Measuring Absolute Arteriolar Cerebral Blood Volume (CBVa) in Human Brain Gray Matter (GM) without Contrast Agent

Introduction: Arteriolar cerebral blood volume (CBVa) is an important physiological parameter regulating tissue perfusion. We demonstrate a novel approach to measure absolute CBVa (CBVa) based on a variant of vascular-space-occupancy (VASO) MRI (1). VASO is a contrast-agent-free MRI technique that is sensitized to micro-vascular CBV changes through nulling of blood signal. Instead of the spatially non-selective inversion used in the original VASO method, a new approach, dubbed inflow VASO (iVASO) (2), was designed in which a spatially non-selective inversion is followed immediately by a spatially selective inversion to flip back the water spins in the imaging slice and the brain above. Thus only the blood water spins below the imaging slice remian inverted. Images are then acquired when the inverted spins flowing into the slice are nulled. As the arterial transit time in human brain gray matter (GM) (400-1400 ms) (3.4) is in the range of inversion times (TI=300-1150 ms) used for blood nulling in VASO MRI (5), iVASO is expected to achieve predominantly arteriolar-selective blood nulling. A control scan can be performed with two consecutive spatially non-selective inversion pulses and identical imaging parameters. By subtracting the inflowing blood nulling scan from the control scan, CBVa values in units of milliliters of blood per 100 milliliters of tissue can be quantified by normalizing the difference signal with an additional normalization factor. We demonstrate this method in healthy human brain GM.