Analytical model of susceptibility-induced MR signal dephasing: effect of diffusion in a microvascular network.
A deterministic analytical model that describes the time course of magnetic resonance signal relaxation due to magnetic field inhomogeneity induced by a vascular network is developed. Both static and diffusion dephasing are taken into account. The contribution of the diffusion dephasing is calculated for relatively large vessels (R>10 microm) or short measurement times when the diffusion length is smaller than the vessel radius. The signal is found to possess the following features: a) an initial deviation from the monoexponential relaxation which is more pronounced for the imaginary part of the signal; b) a deviation from monoexponential relaxation at short echo times for the spin-echo (SE) signal measured as a function of the echo time; c) the echo maximum of the SE signal shifted from the nominal echo time to a shorter time; and d) a diffusion effect much stronger for the SE than for the free induction decay experiment. The model presented agrees within its validity domain with a known Monte Carlo simulation.
Kiselev
V G
VG
Institute of Medicine, Research Center Jülich GmbH, Germany. v.kiselev@fz-juelich.de
Posse
S
S
D001921:Brain / Q000098:blood supply; D046508:Culture Techniques; D004058:Diffusion; D006801:Humans; D008279:Magnetic Resonance Imaging; D008833:Microcirculation / Q000033:anatomy & histology*; D008955:Models, Cardiovascular; D009010:Monte Carlo Method; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted