Evidence for a vascular contribution to diffusion FMRI at high b value.

Journal article

Recent work has suggested that diffusion-weighted functional magnetic resonance imaging (FMRI) with strong diffusion weighting (high b value) detects neuronal swelling that is directly related to neuronal firing. This would constitute a much more direct measure of brain activity than current methods and represent a major advance in neuroimaging. However, it has not been firmly established that the observed signal changes do not reflect residual vascular effects, which are known to exist at low b value. This study measures the vascular component of diffusion FMRI directly by using hypercapnia, which induces blood flow changes in the absence of a change in neuronal firing. Hypercapnia elicits a similar diffusion FMRI response to a visual stimulus including a rise in percent signal change with increasing b value, which was reported for visual activation. Analysis of the response timing found no evidence for an early response at high b value, which has been reported as evidence for a nonhemodynamic response. These results suggest that a large component of the diffusion FMRI signal at high b value is vascular rather than neuronal.

Authors: Miller, K; Bulte, D; Devlin, H; Robson, M; Wise, R

• Publication status: Published
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Volume: 104
• Issue: 52
• Pages: 20967-20972
• Publication date: 2007-12-01
• DOI: 10.1073/pnas.0707257105
• EISSN: 1091-6490
• ISSN: 0027-8424
• Language: English
• Keywords: Algorithms; Time Factors; Cerebrovascular Circulation; Brain Mapping; Models, Statistical; Neurons; Humans; Magnetic Resonance Imaging; Image Processing, Computer-Assisted; Diffusion Magnetic Resonance Imaging; Diffusion; Brain; Models, Neurological