A computerized method for model-less segmentation and registration of ultrasound (US) with computed tomography (CT) images of an organ with a fluid filled chamber. The method is based on correlating between the US image(s) and the CT image(s) by processing the US image(s) by iteratively expanding the CT image segment so that the expanded CT image segment is correlated with the visual boundaries of the US image segment; transforming the CT image(s) according to an estimated US transducer position and estimated US beam direction related to the US image(s) so that at least one of shape and volume of the organ in the CT image is adapted with at least one of shape and volume of the organ of the US image, to form a CT image representation which is correlated with US image(s).