PRECISION AND ACCURACY FOR RAT WHOLE-BODY AND FEMUR BONE-MINERAL DETERMINATION WITH DUAL X-RAY ABSORPTIOMETRY

Precision and accuracy for rat whole body and excised femur bone miner al density (BMD) measurements were evaluated with two dual X-ray absor ptiometry (DXA) systems. The 'small subject' mode on the Norland XR-26 (XR), and the 'ultra high resolution mode' on the Hologic QDR-1000/W( QDR) were used for the analysis. The whole body mode was only availabl e on the XR. The lowest precision error for the whole body was found u sing a scan resolution of 1.0 x 1.0 mm and a scan speed of 15 mm/s. Th e scan spatial resolution of the femur measurement was approximately e ight times higher on the QDR than on the XR. However, the XR allowed a nalysis of an arbitrary region of interest within the femur, which was not easily done with the QDR. Precision for the total femur measureme nt on the QDR (0.5-0.9%) was approximately two to four times superior to that of the XR (1.5-4.3%). The difference may be due to the superio r scan resolution of the QDR. Bone mineral content and BMD on the QDR significantly declined with an increase of water depth (P < 0.001). No significant change was observed on the XR. Both DXA systems demonstra ted an excellent correlation (r greater-than-or-equal-to 0.98) with as h weight under the scan conditions examined. The optimal scan conditio n for the excised femur measurement on the XR was obtained with 1.5-2. 5 cm of perspex or water and a scan speed of 10 nun/s. For the QDR, we recommend scanning the rat femur with approximately 2.5 cm of perspex or water in terms of precision and accuracy.