Biexponential modeling of multigradient-echo MRI data of the brain

Functional MRI (fMRt) using fast multigradient-echo acquisition methods all ows the quantitative determination of the relevant parameter T*(2) Previous ly, the TE-dependent signal decay has been modeled with a monoexponential f unction despite the complex composition of the brain. In this study, biexpo nential modeling was used to evaluate the relaxation of brain parenchyma an d blood separate from that of cerebrospinal fluid. Single-shot multigradien t-echo data acquired with spiral or EPI techniques were analyzed. In phanto m experiments the biexponential method proved to be accurate. Compared to t he biexponential procedure, the monoexponential model overestimated T*(2) ( 72.2 msec vs. 65.3 msec) and underestimated DeltaT*(2) (2.96 msec vs. 3.19 msec) during visual stimulation. The biexponential method may allow intrins ic correction for partial volume effects due to cerebrospinaI fluid. The ac tivation-induced parameter changes are detected with a sensitivity equal to that of a monoexponential method. The resulting T-2* and DeltaT(2)* values describe the experimental data more accurately. (C) 2001 Wiley-Liss, Inc.