Ultra-low Field Research Articles

High-Field-Blinded Assessment of Portable Ultra-Low-Field Brain MRI for Multiple Sclerosis.

MRI is crucial for multiple sclerosis (MS), but the relative value of portable ultra-low field MRI (pULF-MRI), a technology that holds promise for extending access to MRI, is unknown. We assessed white matter lesion (WML) detection on pULF-MRI compared to high-field MRI (HF-MRI), focusing on blinded assessments, assessor self-training, and multiplanar acquisitions. Fifty-five adults with MS underwent pULF-MRI following their HF-MRI. Two neuroradiologists independently assessed pULF-MRI images in an evaluation process, including initial assessment blinded to HF-MRI, self-training with reference to HF-MRI and evaluation of 20 cases with additional T2-fluid-attenuated inversion recovery in an additional plane. A third rater conducted cross-referenced analysis with HF-MRI data to determine true-positive lesions, false-positive areas, and case-level sensitivity and positive predictive value. The mean age of participants was 50 years (standard deviation: 11; 74% women). Initially, Rater 2 marked more false-positive areas than Rater 1 (p = 0.003). After self-training, both raters embraced a conservative approach, with Rater 2 marking fewer false-positive areas (p = 0.01). Both raters maintained 100% case-level sensitivity and positive predictive value for detecting at least one WML, particularly in periventricular areas. Multiplanar acquisitions reduced both false-positive areas and true-positive lesions. True-positive lesions and false-positive areas had similar contrast-to-noise ratios in the juxtacortical region (p = 0.73) but not in periventricular, deep parenchymal regions (p = 0.004, p = 0.01). With adequate training, radiological interpretation of pULF-MRI has high sensitivity and positive predictive value for MS lesions but should be approached conservatively. These results suggest utility for patient triage, potentially reducing diagnostic delay, and screening high-risk individuals.

Ultra-low to Moderate Radiation Level Neutron Dosimetry Measurements with H*10-TMFD vs. ROSPEC, Eberline, and Ludlum Detector Systems.

H*10 neutron dosimetry (unlike gamma dosimetry), requires consideration of neutron energy spectra due to the 20× variation of the weight factor over the thermal-to-fast energy range, as well as the neutron radiation field dose rates ranging from cosmic, ~.01 μSv h-1 levels to commonly encountered ~10-200 μSv h-1 in nuclear laboratories/processing plants, and upwards of 104 Sv h-1 in nuclear reactor environments. This paper discusses the outcome of the comparison of spectrum-weighted neutron dosimetry covering thermal-to-fast energy using the novel H*-TMFD spectroscopy-enabled sensor system in comparison with measurements using state-of-the-art neutron dosimetry systems at SRNS-Rotating Spectrometer (ROSPEC), and non-spectroscopic Eberline ASP2E ("Eberline") and Ludlum 42-49B ("Ludlum") survey instrumentation. The H*-TMFD was validated for gamma blindness using a 2.48×1010 Bq 137Cs source. The background dose rate in Savannah River Nuclear Solutions' (SRNS) low-scatter facility with all neutron sources withdrawn was estimated at 0.005 μSv h-1. From moderately high radiation field tests conducted with the high intensity (1.4 × 109 n s-1) 252Cf source and a total data collection time of ~0.15 h, the predicted dose rates from Eberline (non-spectroscopic), Ludlum (non-spectroscopic), and spectroscopic H*-TMFD instruments were found to be: ~170 μSv h-1, ~200 μSv h-, and ~ 120 μSv h-1, respectively. The equivalent spectroscopic (SRNS measured) H*10 dose rate from ROSPEC value is 130 μSv h-1, within 10% of H*10-TMFD measurement. Tests conducted for ultra-low intensity radiation field used a ~ 1.6 × 103 n s-1 252Cf bare neutron source for which over a collection time of ~18 h, the Eberline meter measured an instantaneous dose/count rate of 0 μSv h-1 and a pulse-integrated dose rate of 0.034 μSv h-1 at ~1 m. In contrast, the H*-TMFD panel located 0.22 m in direct line of sight of the 252Cf source spectroscopically measured ~0.4 μSv h-1 (within +/- 5%) over 1.8 h collection live time-with which spectrum matched perfectly to that of a bare 252Cf source. The H*TMFD predicted value of ~0.4 μSv h-1 was cross-checked and found to be within 10% of LLNL's published value of ~0.37 μSv h-1 (intensity/distance corrected via 1/r2 law of 25.5 μSv h-1at 1 m for a 1 μg 252Cf source); as well as from use of ICRP 74 conversion coefficients and MCNP code simulations. As expected, for a bare 252Cf source, H*TMFD measured epithermal neutron energy-related dose rates are well below 1% of the total dose rates. For ~0.01 μSv h-1 neutron radiation fields, ROSPEC measurements for H*10 dose rates are estimated to take 7+ d, vs. under 2 h with the H*TMFD. The feasibility of using a single CTMFD in survey mode for H*10 dose rate (nSv h- to μSv h-1) measurements within 2-3 min is demonstrated.

