Ultra-low Field Research Articles

3D-Spatial encoding with permanent magnets for ultra-low field magnetic resonance imaging

We describe with a theoretical and numerical analysis the use of small permanent magnets moving along prescribed helical paths for 3D spatial encoding and imaging without sample adjustment in ultra-low field magnetic resonance imaging (ULF-MRI). With our developed method the optimal magnet path and orientation for a given encoding magnet number and instrument architecture can be determined. As a proof-of-concept, we studied simple helical magnet paths and lengths for one and two encoding magnets to evaluate the imaging efficiency for a mechanically operated ULF-MRI instrument with permanent magnets. We demonstrate that a single encoding magnet moving around the sample in a single revolution suffices for the generation of a 3D image by back projection.

Brain and bone cancer targeting by a ferrofluid composed of superparamagnetic iron-oxide/silica/carbon nanoparticles (earthicles)

Despite the advances in molecularly targeted therapies, delivery across the blood-brain barrier (BBB) and the targeting of brain tumors remains a challenge. Like brain, bone is a common site of metastasis and requires therapies capable of discerning the tumor from its healthy cellular milieu. To tackle these challenges, we made a variation on the previously proposed concept of the earthicle and fabricated an aqueous, surfactant-free ferrofluid containing superparamagnetic iron oxide nanoparticles (SPIONs) coated with silicate mesolayers and carbon shells, having 13 nm in size on average. Nanoparticles were synthesized hydrothermally and characterized using a range of spectroscopic, diffractometric, hydrodynamic and electron microscopy techniques. The double coating on SPIONs affected a number of physicochemical and biological properties, including colloidal stability and cancer targeting efficacy. Nanoparticles decreased the viability of glioblastoma and osteosarcoma cells and tumors more than that of their primary and non-transformed analogues. They showed a greater preference for cancer cells because of a higher rate of uptake by these cells and a pronounced adherence to cancer cell membrane. Even in an ultralow alternate magnetic field, nanoparticles generated sufficient heat to cause tumor death. Nanoparticles in MDCK-MDR1 BBB model caused mislocalization of claudin-1 at the tight junctions, underexpression of ZO-1 and no effect on occludin-1 and transepithelial resistance. Nanoparticles were detected in the basolateral compartments and examination of LAMP1 demonstrated that nanoparticles escaped the lysosome, traversed the BBB transcellularly and localized to the optic lobes of the third instar larval brains of Drosophila melanogaster. The passage was noninvasive and caused no adverse systemic effects to the animals. In conclusion, these nanoparticulate ferrofluids preferentially bind to cancer cells and, hence, exhibit a greater toxicity in these cells compared to the primary cells. They are also effective against solid tumors in vitro, can cross the BBB in Drosophila, and are nontoxic based on the developmental studies of flies raised in ferrofluid-infused media. Statement of SignificanceWe demonstrate that a novel, hydrothermally synthesized composite nanoparticle-based ferrofluid is effective in reducing the viability of osteosarcoma and glioblastoma cells in vitro, while having minimal effects on primary cell lines. In 3D tumor spheroids, nanoparticles greatly reduced the metastatic migration of cancer cells, while the tumor viability was reduced compared to the control group by applying magnetic hyperthermia to nanoparticle-treated spheroids. Both in vitro and in vivo models of the blood-brain barrier evidence the ability of nanoparticles to cross the barrier and localize to the brain tissue. These composite nanoparticles show great promise as an anticancer biomaterial for the treatment of different types of cancer and may serve as an alternative or addendum to traditional chemotherapies.

Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity

An enduring mystery about Earth has been the age of its solid inner core. Plausible yet contrasting core thermal conductivity values lead to inner core growth initiation ages that span 2 billion years, from ~0.5 to >2.5 billion years ago. Palaeomagnetic data provide a direct probe of past core conditions, but heretofore field strength data were lacking for the youngest predicted inner core onset ages. Here we present palaeointensity data from the Ediacaran (~565 million years old) Sept-Iles intrusive suite measured on single plagioclase and clinopyroxene crystals that hosted single-domain magnetic inclusions. These data indicate a time-averaged dipole moment of ~0.7 × 1022 A m2, the lowest value yet reported for the geodynamo from extant rocks and more than ten times smaller than the strength of the present-day field. Palaeomagnetic directional studies of these crystals define two polarities with an unusually high angular dispersion (S = ~26°) at a low latitude. Together with 14 other directional data sets that suggest a hyper-reversal frequency, these extraordinary low field strengths suggest an anomalous field behaviour, consistent with predictions of geodynamo simulations, high thermal conductivities and an Ediacaran onset age of inner core growth. A late onset of inner-core growth is inferred from ultra-low palaeomagnetic field strengths about 565 million years ago, as measured in magnetic inclusions in Ediacaran crystals.

Design and Testing of a Multi-Channel 1H/3He Double-Nuclear Transmit Coil Array for Magnetic Resonance Imaging at an Ultra-Low Field

Design and Testing of a Multi-Channel ¹H/³He Double-Nuclear Transmit Coil Array for Magnetic Resonance Imaging at an Ultra-Low Field

Assessment of heteronuclear long-lived states at ultralow magnetic fields.

A study of long-lived spin states in hetero-nuclear spin systems is presented. Since long-lived states are efficiently sustained only when the spins are "strongly coupled", this study necessitates going to "ultralow" magnetic fields, which are much lower than the Earth's field. To do so, we utilize a fast field-cycling device, which rapidly shuttles the sample between an NMR (Nuclear Magnetic Resonance) magnet and a magnetic shield with a very low field inside. While the spin evolution is taking place at an ultralow field, detection is performed at the high field of an NMR spectrometer. We report hetero-nuclear long-lived order in two spin and four-spin systems, given by the CH and CH3 groups of methyl propiolate, and present a detailed analysis of the spectral manifestation of such long-lived states.

DEMAND, a Dimensional Extreme Magnetic Neutron Diffractometer at the High Flux Isotope Reactor

A two-dimensional (2D) Anger camera detector has been used at the HB-3A four-circle single-crystal neutron diffractometer at the High Flux Isotope Reactor (HFIR) since 2013. The 2D detector has enabled the capabilities of measuring sub-mm crystals and spin density maps, enhanced the efficiency of data collection and phase transition detection, and improved the signal-to-noise ratio. Recently, the HB-3A four-circle diffractometer has been undergoing a detector upgrade towards a much larger area, magnetic-field-insensitive, Anger camera detector. The instrument will become capable of doing single-crystal neutron diffraction under ultra-low temperatures (50 mK), magnetic fields (up to 8 T), electric fields (up to 11 kV/mm), and hydrostatic high pressures (up to 45 GPa). Furthermore, half-polarized neutron diffraction is also available to measure weak ferromagnetism and local site magnetic susceptibilities. With the new high-resolution 2D detector, the four-circle diffractometer has become more powerful for studying magnetic materials under extreme sample environment conditions; hence, it has been given a new name: DEMAND.

Three-terminal memtransistors based on two-dimensional layered gallium selenide nanosheets for potential low-power electronics applications

A multi-terminal hybrid system named memtransistor has recently been proposed by combining the concepts of both memristor and field effect transistor (FET) with two-dimensional (2D) layered materials as the active semiconductor layer. In the memtransistors, the gate voltages are capable of modulating not only the transport properties of the fabricated FET, but also the resistive switching (RS) behaviors of the memristor. Herein, we employ mechanically exfoliated 2D layered GaSe nanosheets to prepare GaSe based three-terminal memtransistors. By using Ag as the electrodes, the memristor exhibits non-volatile bipolar RS characteristics. More importantly, under exposure to air for one week, the RS behaviors are dramatically enhanced with the ON/OFF ratio reaching up to 5.3 × 105 and ultralow threshold electric field of ~3.3 × 102 V cm−1. The ultralow threshold electric field of GaSe based memristor could be related to the low migration energy of the intrinsic Ga vacancy in p-type GaSe. Moreover, the GaSe-based memristor shows long-term retention (~104 s) and high cycling endurance (~5000 cycles) simultaneously. Hence, the fabricated three-terminal 2D GaSe memtransistors possess high performance with large switching ratios, ultralow threshold electric field, good endurance and long-term retention. Furthermore, the device demonstrates gate tunability in RS characteristics, suggesting the promising applications in multi-terminal electronic devices with low power consumption and complex functionalities, ranging from non-volatile memory, logic device to neuromorphic computing.

