1. PERFORM Centre; Concordia University; Montreal H4B 1R6 Canada
2. Department of Electrical and Computer Engineering; Concordia University; Montreal H3G 1M8 Canada
3. Department of Neurosurgery; St. Olavs University Hospital; Trondheim NO-7006 Norway
4. Department of Neuroscience; Norwegian University of Science and Technology; Trondheim NO-7491 Norway
5. Norwegian National Advisory Unit for Ultrasound and Image Guided Therapy; St. Olavs University Hospital; Trondheim NO-7006 Norway
6. Department of Medical Technology; SINTEF; Trondheim NO-7465 Norway