Measurement and modeling of x-ray scatter using lead discs in digital fluoroscopy

The lead disc method is a commonly used technique to measure scatter and glare in digital x-ray imaging1,2,3,4, however it is well known that the measurements are dependent upon the size of the disc. A common procedure is to take a series of measurements for a range of disc sizes and to extrapolate them to zero disc size, however the exact technique is not uniform of how this is done. Some use disc radius/diameter as the independent variable with extrapolation, some use non-linear extrapolation, while others use disc area and either linear or non-linear extrapolation. This paper presents a simple geometric model of x-ray scatter based on the ray tracing to calculate an estimate of scatter in the presence of lead discs. Under the experimental conditions used, the model predicted a non-linear relationship with both disc radius and area. A Toshiba mobile surgical x-ray apparatus, model SXT - 6 - 11, was used to measure scatter and glare with different field sizes for a range of disc diameters from 0.17 cm to 12 cm, for 16 cm of lucite. The model was found to be within 2 percent of measured estimates in the case of the 12 cm diameter field of view (FOV) for disc sizes greater than1cm, and greater than 3 cm for the case of the 5 cm FOV.