The Influence of Filtration, Tube Current and Number of Projections on CBCT Image Quality

As cone-beam computed tomography (CBCT) is becoming popular in temporal bone imaging, there is a pressing need to improve the quality of images rendered by this device in temporal bone imaging. This prospective cadaver study aims at evaluating the image quality and assessing the changes that result when three different filter combinations, variation in the number of projections, and tube current are used in CBCT temporal bone imaging. The image acquisition was carried out using three filter combinations, Cu-Al, Cu-Cu and Al-Al, with varying thickness and the number of projections was changed from the standard 100% to 150%. Additionally, 8 mA and 12.5 mA were used in all cases. The quality of the acquired images was then qualitatively (visually) and quantitatively (noise analysis) assessed. The visual assessment was carried out by two radiologists with over 20 years’ experience in the field of diagnostic radiology and the noise analysis (standard deviation), an algorithm-based assessment, was done in MATLAB user interface. The results showed that Copper and Aluminum (Cu-Al) filters offered the best image quality when compared with the Cu-Cu (factory-fitted) and Al-Al filter combinations in both visual and algorithm-based assessments. From the results, it was also demonstrated that increasing the number of projections from the standard 100% number of projections to 150% offered a better characterization of the complex temporal bone anatomy in both visual and noise analysis assessments. Finally, changes in the tube current from 8 mA to 12.5 mA resulted in a minimal change of the image quality when visually assessed. However, the effects of the tube current variations increased when the algorithm-based noise analysis was carried out. In conclusion, variations in the material property of the filter, effective filter inter-positioning, and variations in the number of projections optimize the image quality in CBCT temporal bone imaging. /Kir1