First Principle Modeling of Simultaneous VASO and BOLD fMRI with Two-Photon Microscopy for Optimal Quantification of CBV Changes in Humans

摘要

The vascular space occupancy (VASO) fMRI method probes changes in cerebral blood volume (CBV) under variousphysiological states, including neuronal activation in humans. However, it requires a careful choice of sequenceparameters because the blood oxygen-level dependent (BOLD) effect offsets the VASO signal. Assessing this BOLDcontamination as a function of pulse sequence parameters would improve the quantification of CBV changes withVASO. However, this task requires knowledge of the cerebral vascular geometry of the MRI voxel. Towards this end,optical microscopy can provide high-resolution 3D images of vasculature. Here, we use detailed angiograms of rodentbrain acquired with two-photon microscopy to model fMRI signals (VASO and BOLD) from first principles usingMonte Carlo diffusion of water protons. We present quantitative plots of VASO together with intra- and extravascularBOLD fractional signal changes as a function of echo time (TE), for spin echo (SE) and gradient echo (GRE) pulsesequences, at low to ultra-high magnetic fields. Our results indicate that at 3T, the BOLD contamination of the VASOresponse is under 12% for GRE and 2% for SE up to TE=6 ms, but this contamination is significantly higher at 7T andabove. We also found GRE BOLD intravascular contributions of 85% at 1.5T, 55% at 3T and 4% at 7T and SEintravascular contributions of 70% at 1.5T, 40% at 3T and 10% at 7T. These results may provide important informationto optimize the pulse sequence timing in human VASO and BOLD fMRI, leading the way to a wider application of thesefMRI techniques in healthy and diseased brain.