Exceptional field emission characteristics of self-assembled carbon nanotube sheets with ultra-low turn-on field and outstanding stability

Exceptional field emission characteristics of self-assembled carbon nanotube sheets with ultra-low turn-on field and outstanding stability

Characterization of Nuclear Magnetism At Ultralow and Zero Field Using SQUIDs

Characterization of Nuclear Magnetism At Ultralow and Zero Field Using SQUIDs

Multimodal Measurement System Development of Ultra-Low Field MRI and Magnetoencephalography with Optically Pumped Magnetometers

Multimodal Measurement System Development of Ultra-Low Field MRI and Magnetoencephalography with Optically Pumped Magnetometers

Achieving ultra-low phase transition electric field and high dielectric constant in PbZrO3-based antiferroelectric ceramics by component modulation

Achieving ultra-low phase transition electric field and high dielectric constant in PbZrO3-based antiferroelectric ceramics by component modulation

High sensitivity direct magnetic field detection based metrology for ultra-thin magnetic films and Li-ion cells.

Ultra-low magnetic field sensing is emerging as a tool for materials' diagnostics, particularly for the operando studies of electrochemical systems. A magnetic metrology system having the capability of sensing fields as low as ∼1.88 pT has been setup for such studies using a commercial atomic magnetometer. The magnetometer setup is isolated from environmental perturbations, such as mechanical vibrations, electrical noises, and ambient magnetic fields, in order to measure small signals from the samples under study. Magnetic field measurements on ferromagnetic (permalloy, Ni0.8Fe0.2) thin films, monolayers of MoS2, vanadium doped MoS2, and lithium electro-deposited copper electrodes are performed to demonstrate the sensitivity of the setup. Magnetic field scanning of commercial Li-ion cells has also been performed using this magnetic metrology method, indicating the scope of the setup for operando diagnostics.

Eliminating electromagnetic interference for RF shielding-free MRI via k-space convolution: Insights from MR parallel imaging advances.

Recent advances in ultra-low field MRI have attracted attention from both academic and industrial MR communities for its potential in democratizing MRI applications. One of the most striking features on those advances is shielding-free imaging by actively sensing and eliminating the electromagnetic interference (EMI). In this study, we review the analytical approaches for EMI estimation/elimination, and investigate their theoretical basis and relations with parallel imaging reconstruction. We provide further understanding of the existing approaches, formulating EMI estimation as convolution in k-space or multiplication in spectrum-space. We further propose to use tailored convolutional kernel to adaptively fit the varying EMI coupling across the acquisition window. These methods were evaluated with both simulation study and human brain imaging. The results show that using tailored convolutional kernel can achieve more robust performance against system and acquisition imperfections.

2D Ferroelectric Metal–Organic Frameworks for Ultralow Power Field Effect Transistors

Abstract2D ferroelectrics open a new realm of nonvolatile memory and computing devices, while metal–organic frameworks (MOF) offer tremendous possibilities to design and optimize ferroelectric performance. Integrating a MOF ferroelectric gate with a semiconducting channel provides new strategy toward ultralow power ferroelectric field effect transistors (FeFETs), yet no 2D MOF is experimentally demonstrated to be ferroelectric yet. Here, the study successfully develops 2D ferroelectric MOF nanosheets, {CuL2(H2O)2(NO3)2(H2O)1.5·(CH3OH)}∞ wherein L denotes PhPO(NH4Py)2, abbreviated as {CuIIL2}n‐MOF, and confirm its ferroelectricity down to 7 nm thickness. A large polarization of ≈14.2 µC cm−2, small coercive field of ≈33.3 V µm−1, and excellent endurability >106 cycles are found in 2D {CuIIL2}n‐MOF nanosheets. This enables to fabricate FeFETs using 2D {CuIIL2}n‐MOF as the gate and MoS2 as the channel, achieving an on/off ratio of 107 with ultralow off‐state current of 100 fA and tunable memory window, making it exceptional among known FeFETs and very promising for next‐generation ultralow power memories and computing devices

Utility of novel ultra-low field portable MRI in a remote setting in Canada.

