Abstract:
Since 2008, we have been developing a new method for the quantification of naturally occurring elements in the human body. The technique, called gamma-stimulated spectroscopy (GSS), uses high-energy, tuned gamma-ray beams to stimulate selected energy levels in specific stable isotopes in the body through nuclear resonance fluorescence (NRF). Such selective excitation can be used to detect a variety of human disorders that exhibit differences in element concentration between diseased and healthy tissue. In previous work, we have developed a prototype GSS device using the free-electron-laser (FEL) source at Duke University and demonstrated the selective excitation of iron in water. Here we describe the development of a GEANT4 simulation of the GSS system including the modeling of the NRF process. A monochromatic, collimated gamma source, virtual gamma-ray detectors, and an aqueous iron-copper phantom were simulated in GEANT4. The NRF process was modeled by creating a new NRF process class that calculated the interaction cross-section and the nuclear deexcitation data. The simulation was tested at two source energies (846.7 keV and 3448.41 keV) corresponding to excitable energy levels in natural iron. The resulting spectra showed accurate gamma energy response and emission patterns and exhibited excellent correlation between the simulated and the measured iron concentration. Following benchmarking against experimental data, the simulation will provide an accurate tool for modeling NRF processes in GEANT4 and will be used to guide the development of the clinical GSS system. © 2011 IEEE.