Rapid T-2* mapping using interleaved echo planar imaging

Magnetic resonance imaging methods that are sensitive to Tp are widely used in the study of blood oxygenation changes, most notably in functional stud ies of the brain. In these studies the signal intensity change in T-2*-weig hted imaging is related to the coupling of cerebral blood flow and metaboli sm. Rapid measurement of T-2* itself would offer a valuable method to quant ify blood oxygenation changes indirectly and monitor their time course. An interleaved echoplanar imaging (EPI) sequence is presented here that allows maps of T-2* to be generated in a few seconds. The sequence benefits from reduced geometric distortion and an improved point spread function compared with single-shot EPI, A comparison among a set of T-2*-weighted interleave d EPI images, single-shot EPI, and conventional gradient-echo and spin-echo methods is made using a compartmentalized doped water phantom, The interle aved sequence yields accurate T-2* values when compared with reference meas urements made using the slower gradient-echo technique. Data acquired from the rat brain at 2.35 T prior to and during an anoxic challenge show, with high temporal resolution, the reduction in T-2* associated with increased l evels of deoxyhemoglobin, (C) 1999 Wiley-Liss, Inc.