Influence of calibration materials in single- and dual-energy quantitative CT.

With single-energy (SE) quantitative computed tomography (CT), the density of bone mineral in the vertebral body can be estimated. With dual-energy (DE) quantitative CT, both bone-mineral density and fat content can be measured. The calibration device normally used contains materials mimicking trabecular bone, fat, and hematopoietic tissue. To evaluate the influence of different calibration materials on these estimates, theoretical CT numbers were calculated for the trabecular part of the vertebral body and for different calibration devices. Calibration devices were simulated; they contained either identical materials or various accepted tissue-mimicking materials. For all combinations, quantitative CT data were generated for the SE quantitative CT method and for two DE quantitative CT methods. Only one method provided accurate results under ideal circumstances. The selection of tissue-mimicking materials in the calibration devices is important for the interpretation of results of SE and DE quantitative CT. Errors of more than a factor 2 were found when different types of materials were used.