Magnetic resonance imaging in low back pain: general principles and clinical issues.

The purpose of this article is to provide an overview of the general principles of lumbar magnetic resonance imaging (MRI), including signal generation and image interpretation. Additionally, a discussion of the clinical usefulness as it relates to lumbar MRI is presented using degenerative disk disease as an example. Lumbar MRI provides high-resolution, multiaxial, multiplanar views that have high contrast between soft tissues. Obtaining these images in vivo creates minimal risk for patients and provides examiners with an excellent mechanism to study anatomic detail and the biochemical composition of the lumbar spine. Different tissue characteristics known as T1, T2, and proton density may be accentuated, allowing examiners to detect variations in tissue shape and hydration that may correspond to disease processes. There is strong agreement that lumbar MRI is indicated for the evaluation of patients with risk factors for neoplastic or infectious disorders or in persons with coexisting evidence of neurologic impairment. The utilization of lumbar MRI in patients with low back pain (LBP), however, is controversial. Lumbar MRI has a high technical capacity to detect degenerative disk disease, bulging and herniated disks, and distortions in the thecal sac or nerve roots associated with these conditions. The diagnostic accuracy, however, of most lumbar anatomic impairments related to the symptoms of LBP is low or unknown. Although lumbar MRI remains as an excellent tool to study morphology, findings must be related to data from clinical examinations to provide meaningful judgments.