Computed tomography scanning for the measurement of bone mineral in the human spine.

An investigation into the feasibility of using X-ray computed tomography (CT) to measure disease induced changes in bone mineral content of the human spine is described. A theoretical study of this type of measurement has been made using a mathematical model of osteomalacia. The measured EMI number changes linearly with the mineral content, and the sensitivity is shown to be 1.2 EMI units (EU: 500 scale)/1% change in mineral content in vertebral bone. The physical sensitivity to an equal mineral change in cortical bone is found to be 8.6 times greater. The mineral selectivity of the CT method is such that only about half the change in the EMI number arising from progressive osteomalacia reflects change in actual mineral content, while half is due merely to changes in bone density that accompany demineralization. In addition, the perturbing effects of beam hardening on measurement accuracy are evaluated and shown to be significant. Finally, an experimental measurement indicates that in practice the reproducibility of such measurements would be about 1 EU, and it is shown that the measured parameter correlates well with the calculated total linear attenuation coefficients.