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The biggest drawbacks of existing NMRI (Nuclear Magnetic Resonance Imaging) systems are their physical size, hardware and operating costs, and their lack of portability. This has encouraged low-cost and portable applications that can operate in low magnetic fields and volumes. These studies attempt to fill the gaps in areas such as object and practical medical imaging, substance analysis and determination, production quality and waste control. However, the very weak, inhomogeneous and nonlinear magnetic fields they have are the most important factors that negatively affect the results in these systems. This study was carried out with the idea that a working simulation for design would fill an important gap in examining and evaluating the relevant fields and their results. With this simulation, imaging results can be obtained for computer generated fields and 3D phantom tissues. In this study, magnetic field components in a limited Cartesian space for the static main magnetic field and gradient field coils required for basic NMRI were computerized according to the Biot-Savart principle. A spatial volume region has been determined where the static main magnetic field is sufficiently homogeneous and the gradient fields are sufficiently linear. By rescaling all field magnitudes working together, spin FID signals were generated for virtual 3D phantom in the same limited space, k-space and NMR images were obtained. [ABSTRACT FROM AUTHOR]

Magnetic susceptibility imaging may provide valuable information about chemical composition and microstructural organization of tissue. However, its estimation from the MRI signal phase is particularly difficult as it is sensitive to magnetic tissue properties ranging from the molecular to the macroscopic scale. The MRI Larmor frequency shift measured in white matter (WM) tissue depends on the myelinated axons and other magnetizable sources such as iron‐filled ferritin. We have previously derived the Larmor frequency shift arising from a dense medium of cylinders with scalar susceptibility and arbitrary orientation dispersion. Here, we extend our model to include microscopic WM susceptibility anisotropy as well as spherical inclusions with scalar susceptibility to represent subcellular structures, biologically stored iron, and so forth. We validate our analytical results with computer simulations and investigate the feasibility of estimating susceptibility using simple iterative linear least squares without regularization or preconditioning. This is done in a digital brain phantom synthesized from diffusion MRI measurements of an ex vivo mouse brain at ultra‐high field. [ABSTRACT FROM AUTHOR]

This paper evaluates potential accuracy characteristics of a small-sized goniometer based on nuclear magnetic resonance with an extended dynamic range. This required constructing a model of goniometer errors, estimating its accuracy based on this model, and formulating practical recommendations for the design of such a device based on the accuracy assessment. To evaluate the accuracy of a nuclear goniometer, a theoretical model was built that makes it possible to determine the optimal operating parameters of the cell gas mixture, the ranges of their permissible changes, the sensitivity of the goniometer, and the dependence of its characteristics on external and internal factors. In particular, the dependence of output signal of the device on the parameters of gas mixture and optical pumping has been determined. For a goniometer with a cell volume of 8 cm³, the optimum temperature is 130 °C, and the optimum intensity of the pumping radiation is 5 mW. The dependence of output signal on the measured angle of rotation was also established, as well as the noise and error dependence of the device on the permissible values of its parameters. Based on the model built, parameters of a goniometer with a cell volume of 8 cm3 were determined; the maximum angular sensitivity of such a goniometer with complete suppression of technical noise is δφsen=1.0 arcsec. The greatest contribution to the angle measurement error is from the instability of pumping power Ip (ΔIp/Ip=0.05) – 85 %, magnetic field B0 (ΔB0/B0=10-8) – 13 %, temperature T (ΔT/T=0.1) – 2 %. The goniometer under consideration corresponds to the medium accuracy class, δφtot≥10 arcsec. It could be used in optical manufacturing for operational control, calibration, and certification of optical products. To improve the angular accuracy of the goniometer, it is necessary to increase the stability of the laser pumping intensity [ABSTRACT FROM AUTHOR]

