In this paper, stereo matching and 3D visualization issues are studied for a linear pushbroom stereo model built for 3D gamma-ray (or x-ray) cargo inspection. A fast and automated stereo matching algorithm based on free-form deformable registration is developed to obtain 3D measurements of the objects under inspection. For facilitate stereo matching, an adaptive window min-max method is used to enhance the contrasts and boundaries of the challenging gammaray images. For fast implementation, a multi-resolution approach is also applied. A user interface is designed for interactive 3D measurements and visualization of the objects in interests. Experimental results are presented for real gamma-ray images of a 3D cargo container and the objects inside. The 3D measurements could add more value to today?s cargo inspection techniques.