CONVENTIONAL AND FAST SPIN-ECHO MR-IMAGING - MINIMIZING ECHO TIME

Magnetic resonance imaging is frequently complicated by the presence o f motion and susceptibility gradients. Also, some biologic tissues hav e short T2s. These problems are particularly troublesome in fast spin- echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conv entional spin-echo (SE) imaging to 5 msec and echo spacing (E-space) i n FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sinc radio-frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE ima ges of the upper abdomen were compared with conventional SE images (TE = 11 msec). Also, FSE images with short E-space were compared with co nventional FSE images in multiple body sites. Short TE significantly i mproved the liver-spleen contrast-to-total noise ratio (C/N) (7.9 vs 4 .1, n = 9, P < .01) on T1-weighted SE images, reduced the intensity of ghost artifacts (by 34%, P < .02), and increased the number of availa ble imaging planes by 30%. It also improved delineation of cranial ner ves and reduced susceptibility artifacts. On short E-space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared cris per and measured spleen-liver C/N increased significantly (6.9 vs 4.0, n = 12, P < .01). The delineation of tissues with short T2 (eg, carti lage) and motion artifact suppression were also improved. Short TE met hods can improve image quality in both SE and FSE imaging and merit fu rther clinical evaluation.