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

Herbert Bruder PhD, Abstract Co-Author: Employee, Siemens AG

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

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Thomas G. Flohr PhD, Presenter: Employee, Siemens AG, Forchheim, Germany

Cynthia H. McCollough PhD, Abstract Co-Author: Research grant, Siemens AG Research grant, General Electric Company

Although modern CT systems provide isotropic sub-millimeter resolution, image noise and blooming of calcified plaques pose serious problems for determining the residual vessel lumen in CT angiographic examinations. We propose a method to efficiently reduce the blooming effect using a novel three-dimensional image filter and dual energy CT data acquired with a dual source CT system.

A three material decomposition (water, calcium, iodine) was performed using the ratios of the CT numbers in the low and high kV images, allowing image voxels with CT numbers exceeding a specified threshold to be classified as containing either contrast agent or a significant concentration of calcium. A map of calcium voxels was then determined and used to calculate optimally-adapted local 3D filters for each voxel of the combined kV image in order to reduce blooming without amplifying noise. Edge enhancing filters were applied perpendicular to the calcium interface, while adaptive low pass filters were simultaneously used on tangent planes. The method was performed on computer-simulated phantom data and data acquired on a SOMATOM Definition dual source CT scanner, with one tube operating at 80 kV and the second tube simultaneously operating at 140 kV. A quantitative evaluation of measured calcium volumes versus known volumes was performed using an anthropomorphic chest phantom that contained small cylinders of hydroxyapatite with different densities and size.

The blooming effect, i.e. overestimation of calcium volume, was reduced by up to 42% using the described technique, while simultaneously reducing image noise by 30%.

The use of simultaneously acquired dual energy CT data and locally-adapted 3D filters provides a reduction in calcium blooming by up to 42% while reducing image noise by approximately 30%.

Stenotic lesions, which often occur adjacent to calcified plaques, should be able to be more accurately assessed with the reduction in calcium blooming and image noise provided by this technique.

Raupach, R, Bruder, H, Krauss, B, Schmidt, B, Flohr, T, McCollough, C, Reduction of the Blooming Effect for Calcified Plaques in CT Angiographic Examinations by Means of Dual-Energy CT.  Radiological Society of North America 2006 Scientific Assembly and Annual Meeting, November 26 - December 1, 2006 ,Chicago IL. http://archive.rsna.org/2006/4433566.html