X-ray forward-scatter imaging: experimental validation of model

X-ray scatter imaging is a novel tool under development which obtains diagnostic information from the photons scattered out of the patient. The authors have formulated a semianalytic model to quantify the information obtainable. Their predictions confirm the usefulness of scattered X-rays for various imaging tasks, even when polyenergetic beams are used. In this work, the authors experimentally validate their forward-scatter imaging model using 80 kV beams. The scatter signatures from plastic targets-polymethyl methacrylate (lucite), polycarbonate, polystyrene, polyethylene and nylon-were measured for target thicknesses d=0.5, 1, 2, 3, and 4 cm. The scattered field was sampled in 1° increments from 2° to 12° with a high-purity germanium detector (dΩ=1.61× 1°^-4 sr). The beam diameter at the front surface of the targets is ≅1.51 mm. The approximative dependence of scattering cross-section on angle was in good agreement with predictions. Comparisons of contrast (C) and signal-to-noise ratio (SNR) between experiment and theory were made by scaling and summing the detected numbers of counts so as to approximate an annular detector extending from 2° to 12° from the primary beam. For the task of imaging 2 cm thick lucite versus polycarbonate targets placed at the center of a 15-cm-diam spherical water phantom, the authors obtain C=0.28±0.1, and SNR/(K_air^c)^1/2 (53±20) (mJ/kg)^-1/2, where K_air^c=air collision kerma. The corresponding prediction values are C=0.38, and SNR/ (K_air^c)^1/2 n=68 (mJ/kg)^-1/2