GE Research, Niskayuna, New York.
Department of Radiology and Imaging, Hospital for Special Surgery, New York, New York.
Magn Reson Med. 2020 Aug;84(2):950-965. doi: 10.1002/mrm.28180. Epub 2020 Feb 3.
We investigate the importance of high gradient-amplitude and high slew-rate on oscillating gradient spin echo (OGSE) diffusion imaging for human brain imaging and evaluate human brain imaging with OGSE on the MAGNUS head-gradient insert (200 mT/m amplitude and 500 T/m/s slew rate).
Simulations with cosine-modulated and trapezoidal-cosine OGSE at various gradient amplitudes and slew rates were performed. Six healthy subjects were imaged with the MAGNUS gradient at 3T with OGSE at frequencies up to 100 Hz and b = 450 s/mm . Comparisons were made against standard pulsed gradient spin echo (PGSE) diffusion in vivo and in an isotropic diffusion phantom.
Simulations show that to achieve high frequency and b-value simultaneously for OGSE, high gradient amplitude, high slew rates, and high peripheral nerve stimulation limits are required. A strong linear trend for increased diffusivity (mean: 8-19%, radial: 9-27%, parallel: 8-15%) was observed in normal white matter with OGSE (20 Hz to 100 Hz) as compared to PGSE. Linear fitting to frequency provided excellent correlation, and using a short-range disorder model provided radial long-term diffusivities of D = 911 ± 72 µm /s, D = 1519 ± 164 µm /s, and D = 640 ± 111 µm /s and correlation lengths of l = 0.802 ± 0.156 µm, l = 0.837 ± 0.172 µm, and l = 0.780 ± 0.174 µm. Diffusivity changes with OGSE frequency were negligible in the phantom, as expected.
The high gradient amplitude, high slew rate, and high peripheral nerve stimulation thresholds of the MAGNUS head-gradient enables OGSE acquisition for in vivo human brain imaging.
我们研究了在人类大脑成像中，高梯度幅度和高转换速率对振荡梯度回波（OGSE）扩散成像的重要性，并评估了 MAGNUS 头部梯度插入（200mT/m 幅度和 500T/m/s 转换速率）在 OGSE 上的人脑成像。
在各种梯度幅度和转换速率下进行了余弦调制和梯形余弦 OGSE 的模拟。在 3T 下使用 MAGNUS 梯度对 6 名健康受试者进行了 OGSE 成像，频率高达 100Hz，b 值为 450s/mm 。将其与体内和各向同性扩散体模中的标准脉冲梯度回波（PGSE）扩散进行了比较。
模拟结果表明，为了同时实现 OGSE 的高频和大 b 值，需要高梯度幅度、高转换速率和高外周神经刺激限制。与 PGSE 相比，在正常白质中观察到 OGSE（20Hz 至 100Hz）的扩散率显著增加（平均：8-19%，径向：9-27%，平行：8-15%）。线性拟合到频率提供了极好的相关性，使用短程无序模型提供了径向长程扩散率 D=911±72µm/s、D=1519±164µm/s 和 D=640±111µm/s 以及相关长度 l=0.802±0.156µm、l=0.837±0.172µm 和 l=0.780±0.174µm。正如预期的那样，在体模中，OGSE 频率的扩散率变化可以忽略不计。
MAGNUS 头部梯度的高梯度幅度、高转换速率和高外周神经刺激阈值使 OGSE 能够用于人类大脑的体内成像。
