Alignment of Viewing-Angle Dependent Ultrasound Images

We address the problem of the viewing-angle dependency of ultrasound images for registration. The reflected signal from large scale tissue boundaries is dependent on the incident angle of the beam. This applies an implicit weighting on the ultrasound image, dependent on the viewing-angle, which negatively affects the registration process, especially when utilizing curved linear transducers. We show that a simple reweighting of the images, considering a common physical model for ultrasound imaging, is not feasible. We therefore introduce a new matching function, separating reflectivity and scattering regions, which are the results of two different types of physical interactions of the ultrasound beam with the tissue. We use the local phase for identifying regions of reflectivity, and consider it as one part of our matching function, combining feature- and intensity-based aspects. First experiments provide good results for this novel registration approach.