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.