DuDo-RAC: Dual-domain optimization for ring artifact correction in photon counting CT.

Background And Objective: Due to the inconsistent response of photon counting detectors (PCDs) pixels to X-rays, there is an obvious presence of low-frequency ring artifacts in CT reconstructed images. Traditional CT ring artifact correction methods are ineffective in correcting low-frequency ring artifacts. Although the pixel-wise polynomial correction method can correct low-frequency ring artifacts, there may still remain residual artifacts due to the inaccuracy in the coefficient measurement and the inability of polynomial functions to perfectly model the relationship between the thickness and post-log raw data. To resolve such problems, this work proposes a high and low frequency ring artifact correction method based on dual-domain optimization (DuDo-RAC).

Methods: This method is independent of spectral information and training data, making it suitable for various energy thresholds. Its principle is to model the inconsistent response as pixel-wise polynomial functions, with the coefficients for each pixel being determined via a dual-domain optimization framework. Since ring artifacts manifest as stripes after polar transformations, smoothing operations are utilized to further weaken the residual ring artifacts after the pre-correction process. Furthermore, a multi-resolution gradient loss function is designed to iteratively optimize the polynomial correction coefficients for a better assessment of ring removal performance.

Results: The results have demonstrated that the proposed method can effectively correct the high and low frequency ring artifacts in PCD-CT images while preserving the image structure and details.

Conclusion: DuDo-RAC proposed in this study obtains effective ring artifact correction results in PCD-CT images.