Utility of novel ultra-low field portable MRI in a remote setting in Canada.

Field cycling imaging to characterise breast cancer at low and ultra-low magnetic fields below 0.2 T

BackgroundThis prospective feasibility study explores Field-Cycling Imaging (FCI), a new MRI technology that measures the longitudinal relaxation time across a range of low magnetic field strengths, providing additional information about the molecular properties of tissues. This study aims to assess the performance of FCI and investigate new quantitative biomarkers at low fields within the context of breast cancer.MethodsWe conducted a study involving 9 people living with breast cancer (10 tumours in total, mean age, 54 ± 10 years). FCI images were obtained at four magnetic field strengths (2.3 mT to 200 mT). FCI images were processed to generate T1 maps and 1/T1 dispersion profiles from regions of tumour, normal adipose tissue, and glandular tissue. The dispersion profiles were subsequently fitted using a power law model. Statistical analysis focused on comparing potential FCI biomarkers using a Mann-Whitney U or Wilcoxon signed rank test.ResultsWe show that low magnetic fields clearly differentiate tumours from adipose and glandular tissues without contrast agents, particularly at 22 mT (1/T1, median [IQR]: 6.8 [3.9–7.8] s−1 vs 9.1 [8.9–10.2] s−1 vs 8.1 [6.2–9.2] s−1, P < 0.01), where the tumour-to-background contrast ratio was highest (62%). Additionally, 1/T1 dispersion indicated a potential to discriminate invasive from non-invasive cancers (median [IQR]: 0.05 [0.03–0.09] vs 0.19 [0.09–0.26], P = 0.038).ConclusionsTo the best of our knowledge, we described the first application of in vivo FCI in breast cancer, demonstrating relevant biomarkers that could complement diagnosis of current imaging modalities, non-invasively and without contrast agents.

Proof of concept: Portable ultra-low-field magnetic resonance imaging for the diagnosis of epileptogenic brain pathologies.

High-field magnetic resonance imaging (MRI) is a standard in the diagnosis of epilepsy. However, high costs and technical barriers have limited adoption in low- and middle-income countries. Even in high-income nations, many individuals with epilepsy face delays in undergoing MRI. Recent advancements in ultra-low-field (ULF) MRI technology, particularly the development of portable scanners, offer a promising solution to the limited accessibility of MRI. In this study, we present and evaluate the imaging capability of ULF MRI in detecting structural abnormalities typically associated with epilepsy and compare it to high-field MRI at 3 T. Data collection was conducted within 3 consecutive weeks at the University Hospital Bonn. Inclusion criteria were a minimum age of 18 years, diagnosed epilepsy, and clinical high-field MRI with abnormalities. We used a .064 T Swoop portable MR Imaging System. Both high-field MRI and ULF MRI scans were evaluated independently by two experienced neuroradiologists as part of their clinical routine, comparing pathology detection and diagnosis completeness. Twenty-three individuals with epilepsy were recruited. One subject presented with a dual pathology. Across the entire cohort, in 17 of 24 (71%) pathologies, an anomaly colocalizing with the actual lesion was observed on ULF MRI. For 11 of 24 (46%) pathologies, the full diagnosis could be made based on ULF MRI. Tumors and posttraumatic lesions could be diagnosed best on ULF MRI, whereas cortical dysplasia and other focal pathologies were the least well diagnosed. This single-center series of individuals with epilepsy demonstrates the feasibility and utility of ULF MRI for the field of epileptology. Its integration into epilepsy care offers transformative potential, particularly in resource-limited settings. Further research is needed to position ULF MRI within imaging modalities in the diagnosis of epilepsy.

