Rapid T 2 * Mapping Using Interleaved Echo Planar Imaging

Magnetic resonance imaging methods that are sensitive to T 2* 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 T 2*-weighted imaging is related to the coupling of cerebral blood flow and metabolism. Rapid measurement of T 2* 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 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 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 T 2* values when compared with reference measurements made using the slower gradientecho 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 levels of deoxyhemoglobin. Magn Reson Med 41:368–374, 1999. r 1999 Wiley-Liss, Inc.