The effect of milliamperage, number of basis images, and export slice thickness on contrast-to-noise ratio and detection of mandibular canal on cone beam computed tomography scans: an in vitro study.

Objectives: The aim of this study was to evaluate the effect of milliamperage, number of basis images, and export slice thickness on contrast-to-noise ratio (CNR) and confidence in detecting mandibular canal.

Study Design: Two phantoms were used. Each phantom consisted of a dry mandible with an epoxy resin bone tissue substitute block and a water-equivalent block, submerged in water. Each mandible was scanned with a Morita 3D Accuitomo cone beam computed tomography (CBCT) machine (Morita, Kyoto, Japan). Scans were made with 180-degree and 360-degree rotations, at 4, 6, and 8 mA. Each scan was exported in Digital Imaging and Communications in Medicine (DICOM) format at slice thicknesses of 0.125 mm, 0.25 mm, 0.75 mm, and 1.0 mm, resulting in 24 image sets for each phantom. The CNR was calculated. Variables were analyzed using factorial analysis of variance. The scans were also evaluated by five observers who were asked to state their confidence in detecting the mandibular canal on a four-point confidence scale.

Results: Increasing the number of basis images, milliamperage, or export slice thickness significantly increased the CNR. Reducing the export slice thickness improved observers' confidence in detecting the mandibular canal.

Conclusions: The CBCT acquisition settings should be carefully chosen, depending on specific diagnostic tasks. The lowest slice thickness equal to the voxel size should always be used for exporting CBCT data despite the higher noise.