A cortical-bone structural geometry phantom: dental plaster as a convenient and radiologically similar fabrication material

Evaluating accuracy of structural geometry by DXA methods with an anthropometric proximal femur phantom

DXA-derived bone structural geometry has been reported extensively but lacks an accuracy standard. In this study, we describe a novel anthropometric structural geometry phantom that simulates the proximal femur for use in assessing accuracy of geometry measurements by DXA or other X-ray methods. The phantom consists of seven different interchangeable neck modules with geometries that span the range of dimensions in an adult human proximal femur, including those representing osteoporosis. Ten repeated hip scans of each neck module using two current DXA scanner models were performed without repositioning. After scanner specific calibration, hip structure analysis was used to derive structural geometry. Scanner performance was similar for the two manufacturers. DXA-derived HSA geometric measurements were highly correlated with values derived directly from phantom geometry and position; R² between DXA and phantom measures were greater than 94% for all parameters, while precision error ranged between 0.3 and 3.9%. Despite high R² there were some systematic geometry errors for both scanners that were small for outer diameter, but increasing with complexity of geometrical parameter; e.g. buckling ratio. In summary, the anthropometric phantom and its fabrication concept were shown to be appropriate for evaluating proximal femoral structural geometry in two different DXA systems.

A comparative study between corresponding structural geometric variables using 2 commonly implemented hip structural analysis algorithms applied to dual-energy X-ray absorptiometry images

Hip structural analysis (HSA) has been developed over 20 yr, applied extensively in research, and has demonstrated useful outcomes associating bone structural geometry with bone fragility (research-HSA or r-HSA). In 2007, Hologic Inc. (Bedford, MA) incorporated HSA with some modifications as an option for Hologic dual-energy X-ray absorptiometry (DXA) scanners (clinical HSA or c-HSA). This brought HSA from the research environment into the clinical environment. This article reports a comparison of r-HSA and c-HSA implementations using DXA scans from a group of 191 females. Bland-Altman plots at the narrow-neck (NN) HSA region indicated higher r-HSA areal bone mineral density (mean difference: 0.27 g/cm(2); 21.7% [of mean]); cross-sectional area (0.63 cm(2); 18.7%); cross-sectional moment of inertia (0.26 cm(4); 11.1%), and section modulus (0.22 cm(3); 14.5%) compared with c-HSA. The converse was observed for NN subperiosteal width (-0.09 cm; 3.1%). High linear correlations (r(2) > 0.81) were found between r-HSA and c-HSA NN structural geometric outcomes, with the exception of neck shaft angle (r(2) > 0.47). As differences were significant (p < 0.001), slopes and intercepts are provided to enable linear transformations from r-HSA to corresponding c-HSA structural geometric data.