Scan Coils Research Articles

Effect of metallic materials on magnetic resonance image uniformity: a quantitative experimental study.

To assess quantitatively the effect of metallic materials on MR image uniformity using a standardized method. Six types of 1cm cubic metallic materials (i.e., Au, Ag, Al, Au-Ag-Pd alloy, Ti, and Co-Cr alloy) embedded in a glass phantom filled were examined and compared with no metal condition inserted as a reference. The phantom was scanned five times under each condition using a 1.5-T MR superconducting magnet scanner with an 8-channel phased-array brain coil and head and neck coil. For each examination, the phantom was scanned in three planes: axial, coronal, and sagittal using T1-weighted spin echo (SE) and gradient echo (GRE) sequences in accordance with the American Society for Testing and Materials (ASTM) F2119-07 standard. Image uniformity was assessed using the non-uniformity index (NUI), which was developed by the National Electrical Manufacturers Association (NEMA), as an appropriate standardized measure for investigating magnetic field uniformity. T1-GRE images with Co-Cr typically elicited the lowest uniformity, followed by T1-GRE images with Ti, while all other metallic materials did not affect image uniformity. In particular, T1-GRE images with Co-Cr showed significantly higher NUI values as far as 6.6cm at maximum equivalent to 11 slices centering around it in comparison with the measurement uncertainty from images without metallic materials. We found that MR image uniformity was influenced by the scanning sequence and coil type when Co-Cr and Ti were present. It is assumed that the image non-uniformity in Co-Cr and Ti is caused by their high magnetic susceptibility.

Large-Angle Rocking Beam Electron Diffraction of Large Unit Cell Crystals Using Direct Electron Detector.

We report a large-angle rocking beam electron diffraction (LARBED) technique for electron diffraction analysis. Diffraction patterns are recorded in a scanning transmission electron microscope (STEM) using a direct electron detector with large dynamical range and fast readout. We use a nanobeam for diffraction and perform the beam double rocking by synchronizing the detector with the STEM scan coils for the recording. Using this approach, large-angle convergent beam electron diffraction (LACBED) patterns of different reflections are obtained simultaneously. By using a nanobeam, instead of a focused beam, the LARBED technique can be applied to beam-sensitive crystals as well as crystals with large unit cells. This paper describes the implementation of LARBED and evaluates the performance using silicon and gadolinium gallium garnet crystals as test samples. We demonstrate that our method provides an effective and robust way for recording LARBED patterns and paves the way for quantitative electron diffraction of large unit cell and beam-sensitive crystals.

Optimization of magnetic resonance imaging of the hand

BACKGROUND: Magnetic resonance imaging is one of the leading imaging modalities of the musculoskeletal system. However, when imaging the hand, major problems in magnetic resonance imaging include the lack of specialized coils and reliable fixation devices for the hand, uncomfortable patient posture, motion artifacts, and small anatomical structures in the wrist. These factors inevitably lead to incorrect interpretation. AIM: To improve the quality of magnetic resonance imaging of the hand by developing an approach to coil selection, scanning protocol, and hand positioning and fixation. MATERIALS AND METHODS: A positioning device was developed to prevent hand movements. Two types of coils were evaluated. Magnetic resonance images were evaluated comparatively, as well as by a musculoskeletal radiologist. RESULTS: А head coil is more appropriate when scanning the entire hand, for example, in rheumatic diseases. A knee coil is more appropriate when studying smaller anatomical structures (including the wrist) owing to a smaller field of view and higher resolution. Based on the obtained data, guidelines for the selection of scanning parameters, sequences, and coils for magnetic resonance imaging of the hand were formulated. To prevent motion artifacts, a special fixation device of the patient’s hand was introduced. CONCLUSION: Certain factors directly affect the qualitative magnetic resonance imaging study of the hand, such as safety protocols, scanning parameters, and hand fixation. The guidelines presented in this study and the use of the developed specialized fixation device may improve the quality of magnetic resonance imaging of the hand.

