GRASE - ULTRA-FAST TURBO GRADIENT SPIN-ECHO SEQUENCE - A NEW APPROACHTO FAST MR-IMAGING OF THE MUSCULOSKELETAL SYSTEM

Purpose: Ultra-fast gradient and spin-echo (GRASE) imaging is a hybrid of turbo spin-echo (TSE) and echo-planar imaging (EPI). One scan cons ists of several spin-echoes (SEs) (turbo factor, TF), each of which co nsists of a number of gradient echoes (EPI factor, EF). The aim of our study was to evaluate different combinations of TF and EF in GRASE im aging and to test its usefulness in musculoskeletal imaging. Material and Methods: On a 1.0 T MR unit, 11 GRASE sequences with different com binations of TF and EF (TR/TE 2150/120 ms) were evaluated in phantom s tudies with respect to signal-to-noise (S/N) ratio, nonuniformity of i mages, and geometrical distortion. From this study, the optimal GRASE- sequence was applied to 25 patients with different joint pathologies a nd compared to a T2-weighted TSE sequence (TR/TE 2855/130 ms). Lesion visualization, conspicuity, overall image quality, and artifacts were qualitatively analyzed by two observers independently of each ether. R esults: With respect to S/N ratio, signal nonuniformity, and geometric al distortion, the GRASE sequence with TF/EF 7/3 (S/N 47; signal nonun iformity 11.7%; distortion 1 pixel) proved to be superior to the other GRASE sequences within a scanning time of less than 120 s. In a clini cal study, the GRASE sequence proved superior to T2-weighted TSE (with out fat suppression) in the visualization of bone-marrow and soft-tiss ue lesions (p<0.001) and ligamentous injuries, although the image qual ity was inferior.