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Abstract

Arterial Spin Labeling (ASL) is a magnetic resonance imaging (MRI) method to map the cerebral blood flow (CBF). ASL present a non-invasive alternative to the contrast agent and ASL techniques are capable of providing quantitative information about local tissue blood
flow by tracking the inflow of magnetically labeled arterial blood into an imaging slice. Retinotopy describes the correspondence between visual field locations and their cortical representations. Many studies have used blood oxygenation level-dependent (BOLD) fMRI to non-invasively reveal retinotopic maps. Their accuracy therefore depends on the spatial extent of the metabolic and hemodynamic changes induced by the neural activity. Many studies using gradient-echo MRI at 1.5T and 3T showed that most of the BOLD signal originates from macroscopic veins which might lead to a spatial displacement from the actual site of neuronal activations reducing the specificity for functional localization. In this study we performed perfusion contrast based retinotopic mapping of the human brain at 3T by using arterial spin labeling (ASL) which provides improved sensitivity and better functional
localization relative to the BOLD signal. We determined retinotopic maps from both of the fMRI imaging modalities, tested their robustness and replicability across different sessions, and calculated the overlap of the resulting visual areas V1, V2, V3, hV4, V3A/B obtained between the two imaging modalities. Velocity selective ASL (VS-ASL) is a specific form of ASL methods which labels the blood
below or above a certain velocity threshold by using velocity selective RF pulses instead of a spatial selection. Here we will describe the ASL methods in basics, retinotopy of the human brain with perfusion contrast as an application and the implementation of VS-ASL as a specific pulse sequence.