Katharine Grant PhD, Presenter: Employee, Siemens AG

Joel Garland Fletcher MD, Abstract Co-Author: Grant, Siemens, AG Grant, Genentech, Inc Grant, Johnson & Johnson Consultant, Abbott Laboratories

Lifeng Yu PhD, Abstract Co-Author: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

Thomas Allmendinger, Abstract Co-Author: Employee, Siemens AG

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

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

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

To assess clinical performance of noise or dose reduction techniques in CT requires use of sophisticated and proprietary noise insertion software or exposing the same patient to different dose levels. Dual-source (DS) CT scanner technology enables a potential third alternative, providing simultaneous acquisition of full-dose (FD) and half-dose (HD) images by using CT projection data from both or a single x-ray tube, respectively. The purpose of this work was to investigate whether such a method provides equivalent image quality and dose compared to single source (SS) CT for both FD and HD images.

Tissue-equivalent, torso phantoms mimicking small, medium, large and extra large patients (30, 35, 40 and 45cm lateral dimension) were scanned using SS and DS protocols at 4 tube potentials (80, 100, 120 and 140 kV). For each phantom size, the scanner radiation output (CTDIvol) appropriate for a similarly sized patient was used; the total CTDIvol was matched for the SS and DS scans. SS scans were repeated using half the original CTDIvol. All images were reconstructed with identical parameters, yielding 4 data sets for each phantom: DS FD (projection data from both tube), DS HD (projection data from only one tube), SS FD and SS HD. Noise was measured in multiple regions of interest and compared using a two-tailed paired t-test. Additionally, noise and diagnostic confidence were compared in 5 CT colonography patient exams: FD SS images from the prone scan were compared to FD DS images from the supine scan; and 5 FD DS exams were compared to prior FD SS exams.

Image noise was not significantly different between FD SS and FD DS images at each kV for the 30, 35 and 40cm phantoms (all p>0.1). Noise was not significantly different between HD SS and HD DS images at each kV for the 30, 35 and 40cm phantoms (all p>0.3), except at 80kV for 40cm. As expected, there was ~ 41% increase in noise between the FD and HD images for both SS and DS. There was no difference in noise or diagnostic confidence between SS and DS patient exams (all p=1.0).

For patients ≤ 40 wide, DS CT provides equivalent image quality and dose to SS CT, yet allows simultaneous acquisition of half-dose images.

Half-dose images can be directly obtained from full-dose DS scans, providing an accurate, innovative yet convenient method for evaluating noise and dose reduction methods for ALARA research.

Grant, K, Fletcher, J, Yu, L, Leng, S, Allmendinger, T, Schmidt, B, McCollough, C, Flohr, T, Validation of a Novel Method for Obtaining Low Dose CT Images from Full Dose Clinical Exams for ALARA Research.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11009132.html