School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada.
Imaging Research Center, St. Joseph's Healthcare, Hamilton, Ontario, Canada.
Magn Reson Med. 2019 Jun;81(6):3453-3461. doi: 10.1002/mrm.27682. Epub 2019 Feb 8.
Dynamic phosphorus MR spectroscopic imaging ( P-MRSI) experiments require temporal resolution on the order of seconds to concurrently assess different muscle groups. A highly accelerated pulse sequence combining flyback echo-planar spectroscopic imaging (EPSI) and compressed sensing was developed and tested in a phantom and healthy humans during an exercise-recovery challenge of the lower leg muscles, using a clinical 3T MRI.
A flyback EPSI readout designed to achieve 2.25 × 2.25 cm resolution over a 18 × 18 cm field of view (i.e., 8 × 8 matrix) was combined with compressed sensing through the inclusion of pseudorandom gradient blips to sub-sample the ky-kt dimensions by a factor of 2.7×, achieving a temporal resolution of 9 s. The sequence was first tested in a phantom to assess performance compared to fully sampled EPSI (fidEPSI) and phase encoded chemical shift imaging (fidCSI). Then, tests were performed in 11 healthy volunteers during an exercise-recovery challenge of the lower leg muscles. Voxels containing tissue from different muscle groups were evaluated measuring percentage phosphocreatine (%PCr) depletion, time constant of PCr recovery (τPCr) and intracellular pH at rest and following exercise.
The sequence was capable to track the dynamic PCr response of multiple muscles simultaneously. No statistical differences were found in the metabolite ratio, pH or linewidth when compared with fidEPSI and fidCSI in the phantom study. Dynamic experiments showed differences in PCr depletion when comparing soleus with gastrocnemius muscles. Intracellular pH, τPCr and %PCr decrease were consistent with reported values.
Highly accelerated P-MRSI combining flyback EPSI and compressed sensing is capable of assessing concurrent energy metabolism in multiple muscle groups using a clinical 3T MR system.
动态磷磁共振波谱成像（P-MRSI）实验需要秒级的时间分辨率，以同时评估不同的肌肉群。本研究开发并测试了一种结合回波平面波谱成像（EPSI）和压缩感知的高度加速脉冲序列，在小腿肌肉的运动-恢复挑战中，在临床 3T MRI 中，在体模和健康人体中进行了测试。
设计了一种回飞 EPSI 读出方法，可在 18×18 cm 的视野（即 8×8 矩阵）上实现 2.25×2.25 cm 的分辨率，通过包含伪随机梯度闪烁来对 ky-kt 维度进行 2.7 倍的亚采样，实现了 9 s 的时间分辨率。该序列首先在体模中进行测试，以评估与全采样 EPSI（fidEPSI）和相位编码化学位移成像（fidCSI）相比的性能。然后，在 11 名健康志愿者中进行了测试，在小腿肌肉的运动-恢复挑战中进行了测试。评估了包含来自不同肌肉群的组织的体素，以测量休息时和运动后的磷酸肌酸（%PCr）耗竭百分比、PCr 恢复时间常数（τPCr）和细胞内 pH。
该序列能够同时跟踪多个肌肉的动态 PCr 反应。在体模研究中，与 fidEPSI 和 fidCSI 相比，代谢物比、pH 值或线宽没有统计学差异。动态实验显示，比目鱼肌与腓肠肌的 PCr 耗竭存在差异。细胞内 pH、τPCr 和 %PCr 下降与报道的值一致。
结合回飞 EPSI 和压缩感知的高度加速 P-MRSI 能够使用临床 3T MR 系统评估多个肌肉群的并发能量代谢。