Radio Frequency (RF) coils are necessary for MRI machines and are critical in improving image quality. Due to numerous research efforts in RF coil development, birdcage and surface coils are the most commonly used in clinical applications to enhance medical imaging quality. This article introduces a new surface-type RF coil that is improved by its proximity to the scanned object, boosting its effectiveness. Contrary to past research that examined RF coils operating at one resonant frequency, this study presents a microstrip-based surface RF coil created for dual-frequency use at 64 MHz and 128 MHz, matching the Larmor frequencies for 1.5 T and 3 T MRI machines. The coil was carefully planned, tested, and created, with simulations including a human body model to assess the distribution of the $B_{1}$ field and signal-to-noise ratio (SNR), both essential for assessing the RF coil’s performance in the coronal plane. A tuning circuit was created and tested to maximize resonance at specific frequencies. In contrast, a matching circuit was designed to improve power transfer efficiency between the signal generator and the coil. The suggested RF coil was enhanced by incorporating these circuits, improving overall performance. Both the suggested surface-type microstrip RF coil, which includes tuning and matching circuits, effectively functions at 64 MHz and 128 MHz, as shown by both simulation and experimental results, making it a viable clinical option.

Purpose: To extend quantitative susceptibility mapping to account for microstructure of white matter (WM) and demonstrate its effect on ex vivo mouse brain at 16.4T. Theory and Methods: Previous studies have shown that the MRI measured Larmor frequency also depends on local magnetic microstructure at the mesoscopic scale. Here, we include effects from WM microstructure using our previous results for the mesoscopic Larmor frequency Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$ of cylinders with arbitrary orientations. We scrutinize the validity of our model and QSM in a digital brain phantom including Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$ from a WM susceptibility tensor and biologically stored iron with scalar susceptibility. We also apply susceptibility tensor imaging to the phantom and investigate how the fitted tensors are biased from Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$. Last, we demonstrate how to combine multi‐gradient echo and diffusion MRI images of ex vivo mouse brains acquired at 16.4T to estimate an apparent scalar susceptibility without sample rotations. Results: Our new model improves susceptibility estimation compared to QSM for the brain phantom. Applying susceptibility tensor imaging to the phantom with Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$ from WM axons with scalar susceptibility produces a highly anisotropic susceptibility tensor that mimics results from previous susceptibility tensor imaging studies. For the ex vivo mouse brain we find the Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$ due to WM microstructure to be substantial, changing susceptibility in WM up to 25% root‐mean‐squared‐difference. Conclusion: Ω‾Meso$$ {\overline{\Omega}}^{\mathrm{Meso}} $$ impacts susceptibility estimates and biases susceptibility tensor imaging fitting substantially. Hence, it should not be neglected when imaging structurally anisotropic tissue such as brain WM. [ABSTRACT FROM AUTHOR]

This article studies the optimal design approach for a portable nuclear magnetic resonance (NMR) system for use in non-destructive flow measurement applications. The mechanical and electromagnetic design procedures were carried out using the Ansys Maxwell finite-element analysis (FEA) software tool. The proposed procedure considered homogeneity and strength constraints while ensuring the desired functionality of the intended device for a given application. A modified particle swarm optimization (MPSO) algorithm was proposed as a reference design framework for optimization stages. The optimally designed NMR tool was prototyped, and its functionality was validated via several case studies. To assess the functionality of the prototyped device, Larmor frequency for hydrogen atom was captured and compared with theoretical results. Furthermore, the functionality and accuracy of the prototyped NMR tool is compared to the off-the-shelf NMR tool. Results demonstrated the feasibility and accuracy of the prototyped NMR tool constrained by factors, such as being lightweight and compact.

