Image quality assessment of clinically-applied CBCT protocols using a QAT phantom

Objectives: This study has two main purposes: (1) to evaluate the effect of various clinically applied protocols [changing field of view (FOV), voxel size and tube voltage (kVp)] on CS 9300 CBCT (CareStream SM 749, Rochester, NY) image quality using its quality assurance test (QAT) phantom and (2) to evaluate the efficacy of a newly-designed prototype plugin on ImageJ (National Institutes of Health, Bethesda, MD) which was introduced to measure modulation transfer function (MTF) using a modified slanted-edge method. Methods: Using a specifically constructed QAT phantom, five image quality parameters were assessed-image uniformity, signal-to-noise ratio, contrast, position checking and the MTF-for ten variables, clinically applied protocols on a CS 9300 PREMIUM three-dimensional CBCT device. Results: With FOV and voxel size fixed, high-dose protocols resulted in less image noise and more uniformity. On the other hand, less image uniformity was achieved with less kVp. Moreover, high-dose protocols resulted in a high contrast-to-noise ratio (CNR). There were significant differences in CNR between 60 and 70 kVp as well as between 70 and 90 kVp. Our study identified no difference between MTF and either voxel size or FOV. Conclusions: The image quality of the CS 9300 CBCT varied with variability in exposure protocols and different voxel sizes. The negative association between greater spatial resolution (smaller voxel size) and the MTF shows that the slanted edge method is not ideal for MTF evaluation of CBCT and is therefore not recommended for using it for this purpose.