Detection of iron overload with the ORNL Spallation Neutron Source: An MCNPX simulation study

In previous work we have demonstrated the use of neutrons to detect iron overload in the liver. We are developing a non-invasive technique to measure liver iron concentration in the human body through neutron inelastic scatter spectroscopy. The measurement is performed using an incident neutron beam that scatters inelastically with iron nuclei in the liver, causing characteristic gamma emission that is used to quantify the tissue iron content. Due to its high neutron flux, the Spallation Neutron Source (SNS) at ORNL presents an attractive option for initial development and optimization of the technique. In this manuscript we describe a simulation study to evaluate feasibility of the SNS beam for iron overload detection in the liver. An MCNPX simulation was developed to model the parameters of the SNS beam and scan a liver phantom with tissue iron content varying from 2 mg/g (mild iron overloaded) to 10 mg/g (severe iron overload). A torso phantom filled with water was placed around the liver and used to simulate scattering effects of the human torso. The emitted gamma spectrum was acquired with a simulated ring detector. Background subtraction was performed by substituting the liver with a water phantom. Background corrected spectra were analyzed to identify gamma lines corresponding to iron in the liver tissue. Statistically significant differences with p ≪ 0.05 were identified for the 56Fe gamma line at 847 keV. Counts in the gamma line were found to be higher in the 10 mg/g sample by a factor of 4.72, differing by less than 6% from the expected value of 5. These results demonstrate the feasibility of the SNS beam to determine iron content in liver tissue.