1. A computerized method for model-less segmentation and registration of ultrasound (US) with computed tomography (CT) images of a portion of a patient, comprising: obtaining at least one US image and at east one CT image of east a portion of an organ; identifying a CT image segment of the at least one CT image that depicts at least one fluid filled chamber of said organ; identifying an US image segment of the fluid filled chamber in the at least one US image; correlating between the at least one US image and the at least one CT image by processing the at least one US image 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 at least one CT image according to an estimated US transducer position and estimated US beam direction related to the at least one US image 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 the at least one US image; registering the correlated US image and the related CT image to form a registered image; and displaying the registered image; wherein identifying the CT image segment of the at least one CT image comprises model-less segmenting the CT image into the CT segments, wherein model-less segmenting the CT image comprises: coarsely segmenting the CT image using a Hounsfield value threshold so that contrast enhanced regions that are connected and include a mitral annulus marking are identified; extracting from the coarsely segmented image a left atrium (LA) and a left ventricle (LV) using apex and atrium markings; and subtracting the LA-LV segment from the coarse segment and detecting the connected component closest to an aortic valve marking to extract the aorta.