Quantitative Comparison of Functional Contrast from BOLD-Weighted Spin-Echo and Gradient-Echo Echoplanar Imaging at 1.5 Tesla and H215O PET in the Whole Brain

Spin-echo and gradient-echo echoplanar functional magnetic resonance imaging (fMRI) studies at 1.5 Tesla (T) were used to obtain blood oxygenation level-dependent (BOLD) contrast images of the whole brain in seven strongly right-handed women during execution of a complex motor task. Five subjects underwent subsequent H215O positron emission tomography (PET) studies while performing the same task. Group-averaged results for changes in the MRI relaxation rates R2* and R2 at 1.5T in response to neuronal activation in nine cortical, subcortical, and cerebellar motor regions are reported. Results for each method are grouped according to tissue type—cerebral cortex (precentral gyrus and supplementary motor area), subcortical regions (thalamus and putamen), and cerebellar cortex (superior lobule). The observed changes in R2* from activation-induced oxygenation changes were more variable across brain regions with different tissue characteristics than observed changes in R2. The ratio of ΔR2* to ΔR2 was 3.3 ± 0.9 for cerebral cortex and 2.0 ± 0.6 for subcortical tissue. ΔR2*, ΔR2, and relative blood flow changes were ΔR2* = −0.201 ± 0.040 s−1, ΔR2 = −0.064 ± 0.011 s−1, and Δf/f = 16.7 ± 0.8% in the cerebral cortex; ΔR2* = −0.100 ± 0.026 s−1, ΔR2 = −0.049 ± 0.009 s−1, and Δf/f = 9.4 ± 0.7% in the subcortical regions; and ΔR2* = −0.215 ± 0.093 s−1, ΔR2 = −0.069 ± 0.012 s−1, and Δf/f = 16.2 ± 1.2% in the cerebellar cortex.