Research on gamma image reconstruction method for estimating radiation source distance using the dichotomy method.

To enhance the precision of locating unidentified radiation sources with a coded aperture camera, this study introduces a refined Maximum Likelihood Expectation Maximization (MLEM) algorithm. This algorithm incorporates the dichotomy method to estimate the distance to the radiation source, followed by a superimposition of the calculated system response matrix to predict the source's position within the imaging area. Initially, a system response matrix table is created, listing potential distances from the radiation source to the camera in ascending order. The process involves assessing the mean square error (MSE) and the full width at half maximum (FWHM) of the current image to determine if the hypothesized distance surpasses the actual distance. Following this, a binary search is executed on the matrix table to ascertain the closest lower and upper bounds to the true distance. Subsequently, the system matrices for these boundary distances are aggregated to derive an approximate response matrix. This matrix is then employed in the MLEM algorithm to estimate the radiation source's position. Experimental outcomes indicate that the enhanced algorithm provides superior localization accuracy and a definable distance range (nearest lower and upper bounds) between the radiation source and the camera compared to the conventional MLEM algorithm, thus better facilitating the analysis of hotspots.The proposed method achieves satisfactory reconstruction for a single radiation source and for multiple sources located at the same detector distance; however, its performance in reconstructing multiple sources at differing distances remains to be improved.