Patric Kroepil MD, Presenter: Nothing to Disclose

Hans Dieter Nagel, Abstract Co-Author: Consultant, Koninklijke Philips Electronics NV

Philipp Heusch MD, Abstract Co-Author: Nothing to Disclose

Gael Pentang MSc, Abstract Co-Author: Nothing to Disclose

Gerald Antoch MD, Abstract Co-Author: Nothing to Disclose

Mathias Cohnen MD, Abstract Co-Author: Nothing to Disclose

Iterative reconstruction (IR) algorithms offer potential radiation dose reduction while maintaining image quality. This study was done to investigate the effects of an advanced 4th generation IR technique on subjective and objective image quality (IQ) parameters in low-dose cardiac CTA.

Three datasets of coronary CTA were acquired using prospectively triggered “step and shoot” mode on a 256-slice CT scanner (Brilliance iCT, Philips, Netherlands) with optimized exposure settings. Each dataset was processed 16 times resulting in n=48 image stacks. Data were processed on a prototype IR system using filtered back projection (FBP) and 4 different levels of an advanced IR technique (IDose4, Philips), providing incremental rate of IR (levels 2, 4, 6 and 7) involving both raw and image data space. Image noise was measured in the contrast-enhanced lumen of the aorta. Contrast-to-noise and signal-to-noise ratios (CNR and SNR) were compared at 9 specific coronary locations in all image stacks. Subjective IQ was rated on a 3-point-scale. “Natural” image appearance and artifacts due to image noise were the main criteria of subjective IQ.  

Mean effective dose of cardiac CTA was 1.38 mSv. Mean CNR and SNR were significantly improved with IR when compared to FBP and with every increasing level of IR (range CNR: 9.4 – 19.1; range SNR: 7.2 – 14.7; p<0.0001) with best objective IQ at highest level (iDose level 7) of IR. Subjective image quality, however, was rated best at medium level of IR (iDose level 4) with significant improvement when compared to FBP and more natural appearance of the images when compared to higher levels of IR.

Objective image quality parameters (CNR, SNR) improve with increasing level of IR in cardiac CTA. Subjective IQ, however, reaches best results at medium levels of IR due to combination of minimal artifacts and “natural” image appearance.

Medium level of iterative reconstruction leads to significant improvement of image quality in low dose cardiac CTA suggesting further evaluation in clinical routine.

Kroepil, P, Nagel, H, Heusch, P, Pentang, G, Antoch, G, Cohnen, M, Image Quality in Low-Dose Cardiac CTA at Different Levels of 4th Generation Iterative Reconstruction.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034425.html