Purpose: Estimating magnetic susceptibility using MRI depends on inverting a forward relationship between the susceptibility and measured Larmor frequency. However, an often‐overlooked constraint in susceptibility fitting is that the Larmor frequency is only measured inside the sample, and after successful background field removal, susceptibility sources should only reside inside the same sample. Here, we test the impact of accounting for these constraints in susceptibility fitting. Theory and Methods: Two different digital brain phantoms with scalar susceptibility were examined. We used the MEDI phantom, a simple phantom with no background fields, to examine the effect of the imposed constraints for various levels of SNR. Next, we considered the QSM reconstruction challenge 2.0 phantom with and without background fields. We estimated the parameter accuracy of openly‐available QSM algorithms by comparing fitting results to the ground truth. Next, we implemented the mentioned constraints and compared to the standard approach. Results: Including the spatial distribution of frequencies and susceptibility sources decreased the RMS‐error compared to standard QSM on both brain phantoms when background fields were absent. When background field removal was unsuccessful, as is presumably the case in most in vivo conditions, it is better to allow sources outside the brain. Conclusion: Informing QSM algorithms about the location of susceptibility sources and where Larmor frequency was measured improves susceptibility fitting for realistic SNR levels and efficient background field removal. However, the latter remains the bottleneck of the algorithm. Allowing for external sources regularizes unsuccessful background field removal and is currently the best strategy in vivo. [ABSTRACT FROM AUTHOR]

This article studies the optimal design approach for a portable nuclear magnetic resonance (NMR) system for use in non-destructive flow measurement applications. The mechanical and electromagnetic design procedures were carried out using the Ansys Maxwell finite-element analysis (FEA) software tool. The proposed procedure considered homogeneity and strength constraints while ensuring the desired functionality of the intended device for a given application. A modified particle swarm optimization (MPSO) algorithm was proposed as a reference design framework for optimization stages. The optimally designed NMR tool was prototyped, and its functionality was validated via several case studies. To assess the functionality of the prototyped device, Larmor frequency for hydrogen atom was captured and compared with theoretical results. Furthermore, the functionality and accuracy of the prototyped NMR tool is compared to the off-the-shelf NMR tool. Results demonstrated the feasibility and accuracy of the prototyped NMR tool constrained by factors, such as being lightweight and compact. [ABSTRACT FROM AUTHOR]

We study the evolution of the energy and magnetic moment of a quantum charged particle placed in a homogeneous magnetic field, when this field changes its sign adiabatically. We show that after a single magnetic field passage through zero value, the famous adiabatic invariant ratio of energy to frequency is reestablished again, but with a proportionality coefficient higher than in the initial state. The concrete value of this proportionality coefficient depends on the power index of the frequency dependence on time near zero point. In particular, the adiabatic ratio of the initial ground state (with zero radial and angular quantum numbers) triplicates if the frequency tends to zero linearly as a function of time. If the Larmor frequency attains zero more than once, the adiabatic proportionality coefficient strongly depends on the lengths of the time intervals between zero points, so that the mean energy behavior can be quasi-stochastic after many passages through zero value. The original Born–Fock adiabatic theorem does not work after the frequency passes through zero. However, its generalization is found: the initial Fock state becomes a wide superposition of many instantaneous Fock states, whose weights do not depend on time in the new adiabatic regime. [ABSTRACT FROM AUTHOR]

The magnetic susceptibility of tissue can provide valuable information about its chemical composition and microstructural organization. However, the relation between the magnetic microstructure and the measurable Larmor frequency shift is understood only for a few idealized cases. Here we analyze the microstructure formed by magnetized, NMR‐invisible infinite cylinders suspended in an NMR‐reporting fluid. Through simulations, we scrutinize various geometries of mesoscopic Lorentz cavities and inclusions, and show that the cavity size should be approximately one order of magnitude larger than the width of the inclusions. We also analytically derive the Larmor frequency shift for a population of cylinders with arbitrary orientation dispersion and show that it is determined by the l=2 Laplace expansion coefficients p2m of the cylinders' orientation distribution function. Our work underscores the need to account for microstructural organization when estimating magnetic tissue properties. [ABSTRACT FROM AUTHOR]

