An investigation into dose optimisation for imaging root canal anatomy using cone beam CT.

OBJECTIVES: To identify a dose as low as diagnostically acceptable and a threshold level of image quality for cone beam CT (CBCT) imaging root canals, using maxillary first molar (M1M) second mesiobuccal (MB2) canals of varying complexity for two CBCT scanners. METHODS: Dose-area product (DAP) and contrast-to-noise ratio (CNR) were measured for two scanners at a range of exposure parameters. Subjective-image-quality assessment at the same exposures was performed for three M1Ms of varying MB2 complexity, positioned in an anthropomorphic phantom. Nine raters (three endodontists, three dental radiologists and three junior staff) assessed canal visibility, using a 5-point confidence scale rating. RESULTS: Identification of simple-moderate MB2 canal complexity was achieved at a range of protocols, with DAP values of ≥209.3 and ≥203.2 mGy cm² and CNRs of 3 and 7.6 for Promax®3D and Accuitomo-F170® respectively. For complex canal anatomy, target subjective image quality was not achieved, even at the highest DAP values for both scanners. Junior staff classified significantly more images as undiagnostic compared with senior staff (p = 0.043). CONCLUSIONS: In this first study to address optimisation of CBCT imaging of root canal anatomy, a similar threshold dose for both scanners was identified for M1Ms with simple-moderate MB2 canal complexity. Increasing dose to enhance visualisation of more complex canal anatomy was ineffective. Selection of standard protocols (while avoiding lower kV/mA protocols) instead of high-resolution scans was a practical means of reducing patient dose. CNR is not a transferable measure of image quality.

An analysis of effective dose optimization and its impact on image quality and diagnostic efficacy relating to dental cone beam computed tomography (CBCT)

The potential of high resolution, three-dimensional (3D) images which overcome limitations such as superimposition and anatomical noise of two-dimensional (2D) conventional imaging, has made cone beam computed tomography (CBCT) an increasingly popular imaging modality in many dental applications. It is in light of the increasingly prevalent use of CBCT, particularly in a primary dental care setting, that the goal of this review is to investigate what evidence-based guidance is available to the clinician to justify and reduce radiation risk of this higher dose imaging modality while maintaining diagnostically acceptable images. To this end, the literature on radiation dose and related patient risk was comprehensively investigated, before an analysis of the ways in which dose can be optimized and the implications that optimization has on image quality was discussed. Finally, although it is accepted that CBCT has the potential to improve diagnosis, it is uncertain if its use has positive ramifications on issues of diagnostic efficacy, including clinical decision-making and patient outcome. In order to investigate these issues, the levels of evidence of the existing studies and their validity were assessed. On review of the available literature, it is evident that there is limited practical advice available to dentists regarding dose optimization and any existing protocols may not be readily transferable to every CBCT machine, the manufacturers' role is not often conducive to dose limitation and that the bulk of evidence is at lower levels of evidence. Furthermore, there is minimal supporting evidence to suggest an impact of CBCT on diagnostic thinking and consequent choice of treatment and no evidence of a positive effect of CBCT on patient outcome.