Ultra-fast Digital DPC Yielding High Spatio-temporal Resolution for Low-Dose Phase Characterization.

In the scanning transmission electron microscope, both phase imaging of beam-sensitive materials and characterization of a material's functional properties using in situ experiments are becoming more widely available. As the practicable scan speed of 4D-STEM detectors improves, so too does the temporal resolution achievable for both differential phase contrast (DPC) and ptychography. However, the read-out burden of pixelated detectors, and the size of the gigabyte to terabyte sized data sets, remain a challenge for both temporal resolution and their practical adoption. In this work, we combine ultra-fast scan coils and detector signal digitization to show that a high-fidelity DPC phase reconstruction can be achieved from an annular segmented detector. Unlike conventional analog data phase reconstructions from digitized DPC-segment images yield reliable data, even at the fastest scan speeds. Finally, dose fractionation by fast scanning and multi-framing allows for postprocess binning of frame streams to balance signal-to-noise ratio and temporal resolution for low-dose phase imaging for in situ experiments.

Review of: "The conceptual design of focused ion beam nanolithography uses and integrates similar components: sources, extraction and acceleration, optics, scan coils, sample stage, electron detectors, etc. Interestingly, the focused ion beam nanolithography equipment"

Review of: "The conceptual design of focused ion beam nanolithography uses and integrates similar components: sources, extraction and acceleration, optics, scan coils, sample stage, electron detectors, etc. Interestingly, the focused ion beam nanolithography equipment"

Precision Hall Effect magnetometer.

The article presents a Hall effect magnetometer for use in a desktop Electron Paramagnetic Resonance spectrometer with a permanent magnet system and scanning coils. High accuracy and long-term stability at a small size and low cost are achieved through the use of digital signal processing, sequential data filtering in the time and frequency domains, as well as digital correction of raw data based on calibration information. The exciting current of the Hall sensor has the form of an alternating-signsquare wave formed by a high-speed H-bridge powered by a stable direct current. Generation of control signals, time selection of data, and their accumulation are performed using Xilinx Field-Programmable Gate Array Artix-7. MicroBlaze embedded 32-bit processor is used to control the magnetometer and interface with adjacent levels of the control system. Taking into account the individual characteristics of the sensor, including the offset voltage, the nonlinearity of the magnetic sensitivity, and their temperature dependences, is carried out by correcting the data obtained by calculating a polynomial depending on the raw magnitude of the field induction and the temperature of the sensor. The polynomial coefficients are individual for each sensor, are determined once during the calibration process, and are stored in the dedicated Electrically Erasable Programmable Read-Only Memory. The magnetometer has a high resolution of 0.1 µT and an absolute measurement error of not exceeding 6 µT.

Using Your Beam Efficiently: Reducing Electron Dose in the STEM via Flyback Compensation

Abstract In the scanning transmission electron microscope, fast-scanning and frame-averaging are two widely used approaches for reducing electron-beam damage and increasing image signal noise ratio which require no additional specialized hardware. Unfortunately, for scans with short pixel dwell-times (less than 5 μs), line flyback time represents an increasingly wasteful overhead. Although beam exposure during flyback causes damage while yielding no useful information, scan coil hysteresis means that eliminating it entirely leads to unacceptably distorted images. In this work, we reduce this flyback to an absolute minimum by calibrating and correcting for this hysteresis in postprocessing. Substantial improvements in dose efficiency can be realized (up to 20%), while crystallographic and spatial fidelity is maintained for displacement/strain measurement.

