Tatsuya Umezawa RT, Presenter: Nothing to Disclose

Yun Shen PhD, Abstract Co-Author: Employee, General Electric Company

Fumiko Kimura MD, Abstract Co-Author: Nothing to Disclose

Tomonari Asano RT, Abstract Co-Author: Nothing to Disclose

Chisa Saitoh RT, Abstract Co-Author: Nothing to Disclose

Prospectively gated axial cardiac scanning (AS) is a new method for coronary CT angiography (CCTA) that reduces radiation dose. Additional exposure time to the temporal window (padding time [PT]) enables acquisition of multiple cardiac phases but increases radiation dose. The purpose of this paper is to compared image quality from axial scanning (AS) with different PT and helical scanning (HS) and to compared radiation dose among HS, AS with long PT and with short PT.  

The constant pulsating model of 60, 65, 70 and 80 heartbeat was used on the 64-MDCT (LightSpeed VCT XT, GE Healthcare) with AS scan mode (padding time: 0ms) and HS scan mode for blurring artifact evaluation; the constant/variation model (1, 5 and 10 bpm variation) of 38, 49 and 57 bpm were used on the AS scan mode (padding time: 0, 50, 100 and 200ms) and HS scan mode for banding artifact evaluation. About image quality (IQ) evaluation, Banding Artifact (BA) or Blurring Artifact were scored from 1 (not diagnostic) to 5 (no Artifact) in VR images or/and MPR image. We compared radiation doses among the different AS and HS modes using CTDIvol

The median score for Blurring Artifact was over 4.0 in HS and in AS when heartbeat <=65bpm; and the score was 4.0 in HS with multi sector reconstruction (high temporal resolution) at 70bpm and 80bpm. The median score for Banding Artifact was over 3.0 in AS with 50 ms padding time at 38, 49 and 57 bpm when heartbeat variation < 10bpm. DOSE of HS with ECG mA modulation (55-95%) will reduce 22%, and DOSE of AS with 50ms padding time will reduce 90% to compare normal AS mode without ECG mA modulation.

Axial scanning reduces radiation dose and allows diagnostic imaging in most heartbeat and optimal (minimum) padding time (50ms) keep DOSE reduction factor of AS. AS with 50-msec PT is considered adequate for CCTA in patients with mean HR around 60 and with less than 5 bpm HR instability.

Prospectively gated axial scanning with 50-ms padding time for coronary CT angiography provides adequate diagnostic image quality and markedly reduces radiation dose.

Umezawa, T, Shen, Y, Kimura, F, Asano, T, Saitoh, C, The Evaluation of Image Quality and Padding Time on the Coronary CT Angiography Using Prospectively Gated Axial Cardiac Scans: Pulsating Cardiac Phantom Study.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6020395.html