Verena Obmann MD, Presenter: Nothing to Disclose

Alexander Stork, Abstract Co-Author: Nothing to Disclose

Johannes T. Heverhagen MD, PhD, Abstract Co-Author: Speaker, Bracco Group

Philipp Georg Christian Begemann MD, Abstract Co-Author: Nothing to Disclose

Thorsten Klink MD, Abstract Co-Author: Nothing to Disclose

To evaluate image quality, resolution, and radiation dose of iterative reconstruction (IR) in comparison to filtered back projection (FBP) in a combined phantom and patient study.

The phantom (Catphan®) was helically and axially imaged with a multi-slice CT scanner (Philips Brilliance iCT) using a collimation of 2x128x0.625mm. Varying tube voltages (140, 120, 100, 80 kV) and currents (200, 150, 100, 30 mAs) were combined. 198 phantom data sets were generated applying FBP and IR with increasing iterations (Level 1-7), and reconstructed using a soft and a sharp kernel. Further, 25 chest (100 kV) and abdomen (120 kV) CT scans with small overlap at the basal thorax, were reconstructed with IR (Level 5) and FBP. Two independent observers evaluated image quality, resolution, and radiation doses of both phantom and patient scans. Statistical analysis included Kappa-statistics Wilcoxon-Matched-Pairs test to test for significance.

In phantom scans, image noise was significantly improved using IR by 52.2% (p<0.05) in comparison to FBP, independent from material, scan mode, tube voltage, tube current, and kernel. IR did not negatively affect high-contrast and low-contrast resolution. In low-dose acquisitions (CTDIvol, 5mGy), IR resulted in significant higher low-contrast resolution (detectable object size, 4.5mm vs. 8.4mm; κ=0.85; p<0.01), but low-contrast object detectability decreased. At identical image quality levels of IR and FBP, CTDIvol could be reduced by 26-50% using IR. In patients mean tube current was 124.7 ±57.7 mAs for IR/100kV acquisitions and at 262.1 ±106.7 for FBP/120kV acquisitions (p=0.0004) while image quality was good to excellent applying IR as well as FBP.  

IR improves image quality of lower-dose acquisitions to comparable levels of higher-dose acquisitions reconstructed with FBP. IR does not negatively affect high- and low-contrast resolution, potentially improves low-contrast resolution in low-dose scans. Thus, IR rendered significant reduction of CTDIvol (>50%) in the patient study.

Iterative reconstruction algorithms have been shown valuable for saving CT radiation dose. Implementation in clinical routine protocols shows possible reduction of radiation risks of patients.

Obmann, V, Stork, A, Heverhagen, J, Begemann, P, Klink, T, Saving CT Radiation Dose with Iterative Reconstruction Algorithms: The Influence of Scan and Reconstruction Parameters on Image Quality, Resolution, and CTDIvol  .  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14016924.html