Continuous wave desktop coherent superheterodyne X-band EPR spectrometer

This article describes a desktop X-band superheterodyne spectrometer designed to measure EPR spectra in the vicinity of g = 2. The spectrometer operates in the vicinity of the 9.2 GHz frequency in the power range of about 40 mW–1 nW. The device uses Time Locking concept with digital quadrature detection of intermediate frequency (100 MHz) and the synthesis of all signals used in the device from a single driving oscillator. To register CW spectra, a TE102 rectangular cavity with the capability of matching and frequency tuning is used. The microwave part of the spectrometer is implemented in the form of two non-tunable modules based on microstrip technology and commercially available microwave MMICs. Two modes of operation are provided – both with PLL of microwave sources with a highly stable driving oscillator as a reference and an AFC system without frequency modulation. All signal processing after digitization of the intermediate frequency is performed digitally using FPGA resources. It is possible to record EPR spectra both with magnetic field modulation at various frequencies and without modulation. The bandwidth of the receiving path can be selected from the widest 46 MHz to about 1.5 kHz, which allows the spectrometer to be used both for recording weak signals and for recording fast-flowing processes. The spectrometer uses a magnetic system on permanent magnets Sm-Co with magnetic field uniformity of about 3 * 10−5. Changing the magnetic field in permanent magnets is done using scanning coils which provides a field change of >800 G (p-p). The control of the magnetic field induction in the magnet gap is performed by a specially designed precision Hall effect magnetometer, which provides a resolution of 1 mG with an absolute error of no more than 0.2 G. A personal computer for spectrometer control is connected via Ethernet. The spectrometer is stable and easy to use. The high performance of the spectrometer is confirmed by the recorded spectra.

Three-dimensional reconstruction of magnetic resonance images of carp brain for brain control technology

BackgroundIn the field of animal robot control, brain control technology is currently used to achieve control. It is usually necessary to accurately implant brain electrodes into the animal's brain movement area with the help of a brain stereotaxic apparatus, and apply electrical stimulation to achieve control of the animal. The prerequisite for accurate electrode implantation is to study the internal tissues of the carp skull. New MethodWith the help of 3.0 T magnetic resonance imaging (MRI) instrument and 8_CH MRI scanning coil, carp brain magnetic resonance images was obtained. The visualization tool package VTK and the marching cube algorithm were used for surface rendering, the ray casting algorithm was used for volume rendering and reconstruction. ResultsThe three-dimensional reconstruction results could show the carp skull surface contour and internal tissue details, and the measured coordinates after three-dimensional reconstruction of magnetic resonance images could be transformed into three-dimensional positioning coordinates suitable for brain stereotaxic apparatus. Comparison with existing methodsThe three-dimensional reconstruction images based on magnetic resonance could analyze the relative spatial position relationship between the surface structure of the carp's brain and the internal tissue at any angle, and the three-dimensional positioning coordinates of the brain could be obtained quickly and accurately. ConclusionsThe visualization of carp brain magnetic resonance images based on marching cubes algorithm and ray projection algorithm could obtain ideal reconstruction effects, which could be used in the brain control technology of carp robot.

High temporal-resolution scanning transmission electron microscopy using sparse-serpentine scan pathways

Scanning transmission electron microscopy (STEM) provides structural analysis with sub-angstrom resolution. But the pixel-by-pixel scanning process is a limiting factor in acquiring high-speed data. Different strategies have been implemented to increase scanning speeds while at the same time minimizing beam damage via optimizing the scanning strategy. Here, we achieve the highest possible scanning speed by eliminating the image acquisition dead time induced by the beam flyback time combined with reducing the amount of scanning pixels via sparse imaging. A calibration procedure was developed to compensate for the hysteresis of the magnetic scan coils. A combination of sparse and serpentine scanning routines was tested for a crystalline thin film, gold nanoparticles, and in an in-situ liquid phase STEM experiment. Frame rates of 92, 23 and 5.8 s-1 were achieved for images of a width of 128, 256, and 512 pixels, respectively. The methods described here can be applied to single-particle tracking and analysis of radiation sensitive materials.

