Reliability of voxel values from cone-beam computed tomography for dental use in evaluating bone mineral density

Objectives The aim of this study was to investigate whether it was possible to evaluate bone mineral density (BMD) using voxel values from cone-beam CT (CBCT) for dental use. Materials and methods A water phantom with an aluminum rod and sample tubes containing iodine solutions of various concentration was imaged by CBCT and multi-slice CT (MSCT). Voxel values and CT numbers, respectively, of the samples were measured and their correlation was investigated. In addition, based on the CT numbers of a hydroxyapatite (HA) reference phantom, a conversion formula from voxel value to BMD was obtained. Results There was a positive correlation between the voxel values of CBCT and the iodine concentration of the solutions, regardless of the X-ray dose or the mean energy, although the voxel values had a slight tendency to be saturated at higher iodine concentrations. An excellent correlation between the voxel values and CT numbers was also observed. A regression analysis showed that nonlinear (linear-quadratic model) regression was more appropriate than linear regression fitting for plotting these two values, although the latter might be usable for clinical applications. The conversion formula from the voxel value of CBCT to the equivalent BMD was as follows: y=-0.03669x2+3.602x-350.3 (x: voxel value, y: BMD mg/cm3 HA). Conclusions This study revealed that there was a high correlation between the voxel values of CBCT and the CT numbers of MSCT. Although this was an in vitro study with assumed ideal conditions for measuring voxel values, there was a clear possibility for estimating CT numbers and BMD using the voxel values from the CBCT images, but the relationship was not entirely linear and should be examined further. To cite this article:Nomura Y, Watanabe H, Honda E, Kurabayashi T. Reliability of voxel values from cone-beam computed tomography for dental use in evaluating bone mineral density.Clin Oral Impl Res. 21, 2010; 558-562.doi: 10.1111/j.1600-0501.2009.01896.x.