The ability of blood vessels to modulate vascular tone (i.e. blood volume) is an important normal physiological function, which is compromised in multiple diseases, including diabetes and heart diseases. To date, there is no non-invasive imaging technique to assess dynamic microvascular blood volume response. Herein we present a novel MRI technique to assess vasoactive response in “near” real-time in extra-cranial tissues. We employ a blood-pool agent Gadofosveset (Vasovist) together with a variety of vasoactive gas stimuli. In-vivo results in kidney and liver demonstrate we can visualize dynamic changes in gas-induced blood volume changes, as confirmed on laser Doppler perfusion.