Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands.
Department of Neurology, UMC Utrecht Brain Center, University Medical Center Utrecht, Utrecht, The Netherlands.
Magn Reson Med. 2022 Jul;88(1):266-279. doi: 10.1002/mrm.29209. Epub 2022 Mar 28.
The ADC of brain tissue slightly varies over the cardiac cycle. This variation could reflect physiology, including mixing of the interstitial fluid, relevant for brain waste clearance. However, it is known from cardiac diffusion imaging that tissue deformation by itself affects the magnitude of the MRI signal, leading to artificial ADC variations as well. This study investigates to what extent tissue deformation causes artificial ADC variations in the brain.
We implemented a high-field MRI sequence with stimulated echo acquisition mode that simultaneously measures brain tissue deformation and ADC. Based on the measured tissue deformation, we simulated the artificial ADC variation by combining established theoretical frameworks and compared the results with the measured ADC variation. We acquired data in 8 healthy volunteers with diffusion weighting b = 300 and b = 1000 s/mm .
Apparent diffusion coefficient variation was largest in the feet-to-head direction and showed the largest deviation from the mean ADC at peak systole. Artificial ADC variation estimated from tissue deformation was 1.3 ± 0.37·10 mm /s in the feet-to-head direction for gray matter, and 0.75 ± 0.29·10 mm /s for white matter. The measured ADC variation in the feet-to-head direction was 5.6·10 ± 1.5·10 mm /s for gray matter and 3.2·10 ± 1.0·10 mm /s for white matter, which was a factor of 3.5 ± 0.82 and 3.4 ± 0.57 larger than the artificial diffusion variations. The measured diffusion variations in the right-to-left/anterior-to-posterior direction were a factor of 1.5 ± 1.0/1.7 ± 1.4 and 2.0 ± 0.91/2.5 ± 0.94 larger than the artificial diffusion variations for gray matter and white matter, respectively.
Apparent diffusion coefficient variations in the brain likely largely reflect physiology.
脑组织的 ADC 值在心动周期内会略有变化。这种变化可能反映了生理过程，包括细胞外间隙的混合，这与脑废物清除有关。然而，从心脏扩散成像中可知，组织变形本身会影响 MRI 信号的幅度，从而导致人为的 ADC 变化。本研究旨在探讨组织变形在多大程度上导致了大脑中的人为 ADC 变化。
我们实施了一种具有受激回波采集模式的高磁场 MRI 序列，该序列同时测量脑组织变形和 ADC 值。基于测量到的组织变形，我们通过结合已建立的理论框架模拟了人为的 ADC 变化，并将结果与测量到的 ADC 变化进行了比较。我们在 8 名健康志愿者中采集了 b 值为 300 和 1000 s/mm 的扩散加权数据。
在头脚方向上，表观扩散系数的变化最大，并且在收缩期峰值处与平均 ADC 的偏差最大。从组织变形估计的人为 ADC 变化在头脚方向上灰质为 1.3±0.37·10 毫米/秒，白质为 0.75±0.29·10 毫米/秒。在头脚方向上测量到的 ADC 变化灰质为 5.6·10 ±1.5·10 毫米/秒，白质为 3.2·10 ±1.0·10 毫米/秒，分别比人为扩散变化大 3.5±0.82 倍和 3.4±0.57 倍。在右到左/前到后的方向上测量到的扩散变化在灰质和白质中分别比人为扩散变化大 1.5±1.0/1.7±1.4 倍和 2.0±0.91/2.5±0.94 倍。
大脑中的表观扩散系数变化可能在很大程度上反映了生理过程。