Mutual benefit achieved by combining ultralow-field magnetic resonance and hyperpolarizing techniques.

Ultralow-field (ULF) nuclear magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are promising spectroscopy and imaging methods allowing for, e.g., the simultaneous detection of multiple nuclei or imaging in the vicinity of metals. To overcome the inherently low signal-to-noise ratio that usually hampers a wider application, we present an alternative approach to prepolarized ULF MRS employing hyperpolarization techniques like signal amplification by reversible exchange (SABRE) or Overhauser dynamic nuclear polarization (ODNP). Both techniques allow continuous hyperpolarization of 1H as well as other MR-active nuclei. For the implementation, a superconducting quantum interference device (SQUID)-based ULF MRS/MRI detection scheme was constructed. Due to the very low intrinsic noise level, SQUIDs are superior to conventional Faraday detection coils at ULFs. Additionally, the broadband characteristics of SQUIDs enable them to simultaneously detect the MR signal of different nuclei such as 13C, 19F, or 1H. Since SQUIDs detect the MR signal directly, they are an ideal tool for a quantitative investigation of hyperpolarization techniques such as SABRE or ODNP.

Multi-frequency ODMR of Nitrogen-Vacancy Color Centers in Diamond Crystals in zero magnetic fields

Techniques of optical detection of magnetic resonance, as applied tothe nitrogen-vacancy center in diamond, provide a tool for controlling both electron and nuclear spins. These techniques generally use a combination of microwave (MW) drive field for electronic spin transitions and radiofrequency (RF) drive field for nuclear spin transitions. They are most effective in strong magnetic fields where levels anticrossing (LAC) occurs; therefore NV spin system dynamics is mostly studied under these conditions. Nevertheless, zero-field LAC can probably also be used for controlling electron and nuclear spin states as well for exciting narrow resonances for metrological application, and these perspectives are not yet properly investigated. Here we present two-quantum resonances appearing in ODMR spectra of NV centers in bulk diamond under multi-frequency (MW+RF) resonance excitation in zero and ultra-low magnetic fields, and discuss their specifics.

Scalar relaxation of NMR transitions at ultralow magnetic field.

Nuclear magnetic resonance signals for 1H in simple chlorinated, brominated and deuterated liquids were detected at field strengths between 1 nT and a few μT to investigate the influence of scalar relaxation of the second kind (SR2K). SR2K describes the acceleration in magnetization decay rate for a spin-1/2 nucleus that is scalar coupled to a fast-relaxing quadrupolar nucleus. In agreement with simple theoretical models, the experimental data show that couplings to nuclei with small, nonzero quadrupole moments (2H) give rise to higher transverse relaxation rates at ultralow field than rapidly relaxing quadrupolar nuclei (Cl and Br). This behavior is opposite to the case normally encountered in high-field NMR, and demonstrates that certain nuclei in the spin system may be "weakly coupled" or even decoupled when the applied magnetic field is zero. The results show that the capability for precision determination of NMR frequencies and molecular structural information depends strongly on the composition and topology of the nuclear spin system.

Design of biplanar shim coils for ultra-low field MRI

Design of biplanar shim coils for ultra-low field MRI

A novel special optical fiber with magneto-optic nonreciprocal phase shift under transversely applied magnetic field

A novel special optical fiber, which is very sensitive to magnetic field, is proposed. The two beam lights counter-propagating in this kind of fiber can generate large nonreciprocal phase shift. It can be used in ultra-low magnetic field detection. In this paper, the related theory is derived in detail. The influence of fiber parameters on the effect is simulated and analyzed. It is proved that a magnetic field sensor with pTesla-level precision could be demonstrated with this kind of special fiber in this paper.

