Diurnal variation in lumbar MRI. Correlation between signal intensity, disc height, and disc bulge

There have been no reports indicating diurnal variations in MRI at different portions of each lumbar disc. Eight asymptomatic healthy volunteers between 22 and 29 years old had MRI of their lumbar spine, twice on the same day (in the morning and evening). Forty lumbar discs were studied and the signal intensity change was measured from three portions of each disc (a total of 120 portions). No visible changes could be detected between scans by blinded observers. However, the calculated signal intensity changes showed an average loss of -20.0% (ant., 5 cases), -19.0% (mid, 2 cases), and -17.5% (post., 1 case). Height loss of the disc showed an average loss of -9.9% (ant., 4 cases), -8.3% (mid., 2 cases), and -10.4% (post., 2 cases). An increase of disc bulge at L4-5 level (18.3%) was pronounced, but L5-S1 level was less than others. Loss of body height averaged a loss of 7 mm (0.39% of body height). There was no correlation between reduced signal intensity and height loss at the ant./post. portion (p = 0.42), but there was a close relation at the mid. portion (p = 0.008). Diurnal change of the disc bulge was not correlated with reduced signal intensity (p = 0.48) or height loss (p = 0.16). Intradiscal fluid change was not necessarily influenced by the disc height loss, and height loss did not necessarily have an effect on disc bulge. But diurnal change showed a trend that was reflected in reduced signal intensity, height loss, and an increase of disc bulge which was more apparent from the ant. portion to the post, portion on moving down to the lower levels. Loss of disc height was one factor in the reduction of body height. These changes occurred randomly throughout 5 lumbar disc levels in each case.