Quantitative MR imaging of lumbar intervertebral disks and vertebral bodies: influence of diurnal water content variations.

The influence of diurnal water content variation on T1 and T2 and relative proton density (Nr) in intervertebral disks and vertebral bodies was studied in 10 healthy adult volunteers. T1, T2, and Nr were calculated from a set of 20 images obtained at 1.5 T with five single-section, multiecho sequences at different repetition times. Volunteers were randomized into study (one measurement in the morning and one in the evening) and control (two consecutive measurements in the morning) groups. In the study group, evening mean T1 and Nr in intervertebral disks and in vertebral bodies were significantly (P < .001) less than measured in the morning. Mean T2 in vertebral bodies significantly (P < .05) increased between morning and evening measurements. Diurnal variations were significantly less pronounced in degenerative than in normal intervertebral disks. No significant changes occurred in the control group. Relaxation time and Nr measurements allow sufficiently accurate estimation of diurnal water content variation in cohorts of vertebral bodies and intervertebral disks.