Evaluation of a prototype dual-energy computed tomographic apparatus. II. Determination of vertebral bone mineral content.

A prototype dual-energy computed tomographic (CT) scanner (Siemens Somatom DR3) with rapid kVp switching and prereconstruction processing has been used to measure vertebral bone mineral density. With this approach misregistration and beam hardening inaccuracies can be reduced considerably. Basis material images of aluminum- and Lucite-equivalent density enable measurements of bone mineral density that are nearly independent of the amount of marrow fat. To simulate variable marrow fat, alcohol-water mixtures were used as media in calibration standards. A section of dried trabecular bone was also scanned immersed in varying alcohol-water mixtures. In both simulations it was shown that the dual-energy measurement is nearly independent of marrow composition whereas the single-energy measurement would be strongly influenced by marrow fat. Dual-energy CT was compared to dual-photon absorptiometry (153Gd) for the measurement of bone mineral mass of ten excised human vertebrae. There was a high degree of correlation between the two measurements (r = 0.97). Dual-energy and single-energy CT measurements on 17 patients with suspected metabolic bone disease strongly support the conclusion that the influence of fat can lead to significant errors in single-energy determinations of the mineral density of trabecular bone.