Neutron time-of-flight spectroscopy for depth-resolved quantification through NSECT

With advances in detector technology, gamma-ray detectors are now capable of reporting both time of arrival of a photon and its energy. Although the gamma energies detected from the inelastic scattering of neutrons with elemental nuclei in the tissue of interest are being exploited in Neutron Stimulation Emission Computed Tomography (NSECT) to detect different elemental disorders, the timing information is largely ignored. Here we present a technique to utilize the time of arrival of gamma photons at a detector to locate focal liver lesions in diseases such as hemochromatosis and liver cancer. A GEANT4 simulation of 5-MeV neutrons was used to irradiate a liver phantom with multiple lesions with different iron concentrations. The time of arrival of gamma photons from neutron-⁵⁶Fe inelastic scatter was recorded using a 360 degree, 100% efficient detection system and used to locate the lesions in the beam path. The resulting spectra were resolved in nanosecond time bins (corresponding to the expected arrival time of inelastic-scatter gamma photons from the lesion) and clearly demonstrated the ability to localize the focal liver lesions through neutron time-of-flight (TOF) spectroscopy. The preliminary results showed errors of only 10-20% in lesion position, demonstrating the strong potential of the technique.