Iterative Reconstruction for Ultra-Low-Dose Laxative-Free CT Colonography

Abstract

Iterative reconstruction (IRT) makes it possible to acquire computed tomographic colonography (CTC) images at <50% of the radiation dose of conventional standard-dose filtered back-projection (FBP) without impairing image quality. It has also other significant advantages over FBP, including better noise suppression, reduction of image artifacts, and flexible mathematical formulation. In this pilot study, we explored the potential application of IRT in the implementation of an ultra-low-dose (ULD) laxative-free CTC examination. First, CTC images are reconstructed approximately with FBP to detect regions of fecal tagging and other high-density objects that can generate image artifacts. Next, the detected regions are projected to sinogram domain to guide the IRT process for the minimization of image noise, correction of beam-hardening artifacts, and virtual cleansing of fecal-tagged regions. For pilot evaluation, five patients were prepared for an ULD dual-energy CTC examination by use of non-cathartic dietary fecal tagging with iodine. For one patient, the CTC images were reconstructed by use of both the FBP and IRT methods. Preliminary results showed that the IRT-reconstructed images demonstrated superior image quality over the FBP-reconstructed images.