Diffusion-weighted fMRI has attracted some as a technique that might provide information more directly correlated with actual neural activity than BOLD fMRI.A number of interpretations have been proposed for the diffusion-weighted signal,however many questions remain unanswered.To further examine the dependence of fMRI on b-value,somatosensory forepaw stimulation was conducted on alpha-chloralose anesthetised rats at 7 T.Functional images were acquired at five b-values(b=0,200.800.1400and2000s/mm2)and two echo-times(TE=30and60ms). The mean signal changes from all rats showed a clear difference in signal amplitude between data acquired at differentTEs, although the response shape is qualitatively similar.In contrast to previous human data,the positive stimulus-correlated signal change and post-stimulus undershoot showed a slight downward (but insignificant)trend with increased b-value.Note that the undershoot persists for higher b-values.The IV contribution to the TE=60 ms data may be substantially attenuated because of the relatively short T2 of blood at7T.第36回日本磁気共鳴医学
