Effect of Inflow of Fresh Blood on Vascular-Space-Occupancy (VASO) Contrast

In vascular-space-occupancy (VASO)-MRI,cerebral blood volume (CBV)-weighted contrast Is generated by applying a nonselective inversion pulse followed by imaging when blood water magnetization is zero. An uncertainty in VASO relates to the completeness of blood water nulling. Specifically, radio frequency (RF) coils produce a finite inversion volume, rendering the possibility of fresh, non-nulled blood. Here, VASO-functional MRI (fMRI) was performed for varying inversion volume and TR using body coil RF transmission. For thin inversion volume thickness (delta(tot) < 10 mm), VASO signal changes were positive (Delta S/S = 2.1-2.6%). Signal changes were negative and varied in magnitude for intermediate inversion volumes (delta(tot) = 100-300 mm), yet did not differ significantly (P > 0.05) for delta(tot) > 300 mm. These data suggest that blood water Is in steady state for delta(tot) > 300 mm. In this appropriate range, long-TR VASO data converged to a less negative value (Delta S/S = -1.4% +/- 0.2%) than short-TR data (Delta S/S = -2.2% +/- 0.2%), implying that cerebral blood flow or transit-state effects may Influence VASO contrast at short TR. Magn Reson Med 61:473-480,2009. (C) 2009 Wiley-Liss, Inc.