Quantitative mineral estimations in vertebral bodies by computer tomography

The accuracy of computer tomographic bone density measurements in the axial skeleton was tested by comparing results obtained from the first lumbar body in abdominal phantoms. An almost linear relationship (r=0.998) was found between increasing concentrations of a calcium chloride solution and CT absorption values. The sum of the CT values of sections through the vertebral body correlated well with their ash content (r=0.90) as well as with the hydroxyl apatite values obtained by I125-absorption densitometry (r=0.88). Reproducibility of CT measurements on the phantom was good (coefficient of variation = 1.2% in the spongiosa). Average CT values of separate measurements of the spongiosa and cortex could be correlated with the total spongiosa by a special programme (r=0.95). In the practical application of this technique, possible sources of error must be considered, such as the effect of high energy polychromatic radiation, inhomogeneity of the object being investigated and difficulties in positioning the patient. (orig.)