Gen Uehara

Three dimensionally configured SQUID vector gradiometers for biomagnetic measurement

We proposed a composite superconducting quantum interference devices (SQUIDs) gradiometer with an axial-type gradiometric pick-up coil and two planar-type gradiometric pick-up coils. Three gradiometers are built into a single module in orthogonal position to each other and the pick-up coils of two planar-type gradiometers are concentric. Therefore, the sensor can detect magnetic fields elicited by action currents in a living body as a quasi three-dimensional vector at a specific point. The outward form of the sensors is identical to our conventional axial-type gradiometric SQUID magnetometer. Therefore, the new sensor can be mounted on our conventional sensor array without large modification. We applied the new sensors to the SQUID magnetometer system for the spinal cord evoked magnetic fields and successfully measured the magnetic fields from the spinal cords from small animals.

A 75-ch SQUID Biomagnetometer System for Human Cervical Spinal Cord Evoked Field

A 75-ch SQUID biomagnetometer system for the measurement of the cervical spinal cord evoked magnetic field (SCEF) was developed for the purpose of the noninvasive functional diagnosis of the spinal cord. The sensor array has 25 SQUID vector sensors arranged along the cylindrical surface to fit to the shape of the subjects neck. The magnetic fields, not only in the direction radial to the subjects body surface but also in the tangential direction, are observed in the area of 80 mm times 90 mm at one time. The dewar has a unique shape with a cylindrical main body and a protrusion from its side surface. The sensor array is installed in the protruded part. This design is optimized to detect magnetic signals at the back of the neck of the subject sitting in a reclining position. We applied the developed SQUID system to the cervical SCEF measurement of normal subjects who were given electric pulse stimulation to their median nerves at the wrists. The evoked magnetic signals were successfully detected at the cervixes of all subjects. A characteristic pattern of transition of the SCEF distribution was observed as a reproducible result and the signal components propagating along the spinal cord were found in the time varying SCEF distribution. We expect that the investigation of the propagating signal components would help to establish a noninvasive functional diagnosis of the spinal cord.

High sensitivity double relaxation oscillation superconducting quantum interference devices with large transfer from flux to voltage

Double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) based on Nb/AlOx tunnel junctions have been fabricated and characterized. The estimated relaxation frequencies range from 400 MHz up to 14 GHz. Transfer coefficients from flux to voltage of 2 up to 7 mV/φ0 have been obtained. Both the intrinsic flux noise and the performance in a flux‐locked loop with direct‐voltage readout have been determined. Special attention is paid to the effect of damping resistors on the sensitivity of DROSs. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13h at relaxation frequencies above 2–3 GHz for SQUID inductances of about 30 pH. This sensitivity is very close to the theoretical maximum sensitivity of 6h of a comparable standard type dc SQUID. In a flux‐locked loop based on direct‐voltage readout, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34h has been obtained for a DROS with a SQUID inductance of 29 pH.

Development of an MCG/MEG system for small animals and its noise reduction method

Accurate capture of the biomagnetic signals from a rat or a mouse greatly benefits the development of new medicine and pathology. In order to improve the efficiency and accuracy of biomagnetic measurement of small animals, we developed a biomagnetic measurement system specific to small animal measurement. A superconducting quantum interference device (SQUID) sensor array and a table for the system were newly developed and were integrated into a transportable chassis having dimensions of 1.3 m width × 0.7 m depth × 1.8 m height and housing all principal components for the system. The integrated 9ch low-Tc SQUIDs magnetometer array designed to improve spatial resolution covers 8 mm × 8mm measurement area. We have also developed a real-time noise canceling method suitable for this system. The advantage of this method is that the noise reduction process is carried out in real time. We have confirmed the efficacy of this method using the measurement system which was installed in typical laboratory environment. The noise reduction effect was measured to be roughly 16 dB at power line frequency and its harmonics. We measured an magnetocardiogram (MCG) of a mouse using the system with the real-time noise canceling method, and the feasibility of small animal MCG measurement was ensured.

