A multi-compartmental SE-BOLD interpretation for stimulus-related signal changes in diffusion-weighted functional MRI

• Published in: NMR in biomedicine Vol. 22; no. 7; pp. 770 - 778
• Main Authors: Kershaw, Jeff, Tomiyasu, Moyoko, Kashikura, Kenichi, Hirano, Yoshiyuki, Nonaka, Hiroi, Hirano, Masaya, Ikehira, Hiroo, Kanno, Iwao, Obata, Takayuki
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2009
• Subjects: ADC; Adult; biexponential signal decay; Diffusion Magnetic Resonance Imaging - methods; diffusion-weighting decomposition; Female; functional MRI; Humans; Male; Oxygen - blood; Photic Stimulation; Spin Labels; spin-echo BOLD; Time Factors; Young Adult
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.1391

A new interpretation is proposed for stimulus‐induced signal changes in diffusion‐weighted functional MRI. T2‐weighted spin‐echo echo‐planar images were acquired at different diffusion‐weightings while visual stimulation was presented to human volunteers. The amplitudes of the positive stimulus‐correlated response and post‐stimulus undershoot (PSU) in the functional time‐courses were found to follow different trends as a function of b‐value. Data were analysed using a three‐compartment signal model, with one compartment being purely vascular and the other two dominated by fast‐ and slow‐diffusing molecules in the brain tissue. The diffusion coefficients of the tissue were assumed to be constant throughout the experiments. It is shown that the stimulus‐induced signal changes can be decomposed into independent contributions originating from each of the three compartments. After decomposition, the fast‐diffusion phase displays a substantial PSU, while the slow‐diffusion phase demonstrates a highly reproducible and stimulus‐correlated time‐course with minimal undershoot. The decomposed responses are interpreted in terms of the spin‐echo blood oxygenation level dependent (SE‐BOLD) effect, and it is proposed that the signal produced by fast‐ and slow‐diffusing molecules reflect a sensitivity to susceptibility changes in arteriole/venule‐ and capillary‐sized vessels, respectively. This interpretation suggests that diffusion‐weighted SE‐BOLD imaging may provide subtle information about the haemodynamic and neuronal responses. Copyright © 2009 John Wiley & Sons, Ltd. A new interpretation is proposed for stimulus‐induced signal changes in diffusion‐weighted fMRI. Spin‐echo echo‐planar images were acquired at different diffusion‐weightings while a visual stimulus was presented. Data were analysed using a three‐compartment signal model, with one compartment being purely vascular and the other two dominated by fast‐ and slow‐diffusing molecules in brain tissue. This interpretation suggests that diffusion‐weighted SE‐BOLD imaging may provide subtle information about the haemodynamic and neuronal responses.