Thomas Werncke MD, Dipl Phys, Presenter: Nothing to Disclose

Christian Von Falck MD, Abstract Co-Author: Research Grant, Pro Medicus Limited Research Grant, Siemens AG

Frank K. Wacker MD, Abstract Co-Author: Research Grant, Siemens AG Research Grant, Pro Medicus Limited

Bernhard C. Meyer, Abstract Co-Author: Research Consultant, Pro Medicus Limited

To compare the image quality of a standard single source computed tomography (SSS-CT) with a virtual single source CT (VSS-CT) dataset reconstructed from two raw datasets obtained by dual source CT (DSCT) acquisition in abdominal computed tomography (CT) in order to establish a radiation dose-neutral approach for intra-individual comparison of three acquisition protocols at different radiation dose levels.

An abdominal phantom representing an 80kg male was imaged using DSCT (Somatom Definition, Siemens Healthcare) at three radiation dose levels (RDL) with 120kVp and different tube currents (low, standard, high mAs). For each RDL, raw data was obtained once in single source mode using x-ray tube A only and in dual source mode using 5 different ratios for tube current of x-ray tube A and B (same total radiation dose; A/B: 90/10%, 80/20%, 70/30%, 60/40%, 50/50%). For each RDL, one standard (SSS-CT) and five virtual single source image datasets (VSS-CT50 – 90) were reconstructed. To compare SSS-CT and VSS-CT datasets, image quality was assessed in terms of high and low contrast performance by calculating the modulation transfer function (MTF), image noise, noise power spectrum (NPS) and for low contrast lesion detectability the modified multiscale structural similarity index (MS-SSIM*). A maximum decrease of Δ=5% of image quality compared to SSS-CT was defined as acceptable and a non-inferiority analysis with Δ was performed.

For MTF, non-inferiority was observed for all VSS-CT datasets and RDL (P<0.05). Image noise demonstrated an acceptable increase (<3.2%, P<0.05) for each RDL and NPS showed only minor differences in the mid frequency range. The MS-SSIM* index demonstrated for the high RDL protocol a minor decrease for VSS-CT datasets (<2%, P<0.05). For the standard and low RDL the relative differences of MS-SSIM* index increased and were only in one case above Δ (standard RDL, mean VSS-CT60 5.1%, P>0.05).

Image quality obtained by VSS-CT and SSS-CT using equivalent total radiation exposure to the patient showed only negligible differences in image quality. Therefore, this technique might allow an intra-individual comparison of full and reduced radiation dose protocols within one image acquisition step by splitting the radiation dose between two x-ray tubes of a DSCT.

Radiation dose-splitting with DSCT may enable an iterative, task dependent radiation dose reduction in CT.

Werncke, T, Von Falck, C, Wacker, F, Meyer, B, Virtual Single-source CT Using Dual-source Acquisition: A New Technique for the Dose-neutral Intra-individual Comparison of Different Scan Protocols.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14008537.html