X-ray scatter imaging is a novel tool under development which obtains diagnostic information from the photons scattered out of the patient. We have formulated a semianalytic model to quantify the information obtainable. Our predictions confirm the usefulness of scattered x rays for various imaging tasks, even when polyenergetic beams are used. In this work, we experimentally validate our 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 × 10-4 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, we obtain C = 0.28 ± 0.1, and SNR / (Kair c)1/2 = (53 ± 20) (mJ/kg)-1/2, where Kair c = air collision kerma. The corresponding prediction values are C = 0.38, and SNR / (Kair c)1/2 = 68 (mJ/kg)-1/2.

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22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society
Department of Physics

Leclair, R.J., & Johns, P. (2000). X-ray forward-scatter imaging: Experimental validation of model. Presented at the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society.