Spencer Arthur P C, Nguyen-Duc Jasmine, de Riedmatten Inès, Szczepankiewicz Filip, Jelescu Ileana O
Department of Radiology, Lausanne University Hospital (CHUV), Lausanne, Switzerland.
Faculty of Biology and Medicine, University of Lausanne (UNIL), Lausanne, Switzerland.
Nat Commun. 2025 May 30;16(1):5036. doi: 10.1038/s41467-025-60357-5.
Functional MRI (fMRI) using the blood-oxygen level dependent (BOLD) signal provides valuable insight into grey matter activity. However, uncertainty surrounds the white matter BOLD signal. Apparent diffusion coefficient (ADC) offers an alternative fMRI contrast sensitive to transient cellular deformations during neural activity, facilitating detection of both grey and white matter activity. Further, through minimising vascular contamination, ADC-fMRI has the potential to overcome the limited temporal specificity of the BOLD signal. However, the use of linear diffusion encoding introduces sensitivity to fibre directionality, while averaging over multiple directions comes at great cost to temporal resolution. In this study, we used spherical b-tensor encoding to impart diffusion sensitisation in all directions per shot, providing an ADC-fMRI contrast capable of detecting activity independently of fibre directionality. We provide evidence from two task-based experiments on a clinical scanner that isotropic ADC-fMRI is more temporally specific than BOLD-fMRI, and offers more balanced mapping of grey and white matter activity. We further demonstrate that isotropic ADC-fMRI detects white matter activity independently of fibre direction, while linear ADC-fMRI preferentially detects activity in voxels containing fibres perpendicular to the diffusion encoding direction. Thus, isotropic ADC-fMRI opens avenues for investigation into whole-brain grey and white matter functional connectivity.
利用血氧水平依赖（BOLD）信号的功能磁共振成像（fMRI）为灰质活动提供了有价值的见解。然而，白质BOLD信号仍存在不确定性。表观扩散系数（ADC）提供了另一种fMRI对比方法，对神经活动期间的瞬时细胞变形敏感，有助于检测灰质和白质活动。此外，通过最小化血管污染，ADC-fMRI有潜力克服BOLD信号有限的时间特异性。然而，线性扩散编码的使用引入了对纤维方向性的敏感性，而在多个方向上进行平均会极大地牺牲时间分辨率。在本研究中，我们使用球形b张量编码在每次采集中在所有方向上施加扩散敏感化，提供一种能够独立于纤维方向性检测活动的ADC-fMRI对比。我们在临床扫描仪上进行的两个基于任务的实验中提供了证据，表明各向同性ADC-fMRI在时间上比BOLD-fMRI更具特异性，并且能更平衡地映射灰质和白质活动。我们进一步证明，各向同性ADC-fMRI能独立于纤维方向检测白质活动，而线性ADC-fMRI优先检测包含垂直于扩散编码方向纤维的体素中的活动。因此，各向同性ADC-fMRI为研究全脑灰质和白质功能连接开辟了道路。
