UCL Discovery

Abstract

A new MRI sequence for the rapid simultaneous measurement of T-2 and T-2* is presented. The technique uses the multiple acquisition of spin and gradient echoes with interleaved echo planar imaging (MASAGE-IEPI). IEPI data sets are sampled during and between a pair of short and long echo time spin echoes, allowing the reconstruction of a set of images with different combinations of T-2 and T-2* weighting and the calculation of T-2 and T-2* maps. In the context of neuroimaging, these maps can provide information on cerebral hemodynamics and oxygenation status, either via the deoxyhemoglobin-based BOLD signal or by the effect of exogenous paramagnetic contrast agents. MASAGE-IEPI benefits from the inherent advantages of the IEPI approach, i.e., high time resolution and minimal image distortion, and also has good time efficiency due to the acquisition of multiple image data sets following each excitation pulse. The accuracy of the sequence for the measurement of T-2 and T-2* is verified on phantoms, and the technique is applied to monitor changing hemodynamics in the rat brain during episodes of hypoxia. Data for the generation of maps of T-2 and T-2* are acquired with a time resolution of 12 s to accurately define the rapidly changing time course. As increasing emphasis is placed on the role of T, and T-2* in the direct measurement of physiological parameters such as cerebral metabolic rate of oxygen consumption and blood vessel sizes, MASAGE-IEPI offers an efficient method for the measurement of these two important MRI parameters. (C) 2002 Elsevier Science (USA).