MEASUREMENT OF TRABECULAR BONE-MINERAL DENSITY IN THE DISTAL RADIUS BY 2 GAMMA-RAY COMPUTED-TOMOGRAPHY SCANNERS

The precision and measurement agreement of two gamma-ray computed tomography forearm bone scanners have been evaluated. The inherent precision in vitro for the Stratec SCT 900 scanner was 0.28% compared with 0.04% for the OSCAR scanner. The measurements were linear over the range of densities found in humans. Increasing thickness of the cortical shell dramatically increased trabecular bone attenuation coefficient (TBAC) for the SCT 900, but only slightly affected results with the OSCAR. Short-term precision of the SCT 900 in 22 women (1.26%) was not as good as that previously reported for the OSCAR (0.50%). The measured TBAC for the same patients was significantly greater with the SCT 900. Corrections for the error introduced by the cortical shell of the radius with the SCT were calculated. Using this correction similar TBAC values could be obtained with both scanners, but the variance of the differences was too great for the results to be used interchangeably. Published bone density data for normal subjects indicate that Scottish women lose more trabecular bone in the two decades after 50 years of age than those in the Federal Republic of Germany.