Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Magn Reson Med. 2023 Jun;89(6):2432-2440. doi: 10.1002/mrm.29594. Epub 2023 Feb 5.
To quantify the variations of the power-law dependences on diffusion time t or gradient frequency of extracellular water diffusion measured by diffusion MRI (dMRI).
Model cellular systems containing only extracellular water were used to investigate the dependence of , the extracellular diffusion coefficient. Computer simulations used a randomly packed tissue model with realistic intracellular volume fractions and cell sizes. DMRI measurements were performed on samples consisting of liposomes containing heavy water(D O, deuterium oxide) dispersed in regular water (H O). was obtained over a broad range (∼1-1000 ms) and then fit power-law equations and .
Both simulated and experimental results suggest that no single power-law adequately describes the behavior of over the range of diffusion times of most interest in practical dMRI. Previous theoretical predictions are accurate over only limited ranges; for example, is valid only for short times, whereas or is valid only for long times but cannot describe other ranges simultaneously. For the specific range of 5-70 ms used in typical human dMRI measurements, matches the data well empirically.
The optimal power-law fit of extracellular diffusion varies with diffusion time. The dependency obtained at short or long limits cannot be applied to typical dMRI measurements in human cancer or liver. It is essential to determine the appropriate diffusion time range when modeling extracellular diffusion in dMRI-based quantitative microstructural imaging.
量化通过扩散 MRI（dMRI）测量的细胞外水扩散的扩散时间 t 或梯度频率的幂律依赖性的变化。
使用仅包含细胞外水的模型细胞系统来研究扩散系数 的依赖性。计算机模拟使用具有实际细胞内体积分数和细胞大小的随机堆积组织模型。DMRI 测量是在含有重水（DO，氧化氘）的脂质体分散在普通水中（HO）的样品上进行的。在较宽的范围内（约 1-1000ms）获得了 ，然后拟合幂律方程 和 。
模拟和实验结果均表明，没有单一的幂律能够充分描述在实际 dMRI 中最感兴趣的扩散时间范围内的 行为。以前的理论预测仅在有限的范围内准确；例如， 仅在短时间内有效，而 或 仅在长时间内有效，但不能同时描述其他范围。对于典型人体 dMRI 测量中使用的特定 5-70ms 范围， 经验上很好地符合数据。
细胞外扩散的最优幂律拟合随扩散时间而变化。在短或长时间限制下获得的依赖性不能应用于人类癌症或肝脏的典型 dMRI 测量。在基于 dMRI 的定量微观结构成像中建模细胞外扩散时，确定适当的扩散时间范围至关重要。
