Dynamic CSF Fraction and MAGIC VASO fMRI

This work extends the Multiple Acquisitions with Global Inversion Cycling Vascular Space Occupancy (MAGIC VASO) method to human whole-brain fMRI at 3.0 Tesla and demonstrates the need to consider the dynamic contribution of cerebrospinal fluid (CSF) to the relative VASO signal change (DeltaVASO/VASO). A three-compartment model is proposed to include both the resting and changing fractional CSF contribution (x_c,rest and Deltatimes_c, respectively) to DeltaVASO/VASO. Computer simulations show that a small change in CSF fraction on the order of 5% is enough to eliminate the VASO signal change arising from a 20% change in CBV. A MAGIC VASO sequence that provides whole-brain coverage is demonstrated using a paradigm comprised of visual, motor, and auditory stimulation. Activated regions are quantitatively compared in the corresponding blood oxygenation level-dependent (BOLD) images. Statistically significant signal changes are detected in the visual and motor cortices using both acquisition techniques. The absence of VASO activation for auditory stimulation and the proximity of the auditory cortex to the higher CSF concentration of the insula and superior temporal gyrus support the possibility of a Deltatimes_c contribution to the VASO signal. Without specific knowledge of the CSF components (x_c,rest and Deltatimes_c), inference of DeltaCBV/CBV from DeltaVASO/VASO is severely limited.