MRI of lumbar intervertebral discs. Diurnal variations in signal intensities

Eight volunteers underwent magnetic resonance imaging scans of their lumbar spines to determine diurnal variations in the scan results.

Magnetic resonance imaging of the lumbar spine typically is obtained under the assumption that results are not influenced by the time of day the scan is performed. To validate this assumption, asymptomatic volunteers had magnetic resonance images made of their lumbar spines, twice in one day.

No reports in the literature have indicated visible diurnal variations in magnetic resonance imaging of the spine.

Two magnetic resonance 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 standardization was performed against a saline phantom. Changes in disc height and bulge also were measured. Two blinded neuroradiologists reviewed each scan.

Thirty-nine lumbar discs were studied. No visible changes could be detected between scans by blinded observers. However, 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.

In this group of asymptomatic volunteers, the time of day that a magnetic resonance imaging scan was obtained did not influence the visual interpretation.