The application of PVC hollow fiber ultrafiltration membrane in ultra-low permeability oilfield

Abstract Oil containing wastewater produced from ultra-low permeability oil fields generally needs to be treated to meet the 5-1-1 standard before it can be reinjected. In order to meet the standards for treating oily wastewater in ultra-low permeability oil fields, PVC hollow fiber ultrafiltration membranes and pre-treatment processes for removing oil, suspended solids, sulfides, etc. before the membrane were selected. The application shows that the aeration air flotation flow sand filtration PVC hollow fiber ultrafiltration membrane process can treat oily wastewater, and the treated water can reach the “5-1-1” standard. In the pre-treatment process of PVC hollow fiber ultrafiltration membrane, the silicone rubber membrane aeration device has good oxidation effect, high efficiency in micro nano air flotation for oil removal and suspended solids, and easy management of sand flow filters. This process has economic feasibility and provides technical support for the treatment of oily wastewater in ultra-low permeability oil fields, with great promotional value.

Experimental Study on the Treatment of Produced Water from Carbon Dioxide Drive by Aeration Method

Abstract To further explore the effective development of produced water treatment technologies suitable for low to ultra-low permeability oil fields, and to clarify the water quality characteristics of produced water from CO2 flooding. A study was conducted on the basic water quality characteristics of produced water from low to ultra-low permeability oil fields. Indoor CO2 gas removal experiments were conducted using the aeration method under 40°C atmospheric pressure conditions. The research results indicate that the CO2 content in the extracted water is one of the important influencing factors for the changes in characteristic parameters such as water pH, mineralization, and corrosion rate; Under the condition of 40°C atmospheric pressure test, the aeration method has a significant treatment effect on the produced water from CO2 flooding, which can effectively remove 70% of the CO2 in the water, thereby improving the pH of the water to 8, and effectively inhibiting the corrosion rate of the produced water below 0.076mm/a.

High sensitivity and detectivity of anomalous Hall sensor based on coupled magnetic bilayers

Detection of ultralow magnetic field requires a magnetic sensor with high sensitivity and a low noise level. In this work, we used the Co20Fe60B20/Ti/Co20Fe60B20 magnetically coupled multilayer as the core structure of an anomalous Hall sensor. We adjusted the thickness of the Ti interlayer to modify its perpendicular magnetic anisotropy and interlayer magnetic coupling, thereby improving the sensitivity of the anomalous Hall sensor. Through the investigation of magnetic field response and noise properties of devices with different Ti thicknesses, the highest sensitivity of 34 803 Ω/T and the best magnetic field detectivity of 4.6 nT/Hz at 1 Hz were achieved with a Ti thickness of 2.0 nm at room temperature. This anomalous Hall sensor has both ultrahigh sensitivity and magnetic field detectivity, making it a good candidate for applications in detecting weak magnetic fields.

Enhancing organ and vascular contrast in preclinical ultra-low field MRI using superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) are characterized by their exceptional susceptibility and relaxivity at ultra-low field (ULF) regimes, make them a promising contrast agent (CA) for ULF MRI. Despite their distinct advantages, the translation of these properties into clinically valuable image contrast in ULF MRI remains underexplored. In this study, we investigate the use of SPIONs to generate in vivo MRI contrast at 6.5 mT within the organs and vascular system of rodents. This investigation includes comprehensive SPION characterization and phantom imaging experiments to validate the utility of SPIONs to produce positive image contrast and to facilitate phase-sensitive imaging at ULF. Optimized balanced steady-state free precession (bSSFP) and spoiled gradient echo (SPGR) MRI sequences are used to generate in vivo contrast by leveraging the distinctive properties of SPIONs at ULF. Imaging studies in rodents reveal positive organ contrast attainable in magnitude images, and MRI phase maps can be used to visualize the vascular system. This work demonstrates the effectiveness of SPIONs in enhancing preclinical organ and vascular imaging at ULF; it bridges the gap between the study of the distinctive physical properties of SPIONs and the demonstration of in vivo image contrast.

Achieving a Noise Limit with a Few-layer WSe2 Avalanche Photodetector at Room Temperature.

We engineered a two-dimensional Pt/WSe2/Ni avalanche photodetector (APD) optimized for ultraweak signal detection at room temperature. By fine-tuning the work functions, we achieved an ultralow dark current of 10-14 A under small bias, with a noise equivalent power (NEP) of 8.09 fW/Hz1/2. This performance is driven by effective dark barrier blocking and a record-long electron mean free path (123 nm) in intrinsic WSe2, minimizing dark carrier replenishment and suppressing noise under an ultralow electric field. Our APD exhibits a high gain of 5 × 105 at a modulation frequency of 20 kHz, effectively balancing gain and bandwidth, a common challenge in traditional photovoltaic-based APDs. By addressing the typical challenges of high noise and low gain and minimizing dependence on high electric fields, this work highlights the potential of 2D materials in developing efficient, low-power, and ultrasensitive photodetections.

