Abstract
Introduction: Scatter is an important factor to effect CT image quality, especially in CBCT. X-ray scatter reduces image contrast, increases image noise, introduces pixel value inaccuracy and some image artifact. In this study, we use a Beam Stopper Devices (BSD) to correct the scatter of INER’s Micro CBCT images and expect that the method can be apply to the clinical use of CBCT in the future. Materials and methods: First, We investigate the scatter to primary ratio (SPR) of INER’s Micro CBCT with a cylinder PMMA phantom and different diameter lead foils. The two cylinder phantoms, include a contrast phantom and a PMMA phantom, were used. And we use beam stopper device (BSD) to estimate the scatter of the projection data. By using two projection data, with/without BSD, we can calculate the scatter distribution. And the scatter in the projection data could be removed exactly . Furthermore, we also use the curve fitting method to correct the CBCT images. Some image index, such like contrast index, cup index, normalized standard deviation, and mean pixel value, were evaluated to compare the correction effect between the BSD and curve fitting method. Results and conclusions: The SPR of INER’s Micro CBCT is up to 37.47%. Point BSD method can correctly estimate real scatter distribution of projection data. After Point BSD corrected, image contrast could increased 15%, pixel value were restored to original value nearly, and cup index were reduced 2.5 times. The added noise from Point BSD method is less than Curve Fitting method. Overall, BSD method is better than Curve Fitting method according to our experiments. When T-values are estimated correctly, the BSD method used in CBCT will be very valuable in the future.