The 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 non-selective inversion pulse followed by imaging when blood water magnetization is zero. An uncertainty in VASO relates to the completeness of blood water nulling. Specifically, radiofrequency coils produce a finite inversion volume, rendering the possibility of fresh, non-nulled blood. Here, VASO-fMRI was performed for varying inversion volume and TR using body coil radiofrequency transmission. For thin inversion volume thickness (δtot<10 mm), VASO signal changes were positive (ΔS/S=2.1–2.6%). Signal changes were negative and varied in magnitude for intermediate inversion volumes (δtot =100–300 mm), yet did not differ significantly (P>0.05) for δtot>300 mm. These data suggest that blood water is in steady-state for δtot>300 mm. In this appropriate range, long-TR VASO data converged to a less negative value (ΔS/S=−1.4±0.2%) than short-TR data (ΔS/S=−2.2±0.2%), implying that cerebral blood flow or transit-state effects may influence VASO contrast at short TR