Department of Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden.
GE Research, Niskayuna, New York, United States.
Neuroimage. 2023 Dec 1;283:120409. doi: 10.1016/j.neuroimage.2023.120409. Epub 2023 Oct 13.
The dependence of the diffusion MRI signal on the diffusion time carries signatures of restricted diffusion and exchange. Here we seek to highlight these signatures in the human brain by performing experiments using free gradient waveforms designed to be selectively sensitive to the two effects. We examine six healthy volunteers using both strong and ultra-strong gradients (80, 200 and 300 mT/m). In an experiment featuring a large set of 150 gradient waveforms with different sensitivities to restricted diffusion and exchange, our results reveal unique and different time-dependence signatures in grey and white matter. Grey matter was characterised by both restricted diffusion and exchange and white matter predominantly by restricted diffusion. Exchange in grey matter was at least twice as fast as in white matter, across all subjects and all gradient strengths. The cerebellar cortex featured relatively short exchange times (115 ms). Furthermore, we show that gradient waveforms with tailored designs can be used to map exchange in the human brain. We also assessed the feasibility of clinical applications of the method used in this work and found that the exchange-related contrast obtained with a 25-minute protocol at 300 mT/m was preserved in a 4-minute protocol at 300 mT/m and a 10-minute protocol at 80 mT/m. Our work underlines the utility of free waveforms for detecting time dependence signatures due to restricted diffusion and exchange in vivo, which may potentially serve as a tool for studying diseased tissue.
扩散 MRI 信号对扩散时间的依赖性携带有受限扩散和交换的特征。在这里，我们通过使用专门设计的自由梯度波形来执行实验，以选择性地检测这两种效应，从而试图在人类大脑中突出这些特征。我们对六名健康志愿者使用强梯度（80、200 和 300 mT/m）和超强梯度（80、200 和 300 mT/m）进行了实验。在一个具有 150 种不同的梯度波形的大型实验中，这些梯度波形对受限扩散和交换具有不同的敏感性，我们的结果在灰质和白质中揭示了独特而不同的时间依赖性特征。灰质表现出受限扩散和交换的特征，而白质主要表现出受限扩散的特征。在所有受试者和所有梯度强度下，灰质中的交换速度至少是白质中的两倍。小脑皮层的交换时间相对较短（115 ms）。此外，我们表明，具有定制设计的梯度波形可用于绘制人类大脑中的交换图。我们还评估了该工作中使用的方法在临床应用中的可行性，发现使用 300 mT/m 梯度强度的 25 分钟协议获得的交换相关对比度在 300 mT/m 梯度强度的 4 分钟协议和 80 mT/m 梯度强度的 10 分钟协议中得以保留。我们的工作强调了自由波形在检测体内受限扩散和交换的时间依赖性特征方面的实用性，这可能成为研究病变组织的一种工具。
