Optimizing conventional MR imaging of the spine

With the use of conventional spin-echo pulse sequences with a long repetition time (TR), the echo time (TE) and the number of echoes were varied to minimize cerebrospinal fluid (CSF) flow artifacts in a spine phantom and in cervical spines of three volunteers. The following echo trains were compared in both axial and sagittal planes with a TR of 2,000 msec: TE of 25, 80 msec ("asymmetric"); TE of 40, 80 msec ("symmetric long TE"); and TE of 20, 40, 60, and 80 msec ("symmetric short TE"). Variable degrees of even-echo rephasing of CSF flow artifacts were observed during sagittal but not axial imaging, depending on the echo train used. Even-echo rephasing was most complete with the symmetric short-TE echo train, less complete with the symmetric long-TE echo train, and absent with the asymmetric echo train. Switching the orientation of the phase and frequency encoding gradients and slightly modifying TR on the basis of the heart rate further improved image quality. The results suggest that a symmetric short-TE echo train may be used to provide velocity compensation (similar to that observed with rephasing gradients) on even echoes of conventional spin-echo pulse sequences during spine imaging.