Vessel size imaging (VSI) to provide a measure of vessel radius in the brain has been demonstrated using an injection of contrast agent. Venous vessel radius imaging of brain microvasculature is also possible by exploiting hypercapnia and hyperoxia. However, these respiratory challenges need external devices like masks, monitors, and gas application. In this study, we employ a breath-hold task to mimic hypercapnia for venous VSI. Breath-hold experiments of brain scans were performed on 14 subjects on a 3-T scanner. Parametric maps of mean venous vessel radius were calculated from the changes in R2* and R2,
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