Li Zhaoqing, Liang Chunjing, He Qingping, Feiweier Thorsten, Hsu Yi-Cheng, Li Jianhua, Bai Ruiliang
Department of Physical Medicine and Rehabilitation of the Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, China.
Magn Reson Med. 2025 Jun;93(6):2357-2369. doi: 10.1002/mrm.30454. Epub 2025 Jan 29.
Filter-exchange imaging (FEXI) and diffusion time (t)-dependent kurtosis imaging (DKI(t)) are two diffusion-based methods that have been proposed for in vivo measurements of water exchange rates. Few studies have directly compared these methods. We aimed to investigate whether FEXI and DKI(t) yield comparable water exchange measurements in the human brain in vivo.
Eight healthy volunteers underwent multiple-direction FEXI and DKI(t) acquisitions on a 3T scanner. We performed region of interest (ROI) analysis to determine correlations between FEXI-derived apparent exchange rate (AXR) and DKI(t)-derived reciprocal of exchange time ( ).
In both white matter (WM) and gray matter (GM), DKI(t) revealed substantial diffusion-time dependence of diffusivity and kurtosis. However, at t ≥ 100 ms, the diffusivity showed weak time dependence. In WM, this time dependence may be due to water exchange between myelin water and "free" water with different T values, although other factors, such as remaining restrictive effects from microstructural barriers, cannot be excluded. We found a significant correlation between DKI(t)-derived and FEXI-derived AXR in the axial direction within WM. No such correlation was present in GM, although both values showed similar ranges.
These results suggest that FEXI and DKI(t) could be sensitive to the same water exchange process only when the diffusion time in DKI(t) is sufficiently long, and only in WM. In both GM and WM, the restrictive effect of microstructure is non-negligible, especially at short diffusion times (<100 ms).
滤过交换成像（FEXI）和扩散时间（t）依赖的峰度成像（DKI(t)）是两种基于扩散的方法，已被提出用于体内水交换率的测量。很少有研究直接比较这些方法。我们旨在研究FEXI和DKI(t)在活体人脑中是否能得出可比的水交换测量结果。
8名健康志愿者在3T扫描仪上进行了多方向FEXI和DKI(t)采集。我们进行了感兴趣区域（ROI）分析，以确定FEXI得出的表观交换率（AXR）与DKI(t)得出的交换时间倒数（ ）之间的相关性。
在白质（WM）和灰质（GM）中，DKI(t)均显示扩散率和峰度存在显著的扩散时间依赖性。然而，在t≥100 ms时，扩散率显示出较弱的时间依赖性。在WM中，这种时间依赖性可能是由于髓鞘水和具有不同T值的“自由”水之间的水交换，尽管其他因素，如微观结构屏障的残留限制效应，也不能排除。我们发现在WM内轴向方向上，DKI(t)得出的 与FEXI得出的AXR之间存在显著相关性。在GM中不存在这种相关性，尽管两者的值显示出相似的范围。
这些结果表明，只有当DKI(t)中的扩散时间足够长且仅在WM中时，FEXI和DKI(t)才可能对相同的水交换过程敏感。在GM和WM中，微观结构的限制作用都不可忽略，尤其是在短扩散时间（<100 ms）时。