Ultra-low-field magnetization transfer imaging at 0.055T with low specific absorption rate.

To demonstrate magnetization transfer (MT) effects with low specific absorption rate (SAR) on ultra-low-field (ULF) MRI. MT imaging was implemented by using sinc-modulated RF pulse train (SPT) modules to provide bilateral off-resonance irradiation. They were incorporated into 3D gradient echo (GRE) and fast spin echo (FSE) protocols on a shielding-free 0.055T head scanner. MT effects were first verified using phantoms. Brain MT imaging was conducted in both healthy subjects and patients. MT effects were clearly observed in phantoms using six SPT modules with total flip angle 3600° at central primary saturation bands of approximate offset ±786 Hz, even in the presence of large relative B0 inhomogeneity. For brain, strong MT effects were observed in gray matter, white matter, and muscle in 3D GRE and FSE imaging using six and sixteen SPT modules with total flip angle 3600° and 9600°, respectively. Fat, cerebrospinal fluid, and blood exhibited relatively weak MT effects. MT preparation enhanced tissue contrasts in T2-weighted and FLAIR-like images, and improved brain lesion delineation. The estimated MT SAR was 0.0024 and 0.0008 W/kg for two protocols, respectively, which is far below the US Food and Drug Administration (FDA) limit of 3.0 W/kg. Robust MT effects can be readily obtained at ULF with extremely low SAR, despite poor relative B0 homogeneity in ppm. This unique advantage enables flexible MT pulse design and implementation on low-cost ULF MRI platforms to achieve strong MT effects in brain and beyond, potentially augmenting their clinical utility in the future.

Ultra-low-field magnetic resonance angiography at 0.05 T: A preliminary study.

We aim to explore the feasibility of head and neck time-of-flight (TOF) magnetic resonance angiography (MRA) at ultra-low-field (ULF). TOF MRA was conducted on a highly simplified 0.05 T MRI scanner with no radiofrequency (RF) and magnetic shielding. A flow-compensated three-dimensional (3D)gradient echo (GRE) sequence with a tilt-optimized nonsaturated excitation RF pulse, and a flow-compensated multislice two-dimensional (2D) GRE sequence, were implemented for cerebral artery and vein imaging, respectively. For carotid artery and jugular vein imaging, flow-compensated 2D GRE sequences were utilized with venous and arterial blood presaturation, respectively. MRA was performed on young healthy subjects. Vessel-to-background contrast was experimentally observed with strong blood inflow effect and background tissue suppression. The large primary cerebral arteries and veins, carotid arteries, jugular veins, and artery bifurcations could be identified in both raw GRE images and maximum intensity projections. The primary brain and neck arteries were found to be reproducible among multiple examination sessions. These preliminary experimental results demonstrated the possibility of artery TOF MRA on low-cost 0.05 T scanners for the first time, despite the extremely low MR signal. We expect to improve the quality of ULF TOF MRA in the near future through sequence development and optimization, ongoing advances in ULF hardware and image formation, and the use of vascular T1 contrast agents.

Homogeneous B0 coil design method for open-access ultra-low field magnetic resonance imaging: A simulation study

A multimodal brain function measurement system integrating functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) is expected to be a tool that will provide new insights into neuroscience. To integrate fMRI and MEG, an ultra-low-field MRI (ULF-MRI) scanner that can generate a static magnetic field (B0) with an electromagnetic coil and turn off the B0 during MEG measurements is desirable. While electromagnetic B0 coil has the above advantages, it also has a trade-off between size and the broadness of the magnetic field homogeneity. In this study, we proposed a method for designing a B0 multi-stage circular coil arrangement that determines the number of coils required to maximize magnetic field homogeneity and minimize the total wiring length of the coils. The optimized multi-stage coil arrangement had an external shape of 600 mm in diameter and a maximum height of 600 mm, with an aperture of 600 mm in diameter and 300 mm in height. The magnetic field homogeneity was <100 ppm over a 210 mm diameter spherical volume (DSV). Compared to a previous two coil pairs arrangement with the same magnetic field homogeneity, the diameter was 1/1.9 times smaller, indicating that the newly designed B0 coil arrangement realized a smaller size and wider magnetic field homogeneity.