A mathematical model of radiation field edge localization.

A mathematical model of the average edge slope across the radiation field border in a portal image was investigated in order to improve the precision of edge localization in a previously reported algorithm for automatic extraction of the radiation field from double- and single-exposure portals. The model involves a global rather than a local approach to edge localization, and employs a hyperbolic function with four parameters to characterize the behavior of the radiation field penumbra. The location of the radiation field edge is determined from one of these parameters. This model was tested on a group of portal images acquired with different conditions in our clinic. Evaluation results of this model and improvements in the performance of our portal image segmentation algorithm will be presented.