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July 22, 1992


Author Affiliations

American Medical Association Chicago, Ill

JAMA. 1992;268(4):475. doi:10.1001/jama.1992.03490040048023

In Reply.  —Drs Börner and Schneider note that compared with DEXA, in which measurements of areal bone mineral density (BMD) are made in grams per square centimeter, quantitative computed tomography (QCT), a three-dimensional imaging technique, is capable of assessing bone volume more directly and measures BMD in grams per cubic centimeter. This same observation is made throughout the Diagnostic and Therapeutic Assessment (DATTA) report on DEXA. It follows that QCT separately analyzes cortical and trabecular bone mineral—an important issue insofar as trabecular bone has eight times the bone turnover rate as cortical bone, and bone loss, therefore, first manifests itself in skeletal sites composed largely of trabecular bone such as the spine. Consequently, as noted by Börner and Schneider and in the DATTA report on DEXA, QCT measurements of BMD have somewhat better predictive value for spine fractures than do DEXA measurements. Börner and Schneider, noting the wide demand and