MAGNETIC NAVIGATION SYSTEMS COMPRISED OF MAGNETIC DEVICES AND CONTROLS FOR CONTROLING THE POSITION AND/OR ORIENTATION OF MAGNETIC SUBSTANCES AND DEVICES IN THE BODY; A LINE OF MAGNETIC MEDICAL DEVICES THAT CAN BE MAGNETICALLY NAVIGATED IN THE BODY FOR DIAGNOSTIC AND THERAPEUTIC PURPOSES; CATHETERS; ENDOSCOPES; MAGNETS AND ELECTROMAGNETS FOR MEDICAL APPLICATIONS; ATHERECTOMY DEVICES; MEDICAL GUIDEWIRES; MEDICAL IMAGING APPARATUS; APPARATUS FOR LOCATING MEDICAL DEVICES IN THE BODY; INTERCRANIAL BOLTS; TISSUE SAMPLERS FOR EXTRACTING TISSUE SAMPLES FROM THE BODY; MEDICAL ELECTRODES AND ELECTRODE CATHETERS