The impact of vessel size, orientation and intravascular contribution on the neurovascular fingerprint of BOLD bSSFP fMRI

- The contribution from capillaries is highest for SE, followed by bSSFP and is much lower for GE.
- The intravascular contribution of bSSFP and SE is in the range of 5-10%, and negligible for GE at 9.4T.
- BOLD signal change of GE, SE and bSSFP depend on orientation of cortex to B0.

Monte Carlo simulations have been used to analyze oxygenation-related signal changes in pass-band balanced steady state free precession (bSSFP) as well as in gradient echo (GE) and spin echo (SE) sequences. Signal changes were calculated for artificial cylinders and neurovascular networks acquired from the mouse parietal cortex by two-photon laser scanning microscopy at 1 μm isotropic resolution. Signal changes as a function of vessel size, blood volume, vessel orientation to the main magnetic field B0 as well as relations of intra- and extravascular and of micro- and macrovascular contributions have been analyzed. The results show that bSSFP is highly sensitive to extravascular and microvascular components. Furthermore, GE and bSSFP, and to a lesser extent SE, exhibit a strong dependence of their signal change on the orientation of the vessel network to B0.