IMAGING SYSTEMS FOR BIOMEDICAL APPLICATIONS

MANY OF THE ACTIVITIES OF THE HUMAN BODY MANIFEST THEMSELVES BY THE PRESENCE OF A VERY WEAK MAGNETIC FIELD OUTSIDE THE BODY. THIS FIELD IS SO WEAK THAT AN ULTRASENSITIVE MAGNETIC SENSOR IS NEEDED TO ALLOW SPECIFIC BIOMAGNETIC MEASUREMENTS. SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES (SQUIDS) ARE EXTREMELY SENSITIVE DETECTORS OF MAGNETIC FLUX AND HAVE BEEN USED EXTENSIVELY TO DETECT THE HUMAN MAGNETOCARDIOGRAM AND MAGNETOENCEPHALOGRAM AND OTHER BIOMAGNETIC SIGNALS. TO UTILIZE A SQUID AS A MAGNETOMETER, THE SQUID'S TRANSFER CHARACTERISTICS SHOULD BE LINEARIZED. THIS LINEARIZATION REQUIRES EXTENSIVE PERIPHERAL ELECTRONICS, THUS LIMITING THE NUMBER OF SQUID MAGNETOMETER CHANNELS IN A PRACTICAL SYSTEM. THE PROJECTED DIGITAL SQUID WOULD INTEGRATE THE PROCESSING CIRCUITRY ON THE SAME CRYOGENIC CHIP AS THE SQUID MAGNETOMETER AND ELIMINATE THE SOPHISTICATED PERIPHERAL ELECTRONICS. SUCH A SYSTEM WOULD BE COMPACT, COST EFFECTIVE, AND REQUIRE MINIMAL SUPPORT ELECTRONICS. THIS PROJECT WILL LEAD TO THE DEVELOPMENT OF THIN-FILM DIGITAL MAGNETOMETER/GRADIOMETER CHIPS. IN ADDITION TO HAVING ON-CHIP PROCESSING CIRCUITRY COUPLED TO A SQUID, EACH CHIP WILL ALSO HAVE AN INTEGRATED SUPERCONDUCTING TRANSFORMER TO FACILITATE ITS INTERFACE TO AN EXTERNAL PICK-UP COIL. THIS EFFORT MAKES IT POSSIBLE TO DESIGN AND FABRICATE SINGLE CHIPS THAT WILL CONTAIN ARRAYS OF DIGITAL SQUIDS FOR INTEGRATION IN A MULTICHANNEL SQUID SYSTEM, THEREBY REDUCING THE COST AND COMPLEXITY OF SUCH SYSTEMS. THE PHASE I PROJECT WILL BE CONCERNED WITH THE DESIGN, FABRICATION, AND EVALUATION OF DIGITAL SQUID CHIPS.