Abstract
In this study, we used a directional filtering technique to accurately register the ribs on temporal chest radiographs. Rib registration was the primarily technical objective in this work. In order to accurately extract the ribs, we developed a directional edge function that used rotating kernels through a dynamic search technique to extract various contrast of rib edges. A directionally weighted operator (DWO) with a phase-contrast feature is embedded in the kernel design that allows us to separate the upper and lower bounds of structures in the vertical direction. Broken rib edges were reconnected using a reasoning algorithm by analyzing the rib position and curve. The lung and heart boundaries were extracted using an inverted umbrella filter. Control points were designated at turning points and distributed on smooth edge segments on the temporal images. A thin-plate spline technique took the control points and performed the final registration prior to the temporal image subtraction. We found that the normal chest structures (i.e., ribs, heart, and other normal lung structures) were greatly reduced on the subtraction images. In addition, the contrast of cancer spots was significantly increased.