Feasibility of functional MRI at ultralow magnetic field via changes in cerebral blood volume

We investigate the feasibility of performing functional MRI (fMRI) at ultralow field (ULF) with a Superconducting QUantum Interference Device (SQUID), as used for detecting magnetoencephalography (MEG) signals from the human head. While there is negligible magnetic susceptibility variation to produce blood oxygenation level-dependent (BOLD) contrast at ULF, changes in cerebral blood volume (CBV) may be a sensitive mechanism for fMRI given the five-fold spread in spin-lattice relaxation time (T1) values across the constituents of the human brain. We undertook simulations of functional signal strength for a simplified brain model involving activation of a primary cortical region in a manner consistent with a blocked task experiment. Our simulations involve measured values of T1 at ULF and experimental parameters for the performance of an upgraded ULFMRI scanner. Under ideal experimental conditions we predict a functional signal-to-noise ratio of between 3.1 and 7.1 for an imaging time of 30 min, or between 1.5 and 3.5 for a blocked task experiment lasting 7.5 min. Our simulations suggest it may be feasible to perform fMRI using a ULFMRI system designed to perform MRI and MEG in situ.

NMR relaxation in porous materials at zero and ultralow magnetic fields

NMR detection in the ultralow-field regime (below 10 μT) was used to measure the nuclear spin relaxation rates of liquids imbibed into silica pellets with mean pore diameters in the 10–50 nm range. Heptane, formic acid and acetic acid were studied and relaxation rate data were compared with a conventional field-cycling NMR technique. Detection of 1H-13C spin coupling NMR signals at zero field (∼0.1 nT) allowed spectroscopic identification of molecules inside the porous material and unambiguous measurements of the chemistry-specific relaxation rates in liquid mixtures. In the case of molecules that contain 1H and 13C, spin-singlet state relaxation can provide additional information about the dynamics. Applications and future improvements to the methodology are discussed.

Ultra-low-field magneto-elastocaloric cooling in a multiferroic composite device

The advent of caloric materials for magnetocaloric, electrocaloric, and elastocaloric cooling is changing the landscape of solid state cooling technologies with potentials for high-efficiency and environmentally friendly residential and commercial cooling and heat-pumping applications. Given that caloric materials are ferroic materials that undergo first (or second) order phase transitions near room temperature, they open up intriguing possibilities for multiferroic devices with hitherto unexplored functionalities coupling their thermal properties with different fields (magnetic, electric, and stress) through composite configurations. Here we demonstrate a magneto-elastocaloric effect with ultra-low magnetic field (0.16 T) in a compact geometry to generate a cooling temperature change as large as 4 K using a magnetostriction/superelastic alloy composite. Such composite systems can be used to circumvent shortcomings of existing technologies such as the need for high-stress actuation mechanism for elastocaloric materials and the high magnetic field requirement of magnetocaloric materials, while enabling new applications such as compact remote cooling devices.

Analysis of the ultra-low frequency magnetic field fluctuations prior to the 2016 Kumamoto (Japan) earthquakes in terms of the method of critical fluctuations

The method of critical fluctuations (MCF) is a time series analysis method which provides a way of both identifying the critical state and the departure from it. Its application to the ground-based ultra-low frequency (ULF) magnetic field fluctuations observed prior to the very strong earthquakes (EQs) of magnitudes MW=6.2, MW=6.0 and MW=7.0 which sequentially took place within a two days period (April 14–15, 2016) in Southwest Japan under the city of Kumamoto reveals when the underlying process reached critical state, as well as when it departed from critical state. Specifically, critical dynamics was identified in the raw total geomagnetic field intensity (F) ULF recordings of the Kanoya (Japan) station ∼4 d before the MW=6.2 and ∼5 d before the MW=7.0 event. Moreover, the progressive development of the symmetry breaking phenomenon, which signifies departure from critical state, was identified in later recordings. Specifically the phenomenon evolved from a few hours before the MW=6.0 event until a few hours after the occurrence of the specific EQ, which was a few hours before the MW=7.0 event. The detected combination of phenomena, i.e., the detection of critical state followed by the detection of the departure from the critical state by means of symmetry breaking, indicates that the main event was the third and strongest EQ, while the two preceding EQs were strong foreshocks.

