Elimination of multiple scattering noise in compton scattering imaging

Compton scattering imaging can demonstrate the electron density of a given object which could be important for medical diagnosis. However, clinical application of the technique has not yet been developed, because a clear image can not be obtained for several reasons. The image is seriously contaminated by multiple scattering which is inevitable with Compton scattering. The electron density in a small region of the object is not obtained correctly unless multiple scattering is handled carefully. In the present paper, methods to eliminate multiple scattering in Compton scattering imaging system are discussed. A general purpose Monte Carlo code called EGS4 was used to simulate the processes of an incident photon interacting with a substance inside an object. Simulations were performed using a water sphere phantom with a radius of 10 cm irradiated by a beam of monochromatic X-rays at 100 keV. Scattered photons emitted from the phantom were observed and the ratio of the amount of single Compton scattering from a focal point to that of multiple scattering was calculated. To improve the image quality, elimination of multiple scattering in Compton scattering is indispensable. To this end, θ and Φ-collimators and an energy window were proposed and their effects were estimated quantitatively by simulations. It was shown that by introducing of the proposed methods in the imaging system, the ratio of the Compton scattering signal to the multiple scattering noise, S/N, could be improved from 0.022 to 40. Quantitative results derived from the simulations may be useful for the design of a practical Compton scattering imaging system. (author)