SENSOR APPLICATIONS IN ANALYSIS OF DRUGS AND FORMULATIONS

Several sensors, biosensors, and actuators are designed and mounted to analyze biomedical nutraceuticals, food, and nutraceutical products in this particular issue. Some applications concern classical subjects such as eubacteria determination in agricultural products, flashing material in foods such as the ethyl group’s chemicals, and fruit juices’ inhibitor properties. In contrast, the different applications are more revolutionary, such as safety research, the manufacture of artificial human senses (electronic nose or tongue), or t Ligands are often characterized by nano biosensors, utilizing biomaterials that involve specific aptamers, antibodies, enzymes, polymers, and sensory receptors. The square measurement of several modal sensing elements, integrated with nanomaterials, increases sensitivity such as nano biosensors and increases nano biosensor productivity. For the nano biosensor with increased efficiency, modality sensing components have been incorporated in this case. The square measurement of the elastic (ME) magnetic machine biosensors was used to classify infectious agents by a magnet coil in contemporary juice or milk and to develop direct detection of infectious agents on food scanning coils.

Development of the scanning power supply for 300 keV electron accelerator

This paper describes the development and study of the scanning power supply. This locally designed low energy electron accelerator with the former energy of 140 keV will be upgraded to 300 keV. As the setup, scanning power supply is required to excite the scanning coils and deflect the energetic electron beam across a titanium foil window in horizontal and vertical direction respectively. The excitation current of the scanning coils is determined by the energy of the electron beam and the deflected length. Therefore, the scanning power supply must be functioning automatically and continuously to ensure the uniform dose distribution and unavoidable heat issue. As the result, the scanning power supply using the combination of signal generator and power amplifier has been developed and functioning as expected.

Magnetoelastic Effect in a Ferromagnet in an Acoustic Wave Field

A laboratory setup is considered intended for special physics workshops and demonstration experiments of a lecture course in general physics as well for a study of elastic waves and magnetoelastic phenomena in ferromagnets in a standing wave field excited in a piezoceramic resonator. The acoustic signal and the magnetoelastic response are recorded simultaneously with a dual channel oscilloscope. The ferromagnet is magnetized using Helmholtz coils. The position of the nodes and antinodes in the standing wave of the electromagnetic signal along the length of the rod was determined with a scanning coil, and the wavelength, sound velocity, and elastic modulus were calculated from these data. The properties of standing waves a ferrite and a steel rod as well as on electrical steel tape 50 μm thick glued to a glass rod have been investigated.

High-resolution scanning precession electron diffraction: Alignment and spatial resolution

Methods are presented for aligning the pivot point of a precessing electron probe in the scanning transmission electron microscope (STEM) and for assessing the spatial resolution in scanning precession electron diffraction (SPED) experiments. The alignment procedure is performed entirely in diffraction mode, minimising probe wander within the bright-field (BF) convergent beam electron diffraction (CBED) disk and is used to obtain high spatial resolution SPED maps. Through analysis of the power spectra of virtual bright-field images extracted from the SPED data, the precession-induced blur was measured as a function of precession angle. At low precession angles, SPED spatial resolution was limited by electronic noise in the scan coils; whereas at high precession angles SPED spatial resolution was limited by tilt-induced two-fold astigmatism caused by the positive spherical aberration of the probe-forming lens.

Implementing an accurate and rapid sparse sampling approach for low-dose atomic resolution STEM imaging

