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Quantification of Fluoroscopic Imaging System Contrast by Using Video Waveform Monitoring¹

¹ From the Department of Diagnostic Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905. Presented as a scientific exhibit at the 1999 RSNA scientific assembly. Received April 27, 2000; revision requested July 21 and received August 21; accepted August 22. Address correspondence to J.P.T. (e-mail: taubel.jerome@mayo.edu).

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 fluoroscopically imaged under automatic brightness control. A video waveform monitor or oscilloscope is then used to quantify those video signal voltage levels as a contrast index value, which is defined as the maximum range of the video signal voltage levels of the gray-scale steps. The method is repeatable and allows quantification of the contrast of the imaging system. It can also be used to optimize video parameters, provide comparative data for quality control monitoring, and characterize overall contrast differences between systems. Experience with this method suggests that there is excellent correlation between the clinical perception of image contrast and the contrast index, with contrast index changes of approximately 15% being seen clinically.

Index Terms: Fluoroscopy • Images, enhancement • Phantoms • Video systems