Detection of collimation field in digital radiography using Frobenius norm of Hessian

Collimators are used to focus the radiation beam to a certain anatomical region in order to reduce the patient dose. Redundant shielded region should be removed before diagnostic image processing, as it can impair image enhancement algorithms. Manual selection of irradiated image region is impractical and should be automated. In this paper we propose a Frobenius norm of Hessian based algorithm for automatic collimation field detection. Algorithm validation was performed through, among others, maximum absolute difference between manually annotated and automatically determined collimation region. Our algorithm was tested on a database that contains 680 images and the percentage of correctly annotated regions is 96.03 %.