We outline new approaches to ultrasound (US) probe calibration and US image segmentation that we have developed for computationally guided minimally invasive interventions. Computational US guidance generally requires tracking of the ultrasound images relative to a surgical tool such as a needle or tissue ablator. This in turn necessitates a calibration process. We present a calibration method that is accurate, easy to perform, and supports calibration quality control during use. Treatment planning and monitoring often involves segmentation of anatomical details and structures in the US images. We present new model-based methods for segmenting anatomic structures using tissue stiffness properties calculated from displacement and strain images. We present preliminary results of these methods in phantom and ex-vivo animal experiments.