Quantitative Assessment of Bone Tissue Mineralization with Polychromatic Micro-Computed Tomography

Micro-computed tomography (μCT) has become an important tool for morphological characterization of cortical and trabecular bone. Quantitative assessment of bone tissue mineral density (TMD) from μCT images may be possible; however, the methods for calibration and accuracy have not been thoroughly evaluated. This study investigated hydroxyapatite (HA) phantom sampling limitations, short-term reproducibility of phantom measurements, and accuracy of TMD measurements by correlation to ash density. Additionally, the performance of a global and a local threshold for determining TMD was tested. The full length of a commercial density phantom was imaged by μCT, and mean calibration parameters were determined for a volume of interest (VOI) at 10 random positions along the longitudinal axis. Ten different VOI lengths were used (0.9–13 mm). The root mean square error (RMSE) was calculated for each scan length. Short-term reproducibility was assessed by five repeat phantom measurements for three source voltage settings. Accuracy was evaluated by imaging rat cortical bone (n = 16) and bovine trabecular bone (n = 15), followed by ash gravimetry. Phantom heterogeneity was associated with <0.5% RMSE. The coefficient of variation for five repeat measurements was generally <0.25% across all energies and phantom densities. Bone mineral content was strongly correlated to ash weight (R ² = 1.00 for both specimen groups and both threshold methods). Ash density was well correlated for the trabecular bone specimens (R ² > 0.80). In cortical bone specimens, the correlation was somewhat weaker when a global threshold was applied (R ² = 0.67) compared to the local threshold method (R ² = 0.78).