A multi-compartmental SE-BOLD interpretation for stimulus-related signal changes in diffusion-weighted functional MRI.
A new interpretation is proposed for stimulus-induced signal changes in diffusion-weighted functional MRI. T(2)-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.
Kershaw
Jeff
J
Department of Biophysics, Molecular Imaging Centre, National Institute of Radiological Sciences, Anagawa, Inage-ku, Chiba, Japan.
Tomiyasu
Moyoko
M
Kashikura
Kenichi
K
Hirano
Yoshiyuki
Y
Nonaka
Hiroi
H
Hirano
Masaya
M
Ikehira
Hiroo
H
Kanno
Iwao
I
Obata
Takayuki
T
D000328:Adult; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood*; D010775:Photic Stimulation; D013113:Spin Labels; D013997:Time Factors; D055815:Young Adult
D013113:Spin Labels; D010100:Oxygen