Detection of Iron Overload through Neutron Stimulated Emission Computed Tomography: A Sensitivity Analysis Study

Neutron stimulated emission computed tomography (NSECT) is being developed as a non-invasive technique to diagnose iron overload in the liver. It uses inelastic scatter interactions between fast neutrons and iron nuclei to quantify localized distributions of iron within the liver. Preliminary studies have demonstrated the feasibility of iron overload detection through NSECT using a Monte-Carlo simulation model in GEANT4. The work described here uses the GEANT4 simulation model to analyze iron-overload detection sensitivity in NSECT. A simulation of a clinical NSECT system was designed in GEANT4. Simulated models were created for human liver phantoms with concentrations of iron varying from 0.5 mg/g to 20 mg/g (wet). Each liver phantom was scanned with 100 million neutron events to generate gamma spectra showing gamma-lines corresponding to iron in the liver. A background spectrum was obtained using a water phantom of equal mass as the liver phantom and was subtracted from each liver spectrum. The height of the gamma line at 847 keV (corresponding to Fe) was used as a measure of the detected iron concentration in each background-corrected spectrum. The variation in detected gamma counts was analyzed and plotted as a function of the liver iron concentration to quantify measurement error. Analysis of the differences between the measured and expected value of iron concentration indicate that NSECT sensitivity for detection of iron in liver tissue may lie in the range of 0.5 mg/g – 1 mg/g, which represents a clinically significant range for iron overload detection in humans.