Characterization of Metal Artifacts in X-ray Computed Tomography

TL;DR

This paper rigorously characterizes metal artifacts in X-ray CT using microlocal analysis, revealing their origin from boundary geometry and wavefront set interactions, and provides conditions for artifact absence.

Contribution

It introduces a microlocal analysis framework to understand metal artifacts in CT, linking artifacts to wavefront set properties of the Radon transform of metal regions.

Findings

Metal streak artifacts are mainly caused by boundary geometry.

Artifacts occur when wavefront sets of the Radon transform and its square differ.

A sufficient condition for the absence of artifacts is identified.

Abstract

Metal streak artifacts in X-ray computerized tomography (CT) are rigorously characterized here using the notion of the wavefront set from microlocal analysis. The metal artifacts are caused mainly from the mismatch of the forward model of the filtered back-projection; the presence of metallic subjects in an imaging subject violates the model's assumption of the CT sinogram data being the Radon transform of an image. The increasing use of metallic implants has increased demand for the reduction of metal artifacts in the field of dental and medical radiography. However, it is a challenging issue due to the serious difficulties in analyzing the X-ray data, which depends nonlinearly on the distribution of the metallic subject. In this paper, we found that the metal streaking artifacts cause mainly from the boundary geometry of the metal region. The metal streaking artifacts are produced only when the wavefront set of the Radon transform of the characteristic function of a metal region does not contain the wavefront set of the square of the Radon transform. We also found a sufficient condition for the non-existence of the metal streak artifacts.