Image Quality Evaluation Using Integrated Visual Grading Regression for Optimisation of Computed Tomography Imaging: A Dental Implantology Study

In recent decades, the use of computed tomography modalities has led to more accurate predictions of the outcomes of dental implant therapy. Computed tomography modalities have a radiation dose risk that must always be considered in conjunction with the benefits of its use. Therefore, the need to acquire a clinically acceptable diagnostic image must always be balanced with the radiation dose delivered to the patient. The aim of this study was to define the limit of dose reduction in multi detector computed tomography (MDCT) and cone beam computed tomography (CBCT) that could be achieved without compromising the clinical requirement of the image in pre-surgery implant placement planning. The evaluation outcomes were used to validate a new image quality evaluation method. The clinical implications resultant from this study have significant effects on future phantom studies allowing for the development of protocols for CT and CBCT scans in clinical applications that benefit the patient through lowering patient dose whilst maintaining diagnostic image quality.
The study undertaken was a phantom study, two CT scanners (GE® and Toshiba®) and One CBCT (Planmeca Promax) units were used to acquire several images of the phantoms. Image acquisition was based on different combinations of exposure parameters (kVp and mA). The images were then evaluated by three clinical observers with more than 5-year of dental implantology clinical experience. Inter- and intra-observer reliability agreement were assessed. Image quality was evaluated using a visual grading analysis (VGA) approach. The evaluation consists of anatomical landmark visibility and the clinical eligibility of the image to pre-surgical implant placement assessment. The data were analysed using image quality regression methodology based on overall image quality and clinical decision making.
Results revealed that low dose protocols for MDCT and CBCT can successfully be achieved for implant dentistry. In addition, it was demonstrated that increasing the tube voltage improved the image quality in the GE® MDCT, while in the Toshiba® MDCT, the image quality was not dependent on changes in tube voltage. The acceptable image quality acquired by GE® CT was associated with the lowest radiation dose with exposure settings of 80 kVp and 240 mA, and in Toshiba® was associated with the lowest radiation dose with exposure settings of 100 kVp and 150 mA. It was defined as an acceptable image quality, which answered the clinical questions of implant placement planning.
While in CBCT, the minimum acceptable exposure setting combination demonstrated was 80 kVp, 6 mA with the exposure setting combinations of 80 kVp, 8 mA and 80 kVp, 10 mA enhancing the image quality. Integrated visual grading regression (IVGR) was adopted and tested on the CBCT observation data that resulted in 31% radiation reduction compared to the dose associated with the default clinical use. In conclusion, the radiation dose can be reduced for the images of pre-surgical implant assessment. In addition, the IVGR is a valid method to assess radiation dose reduction of various CT modalities and could be useful for future clinical and phantom studies.