MR blood oxygenation level-dependent signal differences in parenchymal andlarge draining vessels: Implications for functional MR imaging

BACKGROUND AND PURPOSE: One major limitation of current functional MR (fMR) imaging is its inability to clarify the relationship between sites of cort ical neuronal activation, small parenchymal venules that are in close proxi mity to these sites, and large draining veins distant from the active paren chyma, We propose to use gradient-echo blood oxygenation level-dependent (B OLD) fMR time courses to differentiate large draining veins from parenchyma l microvasculature. METHODS: In eight research subjects, five of whom presented with space-occu pying lesions near the central sulcus, gradient-echo fMR imaging was perfor med during alternating periods of rest and motor activation, MR signal time courses from parenchymal regions and draining veins of different diameters , which were identified using contrast-enhanced T1-weighted scans, were eva luated. Percent signal changes (Delta S) and the time to the onset of MR si gnal rise (T-0) were calculated. RESULTS: Mean Delta S for all subjects was 2.3% (SD +/-0.7%) for parenchyma l activation, 4.3% (SD +/-1.0%) for sulcal macrovasculature, and 7.3 (SD +/ -1.1%) for large superficial bridging veins. The mean time to onset of MR s ignal increase was 4.4 seconds for parenchymal task-related hemodynamic cha nges and 6.6 seconds for venous hemodynamic changes, regardless of vessel s ize. Both the differences in Delta S and T-0 were statistically significant between venous and parenchymal activation (P < .0001). CONCLUSION: Gradient-echo fMR imaging reveals hemodynamic task-related chan ges regardless of vessel size and therefore might show macrovascular change s distal to the site of neuronal activity, MR-signal time-course characteri stics (Delta S and T-0) can be used to differentiate between small parenchy mal and larger pial draining vessels, which is especially important in pres urgical planning of neurosurgical procedures involving functionally importa nt brain regions. The knowledge about the differences in Delta S and T-0 be tween micro- and macrovasculature might lead to a more accurate description of the spatial distribution of underlying neuronal activity.