The method for locating hidden subsurface non-metallic pipelines made of high-molecular compounds (polyethylene, polystyrene, PVC, polypropylene) is proposed. It is based on the self-reactance properties of liquids in pipelines, which become apparent under the forced polarization of liquid by turning the magnetic axis of their protons at some angle in relation to the Earth's magnetic field. The precession of the liquid proton axis in the direction to the Earth's magnetic field appears after the end of the polarization pulse action. It results in the appearance of the variable magnetic field of free nuclear precession with Larmor frequency thus testifying to the location of subsurface pipeline with liquid. Proton precession time depends on the liquid and serves as a sign for recognition of the liquid type in a pipeline. [ABSTRACT FROM AUTHOR]

Magnetic susceptibility MRI offers potential insights into the chemical composition and microstructural organization of tissue. However, estimating magnetic susceptibility in white matter is challenging due to anisotropic subvoxel Larmor frequency shifts caused by axonal microstructure relative to the B0 field orientation. Recent biophysical models have analytically described how axonal microstructure influences the Larmor frequency shifts, relating these shifts to a mesoscopically averaged magnetic field that depends on the axons' fiber orientation distribution function (fODF), typically estimated using diffusion MRI. This study is aimed at validating the use of MRI to estimate mesoscopic magnetic fields and determining whether diffusion MRI can faithfully estimate the orientation dependence of the Larmor frequency shift in realistic axonal microstructure. To achieve this, we developed a framework for performing Monte Carlo simulations of MRI signals in mesoscopically sized white matter axon substrates segmented with electron microscopy. Our simulations demonstrated that with careful experimental design, it is feasible to estimate mesoscopic magnetic fields. Additionally, the fODF estimated by the standard model of diffusion in white matter could predict the orientation dependence of the mesoscopic Larmor frequency shift. We also found that incorporating the intra-axonal axial kurtosis into the standard model could explain a significant amount of signal variance, thereby improving the estimation of the Larmor frequency shift. This factor should not be neglected when fitting the standard model., (© 2025 The Author(s). NMR in Biomedicine published by John Wiley & Sons Ltd.)

In this study, the Laplace transform approach have been employed to analyze the bound state solutions of two-dimensional Schrödinger equation with isotropic oscillator plus inverse quadratic potential. The wavefunctions and energy equation were derived. Thereafter, the so-called partition function and the thermodynamic properties were evaluated as a function Larmor frequency in the range 0 < ω L < 100 for some values of parameter λ. The findings showed that both the partition function and thermodynamic properties of the molecules were modified significantly by magnetic interactions, which invariably may alter the macroscopic behaviour of the system examined. • Solutions of two-dimensional Schrödinger equation with IOPIQP via Laplace Transform Approach. • Partition function and thermodynamic properties were evaluated as a function Larmor frequency. • Thermodynamic properties of the molecules were altered significantly by magnetic interactions. [ABSTRACT FROM AUTHOR]

The generation of spin current and spin polarization in a two-dimensional electron gas structure is studied in the presence of Dresselhaus and Rashba spin-orbit couplings (SOC), the strength of the latter being modulated in time by an ac gate voltage. By means of the non-Abelian gauge field approach, we established the relation between the Lorentz spin force and the spin current in the SOC system, and showed that the longitudinal component of the spin force induces a transverse spin current. For a constant (time-invariant) Rashba system, we recover the universal spin Hall conductivity of ..., derived previously via the Berry phase and semi-classical methods. In the case of a time-dependent SOC system, the spin current is sustained even under strong impurity scattering. We evaluated the ac spin current generated by a time-modulated Rashba SOC in the absence of any dc electric field. The magnitude of the spin current reaches a maximum when the modulation frequency matches the Larmor frequency of the electrons. [ABSTRACT FROM AUTHOR]

