  MR vascular Fingerprinting proposes to use the MR Fingerprinting framework to
quantitatively and simultaneously map several microvascular characteristics at
a sub-voxel scale. The initial implementation assessed the local blood
oxygenation saturation (SO 2), blood volume fraction (BVf) and vessel averaged
radius (R) in humans and rodent brains using simple 2D representations of the
vascular network during dictionary generation. In order to improve the results
and possibly extend the approach to pathological environments and other
biomarkers, we propose in this study to use 3D realistic vascular geometries in
the numerical simulations. 28,000 different synthetic voxels containing
vascular networks segmented from whole brain healthy mice microscopy images
were created. A Bayesian-based regression model was used for map
reconstruction. We show on 8 healthy and 9 tumor bearing rats that realistic
vascular representations yield microvascular estimates in better agreement with
the literature than 2D or 3D cylindrical models. Furthermore, tumoral blood
oxygenation estimates obtained with the proposed approach are the only ones
correlating with in vivo optic-fiber measurements performed in the same
animals.
