Accuracy assessment of the axial images obtained from cone beam computed tomography

Objective: The aim of this study was to evaluate accuracy of linear measurements assessed from axial tomograms and the influence of the use of different protocols in two cone beam CT (CBCT) units. Methods: A cylinder object consisting of NylonH (R) (Day Brazil, Sao Paulo, Brazil) with radio-paque markers was radiographically examined applying different protocols from NewTom 3G (TM) (Quantitative Radiology s.r.l, Verona, Veneto, Italy) and i-CAT (TM) (Imaging Sciences International, Hatfield, PA) units. Horizontal (A-B) and vertical (C-D) distances were assessed from axial tomograms and measured using a digital calliper that provided the gold standard for actual values. Results: There were differences when considering acquisition protocols to each CBCT unit. Concerning all analysed protocols from i-CAT (TM) and Newtom 3G (TM), both A-B and C-D distances presented underestimated values. Measurements of the axial images obtained from NewTom 3G (TM) (6 inch 0.16 mm and 9 inch 0.25 mm) were similar to the ones obtained from i-CAT (TM) (13 cm 20 s 0.3 mm, 13 cm 20 s 0.4 mm and 13 cm 40 s 0.25 mm). Conclusion: The use of different protocols from CBCT machines influences linear measurements assessed from axial images. Linear distances were underestimated in both equipments. Our findings suggest that the best protocol for the i-CAT (TM) is 13 cm 20 s 0.3 mm and for the NewTom 3G (TM), the use of 6 inch or 9 inch is recommended. Dentomaxillofacial Radiology (2011) 40, 369-378. doi: 10.1259/dmfr/88722046