Yusuke Seki

Development of multisample biological immunoassay system using HTSSQUID and magnetic nanoparticles

We developed a prototype magnetic immunoassay system using a high temperature superconductor (HTS) superconducting quantum interference device (SQUID) to investigate the performance and usability of the magnetic immunoassay. The system is designed to measure multiple samples and liquid samples, and it can work in an unshielded environment at a medical facility. To reduce the disturbance from environmental noise, the SQUID and samples are covered with three-layers of permalloy magnetic shield. The SQUID and magnetic shield are set in an aluminum box which acts as an RF shield. A gradiometer with a 5 /spl times/ 10 mm pickup coil, which is cooled by liquid nitrogen through a sapphire/Cu rod, is used as a sensor. We also developed a nonmagnetic sample disk with 12 reaction cells and examined 12 samples in one measurement sequence. The measurement process is controlled by a computer, which perform data averaging. Fe/sub 3/O/sub 4/ nanoparticles with a 25-nm diameter were used as test samples. After applying a magnetic field of about 0.1 T, we measured the remanent magnetic field from the Fe/sub 3/O/sub 4/ nanoparticles. The present system could detect 30 pg of Fe/sub 3/O/sub 4/ nanoparticles. This result was obtained by averaging 100 trials under an unshielded laboratory environment. The measurement time for 100 trials was only 100 s.

Open-type magnetocardiograph with cylindrical magnetic shield

We have developed an open-type magnetocardiograph (MCG) with a cylindrical magnetic shield—having an auxiliary magnetic shield—and 64 gradiometers based on low-transition temperature (Tc) superconducting quantum interference devices (SQUIDs). A revolving door is applied to the magnetic shield with the aim of providing easy access to a subject and easy operation. The cryostat attached to the MCG contains 64 low-Tc SQUIDs and is about 1m in height, so there must be an opening through the cylindrical surface of the magnetic shield. The properties of the magnetic shield were simulated using finite-element-method simulations and experiments. The results of the simulations indicated that the auxiliary magnetic shield recovers enough of the shielding performance of a magnetic shield with an opening that it performs like a magnetic shield without an opening. The shielding factor of the developed magnetic shield is above 46dB in the vicinity of the magnetic shield. Accordingly, the open-type MCG can clearly measur...

Open-type hybrid magnetic shield using high-TC superconducting wire and flexible magnetic sheets

An open-ended, cylindrical magnetic shield using high-TC superconducting rings and flexible magnetic sheets has been developed. The superconducting ring is made of Bi2Sr2Ca2Cu3Ox tape wire, and the flexible magnetic sheet is made of Fe–Cu–Nb–Si–B nanocrystalline alloy, which has superior soft magnetic properties. The superconducting rings are set near the open ends of a ferromagnetic cylinder. When a magnetic field is induced in the rings, a shielding current flows so as to keep the magnetic flux through the ring constant. It is concluded that the superconducting rings effectively increase the shielding factor of a magnetic shield.

Two-Dimensional Gradiometer

We developed a two-dimensional gradiometer that detects the gradient of a magnetic field in two orthogonal directions to measure the biomagnetic signal in an unshielded environment. We based the gradiometer on a low-Tc superconducting quantum interference device (SQUID) and wire-wound pickup coil. The gradiometer we developed detects both the axial-second-order and planar-first-order gradient of a magnetic field. The experimental results revealed that its noise-reduction ratio (NRR) was 54 dB from 0.5 to 49 Hz and 14 dB (5 times) larger than that of the axial-second-order gradiometer. Moreover, by using the new gradiometer, we obtained a clear magnetocardiography (MCG) waveform in real time without averaging under an unshielded environment (noise level: 3.8 nT/√Hz at 1 Hz; 150 pT/√Hz at 10 Hz).

Applying high-T/sub C/ superconducting quantum interference devices with a room-temperature pickup coil in the measurement of impedance magnetocardiograms

A high-T/sub C/ superconducting quantum interference device (SQUID) magnetometer - in which a room-temperature pickup coil is used to detect an impedance magnetocardiogram (I-MCG) signal - has been developed. The pickup coil (30-mm diameter) is installed outside the cryostat and is connected to the input coil of the high-T/sub C/ SQUID. The magnetometers noise level is 150 fTHz/sup -1/2/ (>10 kHz). The magnetometer was used to measure I-MCG signals (about 12 pT), which were obtained by applying an ac current (15 kHz) of constant amplitude (7 mA, peak-to-peak) to a healthy male subject.

