Assessing fluoroscopic contrast resolution: a practical and quantitative test tool

Fluoroscopic contrast resolution is commonly determined at a specified kVp by imaging a test object comprised of targets where contrast decreases gradually and sequentially. Threshold contrast or contrast resolution is the contrast of the lowest contrast target that can be perceived. This approach suffers from two problems. First, test object contrast is specified at a x-ray tube voltage that is not always obtainable in practice. Second, the small change in contrast between adjacent targets contributes to observer variability making consistent and reproducible contrast threshold determinations difficult. Described is a contrast resolution test tool that eliminates or reduces these problems. The novel target arrangement allows one to quickly and easily specify the contrast resolution of a fluoroscopic imaging chain to a precision approximately equal to 0.5%. Tables of target contrast versus x-ray tube potential are developed that permit one to employ the test object for contrast resolution determination over the normal range of tube potentials encountered on clinical units.