MR imaging of the lumbar spine: anatomic correlations and the effects of technical variations

A correlative anatomic study, a retrospective review of MR images performed in 35 patients, and a series of tests of the effectiveness of various MR scanning techniques were performed in order to improve comprehension of lumbar spine anatomy depicted on MR images, and thereby facilitate development of an optimal scanning protocol. Correlation of MR images with cryomicrotomed cadaver specimens enhanced understanding of the MR depiction of the intervertebral disks, ligamentum flavum, nerve roots, epidural fat, and epidural veins. Experiments were performed to assess the efficacy of a surface coil applied to the back, a solenoidal surface coil, a standard body coil, and an abdominal compression device in optimizing image quality. Experiments were also performed to determine the effect of alterations in the pulse sequence and variations of the phase-encoding axis. Based on these results, a protocol is proposed for routine imaging of the lumbar spine that yields high-resolution sagittal and oblique images and that does not require a surface coil. The recommended protocol employs heavily T1-weighted images with phase encoding along the z axis for sagittal images and along the x axis for axial images. This protocol yields multiple sagittal and oblique axial images through each of the lumbar disks, a larger field of view than obtained with surface coils, and a reduction of total imaging time to as little as 10 min.