Locating stored iron in the liver through attenuation measurement in NSECT

Neutron stimulated emission computed tomography (NSECT) is a quantitative spectroscopic technique to detect element concentrations in the body. In previous work, we have demonstrated the ability to detect non-uniform distributions of iron overload in liver (in hemochromatosis) with a sensitivity of approximately 5mg/g. The diagnosis of hemochromatosis is performed by detecting characteristic gamma photons emitted by iron nuclei after they undergo inelastic scatter with incident neutrons. The efficiency of detection of the gamma photons is a combination of the attenuation of neutrons passing through the body and the attenuation of gamma photons before reaching the detectors. With non-uniform iron distributions, therefore, the resulting total attenuation depends on the position of the iron store within the body with respect to the neutron beam and the gamma detectors. We are developing an attenuation correction technique which takes into consideration the position of the iron-store in the liver to compute a correction factor based on a combination of neutron and gamma attenuation. In this work we present results from a Monte-Carlo simulation study exploring the effect of the location of the iron-store within the liver. The NSECT scanning geometry used for data collection was simulated in GEANT4. A lesion of iron was placed at different locations within the liver and scanned to obtain an estimate of the detected signal. An estimate of the unattenuated signal was obtained and used to determine the total attenuation in the liver tissue. The attenuation profile was obtained for each position of the lesion and compared against a theoretical value. The results were found to be in agreement with each other, indicating that a theoretically calculated attenuation profile can be accurately used to create attenuation maps and hence locate iron-stores in the liver using NSECT.