Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Medical Scientist Training Program, New York University School of Medicine, New York, NY, USA.
Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Department of Electrical and Computer Engineering, New York Univeristy Tandon School of Engineering, Brooklyn, NY, USA.
Neuroimage. 2020 Jan 1;204:116228. doi: 10.1016/j.neuroimage.2019.116228. Epub 2019 Sep 30.
At very low diffusion weighting the diffusion MRI signal is affected by intravoxel incoherent motion (IVIM) caused by dephasing of magnetization due to incoherent blood flow in capillaries or other sources of microcirculation. While IVIM measurements at low diffusion weightings have been frequently used to investigate perfusion in the body as well as in malignant tissue, the effect and origin of IVIM in normal brain tissue is not completely established. We investigated the IVIM effect on the brain diffusion MRI signal in a cohort of 137 radiologically-normal patients (62 male; mean age = 50.2 ± 17.8, range = 18 to 94). We compared the diffusion tensor parameters estimated from a mono-exponential fit at b = 0 and 1000 s/mm versus at b = 250 and 1000 s/mm. The asymptotic fitting method allowed for quantitative assessment of the IVIM signal fraction f* in specific brain tissue and regions. Our results show a mean (median) percent difference in the mean diffusivity of about 4.5 (4.9)% in white matter (WM), about 7.8 (8.7)% in cortical gray matter (GM), and 4.3 (4.2)% in thalamus. Corresponding perfusion fraction f* was estimated to be 0.033 (0.032) in WM, 0.066 (0.065) in cortical GM, and 0.033 (0.030) in the thalamus. The effect of f* with respect to age was found to be significant in cortical GM (Pearson correlation ρ = 0.35, p = 310) and the thalamus (Pearson correlation ρ = 0.20, p = 0.022) with an average increase in f of 5.1710/year and 3.6110/year, respectively. Significant correlations between f* and age were not observed for WM, and corollary analysis revealed no effect of gender on f*. Possible origins of the IVIM effect in normal brain tissue are discussed.
在极低的扩散加权下，由于毛细血管或其他微循环源的磁化相位失相，扩散 MRI 信号受到体素内非相干运动（IVIM）的影响。虽然在低扩散权重下进行 IVIM 测量已被广泛用于研究体内以及恶性组织中的灌注，但 IVIM 在正常脑组织中的作用和来源尚未完全确定。我们在一组 137 名影像学正常的患者（62 名男性；平均年龄为 50.2±17.8，范围为 18 至 94 岁）中研究了 IVIM 对脑扩散 MRI 信号的影响。我们比较了在 b=0 和 1000 s/mm 与 b=250 和 1000 s/mm 时单指数拟合估计的扩散张量参数。渐近拟合方法允许对特定脑组织和区域的 IVIM 信号分数 f进行定量评估。我们的结果显示，在白质（WM）中，平均扩散系数的平均（中位数）差异约为 4.5（4.9）%，在皮质灰质（GM）中约为 7.8（8.7）%，在丘脑中约为 4.3（4.2）%。相应的灌注分数 f估计为 WM 为 0.033（0.032），皮质 GM 为 0.066（0.065），丘脑为 0.033（0.030）。发现 f与年龄的相关性在皮质 GM（皮尔逊相关 ρ=0.35，p=310）和丘脑（皮尔逊相关 ρ=0.20，p=0.022）中具有统计学意义，f的平均增长率分别为 5.1710/年和 3.6110/年。在 WM 中未观察到 f与年龄之间存在显著相关性，并且相关分析显示 f*不受性别影响。讨论了正常脑组织中 IVIM 效应的可能起源。
