An edge spread technique for measurement of the scatter-to-primary ratio in mammography

An experimental measurement technique that directly measures the magnitude and spatial distribution of scatter in relation to primary radiation is pre sented in this work. The technique involves the acquisition of magnified ed ge spread function (ESF) images with and without scattering material presen t. The ESFs are normalized and subtracted to yield scatter-to-primary ratio s (SPRs), along with the spatial distributions of scatter and primary radia tion. Mammography is used as the modality to demonstrate the ESF method, wh ich is applicable to all radiographic environments. Sets of three images we re acquired with a modified clinical mammography system employing a flat pa nel detector for 2, 4, 6, and 8 cm thick breast tissue equivalent material phantoms composed of 0%, 43%, and 100% glandular tissue at four different k V settings. Beam stop measurements of scatter were used to validate the ESF methodology. There was good agreement of the mean SPRs between the beam st op and ESF methods. There was good precision in the ESF-determined SPRs wit h a coefficient of variation on the order of 5%. SPRs ranged from 0.2 to 2. 0 and were effectively independent of energy for clinically realistic kVps. The measured SPRs for 2, 4, and 6 cm 0% glandular phantoms imaged at 28 kV were 0.21+/-0.01, 0.39+/-0.01, and 0.57+/-0.02, respectively. The measured SPRs for 2, 4, and 6 cm 43% glandular phantoms imaged at 28 kV were 0.20+/ -0.01, 0.35+/-0.02, and 0.53+/-0.02, respectively. The measured SPRs for 2, 4, and 6 cm 100% glandular phantoms imaged at 28 kV were 0.22+/-0.02, 0.42 +/-0.03, and 0.88+/-0.08, respectively. (C) 2000 American Association of Ph ysicists in Medicine.