TH-A-141-07: Characterization of X-Ray Source and Detector Geometry for the Compton Backscatter Imaging System for Medical Applications

Abstract

Purpose: Clinical applicability of Compton backscatter imaging (CBI) systems for medical purposes was previously demonstrated using a CBI system optimized for industrial purposes. In order to optimize CBI for medical imaging, two key CBI system parameters were characterized: 1) x‐ray source and 2) detector geometry. This data can be used to help design systems with optimal spatial resolution, subject contrast, and SNR across clinical imaging applications. Methods: Phantoms of different dimensions and compositions, as well as segmented detectors, were simulated using MCNP‐X, a Monte Carlo transport code. With each set of simulations, a different energy between 20 keV and 1.5 MeV was evaluated. To maximize the potential of MCNP‐X, multiple in‐house C++ and MATLAB algorithms were created to extract and evaluate relevant data from the plethora of MCNP‐X generated information. An analytical model of the system was created to verify the Monte Carlo results. Results: The best subject contrast was observed at lower incident energies, between 30 and 40 keV, and also for smaller detectors. The SNR peaked at higher energies, between 65 and 75 keV, and at detector pixels adjacent to the source. As expected, the penetration power of the beam increased with energy. The spatial resolution of the system became worse (larger PSF) as the size of the detector increased. The absorbed doses to the phantom, per starting particle, increased with the energy, but were either equivalent to or lower than doses observed in transmission imaging at energies of interest. Conclusion: As part of the optimization of a medical CBI system, potential for better images was shown. The ability to design optimal medical CBI systems with x‐ray tubes within diagnostic energy ranges and detectors compatible with diagnostic spatial constraints was demonstrated. CBI can provide single‐sided imaging capability with equivalent or lower absorbed dose.