An attenuation correction technique to correct for neutron and gamma attenuation in the reconstructed image of a neutron stimulated emission computed tomography (NSECT) system

Abstract

Neutron spectroscopy is being developed as a tomographic tool to measure trace element concentration in the body at molecular levels. We are developing a neutron stimulated emission computed tomography (NSECT) system using inelastic scattering of neutrons by target nuclei, to identify elements and their concentration in tissue. An incoming neutron scatters inelastically with an atomic nucleus, which emits a gamma photon of specific energy. This energy, which is detected by an energy-sensitive Gamma detector, is characteristic of the scattering nucleus. The neutron beam and gamma photons undergo considerable attenuation while passing through the body, causing a reduction in detected counts leading to inaccurate reconstruction. We describe a technique to correct for this attenuation as follows. The scanning geometry used for data acquisition is simulated. The lengths of attenuating material lying in the path of the neutron beam are calculated. Neutron attenuation is determined along this path, using attenuation coefficients for each element. Gamma attenuation is calculated similarly for the path between the point of gamma origin and the detector. A transmission profile is then determined for each projection, using the product of the neutron and gamma attenuations for every point along the projection. The inverse of the integral of this profile yields a correction factor. The experimental data is multiplied by the correction factors to yield attenuation corrected projections. After correction, the projection data is seen to represent the known elemental distribution more accurately. This correction technique improves the consistency of the projections, and leads to the improved accuracy in reconstructed NSECT images.