Masakazu Miyamoto

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.

The impact of lesion length and vessel size on outcomes after sirolimus-eluting stent implantation for in-stent restenosis

Objectives: We evaluated the predictors of recurrent restenosis and the impact of lesion length and vessel size on outcomes in patients treated with routine sirolimus-eluting stent (SES) implantation for in-stent restenosis (ISR) of bare-metal stent (BMS). Methods: In this study, 250 consecutive patients with 275 lesions after SES implantation for ISR of BMS were enrolled. Follow-up angiogram was obtained in 239 patients with 258 lesions eight months after implantation (follow-up rate: 95.6%). We compared characteristics of patients and lesions between the two groups (the recurrent restenosis group and the no-restenosis group). Results: Recurrent restenosis was angiographically documented in 43 lesions (16.7%). Recurrent restenosis was found in 30.4% with small vessel lesions (reference diameter of less than 2.5 mm, 92 lesions) and 23% with the diffuse type lesions (106 lesions). Seventy-two per cent of patients had a focal pattern of recurrent restenosis. Previously recurrent ISR lesions (odds ratio (OR) 1.94, 95% confidence interval (CI) 0.94 to 4.06, p = 0.05), reference diameter of less than 2.5 mm (OR 2.41, CI 1.05 to 5.41, p = 0.03), diffuse type restenosis (OR 4.48, CI 2.12 to 9.94, p = 0.0001) and dialysis patients (OR 4.72, CI 1.42 to 15.7, p = 0.01) were independent predictors of recurrent restenosis. Conclusions: Small vessels, diffuse type restenosis and dialysis patients were still the predictors of recurrent restenosis in patients treated with SES for ISR of BMS.

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.

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.

Improvement of SQUID Magnetometer System for Extending Application of Spinal Cord Evoked Magnetic Field Measurement

Superconducting quantum interference device (SQUID)-based spinal cord evoked magnetic field (SCEF) measurement systems are being developed for the diagnosis of spinal cord diseases such as myelopathy. Previous papers have reported several SQUID magnetometers optimized for the detection of the magnetic field evoked by axonal nerve activity at the neck of subjects in sitting or supine positions, thus enabling noninvasive functional imaging of the cervical spinal cord. In this study, we implemented two improvements in the SQUID SCEF system to extend its application range and to make it suitable for practical use in hospitals. One was a newly designed cryostat that was implemented in order to apply the SCEF measurement not only to the cervical region but also to wider regions such as the lumbar or sacral regions. The other improvement was the implementation of SQUID driving electronics to detect not only conventional fast SCEF components accompanied by action potentials but also slow SCEF components resulting from postsynaptic activity. We also implemented direct flux feedback using a set of reference sensors composed of three SQUID magnetometers arranged in an orthogonal orientation in order to reduce noise. We then performed an SCEF measurement using the improved system and successfully observed the distribution of the magnetic field from the sacral region with a peak amplitude of less than 10 fT.

Micro-Magnetocardiography System With a Single-Chip SQUID Magnetometer Array for QT Analysis and Diagnosis of Myocardial Injury in Small Animals

Development of drugs requires electrophysiological studies of small animals like mice, rats or guinea pigs. Electrocardiography (ECG) of hirsute animals is time-consuming. We have developed a micro magnetometer array with a 9-channel superconducting quantum interference device (SQUID) with a 2.5-mm diameter pickup-coil for noncontacting measurement of magnetocardiograms (MCGs) in small animals. The micro-MCG successfully recorded the PQRST complex in mice, rats and guinea pigs. A regional myocardial injury was made in rat hearts with a cryoinjury probe, and the characteristic pattern of the injury was recorded in the MCG. An anterior myocardial injury created a QS pattern in the MCG, and a posterior myocardial injury created a QR pattern in the MCG. Quinidine-induced QT prolongation was successfully detected by micro-MCG in mice and rats. Simultaneous recording of ECG and MCG was conducted after intraperitoneal administration of quinidine (60 mg/kg) in guinea pigs. QT interval corrected for heart rate (QTc) in both ECG and MCG correlated well. The newly developed micro-MCG may facilitate electrophysiological studies of small animals, and may enable high-throughput screening of drug-induced QT abnormality.

SQUID Microscope With Hollow-Structured Cryostat for Magnetic Field Imaging of Room Temperature Samples

We have developed a high-spatial-resolution superconducting quantum interference device (SQUID) microscope for magnetic field imaging of rock samples at room temperature, using a hollow-structured cryostat. A directly coupled low-temperature SQUID with a 200 μm × 200 μm pickup loop, which is mounted on a sapphire conical rod, is separated from room temperature by a thin sapphire window. Precise and repeatable adjustment of the vacuum gap between the SQUID and the sapphire window is performed by rotating a micrometer spindle connected to the sapphire rod through the hollow portion of the cryostat. A spacing of 230 μm between the SQUID and a sample has been achieved. We demonstrated the imaging of the magnetic field on a zircon containing magnetic grains.

SQUID-Based Low Field MRI System for Small Animals

Low field MRI and MEG are based on the ability of SQUID sensors to detect femtotesla magnetic fields. We are now developing a low field MRI system which can be integrated with the MEG system for small animals. The fast switching of the polarizing field inherently induces large transient signals in low field MRI experiments. We have optimized our system to minimize its influence and to improve the SNR of the MRI signal, by modifying a SQUID gradiometer and FLL (fluxed-locked loop) circuit and by reducing the back electromotive force of the polarizing coil. Our system includes five sets of magnetic field and gradient coils. Employing the “target field method” for the design of shielded planar coils, we achieved the measurement field homogeneity of 0.5% over 40 mm DSV (diameter sphere volume). We observed 4 pT NMR signal from 30 ml water by applying the polarizing field of 4.4 mT and the measurement field of 47 μT (1.9 kHz). The magnetic field noise spectral density is 9 fT/√Hz.

Fabrication and characterization of an integrated 9-channel Superconducting quantum interference device magnetometer array

We have fabricated and characterized nine Superconducting Quantum Interference Device (SQUID) magnetometers, which were integrated on a single chip. The magnetometers are based on a directly-coupled multiloop SQUID with Nb/Al-AlO/sub x//Nb junctions, and are arranged in a 3 /spl times/ 3 matrix in the area of 10 mm /spl times/ 10 mm. The diameter of the circular pick-up loop of each magnetometer is 2.5 mm and the distance between neighboring magnetometers is 2.75 mm. In the operation with a flux locked loop (FLL) with direct voltage readout, typical flux-locked noise level of less than 3/spl times/10/sup -6/ /spl Phi//sub 0///spl radic/Hz in the white region were obtained with the magnetometer in a superconductive shield. From the calibration of the sensitivity, typical field noise was measured to be 7 fT//spl radic/Hz. In combination with a small cryostat, we expect that this magnetometer will be useful for multi-channel measurement of magnetic fields requiring highly spatial resolution in various applications.