Cheng Zhou MD, Abstract Co-Author: Nothing to Disclose

Wing Kei Wong, Presenter: Nothing to Disclose

Isao Tanaka, Abstract Co-Author: Nothing to Disclose

Siu Ki Yu PhD, Abstract Co-Author: Nothing to Disclose

Yun Shen PhD, Abstract Co-Author: Employee, General Electric Company

Eiko Ueno MD, Abstract Co-Author: Nothing to Disclose

Haruhiko Machida MD, Abstract Co-Author: Nothing to Disclose

Gladys G. Lo MD, Abstract Co-Author: Nothing to Disclose

By using MARS, the metal artifact that was caused by an artificial joint implant can be reduced effectively for energies below 90 keV in monochromatic CT images.

In Computed Tomography (CT), artifacts caused by different kinds of metallic implants presence in the reconstructed images and impose limitations on the reliability of the results. Variety techniques had been attempted to reduce such artifacts in CT. Recently, a metal artifact reduction software (MARS) is available on a high definition CT (HDCT) scanner to reduce the effect of the artifact in monochromatic images by using spectral imaging (SI) technique.

An artificial joint implant which made of Cobalt-Chromium alloy and covered with layers of scanning resin (dental material) and acrylic resin, was used to evaluate the reduction. The implant was submerged in distilled water and scanned using dual energy mode on a HDCT scanner. A series of monochromatic CT images (ranging from 40 keV to 140 keV) were then reconstructed using the SI technique, and MARS was applied to the images to reduce the metal artifact. The standard deviation (SD) of the CT number was measured in an area below the implant (SDH) and in a remote area of distilled water as the background (SDW). A metal artifact indicator, Artifact Index (AI), was calculated by the square root of the difference between the squares of SDH and SDW. The AI values for both with and without application of MARS for all monochromatic images were calculated and compared.

As the monochromatic energy increases, the image noise hence the AI value decreases until they reached plateau at 110 keV for images without MARS, and at 70 keV for images with MARS. The metal artifact can be largely reduced by applying MARS to the monochromatic images with energies below 90 keV (70.0% AI reduced at 40 keV, and 13.7% at 90 keV). For energies above 90 keV, the AI values were comparable for both with and without application of MARS.

Zhou, C, Wong, W, Tanaka, I, Yu, S, Shen, Y, Ueno, E, Machida, H, Lo, G, Effectiveness Evaluation of Metal Artifact Reduction Software in Computed Tomography Spectral Imaging: A Phantom Study with a Metallic Hip Joint Implant.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9006366.html