Do diurnal changes in loading affect the interpretation of MRI scans of the lumbar spine?

We tested the hypothesis that the visual interpretation of magnetic resonance imaging (MRI) scans of the asymptomatic lumbar spine are affected by diurnal changes in fluid exchange in the intervertebral discs. Ten male subjects carried a 20-kg backpack in the intervening 3-h period between two MRI scans of the lumbar spine. After the subjects arrived at the MRI center (within 45 min of awakening), they lay on a bed for 45 min. The first set of MRI scans were obtained. Each subject was then fitted with a 20-kg backpack. After they walked for 3 h, the pack was removed, and a second set of MRI scans were obtained immediately. The sets of MRI scans were reviewed by three radiologists: none of the three radiologists found differences in the interpretation of the MRI scans. On the basis of these results, diurnal changes in fluid exchange in the asymptomatic intervertebral disc (exaggerated in our case by the backpack) are undetectable by visual reading of MRI scans.