Kazuyoshi Saito

Achievement of 1020 MHz NMR

We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the worlds highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the (2)H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a (1)H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as (17)O; a (17)O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.

Application of magnetic resonance imaging to non-destructive void detection in watermelon

A novel application of magnetic resonance imaging (MRI) is described. The possibility of utilizing MRI for non-destructive quality evaluation of watermelons was studied. In this study, we applied MRI to the detection of internal voids in watermelons. In order to increase the measurement rate, we employed a one-dimensional projection profile method instead of observing a two-dimensional cross-sectional image. The void detection was carried out with this technique over 30 samples and 28 samples were correctly evaluated. The measurement rate was 900 ms per sample, which is an acceptable speed for a sorting machine in the agricultural field.

1020 MHz single-channel proton fast magic angle spinning solid-state NMR spectroscopy

This study reports a first successful demonstration of a single channel proton 3D and 2D high-throughput ultrafast magic angle spinning (MAS) solid-state NMR techniques in an ultra-high magnetic field (1020MHz) NMR spectrometer comprised of HTS/LTS magnet. High spectral resolution is well demonstrated.

New 7 T superconducting magnet system for bacterial cultivation

Abstract A new superconducting magnet system for bacterial cultivation has been developed. The superconducting magnet has a horizontal room temperature bore with a diameter of 160 mm, and provides a homogeneous magnetic field of 7 T ± 0.5% for a 200 mm long × 100 mm diameter region. This homogeneous field region contains an incubator, where bacteria are cultivated aerobically at 10–70 °C ± 0.1 °C while being shaken. The culture exposed to the high magnetic field is compared with a control culture incubated at below geomagnetic field strength. Cultivation of Escherichia coli was carried out both in homogeneous and in inhomogeneous fields, and 1.4–3.6 times the number of viable cells of the control culture was observed in a stationary phase.

Successful Upgrading of 920-MHz NMR Superconducting Magnet to 1020 MHz Using Bi-2223 Innermost Coil

We succeeded in upgrading the 920-MHz nuclear magnetic resonance (NMR) superconducting magnet (21.6 T) to 1020 MHz (24.0 T) by replacing the innermost Nb3Sn coil with a (Bi,Pb)2Sr2Ca2Cu3O10 (Bi-2223) coil. The 920-MHz NMR spectrometer had been installed in the National Institute for Materials Science, Tsukuba, Japan, in 2001. It has been operated in the persistent mode for six years. The upgrading project started in 2006. A Bi-2223 coil was developed as the innermost coil instead of the Nb3Sn one. The newly installed Bi-2223 innermost coil is connected to Nb3Sn and NbTi coils in series. The upgraded NMR magnet was seriously damaged by the Great East Japan Earthquake in March 2011. After more than two years of restoration and additional improvements of current leads and the power supply system, the magnet was cooled down to below 1.8 K in August 2014. The magnet successfully generated 24.0 T, corresponding to 1020 MHz, in October 2014. To achieve the required homogeneity and stability of the magnetic field, not only superconducting and room-temperature shim coils but also ferromagnetic shims were used. The 1020-MHz superconducting NMR magnet has been operated in a power-supply-driven mode for six months.

Analysis of an Abnormal Event in a 3-T MRI Magnet Wound With Bi-2223 Tape Conductors

We have designed and fabricated a 3-T Magnetic Resonance Imaging (MRI) magnet system for the human brain, which was wound with Bi-2223 tape conductors. The magnet was successfully energized to 1.5 T and then up to 3.0 T. The magnet experienced more than 60 ramp-up and down processes to 1.5 T with no trouble. A magnetic field of 3.0 T (184.8 A) could be maintained for longer than 3 h without any problems. However, abnormal voltage behavior was observed during the ramp down for the third trial to 3.0 T, and the temperature rapidly increased with a ramping rate of 1.7 K/min. To investigate the cause, we opened the cryostat and inspected the inside of the magnet. In addition, we have analyzed the details of this event using the recorded current, voltage, and temperature data. The purpose of this paper is to report the investigation of this abnormal event in the magnet.

Shimming for the 1020 MHz LTS/Bi-2223 NMR Magnet

Using a Bi-2223 innermost coil, the worlds first NMR magnet with a frequency beyond 1 GHz has been developed and operated at the National Institute for Materials Science during 2014-2015. The existing 920 MHz (21.6 T) NMR magnet was successfully upgraded to a 1030 MHz (24.2 T) magnet by replacing the Nb3Sn innermost coil with a Bi-2223 coil. After charging the magnet to 1020 MHz (24.0 T), a shimming operation was started to obtain the homogeneous magnetic field required for NMR measurements. However, a large magnetic field inhomogeneity appeared, which could not be compensated using conventional shimming methods, i.e., superconducting and room temperature shim coils. Therefore, a new ferromagnetic shimming technology was applied, which achieved powerful and fast-acting field compensation and performed comparably to active shimming. This enabled effective compensation of the magnetic field inhomogeneity, leading to a subsequently excellent NMR resolution test result of 0.7 ppb. This NMR resolution enables NMR measurements for a membrane protein sample.

Sugar Content Detection in Watermelon

A new usage of MRI as a sorting machine based on the sugar content was developed. The relationship between two NMR relaxation times T1 ,T2 and the sugar content was investigated in watermelons and used for evaluation of the sugar content. It was found that the multiple regression analysis using both T1 and T2 was a good indicator for sugar content and T2 could be used for distinguishing over-ripened watermelons. The speed of evaluation of 6 seconds per sample was attaind.

Development of the superconducting magnet system for a bioreactor

A superconducting magnet for a bioreactor system was developed in order to determine the biotechnical and biomedical responses of microorganisms to a high magnetic field. The magnet has a horizontal bore, and the field strength at the center is 7 tesla at an operating current of 120 Amperes. The room-temperature bore diameter is 160 mm. Persistent current mode and detachable power leads are adopted. A cryocooler was installed to cool the radiation shields, which enable continuous operation for 6 months without the need to resupply liquid helium. Magnetic shields cover the cryostat to minimize the leakage field. Two reactors are installed inside and outside of the bore. Magnetic shields also cover the outside reactor in order to reduce the strength of the magnetic fields to less than the geomagnetic level. The temperatures of the reactors are controllable, ranging from 283K to 343K with /spl plusmn/0.1K. >

Superconducting joint of REBCO wires for MRI magnet

A high temperature superconducting wire (HTS wire) is promising for various superconducting magnet applications because it operates at a higher temperature than a low temperature superconducting wire (LTS wire) is. Particularly, a MRI magnet using the HTS wires (HTS-MRI magnet) is expected to obtain light-weight, compact and low operating cost compared to a LTS-MRI magnet. The MRI magnets are generally operated by a persistent current mode. A magnet of the persistent current mode consists of multiple superconducting magnets and persistent current switch (PCS) that connects with superconducting joints. However, the superconducting joint of the HTS wires has not been realized stably at this time. We have developed a superconducting joint by using a commercial REBCO wire. The HTS-MRI magnet requires that resistivity of less than 10−12 ohm and current capacity of more than 100 A is achieved by a direct-joint between superconducting layers of the two REBCO wires. Moreover, measurement equipment for low joint resistivity was prepared as measuring the decay of the magnetic field in the one-turn loop. In our R&D, the joint resistance and the critical current were achieved with 155 A and 5.3×10−13Ω.