Methods: A desktop X-ray μCT system was used (SkyScan 1172, Belgium). (1) Intra-phantom homogeneity and spatial variation of linear X-ray attenuation coefficients was examined. Intra-scan variation was assessed as the variation of grey values among the top, middle and bottom of a K2HPO4 solution at the density of 1g/cm3. (2) In order to explore the extent to which high density objects could interfere with the x-ray interpretation of the homogeneous K2HPO4 solution, three hydroxyapatite discs, at 1.52 g/cm3, 1.85 g/cm3, 2.08g/cm3, were prepared and scanned alongside the K2HPO4 solution. (3) Our recently study developed a new calibration system, by which the calibration range was extended to 2.08 g HA/cm3, in contrast, commonly used calibration phantoms are made of a soft-tissue equivalent resin and minerals, ranging from 0-0.8 g HA/cm3, making extrapolation of the calibration curve necessary. A comparison was made between the mineral density values of dentine of 8 human teeth calibrated by HA-resin phantom and our calibration phantoms.
Results: intra-scan variation was assessed within one scan of the K2HPO4 solution at 1g/cm3. The results showed the K2HPO4 solution was essentially uniform, and no statistical difference (P=0.05) was found among the top, middle and bottom regions of the solution. However, when the HA discs were placed alongside the solution, a significant difference was detected among the corresponding K2HPO4 solution sections (P<0.05). Lastly, an underestimation of 0.12-0.34 g/cm3 was introduced by extrapolation of the calibration curve obtained from the commercial HA-resin phantom.
Conclusion: the non-uniform distribution of grey values within a uniform sample was indicative of potential beam hardening artifacts, therefore great caution should be paid to non-homogeneous tooth samples, where dentine was surrounded by a dense layer of enamel.
NIH (DE015272) and NHMRC (512524).