Rigid Registration of Freehand 3D Ultrasound and CT-Scan Kidney Images
  This paper presents a method to register a preoperative CT volume to a sparse set of intraoperative US slices. In the context of percutaneous renal puncture, the aim is to transfer a planning information to an intraoperative coordinate system. The spatial position of the US slices is measured by localizing a calibrated probe. Our method consists in optimizing a rigid 6 degree of freedom (DOF) transform by evaluating at each step the similarity between the set of US images and the CT volume. The images have been preprocessed in order to increase the relationship between CT and US pixels. Correlation Ratio turned out to be the most accurate and appropriate similarity measure to be used in a Powell-Brent minimization scheme. Results are compared to a standard rigid point-to-point registration involving segmentation, and discussed. 
Antoine Leroy (TIMC - IMAG), Pierre Mozer (TIMC - IMAG), Yohan Payan   (TIMC - IMAG), Jocelyne Troccaz (TIMC - IMAG)