Magnetic Resonance Imaging (MRI) is considered the best non-invasive imaging method for soft tissue anatomy and is responsible for saving countless lives each year. MRI is held as the gold standard for diagnosis of mild to moderate traumatic brain injuries. However, conventional MRI relies on very high, fixed strength magnetic fields (> 1.5 T) with parts-per-million homogeneity, which requires very large and expensive magnets that can only be used in highly controlled settings in well-funded medical centers. Traditional high-field MRI is not available in rural settings, is not deployable to emergency situations or battlefield hospitals, and is more expensive than what poor and developing countries can afford. We will present progress toward developing a portable MRI machine based on SQUID (superconducting quantum interference device) sensor technology and ultra-low-field MRI techniques. We will show brain images acquired inside a shielded room and phantom images acquired in an unshielded setting.

The authors gratefully acknowledge the support from the Los Alamos National Laboratory LDRD office through grant 20130121DR.

Highly sensitive measurement for very weak magnetic characteristics of magnetic particles in solution or solution itself is demanded for various applications such as biomedical examinations. We previously reported a compact vibrating-sample magnetometer using a high critical temperature superconductor (HTS-) SQUID. In this study, higher sensitivity and additional performance with relaxation measurement were achieved by improvement of the driving mechanism, high resolution electric magnet and optimization SQUID detection unit. For sample vibration to detect the M-H characteristic, a servomotor was used instead of a linear actuator to precisely control the vibration position and increase the speed. This rotation of the sample enabled switching of the applied magnetic field to the sample, and then relaxation of magnetization was enabled. To detect the magnetic signal from the sample, a first order differential pick-up coil using normal conducting wire connected to the input coil of HTS-SQUID was used. To reduce incidental noise caused by imbalance of the differential detection coil, an additional small compensation coil was connected. More than 4 times vibrating speed was achieved by the servomotor. To measure the M-H characteristic, the sample was vibrated under a DC magnetic field and the magnetization signal was detected by the differential pickup coil equipped between the magnetic poles. The resolution of the applied magnetic field was 40 uT, and the maximum value was 500 mT. A DC magnetic field or an AC magnetic field with a DC bias can be applied to the sample. By the system configuration, high resolution of magnetic moment to the order of 10-11 Am2 was obtained. The magnetic relaxation signal from the sample was measured by one more same type differential detection coil equipped out of the electric magnet by rotating instead of vibrating the sample. The relaxation time was measured by changing the acceleration speed from the electric magnet to the outer detection coil. Using the developed magnetometer, the magnetization curves of water with diamagnetic character and low-concentrated iron nanoparticles with superparamagnetic character in solution were successfully characterized, and also the time change of the relaxation phenomenon of the nanoparticles was measured.

This work was supported by the “Strategic Promotion of Innovative R&D” program funded by the Japan Science and Technology Agency (JST)

Magnetization measurements of Fe3O4 nanoparticles have been performed using a nanosized Superconducting Quantum Interference Device (nanoSQUID).
The nanosensor consists of a superconducting loop interrupted by two Dayem nanobridges. The characterization of the nanodevice in the temperature range from 1.2K to 4.2 K includes measurements of current-voltage, critical current vs. magnetic flux characteristic and flux noise[1-3]. Due to the hysteretic nature of the Current-Voltage characteristic, the nanoSQUIDs are operated as magnetic flux to current converter. A proper feedback circuit has been employed to increase the dynamic range of the nanosensor and to measure the M(H) curve of Magnetic NanoParticle (MNP) deposited on its surface. The sensors can be also employed in the small signal mode regime for the magnetic relaxation measurements[4,5].
A cryogenic VTI (Variable Temperature Insert) has been equipped with precision rotator to align the SQUID plane to the magnetic field produced by a Cryogenic Free Magnet (CFM).
The align procedure in essential to minimize the magnetic field, generated by the CFM, threading the SQUID loop and to optimize the SQUID response to the magnetic moment generated by the MNP.
In order to measure the magnetization of MNP a second SQUID without MNP on the same chip is measured to evaluate the misalignment angle and to eventually subtract the signal due to the CFM.
Measurements of magnetization as a function of the external magnetic field for magnetic nanoparticle of different diameters will be reported. The magnetization curves show a magnetic histeresis indicating a blocking temperature above the cryogenic measuring temperature. The sigmoid shape of the virgin curves indicates the presence of dipole–dipole interparticle interactions which tend to resist to the magnetization process.
Magnetic relaxation measurements with a time resolution below 0.1s have also been performed and they will be reported.
[1] R. Russo et al. Journal of Nanoparticle Research 13, 5661-5668 (2011)
[2] R. Russo et al Appl. Phys. Lett. 101, (2012) 122601; doi: 10.1063/1.4751036
[3] R.Russo et al (2014) SUST 27 (4), 044028
[4] C. Granata, et al. (2013) EPJ B, , vol. 86, 272, doi: 10.1140/epjb/e2013-40051-2
[5] C. Granata, et al. (2013) Appl. Phys. Lett, vol. 103, 102602

