3-D isotropic imaging of environmental sources using a compact gamma camera

In this work, the three-dimensional (3-D) position information of a radiation source is determined by a compact gamma ray imaging system. Two-dimensional (2-D) gamma ray images were obtained from different positions by the gamma camera and the third dimension, the distance between the detector and the radiation source, was calculated using triangulation. Additionally, a CCD camera is attached to the top of the gamma camera and provides associated 2-D visual information. The inferred distances from the center of the two measurement points and a radiation source had less than a 5% error for sources within 3 m and ±45° FOV. From the measured distances and camera intrinsic efficiencies ε(θ,φ) from MCNP simulations, the activity of the source was normally determined within 80% of the true value depending upon source position. The parallax between the two visual images was corrected using the inferred distance between the detector and the radiation source. The radiation image from gamma camera and the visual image from CCD camera are superimposed into one combined image using a maximum-likelihood (ML) algorithm to make the image alignment more precise. Energy dependent response functions were found to be better than a fixed energy response function for ML image processing.