SCATTER COMPENSATION IN DIGITAL CHEST RADIOGRAPHY USING THE POSTERIORBEAM STOP TECHNIQUE

A new scatter compensation technique for computed radiography based on posterior beam stop (PBS) sampled scatter measurements and the bicubi c spline interpolation technique was proposed. Using only a single exp osure, both the clinical image and an array of scatter measurements, w hich were interpolated into a smooth scatter-only image, were simultan eously acquired. The scatter was subtracted from the clinical image to generate the primary-only image. To gauge the accuracy of scatter est imation, both quantitative and interpolation errors were evaluated. Th e PBS measurements were compared against the standard beam stop method at 16 locations in an anatomical phantom, resulting in quantitative e rrors of 2.7% relative to the scatter or 6.8% relative to the primary. Also measured were the interpolation error over 64 interpolation samp le locations and 64 midpoint sample locations in the anatomical phanto m. The combined interpolation error was 1.9% relative to the scatter o r 8.0% relative to the primary. At the interpolation sample locations, the errors were identical between the phantom radiograph and digital portable chest radiographs from five patients. By summing the quantita tive and interpolation errors in quadrature, the overall error of the PBS SISTER (scatter interpolation-subtraction technique for radiograph y) method was 3.3% relative to the scatter or 10% relative to the prim ary, which was adequate for dual-energy imaging purposes (less than 10 % error relative to the scatter or 20% relative to the primary). The c hange of image contrast, noise, and signal-to-noise ratio (SNR) at six locations in the anatomical phantom were quantitatively analyzed. Con trast and noise were equally enhanced in all anatomical regions, resul ting in approximately the same SNR before and after compensation. The average contrast over all six locations increased 2.8 times, average n oise increased 4.9 times, and average SNR barely decreased to 99%. Thi s technique therefore provided accurate scatter compensation by custom measurements of each patient, preserved the SNR, required only one ex posure with no dose increase, and performed at low computational cost.