Robert D. McGregor MD, Presenter: Advisory Board, Lantheus Medical Imaging, Inc

Anita Lloyd, Abstract Co-Author: Nothing to Disclose

Robert Leslie Lloyd MD, Abstract Co-Author: Nothing to Disclose

Iterative reconstruction algorithms have the potential to reduce dose. The purpose of this study was to retrospectively compare radiation dose, noise, and diagnostic acceptability in the same patients with reduced dose scans reconstructed with Iterative Reconstruction in Image Space (IRIS) and routine dose scans reconstructed with filtered back projection (FBP).

Fifty eight patients consecutive patients were identified who had undergone Abdominal CT with a routine dose (120 kVp ref mAs 230) and reduced dose (120 kVp ref mAs 120). All scans were acquired on the same scanner (Siemens Definition AS+) with 4D dose modulation. The routine dose was reconstructed with FBP and the reduced dose with IRIS. CTDIvol and Dose Length Product (DLP) were recorded for all patients. Two radiologists independently reviewed the anonymized scans for diagnostic acceptability, artefacts, noise and sharpness. Objective noise was measured by standard deviation of a Region of Interest in the right lobe of the liver.

The fifty eight patients had a mean age of 62.8 years (62% female). The time between scans was 3.4 (2.3, 7.9) months. (median, interquartile range) The mean CTDIvol, DLP, and effective dose for the routine dose with FBP were 18.0 mGy, 856 mGycm, and 12.8mSV respectively compared to 9.4 mGy, 440 mGycm, and 6.6 mSv for the reduced dose IRIS scans. The dose reductions for the IRIS reconstruction in comparison to the FBP method were 45.6% for CTDIvol (p <.001) and 46.6 % for DLP (p<.001). The objective noise was less for IRIS (10.0) as compared to FBP (11.0) p=.0004. There was no significant difference in diagnostic acceptability between the routine dose with FBP and reduced dose with IRIS for Radiologist 1 (p=0.14) or Radiologist 2 (p=0.30). 

Compared to filtered back projection low dose iterative reconstruction in image space allows a significant reduction in dose without loss of diagnostic acceptability in abdominal CT scans.

Introduction of iterative reconstruction will allow reduction of radiation dose without reducing diagnostic acceptability.

McGregor, R, Lloyd, A, Lloyd, R, Abdominal CT: Comparison of Reduced Dose Iterative Reconstruction in Image Space with Routine Dose Filtered Back Projection in 58 Patients.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12037306.html