Evaluation of low contrast resolution using contrast-to-noise ratio in CT

We evaluated low contrast resolution in CT images from various apparatuses by using the second recommendation of the x-ray CT commission. This method is based on visual assessment by an observer using a CT performance evaluation phantom. We evaluated CT images with low contrast resolution using the contrast-to-noise ratio (CNR) in terms of quantity of data, region of interest (ROI) size, and the relation between the second recommendation and CNR, and compared various kinds of machines according to CNR. We found that this method had certain factors that influenced the precision of measurement. However, there was a correlation between CNR and visual evaluation, and we were able to evaluate low contrast resolution in each apparatus. This method was considered a useful step, because low contrast resolution could be easily evaluated. (author)