Keiko Matsumoto MD, Presenter: Nothing to Disclose

Yoshiharu Ohno MD, PhD, Abstract Co-Author: Research grant, Toshiba Corporation Research grant, Koninklijke Philips Electronics NV Research grant, Bayer AG Research grant, DAIICHI SANKYO Group

Hisanobu Koyama MD, Abstract Co-Author: Nothing to Disclose

Atsushi Kono MD, Abstract Co-Author: Nothing to Disclose

Yumiko Onishi MD, Abstract Co-Author: Nothing to Disclose

Daisuke Takenaka MD, Abstract Co-Author: Nothing to Disclose

Sumiaki Matsumoto MD, PhD, Abstract Co-Author: Research grant, Toshiba Corporation

Munenobu Nogami MD, PhD, Abstract Co-Author: Nothing to Disclose

Kazuro Sugimura MD, Abstract Co-Author: Research grant, Toshiba Corporation Research grant, Koninklijke Philips Electronics NV Research grant, Mitsubishi Corporation Research grant, Bayer AG Research grant, Eisai Co, Ltd Research grant, DAIICHI SANKYO Group Research Consultant, Shionogi & Co, Ltd

et al, Abstract Co-Author: Nothing to Disclose

To determine the optimized dose for detection of various sized focal ground-glass opacities (GGOs) and partly solid nodules at 64-detector row CT system with three dimensional (3D) automatic exposure control (AEC) in chest phantom study.

A chest CT phantom including simulated focal GGOs and partly solid nodules, whose diameters were from 2 mm to 14 mm in steps of 2 mm, was scanned at a 64-detector row CT without and with 3D AEC. 3D AEC performed by combination of angular modulation on xy-axis and z-axis modulation according to the estimated standard deviation (SD) of image noise from localizer radiographs. On CT scan with 3D AEC, SD were changed from 40 to 200 in steps of 20. All other parameters were fixed at every CT scans without and with 3D AEC. The probability and image quality of each simulated abnormality were visually assessed by two chest radiologists with a five-point scoring system. Interobserver agreements were assessed by kappa analysis. Then, identification and image quality of CT scan with 3D AEC at each SD were compared with that of CT scan without 3D AEC by ROC analysis and ANOVA.

Both interobserver agreements were substantial (identification: kappa=0.76; image quality: kappa=0.69). When SDs equal to or less than 160 were adapted, Azs of CT scan with 3D AEC (Azs>0.94) had no significant difference with that of CT scan without 3D AEC (Az=0.96, p>0.05).   When SDs equal to or less than 120 were adapted, image quality of CT scan with 3D AEC had no significant difference with that of CT scan without 3D AEC (p>0.05). Radiation dose of CT scan without 3D AEC was determined as 10.28mSv. Radiation doses of CT scan with 3D AEC were determined as 2.59mSv at SD=160 and 3.76mSv at SD=120.

This phantom study shows 3D automatic exposure control makes it possible to optimize radiation dose for detection of various sized focal GGOs and partly solid nodules at 64-detector row CT examination.

3D automatic exposure control can reduce 75 % radiation dose for screening, and almost 63 % radiation dose for assessment of GGOs and partly solid nodule at chest 64-detector row CT examination.

Matsumoto, K, Ohno, Y, Koyama, H, Kono, A, Onishi, Y, Takenaka, D, Matsumoto, S, Nogami, M, Sugimura, K, et al, , 64-Detector Row Chest CT Examination with 3D Automatic Exposure Control: Dose Optimization for Detection of Focal Ground Glass Opacities and Partly Solid Nodules.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6015131.html