Rapid T2 mapping using interleaved echo planar imaging

Magnetic resonance imaging methods that are sensitive to T2* are widely used in the study of blood oxygenation changes, most notably in functional studies of the brain. In these studies the signal intensity change in T2*‐weighted imaging is related to the coupling of cerebral blood flow and metabolism. Rapid measurement of T2* itself would offer a valuable method to quantify blood oxygenation changes indirectly and monitor their time course. An interleaved echoplanar imaging (EPI) sequence is presented here that allows maps of T2* 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 T2*‐weighted interleaved EPI images, single‐shot EPI, and conventional gradient‐echo and spin‐echo methods is made using a compartmentalized doped water phantom. The interleaved sequence yields accurate T2* values when compared with reference measurements 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 T2* associated with increased levels of deoxyhemoglobin. Magn Reson Med 41:368–374, 1999. © 1999 Wiley‐Liss, Inc.