The growing interest in 3D-DXA reconstructions for possible uses in fracture risk prediction or patient follow-up, e.g., in conjunction with finite element analyses, asks for precision data to increase the interpretability of results making use of the 3D-DXA technique. Using two datasets and a total of 2427 DXA scans of the proximal femur we evaluated the short- and long-term precision of standard DXA measurements. All the available scans were reconstructed using 3D-Shaper software and processed through a nonlinear finite element pipeline for femoral strength estimation. Short- and long-term precision were computed for thirty 3D-DXA-based parameters as well as femoral strength in fall and stance configurations. Precision errors were related to change rates of the respective parameters by calculating the trend assessment interval (TAI). Simultaneously, spatially resolved precision errors were computed for cortical parameters and error progression from DXA to 3D-DXA and FEA was considered. Precision errors were amplified through the different processing steps. Long-term precision errors were 1.6%, 2.0% and 7.5% for total hip aBMD, total hip integral vBMD and strength in fall, respectively. Errors between processing steps were only weakly correlated. Higher change rates for vBMD and strength compensated the larger precision errors, resulting in similar TAIs for total hip aBMD (5.5 years), total hip integral vBMD (4.6) and strength (5.8), respectively. Relative local precision errors of cortical parameters were largest in the superior and anterior neck region and above the lesser trochanter. 3D-DXA and thereon based FEA may offer interesting insights into the densitometric and mechanical quality of the proximal femur. The here reported results should offer a help for the interpretation of sequential measurements where these are required.The standard method to investigate bone health is dual energy x-ray absorptiometry, short DXA, which produces 2D images. More detailed information about the bone structure can be obtained through computed tomography, which produces three-dimensional images. By the application of statistical methods similar 3D images can be obtained from standard DXA images and can be used to compute bone strength using techniques known from different engineering disciplines. Such so-called 3D-DXA images have received more and more interest lately. To interpret repeated measurements of the same patient, knowledge about measurement precision is indispensable. Using DXA scans from patients in two studies we performed a thorough analysis of the precision of DXA and 3D-DXA-based bone parameters and strength. Several 3D-DXA-based parameters performed similarly well as DXA parameters in this context. The gained knowledge is useful to correctly define the approach for repeated measurements on individual patients and may be used to design clinical trials.
Gugler et al. (Thu,) studied this question.