The visualization of RF probe electric fields

Chen, C N; Hoult, D. I.

doi:10.1002/mrm.1910290316

Cited by 10 publications

(10 citation statements)

References 4 publications

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“…Significance level was determined by a t-test between the rest and stimulation periods. Thus, all image based processing was performed with ImageJ (Version 1.42q; National Institutes of Health, Bethesda, USA; http://rsbweb.nih.gov/ij) using custom-made plug-ins and macros that utilize the Apache Commons Maths Library (Version 2.1; The Apache Software Foundation; http://www.apache.org) [21]. BOLD signal maps were color-coded and overlaid on the corresponding mean signal intensity EPI images for visual presentation.…”

Section: Methodsmentioning

confidence: 99%

“…To reduce the image drift induced by the increasing gradient heating due to the extreme duty cycle [21] and the interference between echo and diffusion gradient pulse [22], rigorous image processing was applied, as previously described in detail [20]. After the co-registration of all individual images, we used DSI Studio (dsi-studio.labsolver.org) to reconstruct DSI data, to calculate gFA maps (generalized fractional anisotropy), and to perform tractography [13].…”

Section: Methodsmentioning

confidence: 99%

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White Matter Reorganization and Functional Response after Focal Cerebral Ischemia in the Rat

Kalthoff

Kim

et al. 2012

PLoS ONE

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After stroke, the brain has shown to be able to achieve spontaneous functional recovery despite severe cerebral damage. This phenomenon is poorly understood. To address this issue, focal transient ischemia was induced by 60 min middle cerebral artery occlusion in Wistar rats. The evolution of stroke was followed using two magnetic resonance imaging modalities: diffusion spectrum imaging (acquired before, one and four weeks after stroke) and functional magnetic resonance imaging (acquired before and five weeks after stroke). To confirm the imaging observations, immunohistochemical staining for myelin, astrocytes and macrophages/microglia was added. At four weeks after stroke, a focal alteration of the diffusion anisotropy was observed between the ipsilesional ventricle and the lesion area. Using tractography this perturbation was identified as reorganization of the ipsilesional internal capsule. Functional imaging at five weeks after ischemia demonstrated activation of the primary sensorimotor cortex in both hemispheres in all rats except one animal lacking a functional response in the ipsilesional cortex. Furthermore, fiber tracking showed a transhemispheric fiber connection through the corpus callosum, which-in the rat without functional recovery-was lost. Our study shows the influence of the internal capsule reorganization, combined with inter-hemispheric connections though the corpus callosum, on the functional activation of the brain from stroke. In conclusion, tractography opens a new door to non-invasively investigate the structural correlates of lack of functional recovery after stroke.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

White Matter Reorganization and Functional Response after Focal Cerebral Ischemia in the Rat

Kalthoff

Kim

et al. 2012

PLoS ONE

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“…The RF energy deposited by a coil during MRI experiments results in focal temperature increases (24). Several MRI‐based strategies have evolved over the years to measure this temperature change via changes in T 1 or chemical shift of the water signal (25–28).…”

Section: Methodsmentioning

confidence: 99%

Three‐dimensional T_1ρ‐weighted MRI at 1.5 Tesla

Borthakur

Wheaton

Charagundla

et al. 2003

Magnetic Resonance Imaging

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Purpose: To design and implement a magnetic resonance imaging (MRI) pulse sequence capable of performing threedimensional T 1 -weighted MRI on a 1.5-T clinical scanner, and determine the optimal sequence parameters, both theoretically and experimentally, so that the energy deposition by the radiofrequency pulses in the sequence, measured as the specific absorption rate (SAR), does not exceed safety guidelines for imaging human subjects. Materials and Methods:A three-pulse cluster was preencoded to a three-dimensional gradient-echo imaging sequence to create a three-dimensional, T 1 -weighted MRI pulse sequence. Imaging experiments were performed on a GE clinical scanner with a custom-built knee-coil. We validated the performance of this sequence by imaging articular cartilage of a bovine patella and comparing T 1 values measured by this sequence to those obtained with a previously tested two-dimensional imaging sequence. Using a previously developed model for SAR calculation, the imaging parameters were adjusted such that the energy deposition by the radiofrequency pulses in the sequence did not exceed safety guidelines for imaging human subjects. The actual temperature increase due to the sequence was measured in a phantom by a MRI-based temperature mapping technique. Following these experiments, the performance of this sequence was demonstrated in vivo by obtaining T 1 -weighted images of the knee joint of a healthy individual. Results:Calculated T 1 of articular cartilage in the specimen was similar for both and three-dimensional and twodimensional methods (84 Ϯ 2 msec and 80 Ϯ 3 msec, respectively). The temperature increase in the phantom resulting from the sequence was 0.015°C, which is well below the established safety guidelines. Images of the human knee joint in vivo demonstrate a clear delineation of cartilage from surrounding tissues. Conclusion:We developed and implemented a three-dimensional T 1 -weighted pulse sequence on a 1.5-T clinical scanner.

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“…This makes the task of quantification of RF heating (SARs and temperature rises) and its correlation with the electric field more difficult as precise measurement techniques, and rigorous [16] computational methods are required for their evaluation. As MRI RF induced SARs and power deposition in tissues have been reported by many authors [9,[17][18][19][20] using computational electromagnetics, these calculations/simulations along with electric field [16,21,22] and RF heating measurements [23,24] have confirmed temperature changes in biological samples during MRI scans. In this context, the fluorooptic techniques, for instance, have shown that they are capable of relatively accurate temperature measurements [25].…”

Section: Introductionmentioning

confidence: 87%