7T MR Thermometry technique for validation of system-predicted SAR with a home-built radiofrequency wrist coil.
7T MR Thermometry technique for validation of system-predicted SAR with a home-built radiofrequency wrist coil.
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DOI：
10.1002/mp.14641
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发表时间：
2021-03
期刊：
影响因子：
3.8
通讯作者：
Felmlee JP
中科院分区：
文献类型：
--
作者：
Fagan AJ;Jacobs PS;Hulshizer TC;Rossman PJ;Frick MA;Amrami KK;Felmlee JP
开发了一种7 T磁共振测温（MRT）技术，以验证系统测量的发射射频（RF）功率与系统预测SAR值之间的转换因子。为超高磁场MRI系统开发的新型RF线圈的转换因子用于确保不超过组织中RF能量沉积的监管限值，特别是局部10 g平均比吸收率（SAR 10 g）。MRT可用于验证此因素，确保MRT测量的SAR值不超过系统预测的值。构建了一个直径为14 cm的高通鸟笼式RF线圈，用于在7 T下对手腕进行成像。开发了一种高空间和时间分辨率的双回波梯度回波MRT技术，该技术采用质子共振频率法，将准同时RF感应加热和温度变化测量结合起来。该技术允许在4分钟的加热周期内每20秒进行一次高温度分辨率测量（~ ± 0.1°C），具有高空间分辨率（2.56 mm 3体素大小），并避免了由严重的磁致伸缩性引起的B 0不均匀性引起的相位不连续性。MRT是在由聚乙烯吡咯烷酮制成的体模上进行的，以模拟肌肉组织在297.2 MHz下的介电特性。将MRT和四个嵌入体模的光纤温度传感器测量的温度变化进行比较。通过比较体模中模拟和测量的B1+图，开发并验证了线圈和体模的电磁模拟。通过模拟确定线圈内最大SAR的位置，并在位于SAR热点位置的手腕大小的肉块内进行MRT。比较了体模和肉的MRT测量和系统预测SAR值。来自MRT的温度变化测量结果与来自光纤温度传感器的温度变化测量结果密切匹配。通过模拟和MRT测量的B1+和SAR图之间的密切相关性验证了模拟。使用2 kg−1的线圈转换因子，MRT测量的点SAR值在均匀体模或模拟位于SAR热点位置的手腕的肉块中均未超过系统预测的SAR 10 g。开发了一种具有高空间和时间分辨率的高精度MRT技术。该技术可用于确保在实践中不超过系统预测的SAR值，从而对新构建的RF腕部线圈提供的SAR水平进行独立验证。MRT技术易于推广，以在7 T下对其他RF线圈进行安全性评价。
A 7T magnetic resonance thermometry (MRT) technique was developed to validate the conversion factor between the system-measured transmitted radiofrequency (RF) power into a home-built RF wrist coil with the system-predicted SAR value. The conversion factor for a new RF coil developed for ultra high magnetic field MRI systems is used to ensure that regulatory limits on RF energy deposition in tissue, specifically the local 10g-averaged specific absorption rate (SAR10g), are not exceeded. MRT can be used to validate this factor by ensuring that MRT-measured SAR values do not exceed those predicted by the system. A 14 cm diameter high-pass birdcage RF coil was built to image the wrist at 7T. A high spatial and temporal resolution dual-echo gradient echo MRT technique, incorporating quasi-simultaneous RF-induced heating and temperature change measurements using the proton resonance frequency method, was developed. The technique allowed for high temperature resolution measurements (~ ± 0.1°C) to be performed every 20 s over a 4 minute heating period, with high spatial resolution (2.56 mm3 voxel size) and avoiding phase discontinuities arising from severe magnetic susceptibility-induced B0 inhomogeneities. MRT was performed on a phantom made from polyvinylpyrrolidone to mimic the dielectric properties of muscle tissue at 297.2 MHz. Temperature changes measured with MRT and four fiber optic temperature sensors embedded in the phantom were compared. Electromagnetic simulations of the coil and phantom were developed and validated via comparison of simulated and measured B1+ maps in the phantom. The position of maximum SAR within the coil was determined from simulations, and MRT was performed within a wrist-sized piece of meat positioned at that SAR hotspot location. MRT-measured and system-predicted SAR values for the phantom and meat were compared. Temperature change measurements from MRT matched closely to those from the fiber optic temperature sensors. The simulations were validated via close correlation between the simulated and MRT-measured B1+ and SAR maps. Using a coil conversion factor of 2 kg−1, MRT-measured point-SAR values did not exceed the system predicted SAR10g in either the uniform phantom or in the piece of meat mimicking the wrist located at the SAR hotspot location. A highly accurate MRT technique with high spatial and temporal resolution was developed. This technique can be used to ensure that system-predicted SAR values are not exceeded in practice, thereby providing independent validation of SAR levels delivered by a newly-built RF wrist coil. The MRT technique is readily generalizable to perform safety evaluations for other RF coils at 7T.
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DOI：
10.1002/jmri.27319
发表时间：
2021-03
期刊：
Journal of magnetic resonance imaging : JMRI
影响因子：
--
作者：
Fagan AJ;Bitz AK;Björkman-Burtscher IM;Collins CM;Kimbrell V;Raaijmakers AJE;ISMRM Safety Committee
通讯作者：
ISMRM Safety Committee
影响因子：
2.9
作者：
Hoffmann, Jens;Henning, Anke;Avdievich, Nikolai I.
通讯作者：
Avdievich, Nikolai I.
DOI：
10.1097/rmr.0000000000000206
发表时间：
2019-06-01
期刊：
Topics in magnetic resonance imaging : TMRI
影响因子：
--
作者：
Kraff, Oliver;Quick, Harald H
通讯作者：
Quick, Harald H
影响因子：
3.5
作者：
Gosselin, Marie-Christine;Neufeld, Esra;Kuster, Niels
通讯作者：
Kuster, Niels
DOI：
10.1186/s40349-018-0115-5
发表时间：
2018-08-13
期刊：
JOURNAL OF THERAPEUTIC ULTRASOUND
影响因子：
--
作者：
Ozhinsky, Eugene;Salgaonkar, Vasant A.;Rieke, Viola
通讯作者：
Rieke, Viola