Questionable accuracy of CBCT in determining bone density: A comparative CBCT-CT in vitro study

The accuracy of the estimation of radiological bone density with the use of the cone-beam computed tomography (CBCT) grayscale is still questionable. Standardization and correlation with the gold standard computed tomography (CT) Hounsfield units (HU) is required prior to clinical application.

The objective of the present study was to evaluate the reliability of the grayscale for the estimation of bone density, using samples with intact soft tissue in order to substantiate the clinical use of the scale.

A total of 240 sites in 20 goat heads were scanned to obtain radiological bone mineral density via Hounsfield units in CT and the grayscale in CBCT. The anatomical architecture of soft tissues was preserved for all samples. Two observers obtained the data, which consisted of 3 variables (mean, minimum and maximum) for both scales. The statistical analysis of the data was conducted using Cronbach's alpha, Pearson's correlation coefficients, the independent samples t tests, and regression analysis.

Differences in the means of the mean, minimum and maximum values between the 2 scales were statistically highly significant (p = 0.000). The correlation coefficients for the mean, minimum and maximum values of the 2 scales were 0.496, 0.037 and 0.396, respectively. Regression analysis revealed that the R2 values for the mean, minimum and maximum values were 29.79%, 21.05% and 19.45%, respectively.

The positive but weak correlation between the 2 scales and the low predictive reliability of the grayscale reveals its questionable applicability for the estimation of density in comparison with the standard HU.