QUANTITATIVE CT AS AN EXAMPLE OF THE VALU E AND OF INTERPRETATION OF OSTEODENSITOMETRIC DATA

Quantitative CT of the axial skeleton (aQCT) may serve as an example o f the evaluation and interpretation of osteodensitometric data as it i s the only state-of-the-art technique with valid longitudinal observat ions. The value of bone density measurements in interindividual cross sections refers to a grading derived from a representative reference p opulation and provides an evaluation of fracture risk. The presence an d rate of any bone loss can only be evaluated in an intraindividual lo ngitudinal follow-up. Adequate follow-up for trabecular bone requires at least 3 to 5 year intervals to discriminate between different loss rates. Bone losses induced by steroid therapy or immobilisation may ha ve faster kinetics apparent within months; bone density increase due t o hormone substitution may be significant after one to two years. Morp hological data allow critical evaluation of the quantitative measureme nts, eliminating false values and differentiating between rarefying an d destructive osteopenia.