Accuracy of three-dimensional measurements using cone-beam CT

Lesions causing intraosseous defects in the head and neck region are difficult to diagnose using two-dimensional radiography, and three-dimensional (3D) data provided by CT is useful but often difficult to obtain. Recently, cone-beam CT (CBCT) was made available, with the potential to become a practical tool in dentistry. However, there is limited evidence to prove that defect volume can be determined accurately. Therefore, this in vitro validation study aimed at establishing whether linear and 3D CBCT, using volumetric measurements, is accurate for determining osseous defect sizes.

Depth and diameter of simulated bone defects in (i) an acrylic block and (ii) a human mandible were blindly measured electronically by five examiners using CBCT. Linear measurements were compared with predetermined machined dimensions. Using software, volume extraction was performed by another examiner on the acrylic phantom and compared with known dimensions. Data were analysed using paired t-tests.

Using the acrylic block, mean width accuracy was -0.01 mm (+/- 0.02 SE) and mean height difference was -0.03 mm (+/- 0.01 SE; P > 0.05). For the human mandible, mean width accuracy was -0.07 mm (+/- 0.02 SE) and mean height accuracy was -0.27 mm (+/- 0.02 SE; P < 0.01). Volume accuracy was -6.9 mm3 (+/- 4 SE) for automated calculations and -2.3 mm3 (+/- 2.6 SE) for the manual measurements (P < 0.001).

CBCT has the potential to be an accurate, non-invasive, practical method to reliably determine osseous lesion size and volume. Further clinical validation will lead to a vast array of applications in oral and maxillofacial diagnosis.