Image quality assessment tools for optimization of CT images

Purpose: Producing high quality images in CT is important for image interpretation and to obtain the maximum diagnostic information from the images. Higher quality CT images normally implies higher radiation dose to the patient. Hence there is a need for knowledge of image quality assessment tools in CT in order to recognise images of adequate diagnostic efficacy. Discussion: Image quality can be defined in terms of physical, psychophysical and observer performance tests. Examples of physical measures are: uniformity, linearity and noise; while psychophysical tests include spatial resolution and contrast resolution. These are discussed with their relevance to CT image quality optimization.Observer performance measures such as: visual grading analysis (VGA) and receiver operator characteristic (ROC) analysis are reviewed, highlighting their relevance to the analysis of image quality in CT. Conclusion: Measurements of objective image quality parameters should be conducted on a regular basis as part of a quality assurance program in order to guarantee the performance of the CT unit throughout its whole period of use.The use of image criteria in the evaluation of image quality in CT was recommended by the European Commission in their document EUR 16262. However, the weighting of these criteria should be adjusted depending on their importance to the anatomical area and pathology being investigated. VGA and ROC analysis are scientific methods of analysing image quality and can be used to assess the effectiveness of optimizing CT image quality.This paper has identified the situations when each should be used and why.