Quantitative computed tomography scanning for measurement of bone and bone marrow fat content. A comparison of single- and dual-energy techniques using a solid synthetic phantom.

Quantitative CT (QCT) has become a popular method for estimating bone mineral content. In addition, QCT can be used to estimate the fat content of trabecular bone. Although the latter has received little attention, it may prove to be clinically significant. Using a set of custom-built, tissue-mimicking plastic inserts in an anthropomorphic phantom, we tested a variety of methods for estimating mineral and fat content. We also investigated the influence of patient size, reconstruction circle size, and reference phantom choice on the accuracy of the results. Best estimates were obtained when there was a match between patient and reconstruction circle size. Single-energy methods yielded the best estimates of mineral content for inserts that did not contain fat, and dual-energy methods yielded the best estimates for inserts that contained fat. A dual-energy method that we developed was best in estimating the mineral and fat content of the latter inserts. We found that an external calibration reference phantom containing aqueous solutions of K2HPO4 could be used satisfactorily to estimate the mineral content of trabecular bone mimicking inserts; however, more representative materials must be used for accurate estimates of fat content.