Writing an introduction

Introduction

            Metal streak artifact is the major problem in the computed tomography. It appears as bright and dark streaks throughout the cross section images and around the metal. It is caused by multiple mechanisms, some of which are related to the metal itself, and some of which are related to metal edges. The metal itself causes beam hardening, scatter effects and Poisson noise. The metal edges causes streaks due to under sampling, motion, cone beam, and windmill artifacts.  Beam hardening and scatter result in dark streak between metal. Various techniques for metal artifact reduction have been introduced in the literature for improved computed tomography image quality. Boas (2011) reported that metal artifacts due to photon starvation, beam hardening, and motion can suppress by his metal artifact reduction technique (p.894-902). Raoul (2012) noted that quantitative assessment of clinical images demonstrated improved image quality for Radon transformation and forward projection by using scanner’s original raw data techniques of metal artifact reduction but the technique that using scanner’s original raw data showed better image quality than the other technique (p.1125-1132). Koehler (2012) presented a new technique for suppress metal artifact, which is based on a sinogram interpolation technique. All of the current techniques and methods for reducing metal artifacts in computed tomography images have not achieved widespread in clinical use and some techniques can produce new artifacts in the computed tomography images.

            The aim of this study is to develop the computer software to suppress the metal artifact in the computed tomography images by iterative reconstruction technique. It should be improve image quality and diagnostic confidence of the metallic artifact region in the routine clinical application. The new iterative reconstruction algorithm will be implemented to Department of Radiology, King Chulalongkorn Memorial Hospital for reduction the metal artifact in the patients.

Assignment 1: Citation

Evaluation of Two Iterative Techniques for Reducing Metal Artifacts in Computed Tomography

F. Edward Boas , MD , PhD, Dominik Fleischmann , MD

Purpose: To evaluate two methods for reducing metal artifacts in computed tomography (CT) the metal deletion technique (MDT) and the selective algebraic reconstruction technique (SART) and compare these methods with filtered back projection (FBP) and linear interpolation (LI).

Materials and Methods: The institutional review board approved this retrospective HIPAA compliant study; informed patient consent was waived. Simulated projection data were calculated for a phantom that contained water, soft tissue, bone, and iron. Clinical  projection data were obtained retrospectively from 11 consecutively identified CT scans with metal streak artifacts, with a total of 178 sections containing metal. Each scan was reconstructed using FBP, LI, SART, and MDT. The simulated scans were evaluated quantitatively by calculating the average error in Hounsfield units for each pixel compared with the original phantom. Two radiologists who were blinded to the reconstruction algorithms used qualitatively evaluated the clinical scans, ranking the overall severity of artifacts for each algorithm. P values for comparisons of the image quality ranks were calculated from the binomial distribution.

Results: The simulations showed that MDT reduces artifacts due to photon starvation, beam hardening, and motion and does not introduce new streaks between metal and bone. MDT had the lowest average error (76% less than FBP, 42% less than LI, 17% less than SART). Blinded comparison of the clinical scans revealed that MDT had the best image quality 100% of the time (95% confidence interval: 72%, 100%). LI had the second best image quality, and SART and FBP had the worst image quality. On images from two CT scans, as compared with images generated by the scanner, MDT revealed information of potential clinical importance.

Conclusion: For a wide range of scans, MDT yields reduced metal streak artifacts and better-quality images than does FBP, LI, or SART.

Reference: Boas EF. and Fleischmann D.(2011). Evaluation of Two Iterative Techniques for Reducing Metal Artifacts in Computed Tomography. Radiology, 259(3), 894-902.

Citation

(1) Boas EF and Fleischmann D (2011) report that "MDT reduces artifacts due to photon starvation, beam hardening, and motion and does not introduce new streaks between metal and bone" (p.894-902).

(2) Boas EF and Fleischmann D (2011) note that metal artifacts due to photon starvation, beam hardening, and motion was suppressed by metal artifact reduction (MDT) technique (p.894-902).