1. A method for registering a three dimensional ultrasound image with an intensity magnetic resonance image comprising gradient information, comprising the steps of: identifying an anatomical boundary from said gradient information; producing a filtered magnetic resonance image by processing said intensity magnetic resonance image with an image filter; and registering said ultrasound image with said filtered magnetic resonance image; wherein said three dimensional ultrasound image is an intraoperative three dimensional ultrasound image, said intensity magnetic resonance image is a pre-operative intensity magnetic resonance image, and said filtered magnetic resonance image simulates the appearance of an ultrasound image.