Design of an ultralow power CNTFET based 9T SRAM with shared BL and half select free techniques

AbstractIn this paper, we propose a new design of high‐performance ultralow power carbon nanotube field effect transistor (CNTFET)‐based nine‐transistor static random access memory (SRAM) cell and its implementation using shared bitline (BL) and half‐select free techniques. Simulations of the 9T SRAM design, using CNTFET compact model, have presented merits over the silicon‐complementary‐metal oxide semiconductor (CMOS) SRAM cell in terms of leakage current, power consumption, and stability. Uses of the half‐select free technique eliminate the conflict between read and write operations and shared BL technique offers reduced physical layout area and enhanced data access speed. Further, uses of the increased number of tubes or say CNT array in the CNTFET device increases the probability of functionality (>95%) with a high yield SRAM cell.

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T2 contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two orders of magnitude larger than typical commercial Gd-based T1 contrast agents operating at high fields (1.5 T and 3 T). The significantly enhanced r1 value at ultra-low fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ”). SPION-based T1-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxide-based nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information.

The Relationship Equation Between the Properties of Imbibition Agent and Imbibition Efficiency

Based on a large number of physics simulation experiment data, mathematics relationship problems of the correlation of imbibition efficiency influence factors have been solved, and the correlation equation have been established. Field ML and field YT was chosen to represent the extra-low permeability field, Field JY and field QX was chosen to represent the ultra-low permeability field. The impact trend of imbibition efficiency with interfacial tension, emulsion stability, penetration force and viscosity has been found. A result has been found through the R factor analysis by common factor variance and coefficient of variation method, the impact order on imbibition efficiency of oil-wet core or oil sand is interfacial tension, emulsion stability, viscosity ratio and penetration force ratio. The four factors and three factors structural equation models have been established, and passed the model test. The impact of cross term is considered. This study has great significance in analyzing the factors affecting the imbibition efficiency.

OA020] Fast field-cycling MRI: Novel contrast changes through switched magnetic fields

Purpose Fast Field-Cycling MRI (FFC-MRI) is a novel MRI technique in which the external magnetic field ( B 0 ) is switched during the imaging experiment, always returning to the same value ( B 0 D ) for signal detection. By doing this, FFC-MRI grants access to information which is invisible to conventional MRI scanners, including the variation of T 1 with magnetic field. These measurements, known as T 1 -dispersion, exhibit great promise as a new form of endogenous image contrast, and may have application in the early diagnosis of a range of diseases. Construction of an MR imaging system capable of rapidly switching magnetic fields, and reaching ultra-low fields (200 μT or lower), requires novel magnets, power supplies and control electronics. Here we will describe progress on a whole-body human sized FFC imaging system and preliminary results from a clinical trial imaging acute stroke using FFC-MRI. Methods The magnet (Tesla Engineering Ltd, UK) is of a resistive design with a length of 2 m and an inner bore diameter of 500 mm; it is capable of achieving a maximum field strength ( B 0 D ) of 0.2 T (8.52 MHz proton Larmor frequency). The system can switch between zero and maximum field in 12 ms, corresponding to a maximum dB/dT of 16.7 T/s. The gradients and RF system are controlled by a commercial MRI console (MR Solutions Ltd, UK) while the main magnet coil, shim coils and earth’s-field cancellation coils (necessary for ultra-low field operation) are controlled by a dedicated embedded computer running in-house software written in Labview (National Instruments, US). Results The prototype system has been fully commissioned and is now operational. FFC-MRI imaging of patients (with full ethical permissions granted) using the system has now commenced as part of a clinical study on imaging acute stroke. It is hoped that the new information afforded by FFC-MRI will aid in the detection and assessment of stroke. Conclusions The novel system design described here will allow us to explore the unique T 1 dispersion contrast made available by FFC-MRI. Future work will concentrate on identifying how this newly accessible region of the T 1 dispersion curve can be exploited for clinical diagnosis.