The Relationship between Subjective and Objective Parameters in CT Phantom Image Evaluation

OBJECTIVE: To evaluate whether there is a relationship between subjective parameters determined by a reviewer (spatial resolution, low contrast resolution, and artifacts) and objective parameters (the CT number of water, noise, and image uniformity) in CT phantom image evaluations. MATERIALS AND METHODS: We reviewed the CT results of phantom image evaluations conducted by Korean Institute for Accreditation of Medical Image (KIAMI) from May 2007 to June 2007. We compared the objective parameters against the pass or fail groups for the subjective parameters. We also evaluated whether there is a relationship between the artifact types and the other subjective parameters. RESULTS: The mean noise value was significantly higher in the fail groups for the subjective parameters compared to the pass groups (p = 0.006). Specifically, noise and low contrast resolution were found to have a statistically significant positive correlation (r = 0.183, p < 0.001). In the fail group for low contrast resolution, the failure due to artifacts was significantly higher than the pass group (p < 0.001). In contrast, no statistically significant differences were found for the mean CT number of water, noise, or image uniformity based on the types of artifacts. CONCLUSION: Subjective CT image parameters evaluated by a reviewer correlate with objectively measured parameters, especially noise. Therefore, a stricter noise standard might be able to improve the subjective parameters results, such as low contrast resolution.

Review of Failed CT Phantom Image Evaluations in 2005 and 2006 by the CT Accreditation Program of the Korean Institute for Accreditation of Medical Image

OBJECTIVE: The CT accreditation program was established in 2004 by the Korean Institute for Accreditation of Medical Image (KIAMI) to confirm that there was proper quality assurance of computed tomography (CT) images. We reviewed all the failed CT phantom image evaluations performed in 2005 and 2006. MATERIALS AND METHODS: We analyzed 604 failed CT phantom image evaluations according to the type of evaluation, the size of the medical institution, the parameters of the phantom image testing and the manufacturing date of the CT scanners. RESULTS: The failure rates were 10.5% and 21.6% in 2005 and 2006, respectively. Spatial resolution was the most frequently failed parameter for the CT phantom image evaluations in both years (50.5% and 49%, respectively). The proportion of cases with artifacts increased in 2006 (from 4.5% to 37.8%). The failed cases in terms of image uniformity and the CT number of water decreased in 2006. The failure rate in general hospitals was lower than at other sites. In 2006, the proportion of CT scanners manufactured before 1995 decreased (from 12.9% to 9.3%). CONCLUSION: The continued progress in the CT accreditation program may achieve improved image quality and thereby improve the national health of Korea.