Unshielded fetal magnetocardiography system using two-dimensional gradiometers

We performed fetal magnetocardiography (fMCG) measurements in an unshielded hospital environment to demonstrate our developed fMCG system using two-dimensional (2D) gradiometers based on low-T c superconducting quantum interference devices. The subjects were 25 pregnant women, including two subjects with twin pregnancies, or 27 fetuses, in this study. The 2D gradiometer was optimized for fMCG measurements and detected both the axial second-order gradient and planar-first-order gradient of a magnetic field. Depth of the fetal heart was also measured by using ultrasonography before fMCG measurement. As a result, the QRS peaks of the fMCG waveform were detected in real time for 15 cases including early fetal gestational periods as 24 and 25 weeks. Moreover, the P and T waves were also detected in some cases by averaging. These results demonstrate that the developed unshielded fMCG system can detect fMCG waveforms in an unshielded hospital environment.

Simultaneous measurement of neuronal activity and cortical hemodynamics by unshielded magnetoencephalography and near-infrared spectroscopy

Abstract. The correlation between neuronal activity and cortical hemodynamics, namely, neurovascular coupling (NVC), is important to shed light on the mechanism of a variety of brain functions or neuronal diseases. NVC can be studied by simultaneously measuring neuronal activity and cortical hemodynamics. Consequently, noninvasive measurements of the NVC have been widely studied using both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). However, electromagnetic interference between EEG and fMRI is still a major problem. On the other hand, near-infrared spectroscopy (NIRS) is another promising tool for detecting cortical hemodynamics because it can be combined with EEG or magnetoencephalography (MEG) without any electromagnetic interference. Accordingly, in the present study, a simultaneous measurement system—combining an unshielded MEG using a two-dimensional gradiometer based on a low-Tc superconducting quantum interference device (SQUID) and an NIRS using nonmagnetic thin probes—was developed. This combined system was used to simultaneously measure both an auditory-evoked magnetic field and blood flow change in the auditory cortex. It was experimentally demonstrated that the combined unshielded MEG/NIRS system can simultaneously measure neuronal activity and cortical hemodynamics.

Demonstration of Unshielded Fetal Magnetocardiography System Using Two-Dimensional Gradiometers

We performed fetal magnetocardiography (fMCG) measurements in an unshielded hospital environment to demonstrate our developed fMCG system using two-dimensional (2D) gradiometers based on low-T c superconducting quantum interference devices. The subjects were 25 pregnant women, including two subjects with twin pregnancies, or 27 fetuses, in this study. The 2D gradiometer was optimized for fMCG measurements and detected both the axial second-order gradient and planar-first-order gradient of a magnetic field. Depth of the fetal heart was also measured by using ultrasonography before fMCG measurement. As a result, the QRS peaks of the fMCG waveform were detected in real time for 15 cases including early fetal gestational periods as 24 and 25 weeks. Moreover, the P and T waves were also detected in some cases by averaging. These results demonstrate that the developed unshielded fMCG system can detect fMCG waveforms in an unshielded hospital environment.

Process of fabricating YBCO SQUIDs for 51-channel HTS MCG system

We have constructed a high throughput HTS SQUID fabrication process to develop a 51-channel HTS MCG system. To increase the process throughput of the YBCO deposition, we designed and developed a new deposition system based on a pulsed laser deposition technique. In this deposition system, nine YBCO thin films could be deposited in one deposition sequence by successively depositing the YBCO thin films one by one. In addition to the improvement of the fabrication throughput, the magnetometer pattern was designed to improve the yield of the SQUID fabrication. In our magnetometer design, four SQUIDs were connected with one pickup coil. The yield of good magnetometer chips could be increased by selecting the best SQUID among the four. Using the developed SQUID fabrication process, about one hundred magnetometers were fabricated in a month. The 51-channel HTS MCG system was successfully developed and used for clinical testing.

Shielding effect of an open-type hybrid magnetic shield with high-Tc superconducting loops

Double-D-shaped high-Tc superconducting loops were used to form an open-ended, cylindrical magnetic shield for biomagnetic measurements. The total magnetic flux through such a superconducting loop stays constant; thus, the loop can shield a cylindrical magnetic shield from an external magnetic field that penetrates into it from its open ends. The high-Tc superconducting loops are made of Bi2Sr2Ca2Cu3Ox tape wire, and the cylindrical magnetic shield is made of flexible magnetic sheets composed of Fe–Cu–Nb–Si–B nanocrystalline alloy. Both axial and transverse magnetic field noise in the shield were measured with high-Tc superconducting quantum interference devices. These measurements indicate that the double-D-shaped high-Tc superconducting loops at each open end of a cylindrical magnetic shield reduce not only axial but also transverse magnetic field noise in the magnetic shield.