High sensitivity double relaxation oscillation superconducting quantum interference devices

Double relaxation oscillationsuperconducting quantum interference devices(SQUIDs) (DROSs) have been fabricated with estimated relaxation frequencies up to 14 GHz. Both the intrinsic flux noise and the performance in a flux locked loop with direct voltage readout have been studied. In flux locked loop, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34 h has been obtained for a DROS with a SQUIDinductance of 29 pH. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13 h at relaxation frequencies higher than about 3 GHz.

Asymmetric Bias Injection Technique for Drung-Type Superconducting Quantum Interference Devices

An asymmetric bias current injection method is developed to reduce bias-caused noise in Drung-type SQUID (superconducting quantum interference devices) without adding extra coils. A measuring scheme for ∂Φ/∂Ib is tested, and it is demonstrated that the reduction is from 100 to 150 times that attained by the conventional SQUID biasing method. It is revealed that the direction of APF (additional positive feedback) coil winding is important in attaining this reduction.

A SQUID System for Measurement of Spinal Cord Evoked Field of Supine Subjects

An LTS SQUID biomagnetometer system was developed for the non-invasive diagnosis method of the spinal cord function for orthopedic and neurologic application. The developed biomagnetometer system is characterized by a uniquely shaped cryostat. It has a vertical cylinder-shaped main body and a protrusion from its side surface. An array of SQUID vector gradiometers with a 5 times 8 matrix-like arrangement for 90 mm times 140 mm observation area is installed in the protrusion. Supine subjects are able to fit their cervixes stably to the sensor array by putting them against the protrusion during the measurement. The sensors directed vertically upwards detect magnetic signals from the back of the cervix. An X-ray imaging apparatus is integrated to the SQUID system for the in-situ acquisition of the anatomical information that reveals the position of cervical vertebrae relative to the location of the sensor array. For the performance verification of the developed system, we examined the spinal cord evoked field measurement of a normal subject. We succeeded in observing the transition of the cervical magnetic field distribution induced by the electric pulse stimulation on the median nerve at the subjects wrist.

System integration and trade-offs of SQUID system for biomagnetic applications

Abstract We have been developing SQUID systems for various applications, with special emphasis on systems for biomagnetic applications. In 1987, Koyanagi and Kado fabricated and integrated a SQUID system made entirely of thin-film integrated SQUID. Research and development activities on multichannel SQUID system integration has been undertaken by various groups. The Superconducting Sensor Laboratory (SSL) project was one of the most significant of these activities. Such activities in North America and Europe have mostly been pursued by commercial groups, who have been fabricating commercial systems for end users. However, large-scale system distribution to end users is still impractical because of high costs and the lack of user-friendliness. As former members of the SSL project, some of us at the Kanazawa Institute of Technology began the development of SQUID systems aimed at overcoming previous problems such as high cost and the low level of user-friendliness. In this paper, we describe our concept of system integration and the level of the system’s sophistication.

Design and fabrication of multichannel DC SQUIDs for biomagnetic applications

A hybrid DC superconducting quantum interference device (SQUID) system is developed for biomagnetic applications. It consists of a high-performance square-shaped double-washer DC SQUID and a highly accurate planar pick-up coil. The DC SQUID device and the pick-up coil are designed and fabricated separately. Coupling this device and the separately fabricated pick-up coil allows flexibility in the construction of multichannel systems as well as sensitivity and stability.<<ETX>>

Evaluation of Drung-type magnetometers for multi-channel systems

The properties of a prototype Drung-type SQUID with single-digit or smaller dynamic resistance, decreased using asymmetric bias current injection, are examined. Magnetic field resolution of 2.2 fT Hz-1/2 at 1 kHz and high sensitivity are obtained. A highly reliable ceramic package is developed for multi-channel applications. A prototype 256-channel system for biomagnetic application using mass-produced SQUIDS is built, and the successful operation of 206 channels is verified.