Jens Hansen DIPLPHYS, Presenter: Nothing to Disclose

Mark Oliver Wielpuetz, Abstract Co-Author: Nothing to Disclose

Gregor Pahn DIPLPHYS, Abstract Co-Author: Nothing to Disclose

Stephan Skornitzke, Abstract Co-Author: Nothing to Disclose

Hans-Ulrich Kauczor MD, Abstract Co-Author: Research Grant, Boehringer Ingelheim GmbH Research Grant, Siemens AG Research Grant, Bayer AG Speakers Bureau, Boehringer Ingelheim GmbH Speakers Bureau, Siemens AG Speakers Bureau, Novartis AG

Wolfram Stiller PhD, DIPLPHYS, Abstract Co-Author: Nothing to Disclose

Study aim was an objective assessment of the pure iodine enhancement vector in the CT number diagram, i.e. CT numbers at low versus high tube voltage (xlow vs. xhigh), and the determination of its influence on the accuracy of quantitative dual-energy CT (DECT) iodine measurements.

CT numbers of various iodine concentrations were assessed for 3 different DE acquisition modes with and without tin (Sn) filtration (80/140kVp, 80/Sn140kVp, 100/Sn140kVp). Measurements were performed at the isocenter free-in-air and at 8 positions across the field-of-view (FOV) (isocenter distance: 0.0-14.0cm, increment: 2.0cm) within a cylindrical acrylic phantom (Ø=32.0cm). CT numbers were determined on more than 100 slices using custom software developed in-house. Linear regression of CT numbers of the iodinated solutions was used to define the iodine-enhancement vector in the CT number diagram (xlow vs. xhigh). The non-enhanced CT number vector was calculated from two data points not containing iodine (air, acrylic). Absolute iodine quantification for each pixel within a region of interest (ROI) was determined as the distance along the iodine enhancement vector to both vectors’ intersection, and was compared to nominal concentration.

Slope and intercept of the regression strongly depend on acquisition mode and presence of attenuating material, e.g. distance to the non-enhanced CT number vector drops to 75% in the phantom compared to free-in-air. For tin-filtered acquisitions, regression slopes of the iodine vector are comparable for both experimental setups (<12% difference), without tin filtration slopes differ by 20%. Mean and nominal iodine concentrations match with relative differences <10%, but showing standard deviations up to 80% within a single ROI. Absolute iodine concentration is overestimated independent of DECT acquisition mode and FOV position. Quantification accuracy increases for iodine concentrations >5mg/ml with relative errors <20% and is best for tin-filtered DECT.

Iodine quantification is very sensitive to DECT acquisition mode and absorption thickness of the scanned object. A large number of evaluated pixels is necessary for a reliable determination.

Iodine quantification is very sensitive to DECT acquisition mode and absorption thickness of the scanned object. A large number of evaluated pixels is necessary for reliable quantification.

Hansen, J, Wielpuetz, M, Pahn, G, Skornitzke, S, Kauczor, H, Stiller, W, Objective Accuracy Assessment of Iodine Quantification for Dual-energy Computed Tomography (DECT) Based on Three-material Decomposition: Influence of Dual-energy (DE) Acquisition Mode and Subject Absorption Thickness.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045457.html