Functional MRI measurements of vasculature must be robustly validated pre-clinically. Optical computed tomography (CT) offers high-resolution ex vivo 3D imaging of perfused vasculature using India ink staining. We compared optical CT measurements of murine kidney blood volume with previously published MRI relative blood volume measurements. Fractional blood volumes of different kidney regions in optical CT images were calculated using Frangi vessel filtering, for three concentrations of India ink-staining. Significant positive correlations were found between optical CT and MRI measurements for 10% and 15% India ink staining. This is a potentially promising method for easily and cheaply validating MRI vasculature measurements.