Quantification of fluoroscopic imaging system contrast by using video waveform monitoring

A noninvasive method was developed for quantifying the overall contrast of fluoroscopic imaging systems within the clinical setting by using a simple phantom and common video test equipment. In this method, an acrylic phantom with four holes filled with varying amounts of air and aluminum is placed on the entrance exposure side of a patient-equivalent acrylic phantom. The air- and aluminum-filled holes provide a stepped gray-scale pattern that is displayed on the examination room viewing monitor when the phantom is fluo roscopically imaged under automatic brightness control. A video waveform mo nitor or oscilloscope is then used to quantify those video signal voltage l evels as a contrast index value, which is defined as the maximum range of t he video signal voltage levels of the gray-scale steps. The method is repea table and allows quantification of the contrast of the imaging system. It c an also be used to optimize video parameters, provide comparative data for quality control monitoring, and characterize overall contrast differences b etween systems. Experience with this method suggests that there is excellen t correlation between the clinical perception of image contrast and the con trast index, with contrast index changes of approximately 15% being seen cl inically.