MRI OF LUMBAR INTERVERTEBRAL DISKS - DIURNAL-VARIATIONS IN SIGNAL INTENSITIES

Study Design. Eight volunteers underwent magnetic resonance imaging sc ans of their lumbar spines to determine diurnal variations in the scan results. Objectives. Magnetic resonance imaging of the lumbar bar spi ne typically is obtained under the assumption that results are not inf luenced by the time of day the scan is performed. To validate this ass umption, asymptomatic volunteers had magnetic resonance images made of their lumbar spines, twice in one day. Summary of Background Data. No reports in the literature have indicated visible diurnal variations i n magnetic resonance imaging of the spine. Methods. Two magnetic reson ance imaging scans were obtained of each volunteer's lumbar spine, the first 1 to 1.5 hours after waking and the second 8 to 10 hours later. The signal intensity was measured from each disc and mathematical sta ndardization was performed against a saline phantom. Changes in disc h eight and bulge also were measured. Two blinded neuroradiologists revi ewed each scan. Results. Thirty-nine lumbar discs were studied. No vis ible changes could be detected between scans by blinded observers. How ever, the calculated signal intensity change was an average loss of 13 .5%. An increase in disc bulge was measured in 48.6% of the discs. Con clusions. In this group of asymptomatic volunteers, the time of day th at a magnetic resonance imaging scan was obtained did not influence th e visual interpretation.