Functional perfusion imaging (p-fMRI) was applied for the first time to a cognitive
paradigm that produces activations in a number of brain regions. An adapted single-trial
version of the color-word Stroop interference task was used as a paradigm. This experiment
is known to produce robust activations in the lateral prefrontal, the fronto-median,
and parietal cortices. Perfusion contrast was created by continuous arterial spin
labeling (CASL) of the blood in the left common carotid artery, and was applied for
all repetitions of the functional run in a quasi-continuous fashion, i.e., it was
interrupted only during image acquisition. For imaging, a spin-echo (SE) echo planar
imaging (EPI) sequence with a 64×36 acquisition matrix was used. A short echo time
of TE=13 ms was employed in order to suppress blood oxygen level dependent (BOLD)
signals. For comparison, BOLD contrast was detected using conventional gradient-echo
(GE) or SE-EPI. Positive activations in BOLD imaging appear in p-fMRI as negative
signal changes corresponding to an enhanced transport of inverted water spins into
the region of interest (i.e., increased cerebral blood flow [CBF]). Negative BOLD
responses (areas of deactivation) appear as positive signal changes in p-fMRI indicating
areas with decreased CBF. p-fMRI was capable of reproducing most of the GE-BOLD-fMRI
activations and deactivations as signal changes of opposite sign. The localization
of the local maxima of p-fMRI agreed reasonably with SE-BOLD-fMRI and GE-BOLD-fMRI.
Significant shifts between the covered areas of each contrast were also detected.
In certain areas, p-fMRI yielded a low sensitivity compared to BOLD-fMRI. The quantification
of CBF changes during cognitive task activation is demonstrated for several well-separated
cortical areas. The observation of a decreased CBF during the Stroop task in the parietomedian
cortex confirms previous PET results which showed decreases of CBF in well-separated
cortical regions related to a decrease in neuronal activity.
