Chakwizira Arthur, Zhu Ante, Foo Thomas, Westin Carl-Fredrik, Szczepankiewicz Filip, Nilsson Markus
Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden.
GE Research, Niskayuna, New York, USA.
ArXiv. 2023 Apr 5:arXiv:2304.02764v1.
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 that are 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 gradient waveforms with different sensitivities to restricted diffusion and exchange (150 samples), our results reveal unique time-dependence signatures in grey and white matter, where the former is characterised by both restricted diffusion and exchange and the latter predominantly exhibits restricted diffusion. Furthermore, we show that gradient waveforms with independently varying sensitivities to restricted diffusion and exchange can be used to map exchange in the human brain. We consistently find that exchange in grey matter is at least twice as fast as in white matter, across all subjects and all gradient strengths. The shortest exchange times observed in this study were in the cerebellar cortex (115 ms). We also assess the feasibility of future clinical applications of the method used in this work, where we find that the grey-white matter exchange contrast obtained with a 25-minute 300 mT/m protocol is preserved by a 4-minute 300 mT/m and a 10-minute 80 mT/m protocol. Our work underlines the utility of free waveforms for detecting time-dependence signatures due to restricted diffusion and exchange , which may potentially serve as a tool for studying diseased tissue.
扩散磁共振成像信号对扩散时间的依赖性带有受限扩散和交换的特征。在此，我们试图通过使用对这两种效应具有选择性敏感性的自由梯度波形进行实验，来突出人类大脑中的这些特征。我们使用强梯度和超强梯度（80、200和300 mT/m）对六名健康志愿者进行了检查。在一项具有大量对受限扩散和交换具有不同敏感性的梯度波形（150个样本）的实验中，我们的结果揭示了灰质和白质中独特的时间依赖性特征，其中前者的特征是受限扩散和交换，而后者主要表现为受限扩散。此外，我们表明，对受限扩散和交换具有独立变化敏感性的梯度波形可用于绘制人类大脑中的交换情况。我们始终发现，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。本研究中观察到的最短交换时间出现在小脑皮质（115毫秒）。我们还评估了本研究中使用的方法未来临床应用的可行性，发现在25分钟300 mT/m方案下获得的灰白质交换对比度在4分钟300 mT/m和10分钟80 mT/m方案下得以保留。我们的工作强调了自由波形在检测由于受限扩散和交换引起的时间依赖性特征方面的效用，这可能潜在地成为研究病变组织的工具。
