Purpose: To implement an accelerated MR-acquisition method allowing to map sodium T₂^* relaxation and absolute concentration within skeletal muscles at 3T. Methods: A fast-2D density-weighted concentric-ring-trajectory ²³Na-MRSI technique was used to acquire 64 time-points of FID with a spectral bandwidth of 312.5 Hz from a 2.5 x 2.5 mm²Na in-plane resolution within about 15 minutes. The fast relaxing ²³Na signal was localized with a single-shot, inversion-recovery based, non-echo (SIRENE) OVS method. The sequence was verified using simulation and phantom studies before implementing it in human calf muscles. Within two same-day sessions, 2D-SIRENE-MRSI (UTE = 0.55 ms) and 3D-MRI (UTE = 0.3 ms) data were acquired. The T₂^* values were fitted voxel-by-voxel using a bi-exponential model for the 2D-MRSI data. Within-subject coefficients of variation were estimated for both acquisition methods. Results: The MRSI-FID data allowed for fast and slow T₂^* mapping of the calf muscles in vivo with minimal sensitivity reduction. The spatial-distributions of ²³Na concentration for both in vivo MRSI and 3D-MRI acquisitions were significantly correlated (r = 0.7, P<0.001). The test-retest results rendered high reliability for both MRSI (CV = 5%) and 3D MRI (CV = 6%). The mean T₂^*_fast in calf muscles was 0.7 ± 0.1 (contribution fraction = 37%), while T₂^*_slow was 13.2 ± 0.2 ms (63%). The mean absolute muscle ²³Na concentration calculated from the T₂^*-corrected data was 28.6 ± 3.3 mM. Conclusion: The proposed MRSI technique is a reliable technique to map sodium's absolute concentration and T₂^* within a clinically acceptable scan time at 3T.

中文翻译：

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在3 T时使用加速的2D-FID磁共振光谱成像进行快速的体内23Na成像和T2 *映射：概念验证和可靠性研究

目的：实施加速的MR采集方法，以绘制3T时钠T ₂ ^*弛豫和骨骼肌中绝对浓度的图。方法：使用快速二维密度加权同心环轨迹²³ Na-MRSI技术，以2.5 x 2.5 mm ² Na的面内分辨率在大约30到100微米范围内获取64个FID时间点，其光谱带宽为312.5 Hz。15分钟。快速放松²³Na信号通过单次，基于反转恢复的非回波（SIRENE）OVS方法进行定位。在人类小腿肌肉中实施该序列之前，已通过仿真和幻像研究对其进行了验证。在两个当天的会议中，获取了2D-SIRENE-MRSI（UTE = 0.55 ms）和3D-MRI（UTE = 0.3 ms）数据。使用2D-MRSI数据的双指数模型将T ₂ ^*值逐像素拟合。两种采集方法均估算了受试者内部的变异系数。结果： MRSI-FID数据可实现体内小腿肌肉的快速和缓慢T ₂ ^*定位，而灵敏度降低最小。²³的空间分布体内MRSI和3D-MRI采集的Na浓度均显着相关（r = 0.7，P <0.001）。重新测试的结果为MRSI（CV = 5％）和3D MRI（CV = 6％）都提供了很高的可靠性。小腿肌肉的平均T ₂ ^*_快为0.7±0.1（贡献率= 37％），而_缓慢的T ₂ ^*则为13.2±0.2 ms（63％）。由T ₂ ^*校正的数据计算出的平均绝对肌肉²³ Na浓度为28.6±3.3 mM。结论：拟议的MRSI技术是在临床上可接受的3T扫描时间内绘制钠的绝对浓度和T ₂ ^*的可靠技术。