Niels R. van der Werf, Abstract Co-Author: Nothing to Disclose

Martin J. Willemink MD, Abstract Co-Author: Nothing to Disclose

Bronislaw Abramiuc, Abstract Co-Author: Nothing to Disclose

Tineke Petra Willems MD, PhD, Abstract Co-Author: Nothing to Disclose

Tim Leiner MD, PhD, Abstract Co-Author: Speakers Bureau, Koninklijke Philips NV Research Grant, Bayer AG Research Grant, Bracco Group

Marcel Greuter PhD, Presenter: Nothing to Disclose

Iterative reconstruction (IR) in computed tomography (CT) enables lowering of radiation dose while maintaining image quality with respect to conventional filtered back projection (FBP). Iterative Model Reconstruction (IMR) is a model-based algorithm, which should improve image quality further than other IR methods. Because the influence of IMR on coronary calcium scoring (CCS) is still unknown, we aimed to evaluate the influence of motion and dose on CCS in IMR reconstructed CT.

In the center of an anthropomorphic thorax phantom a calcium hydroxyapatite-containing cylinder (198.4 mm3 and 157.1 mg calcification) was translated at varying speeds by a computer controlled lever. An extension ring around the thorax was used to obtain a more realistic attenuation profile. Clinical protocol parameters for medium sized patients were used for all scans with a 256-slice CT system (Brilliance iCT, Philips Healthcare). CT data were reconstructed with filtered back projection (FBP) and IMR at three increasing noise reduction levels. Images were obtained for seven velocities of the cylinder (0 to 60 mm/s) at routine dose level, and at reduced dose levels of 40 and 80%. Each position of the setup was repeated five times with small translations. CCS was quantified as Agatston scores with vendor’s software.

At 0 mm/s CCS with FBP was 422±16, 428±14 and 492±18 for routine dose, 40% and 80% reduced dose, respectively. At the highest IMR level CCS reduced with 4-6% to 400±15, 408±22 and 465±19. At 60 mm/s CCS with FBP increased with 73-94% to 861±97, 826±43 and 855±80. At the highest IMR level CCS increased with 1-5% to 905±102, 854±35 and 866±87.

Coronary calcium scores are overestimated up to 94% due to motion. Reduced dose levels and IMR decrease scores for low velocities, but increase at elevated velocities.

Coronary calcium scoring is highly influenced by motion of the coronary artery, dose levels and iterative reconstruction and might result in wrong patient’s risk estimates.

van der Werf, N, Willemink, M, Abramiuc, B, Willems, T, Leiner, T, Greuter, M, Influence of Motion and Dose on Calcium Scores in IMR Reconstructed CT: A Dynamic Phantom Study.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14006523.html