1. A system for imaging a target in a patient's body, the system comprising: a catheter comprising a position sensor, an ultrasonic imaging sensor and at least one electrode, the position sensor transmitting electrical signals indicative of positional information of a portion of the catheter adapted to be positioned in the patient's body, the positional information being location and orientation coordinates of the position sensor at the portion of the catheter, and the ultrasonic imaging sensor transmitting ultrasonic energy at the target in the patient's body, receiving ultrasonic echoes reflected from the target in the patient's body and transmitting signals relating to the ultrasonic echoes reflected from the target in the patient's body, and the at least one electrode measuring electrical activity data points on the target; a positioning processor operatively connected to the catheter for determining location and orientation coordinates of the position sensor at the portion of the catheter based on the electrical signals transmitted by the position sensor and configured to generate an electro-anatomical map of the target using the electrical activity data points from the at least one electrode and the location and orientation coordinates derived from the electrical signals transmitted by the position sensor of the catheter; an image processor operatively connected to the catheter and the positioning processor, the image processor being configured to: (i) generate at least two two-dimensional ultrasonic images of the target based on the signals transmitted by the ultrasonic imaging sensor, (ii) determine positional information comprising three-dimensional location coordinates for pixels corresponding to contours-of-interest tagged on the generated at least two two-dimensional ultrasonic images, said one or more contours-of-interest identifying one or more features of the target, using three-dimensional location coordinates of the position sensor at the portion of the catheter determined by the positioning processor, and (iii) construct a three-dimensional model from the at least two two-dimensional ultrasonic images based on the determined positional information; and a display for displaying the three-dimensional model and the at least two two-dimensional ultrasonic images and for displaying the electro-anatomical map on the three-dimensional model.