SU‐F‐18C‐15: Model‐Based Multiscale Noise Reduction On Low Dose Cone Beam Projection

Abstract

Purpose:To improve image quality of low dose cone beam CT for patient positioning in radiation therapy.Methods:In low dose cone beam CT (CBCT) imaging systems, Poisson process governs the randomness of photon fluence at x‐ray source and the detector because of the independent binomial process of photon absorption in medium. On a CBCT projection, the variance of fluence consists of the variance of noiseless imaging structure and that of Poisson noise, which is proportional to the mean (noiseless) of the fluence at the detector. This requires multiscale filters to smoothen noise while keeping the structure information of the imaged object. We used a mathematical model of Poisson process to design multiscale filters and established the balance of noise correction and structure blurring. The algorithm was checked with low dose kilo‐voltage CBCT projections acquired from a Varian OBI system.Results:From the investigation of low dose CBCT of a Catphan phantom and patients, it showed that our model‐based multiscale technique could efficiently reduce noise and meanwhile keep the fine structure of the imaged object. After the image processing, the number of visible line pairs in Catphan phantom scanned with 4 ms pulse time was similar to that scanned with 32 ms, and soft tissue structure from simulated 4 ms patient head‐and‐neck images was also comparable with scanned 20 ms ones. Compared with fixed‐scale technique, the image quality from multiscale one was improved.Conclusion:Use of projection‐specific multiscale filters can reach better balance on noise reduction and structure information loss. The image quality of low dose CBCT can be improved by using multiscale filters.