Rapid combined T1 and T2 mapping using gradient recalled acquisition in the steady state

Abstract

A novel, fully 3D, high-resolution T1 and T2 relaxation time mapping method is presented. The method is based on steady-state imaging with T1 and T2 information derived from either spoiling or fully refocusing the transverse magnetization following each excitation pulse. T1 is extracted from a pair of spoiled gradient recalled echo (SPGR) images acquired at optimized flip angles. This T1 information is combined with two refocused steady-state free precession (SSFP) images to determine T2. T1 and T2 accuracy was evaluated against inversion recovery (IR) and spin-echo (SE) results, respectively. Error within the T1 and T2 maps, determined from both phantom and in vivo measurements, is approximately 7% for T1 between 300 and 2000 ms and 7% for T2 between 30 and 150 ms. The efficiency of the method, defined as the signal-to-noise ratio (SNR) of the final map per voxel volume per square root scan time, was evaluated against alternative mapping methods. With an efficiency of three times that of multipoint IR and three times that of multiecho SE, our combined approach represents the most efficient of those examined. Acquisition time for a whole brain T1 map (25 x 25 x 10 cm) is less than 8 min with 1 mm3 isotropic voxels. An additional 7 min is required for an identically sized T2 map and postprocessing time is less than 1 min on a 1 GHz PIII PC. The method therefore permits real-time clinical acquisition and display of whole brain T1 and T2 maps for the first time. © 2003 Wiley-Liss, Inc.