Abstract: This paper presents a GPGPU-based real-time virtual colon flattening method that allows dynamic modification of the CT segmentation threshold during a colon observation.First,a cylindrical lighting model is built by leveraging the tangent of each point on the colon's center line.Then a GPGPU-based ray-casting volume rendering algorithm is employed to generate the flatten colon surface according to the CT segmentation threshold of the colon's inner surface.Experimental results show that the proposed method achieves real-time performance(up to 50 frames per second),and improves the adaptability and accuracy of the virtual colon flattening.