A decade after the emergence, micro-Tesla nuclear magnetic resonance (NMR) gets attracting interests of SQUID researchers. SQUID operation in a harsh environment where strong magnetic pulses are applied is technically tricky thus we can say that μT-NMR is at the cutting edge of SQUID technology. A weak sample polarization, slow magnetization maneuver, flux-creeping noise in a SQUID pick-up coil, and long-lasting eddy currents along the wall of a magnetically shielded room (MSR) limit the detection sensitivity of NMR signals. For solutions for those problems, we introduce dynamic nuclear polarization (DNP), circularly polarized B₁ excitation, superconductive magnetic hysteresis, and a new design of an MSR, respectively. These breakthrough techniques improve the performance of the NMR system and enable to widen the range of applications.
We can utilize particular physical properties in a low magnetic field to invent new applications of the SQUID NMR technology. In this presentation, we introduce several μT specific applications; 2D NMR spectrum in a strongly coupled regime for material identification [1], a spinecho magnetometer for a new standard for low range magnetic fields [2], T₁-enhanced contrast MRI for cancer mapping [3], Non-field-recycling DNP MRI with limit-breaking enhancement factor [4], and biomagnetic resonance [5, 6]

[1] J. H. Shim, et al., “Two-dimensional NMR spectroscopy of ¹³C methanol at less than 5 μT”, J. Magn. Reson. 246, 4-8 (2014)
[2] J. H. Shim, et al., “Proton spin-echo magnetometer: A novel approach for magnetic field measurement in residual field gradient”, Metrologia, submitted
[3] S. -J. Lee, et al., “T₁ relaxation measurement of ex-vivo breast cancer tissues at ultra-low magnetic fields”, BioMed Research International, 385428 (2015)
[4] S. –J. Lee. et al., “Magnetic resonance imaging without field cycling at less than Earth’s magnetic field”, Appl. Phys. Lett. 106(10), 103702 (2015)
[5] K. Kim, et al., “Toward a brain functional connectivity mapping modality by simultaneous imaging of coherent brainwaves”, Neuroimage 91(1; Issue cover article), 63-69 (2014)
[6] K. Kim, “Toward cardiac electrophysiological mapping based on micro-Tesla NMR: a novel modality for localizing the cardiac reentry”, AIP Adv. 2, 022156 (2012)

This work was supported by World Class Laboratory (WCL) grant from Korea Research Institute of Standard and Science (KRISS)

Development of broadband superconductor sensors / amplifiers capable of providing high Spurious-Free Dynamic Range (SFDR) is now extremely topical, especially in the view of development of broadband receiving systems with direct digitizing. Such high-performance receivers become quite real with the state-of-the-art progress in superconductor Analog-to-Digital Converters (ADC). This presentation is to observe our theoretical and experimental studies of Superconducting Quantum Arrays (SQA) suggested for development of the broadband sensors / amplifiers realizing high SFDR. Integrating SQA with a broadband input microwave line or with a superconducting flux concentrator to apply an input magnetic signal to all array cells, one can design a broadband high-performance amplifier or active electrically small antenna of a transformer type. Moreover, SQA in the form of 2D array of superconducting quantum cells with nonsuperconducting electric connection of the cells can be used directly as an active ESA of a transformer-free type.

This work was supported by Grants PGSS 4871.2014.2 and Russian Ed.&Sci Ministry Grant 14.613.21.0022 (RFMEFI61314X0022).