Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States of America; Division of Neuropharmacology and Neurologic Diseases, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States of America.
Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States of America.
Magn Reson Imaging. 2021 Apr;77:194-203. doi: 10.1016/j.mri.2020.12.015. Epub 2020 Dec 23.
BACKGROUND: Diffusion MRI (dMRI) data acquisition protocols are well-established on modern high-field clinical scanners for human studies. However, these protocols are not suitable for the chimpanzee (or other large-brained mammals) because of its substantial difference in head geometry and brain volume compared with humans. Therefore, an optimal dMRI data acquisition protocol dedicated to chimpanzee neuroimaging is needed. METHODS: A multi-shot (4 segments) double spin-echo echo-planar imaging (MS-EPI) sequence and a single-shot double spin-echo EPI (SS-EPI) sequence were optimized separately for in vivo dMRI data acquisition of chimpanzees using a clinical 3T scanner. Correction for severe susceptibility-induced image distortion and signal drop-off of the chimpanzee brain was performed and evaluated using FSL software. DTI indices in different brain regions and probabilistic tractography were compared. A separate DTI data set from n=34 chimpanzees (13 to 56 years old) was collected using the optimal protocol. Age-related changes in diffusivity indices of optic nerve fibers were evaluated. RESULTS: The SS-EPI sequence acquired dMRI data of the chimpanzee brain with approximately doubled the SNR as the MS-EPI sequence given the same scan time. The quality of white matter fiber tracking from the SS-EPI data was much higher than that from MS-EPI data. However, quantitative analysis of DTI indices showed no difference in most ROIs between the SS-EPI and MS-EPI sequences. The progressive evolution of diffusivity indices of optic nerves indicated mild changes in fiber bundles of chimpanzees aged 40 years and above. CONCLUSION: The single-shot EPI-based acquisition protocol provided better image quality of dMRI for chimpanzee brains and is recommended for in vivo dMRI study or clinical diagnosis of chimpanzees (or other large animals) using a clinical scanner. Also, the tendency of FA decrease or diffusivity increase in the optic nerve of aged chimpanzees was seen but did not show significant age-related changes, suggesting aging may have less impact on optic nerve fiber integrity of chimpanzees, in contrast to previous results for both macaque monkeys and humans.
背景：扩散磁共振成像（dMRI）数据采集方案在现代高场临床扫描仪上已经得到充分确立，适用于人类研究。然而，由于与人类相比，黑猩猩（或其他大颅类哺乳动物）的头部几何形状和脑容量存在显著差异，这些方案并不适用于黑猩猩。因此，需要开发一种专门针对黑猩猩神经影像学的优化 dMRI 数据采集方案。
方法：使用临床 3T 扫描仪，分别对多回波（4 段）双回波平面成像（MS-EPI）序列和单次双回波 EPI（SS-EPI）序列进行优化，以获取黑猩猩体内的 dMRI 数据。使用 FSL 软件对黑猩猩大脑的严重磁化率诱导的图像失真和信号衰减进行校正，并对其进行评估。比较了不同脑区的 DTI 指数和概率追踪结果。使用优化方案，对 n=34 只（13 至 56 岁）黑猩猩的独立 DTI 数据集进行了采集。评估了视神经纤维弥散系数随年龄的变化。
结果：与 MS-EPI 序列相比，在相同的扫描时间内，SS-EPI 序列获取的黑猩猩大脑 dMRI 数据的 SNR 提高了约两倍。SS-EPI 数据的白质纤维追踪质量明显高于 MS-EPI 数据。然而，定量分析 DTI 指数显示，SS-EPI 和 MS-EPI 序列在大多数 ROI 之间没有差异。视神经弥散系数的渐进性变化表明，40 岁及以上的黑猩猩纤维束有轻微变化。
结论：基于单次激发 EPI 的采集方案为黑猩猩大脑的 dMRI 提供了更好的图像质量，推荐在临床扫描仪上用于黑猩猩（或其他大型动物）的体内 dMRI 研究或临床诊断。此外，在年龄较大的黑猩猩中，视神经的 FA 值降低或弥散度增加的趋势可见，但没有显示出与年龄相关的显著变化，这表明与猕猴和人类的先前结果相比，衰老对黑猩猩视神经纤维完整性的影响可能较小。
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