil modeling (intrinsic RF B 1 distribution, coi...

show abstract

Section: Discussionmentioning

confidence: 99%

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

Alecci

Collins

Smith

et al. 2001

Magnetic Resonance in Med

Self Cite

121

View full text Add to dashboard Cite

show abstract

“…7B and 7C). If the 3D distribution of spin probes in a subject animal must be determined precisely, 3D EPR acquisitions must be performed and co-registration, as in EPR/ NMR co-imaging, can be performed to provide an anatomical map of the location of free radicals in the body [8,27,[36][37][38]. However, this is beyond the focus and scope of the present work.…”

Section: Epr Imaging In An Anesthetized Ratmentioning

confidence: 99%

“…Under these circumstances, it is considered that an RF frequency of 250 MHz or 300 MHz is suitable for EPR spectroscopy and imaging with larger subjects with a cross-section of 50-60 mm, such as with an adult rat. However, there have been only a few reports on RF resonators that are suitable for EPR spectroscopy and imaging and that can provide sufficient space to accommodate the body of a rat [5][6][7][8]. A variety of MRI coils with a frequency range of 300 to 400 MHz have been reported for small animal and human imaging [9][10][11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

“…The application of longitudinally-detected electron spin resonance (LODESR) to rats has also been reported [18,19]. Moreover, proton-electron double resonance (PEDRI), also known as Overhauserenhanced MRI (OMRI), can be used for free radical imaging in rats [8,[19][20][21]. Nevertheless, the scope of RF resonators reported for EPR imaging in rats has been quite limited and there is a need for resonators that are more suitable for sensitive and stable operation in this important in vivo model.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Hirata

Deng

et al. 2008

Journal of Magnetic Resonance

View full text Add to dashboard Cite

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.

show abstract

“…Since living animals are lossy samples that heavily load the resonator, the resonator design requires special coupling and high loaded Q characteristics (12)(13)(14)(15). Several articles have reported RF resonators that can provide sufficient space for living animals in EPR spectroscopy and imaging (16)(17)(18)(19)(20), however, these resonators have been designed for lower frequencies.…”

Section: Introductionmentioning

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

View full text Add to dashboard Cite

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.

show abstract

Nitroxide free radical clearance in the live rat monitored by radio-frequency CW-EPR and PEDRI

Cited by 29 publications

References 11 publications

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

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

Contact Info

Product

Resources

About