Effects of exposure parameters and slice thickness on detecting clear and unclear mandibular canals using cone beam CT

Abstract

Objectives: The purpose of this study was to clarify the effects of exposure parameters and image-processing methods when using CBCT to detect clear and unclear mandibular canals (MCs). Methods: 24 dry half mandibles were divided into 2 groups with clear and unclear MCs based on a previous CBCT study. Mandibles were scanned using a CBCT system with varying exposure parameters (tube voltages 60 kV, 70 kV and 90 kV; and tube currents 2 mA, 5 mA, 10 mA and 15 mA) to obtain a total of 144 scans. The images were processed with different slice thicknesses using ImageJ software (National Institutes of Health, Bethesda, MD). Five radiologists evaluated the cross-sectional images of the first molar region to detect the MCs. The diagnostic accuracy of varying exposure parameters and image-processing conditions was compared with the area under the curve (Az) in receiver-operating characteristic analysis. Results:The Az values for clear MCs were higher than those for unclear MCs (p , 0.0001). With increasing exposure voltages and currents, Az values increased, but no significant differences were found with high voltages and currents in clear MCs (p 5 1.0000 and p 5 0.9340). The Az values of serial images were higher than those of overlaid images (p , 0.0001), and those for thicker slices were higher than those for thinner slices (p , 0.0001). Conclusions: Our findings indicate that detection of unclear MCs requires either higher exposure parameters or processing of the images with thicker slices. To detect clear MCs, lower exposure parameters can be used.

Prediction of detectability of the mandibular canal by quantitative image quality evaluation using cone beam CT

“…In Experiment 1, the Az values increased as the voltage increased. This result supports the findings of Jasa et al 15 . We next assessed the correlation between the number of holes obtained from our previous study and the Az values from the ROC analysis.…”

“…The number of extracted holes and the Az values of clear ( Figure 7a) and unclear ( Figure 7b) MCs obtained in the previous study 15 The number of holes and the Az value increased under better scanning conditions in both Experiments 1 and 2. In particular, images with more than 70 extracted holes corresponded almost exactly with the Az values of more than 0.8.…”

“…For Experiment 2, the ROC analysis data were retrieved from our previous study on the detectability of the MC in a CS 9300C Select CBCT system. 15 In this previous study, the ROC analysis divided the visibility of the MC into two groups ("clear" and "unclear").…”

“…Our evaluation method with phantoms containing holes should be closely related to detecting the MC in that both are dependent on the detection of small mass changes. Although one previous study investigated the detectability of the MC in CBCT using ROC analysis with observers, 15 no studies have developed a quantitative evaluation method without the use of observers.…”

Radiological and Morphometric Features of Canalis Sinuosus in Russian Population: Cone-Beam Computed Tomography Study

“…However, several studies demonstrated different conclusions on the dependence of the slice thickness of CBCT scans and the detection of the anatomical and other structures, as well as the way that reduces artefacts [18][19][20][21][22][23][24]. Our choice of slice thickness was 1 mm for good and moderate detection of CS without missing it and with high reduction of artefacts in this case.…”