Rainer Raupach PhD, Abstract Co-Author: Employee, Siemens AG, Forchheim, Germany

Christoph R. Becker, Abstract Co-Author: Nothing to Disclose

Thorsten R. C. Johnson MD, Abstract Co-Author: Speakers Bureau, Siemens AG Research grant, Bayer AG

Bernhard Krauss PhD, Abstract Co-Author: Employee, Siemens AG, Forchheim, Germany

Thomas G. Flohr PhD, Abstract Co-Author: Employee, Siemens AG

Bernhard Schmidt PhD, Presenter: Employee, Siemens AG

To reduce metal artifacts in dual energy CT images, and improve diagnostic quality.

CT images usually suffer from artifacts in the presence of metal objects which can impair the diagnosis. Those artifacts are caused by a combination of various physical effects. However, in many clinically relevant situations the beam hardening effect is dominant. We have derived a method to reduce metal artifacts for dual source dual energy scans. Using the information from both energies so called mono-energetic images could be reconstructed that correspond to the attenuation at a specific X-ray photon energy. This calculation was based on a decomposition into either the different physical absorption mechanisms or, equivalently, suitable base materials. Metal artifacts could be minimized by optimizing the material decomposition model, consequently leading to improved image quality. The presented method was applied to phantom as well as patient data taken from clinical routine (Definition Flash, Siemens, Forchheim). Artifact reduction was quantified in phantom data by comparison with a reference scan without the metal insert. In patient data, a visual image quality rating was applied.  

In both, phantom and patient data, metal artifacts were substantially less in the images coming from the x-ray tube running at the higher energy (140Sn kV). Calculated mono-energetic images showed for low and medium energy levels similar artifacts as the initial data. Artifacts were stronger for lower energies. However, for increasing energies artifacts were reduced. Optimal results were obtained for mono-energetic images at an energy level of 120-130 keV. For example in the case of a titanium hip prostheses of a pelvis phantom, artifact were reduced from -125 HU at 80kV and -16 HU at 140Sn kV to 0 HU at 130 keV or from 134 HU and 18 HU to -8 HU respectively. Similar results were obtained in case of patient with hip prostheses.

Mono-energetic images derived from dual energy dual source data allow to reduce metal artifacts substantially by selecting the appropriate energy level for the mono-energetic image.

In the presence of metal, CT images might suffer from artifacts. Mono-energetic images from DE data show promising results to improve diagnostic quality in those cases.

Raupach, R, Becker, C, Johnson, T, Krauss, B, Flohr, T, Schmidt, B, Metal Artifact Reduction for Dual Source Dual Energy Computed Tomography.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9016109.html