Dual Energy Radiography versus Quantitative Computer Tomography for the Diagnosis of Osteoporosis

Abstract

In this study we compared dual energy radiography (DER), a new, highly precise x-ray densitometric technique recently devised for measurements of vertebral mineral density and quantitative computer tomography (QCT), a densitometric technique that selectively measures the trabecular compartment of the vertebra. DER and QCT measurements were obtained in 56 healthy (H) and 48 fractured osteoporotic (OP) women using a Hologic QDR 1000 bone densitometer and a GE 9800 scanner, respectively. DER was significantly correlated with QCT in both the H (r = 0.75; P < 0.0001) and the OP subjects (r = 0.58; P < 0.0001). DER decreased significantly with age in the H (P < 0.05), but not in the OP women, whereas QCT was related to age in both the H (P < 0.0001) and the OP subjects (P < 0.01). The rate of bone loss with age was also higher with QCT than with DER in both normal and osteoporotic women. The difference in bone density between the H and the OP subjects was larger (P < 0.05) with QCT than with DER. Receiver operating characteristic analysis revealed that QCT was a better predictor of vertebral fractures than DER. A larger percentage of OP subjects were 2 SD or more below the normal predicted value with QCT (41%) than with DER (29%). Furthermore, the slopes of the regressions of bone density with age for normal and osteoporotic women were significantly different (P < 0.05) with QCT but not with DER. These findings are consistent with a disproportionate loss of trabecular bone with age in osteoporosis. Although a marrow fat-dependent underestimation of QCT may have contributed to our findings, we conclude that QCT, by selectively measuring trabecular bone, discriminates better between normal and osteoporotic women than DER.