Magnetization Transfer Enhanced Vascular-space-occupancy (MT-VASO) MRI with Whole Brain Coverage

Introduction: Vascular-space-occupancy (VASO) MRI (1) produces cerebral blood volume (CBV)-weighted images by employing inversion recovery to null the blood signal. Depending on the TR used, the residual magnetization in tissue, however, is only about 10-20% of the equilibrium signal intensity at the time of inversion (TI), which yields a relatively low signal-to-noise ratio (SNR). It has been demonstrate that by applying an MT pulse before the VASO inversion pulse (2), we can prepare a smaller tissue magnetization before inversion and accelerate the tissue recovery process after inversion to obtain a higher tissue signal and consequently boost the SNR and contrast-to-noise ratio (CNR), based on the fact that tissue signal can be strongly modulated by the MT pulse while blood has very little MT effect when using medium irradiating power and/or a frequency offset far away from water (>20ppm). Recent work (3,4) has shown that use of the 3D gradient spin echo (GraSE) sequence for the original VASO approach improves slice coverage and SNR/CNR, compared to using echo-planar-imaging (EPI). Here, the MT enhanced VASO (MTVASO) technique is extended from single-slice to whole-brain coverage using 3D GraSE sequence. The sensitivity (SNR) of this approach is compared to the widely used 2D multi-slice (MS) gradient echo (GE) EPI based conventional VASO protocol (5).