Quantitative CT of the spine. Significance of intervertebral body variability

Quantitative CT of the spine has been used to predict and to identify a population at increased risk for fracture. This effort has been limited, in part, by the considerable range in normal values of mineral content. We studied the mineral contents of individual vertebral bodies to evaluate our empirical observation that mineral content changes from one vertebral body to the next and to assess the effect of this variability upon mineral content determination. Fifty-nine patients referred for the evaluation of osteoporosis were studied by single energy and dual energy quantitative CT. Variability among patients and fluctuations in the CT machine were corrected by a bone density phantom. Measured bone mineral contents were normalized by taking these variations into account. Analysis of covariance and t-tests indicated significant differences in the measured mineral contents from the T12 to the L3 vertebral bodies. Mean mineral contents for different vertebra were significantly different for both the single energy and dual energy methods, decreasing from T12 to L3. The measured mineral contents of the vertebral bodies within a given patient were highly correlated. The high correlation of the mineral contents of the vertebral bodies within a given patient strengthens the conclusions that individual vertebral content measurement is a valid predictor for the mineral content of vertebrae. The current method of averaging several vertebral bodies improves the reliability of an overall measurement of mineral content.