1. A system for guiding an instrument through a region of a subject, comprising: a non-imaging instrument configured to be moveable through the subject; a first tracking device connected near a distal end of the instrument; an ultrasound imaging system to generate an image of the subject; a second tracking device associated with the ultrasound imaging system; a tracking system to track the first tracking device within the subject and the second tracking device; an external imaging system configured to be external to the subject and of a different imaging modality than the ultrasound imaging system; and a display device, wherein an instrument image is generated based on the tracked location of the first tracking device, the second tracking device, and the generated image; wherein a second image generated with the external imaging system and the instrument image is registered to the subject and one another and displayed at one time on the display device.