Kazushi Yokomachi RT, Presenter: Nothing to Disclose

Fuminari Tatsugami, Abstract Co-Author: Nothing to Disclose

Toru Higaki, Abstract Co-Author: Nothing to Disclose

Chikako Fujioka RT, Abstract Co-Author: Nothing to Disclose

Masao Kiguchi RT, Abstract Co-Author: Nothing to Disclose

Kazuo Awai MD, Abstract Co-Author: Research Grant, Toshiba Corporation Research Grant, Hitachi Ltd Research Grant, Bayer AG Research Consultant, DAIICHI SANKYO Group Research Grant, AZE, Ltd

Eiji Nishimaru RT, Abstract Co-Author: Nothing to Disclose

The coronary artery calcium (CAC) score measured on fast CT scanners is an unequivocal marker of coronary atherosclerosis. However, the high image quality of CAC scans is achieved at the expense of high radiation exposure to the patient. Adaptive iterative reconstruction (IR) coupled with a new reconstruction algorithm can reduce the image noise and is expected to reduce the radiation dose required for a noise level similar to that of filtered back projection (FBP). The purpose of this study was to assess the possibility of reducing the radiation dose for CAC scoring using IR and a 320-detector CT scanner.

We scanned a cardiac CT calibration phantom (QRM, Germany) that featured different calcium hydroxyapatite concentrations on a 320-detector CT scanner (Aquilion One, Toshiba) with prospective ECG-triggering. At a tube current of 80 mA, the noise level was 20 HU on scans of 3-mm-thick slices. Images were acquired at 120 kV and tube currents of 80-, 50-, 30-, and 20 mA. We scanned the phantom 5 times in each series. We generated images at 3 IR strength levels [low, moderate, and high] (adaptive iterative dose reduction 3D: AIDR-3D; Toshiba) and FBP images. For each examination we calculated the CAC score using the Agatston algorithm (130-HU threshold), the calcium mass scores, and the image noise on a workstation and compared the CAC measurements to assess the possibility of reducing the radiation exposure using AIDR-3D.

For the FBP images, the mean CAC scores at tube currents of 80-, 50-, 30-, and 20 mA were 755 ± 25, 924 ± 39, 2234 ± 79, and 5543 ± 260, respectively; the mass scores at each tube current were 182 ± 2, 209 ± 4, 362 ± 3, and 698 ± 27, respectively. The CAC- and mass scores on images acquired at 30 mA and reconstructed with high-level AIDR-3D were comparable to the values on images obtained at 80 mA and reconstructed with FBP (764 ± 22 vs. 755 ± 25, p = 0.40; 178 ± 2 vs. 182 ± 2, p = 0.11, respectively).

The use of high-level AIDR 3D made it possible to reduce the radiation dose by 63% for CAC measurements without impairing the quantification of coronary calcification.

Based on the results of our phantom study we suggest that with high-level AIDR-3D a radiation dose reduction by 63% is possible for CAC measurements using 320-detector CT.

Yokomachi, K, Tatsugami, F, Higaki, T, Fujioka, C, Kiguchi, M, Awai, K, Nishimaru, E, Radiation Dose Reduction for Coronary Artery Calcium Scoring at 320-Detector CT with Iterative Reconstruction: Study Using a Cardiac CT Calibration Phantom.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12029930.html