Because of the growing interest in low dose computed tomography (CT) scanning, noise has become a major issue in CT imaging. Diffusion filtering is a well-known technique for filtering noise from images. We propose a hybrid diffusion model, which combines edge-enhancing diffusion (EED) and coherence-enhancing diffusion (CED) in a continuous manner. This diffusion model is compared with five existing diffusion schemes. Quantitative experimental results are presented on clinical CT chest scans, using high dose and simulated low dose scans.