Effect of Tube Current on Linear Measurement Accuracy of Cone Beam Computed Tomography Images

Abstract

Objective: To compare the accuracy of linear bone measurements on Cone Beam Computed Tomography (CBCT) images obtained using different tube currents. Methods: Twelve reference points were prepared by using burs and heated gutta-percha on each of the ten dry mandibles for horizontal and vertical measurements on anterior and posterior segments. Images were obtained with Kodak 9000 3D cbct system at 5 different tube currents (2 mA, 3.2 mA, 6.3 mA, 10 mA and 15 mA). Three radiologists did total of 1200 linear measurements. True lengths were determined with a digital caliper. Height and width measurements from each of the mA settings were compared to the gold standard using Bland and Altman plots. Overall comparison of the measurements was done using repeated measures ANOVA. Correlation between individual measurements of each observer was assessed with Pearson’s correlation analysis. Results: No differences were found in the height and width measurements for both anterior (p>0.05) and posterior (p>0.05) measurements for different mA settings. Increase in mA caused an increase in the geometric accuracy of cbct images (p>0.05). Mean deviations from the gold standard ranged between - 0.7 and +0.12 mm among the lowest and highest tube settings. The correlation between observers’ measurements ranged between 0.97 and 0.98 for increasing tube settings. Conclusion: Tube current may be reduced as low as 2mA without jeopardizing linear measurement accuracy. Keywords: Tube current, linear measurement, accuracy, cone beam CT, computed tomography, bone measurements.