We report measurements of electron-spin-echo envelope modulation (ESEEM) performed at millikelvin temperatures in a custom-built high-sensitivity spectrometer based on superconducting micro-resonators. The high quality factor and small mode volume (down to 0.2 pL) of the resonator allow us to probe a small number of spins, down to 5×10². We measure two-pulse ESEEM on two systems: erbium ions coupled to 183W nuclei in a natural-abundance CaWO4 crystal and bismuth donors coupled to residual 29Si nuclei in a silicon substrate that was isotopically enriched in the 28Si isotope. We also measure three- and five-pulse ESEEM for the bismuth donors in silicon. Quantitative agreement is obtained for both the hyperfine coupling strength of proximal nuclei and the nuclear-spin concentration. [ABSTRACT FROM AUTHOR]

We introduce a low-complexity, low-cost, yet sufficiently accurate automatic tune and match system for NMR and MRI applications. The ArduiTaM builds upon an Arduino Uno embedded system that drives a commercial frequency synthesiser chip to perform a frequency sweep around the Larmor frequency. The generated low-power signal is fed to the NMR coil, after which the reflected waves are detected using a directional coupler and amplified. The signal shape is then extracted by means of an envelope detector and passed on to the Arduino, which performs a dip search while continuously generating actuator control patterns to adjust the tune and match capacitors. The process stops once the signal dip reaches the Larmor frequency. The ArduiTaM works readily with any spectrometer frequency in the range from 1 to 23 T. The speed of the ArduiTaM is mainly limited by the clock of the Arduino and the capacitor actuation mechanism. The Arduino can easily be replaced by a higher-speed microcontroller, and varactors can replace stepper-motor controlled variable capacitors. The ArduiTaM is made available in open source, and so is easily duplicated. [ABSTRACT FROM AUTHOR]

A reactive-element based Decoupling Network (DN) for 7-Tesla Magnetic Resonance Imaging (MRI) phased arrays is presented to compensate for the effect of mutual coupling between array elements. The DN network consists of two reactive elements connected in parallel between a two-element array, each element in the array is a rectangular loop-shape microstrip transmission line Radio Frequency (RF) coil. Integrated with an L-shaped tunable matching network, the decoupled elements can be tuned easily to operate at the working frequency of the 7-Tesla MRI system. Numerical modeling is carried out using CST to design, characterize and verify the performance of the decoupling and matching network for a two-element MRI array. [ABSTRACT FROM AUTHOR]

In the weak field approximation, we study the gravitational lensing by spherical symmetric compact object immersed in magnetic field in the presence of magnetized plasma. The external magnetic field causes the split of the deflection angle of the photon, Einstein ring and Einstein cross as the counterpart of the Zeeman effect. In particular, the magnetic field affects the magnification of images, creating additional components. We also study the time delay of an electromagnetic signal due to the geometry and the gravitational field around the lensing source. We show that the time delay of the electromagnetic signal strongly depends on the plasma parameters, and it slightly decreases in the plasma in comparison with that in vacuum. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to measure the magnetic gradient by an Mz atomic magnetometer using a micro-fabricated shaped rubidium vapor cell. The shaped vapor cell is fabricated by a chemical foaming process. Four micro radio frequency (RF) coils are mounted on the shaped rubidium vapor cell. Magnetic fields at the four points corresponding to the RF coils along the laser beam propagation are obtained by measuring Larmor frequency of the rubidium atoms inside the vapor cell. The magnetic gradients are also acquired with the measured magnetic fields. The measurement is performed in a magnetic shield environment. A dc electrical coil is taken to produce an existed magnetic field for the measurement and the theoretical magnetic field distribution is calculated. It is demonstrated that the measured magnetic fields and magnetic gradients correspond well with the calculated ones. Results show that the absolute error of the magnetic field is less than $0.1~\mu \text{T}$ , the relative error of the magnetic field is below 0.8%, and the relative error of the magnetic gradient is below 5.5%. Results also indicate that the atomic magnetometer has a sensitivity of 5 pT/Hz1/2 from 1 to 2 Hz. The Mz atomic magnetometer is potentially useful for applications requiring gradient field information. [ABSTRACT FROM AUTHOR]