While aberration correction for scanning transmission electron microscopes (STEMs) dramatically increased the spatial resolution obtainable in the images of materials that are stable under the electron beam, the practical resolution of many STEM images is now limited by the sample stability rather than the microscope. To extract physical information from the images of beam sensitive materials, it is becoming clear that there is a critical dose/dose-rate below which the images can be interpreted as representative of the pristine material, while above it the observation is dominated by beam effects. Here, we describe an experimental approach for sparse sampling in the STEM and in-painting image reconstruction in order to reduce the electron dose/dose-rate to the sample during imaging. By characterizing the induction limited rise-time and hysteresis in the scan coils, we show that a sparse line-hopping approach to scan randomization can be implemented that optimizes both the speed of the scan and the amount of the sample that needs to be illuminated by the beam. The dose and acquisition time for the sparse sampling is shown to be effectively decreased by at least a factor of 5× relative to conventional acquisition, permitting imaging of beam sensitive materials to be obtained without changing the microscope operating parameters. The use of sparse line-hopping scan to acquire STEM images is demonstrated with atomic resolution aberration corrected the Z-contrast images of CaCO3, a material that is traditionally difficult to image by TEM/STEM because of dosage issues.

Double-Layer Planar Coil Detector for Improved Detection of Salmonella on Food Contact Surfaces

This paper presents an investigation into improved, direct Salmonella detection on food contact surfaces using a double-layer planar coil detector and wireless phage-based magnetoelastic (ME) biosensors. Comparing with the single-layer coil detectors used in our previous research, double-layer coils with appropriate designs allow for better magnetic excitation of the biosensor and sensitivity of detection. In this way, a longer stand-off distance (distance between the sensor and detector), which may be necessary for testing surfaces with large roughness and curvatures, can be achieved. In addition, smaller biosensors (e.g., sub-millimeter long) with higher mass sensitivity can also be measured with this sensitive double-layer coil detector. Standard microelectronic fabrication techniques (photolithography, electroplating, etching and sputtering) were used to fabricate double-layer coils with various design parameters, including the thickness of layers, width, height, and spacing of coil turns. Both theoretical calculations and experimental data showed that the above coil geometric parameters have large effects on the signal amplitude, stand-off distance and detection sensitivity. Finally, with the newly fabricated double-layer coil detector, detection of Salmonella on a food-grade, ultra-high-molecular-weight polyethylene (UHMW-PE) surface was demonstrated. Multiple biosensors were measured simultaneously with a longer detection distance (> 1 mm). This double-layer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.

Development of a fast electromagnetic beam blanker for compressed sensing in scanning transmission electron microscopy

The concept of compressed sensing was recently proposed to significantly reduce the electron dose in scanning transmission electron microscopy (STEM) while still maintaining the main features in the image. Here, an experimental setup based on an electromagnetic beam blanker placed in the condenser plane of a STEM is proposed. The beam blanker deflects the beam with a random pattern, while the scanning coils are moving the beam in the usual scan pattern. Experimental images at both the medium scale and high resolution are acquired and reconstructed based on a discrete cosine algorithm. The obtained results confirm that compressed sensing is highly attractive to limit beam damage in experimental STEM even though some remaining artifacts need to be resolved.

Direct-write liquid phase transformations with a scanning transmission electron microscope.

The highly energetic electron beam (e-beam) in a scanning transmission electron microscope (STEM) can induce local changes in the state of matter, ranging from knock-on and atomic movement, to amorphization/crystallization, and to localized chemical/electrochemical reactions. To date, fundamental studies of e-beam induced phenomena and practical applications have been limited by conventional STEM e-beam rastering modes that allow only for uniform e-beam exposures. Here, an automated liquid phase nanolithography method has been developed that enables the direct writing of nanometer scaled features within microfabricated liquid cells. An external e-beam control system, connected to the scan coils of an aberration-corrected STEM, is used to precisely control the position, dwell time, and scan rate of a sub-nanometer STEM probe. Site-specific locations in a sealed liquid cell containing an aqueous solution of H2PdCl4 are irradiated to deposit palladium nanocrystals onto silicon nitride membranes in a highly controlled manner. The threshold electron dose required for the radiolytic deposition of metallic palladium has been determined, the influence of electron dose on the nanolithographically patterned feature size and morphology is explored, and a feedback-controlled monitoring method for active control of the nanofabricated structures through STEM detector signal monitoring is proposed. This approach enables fundamental studies of electron beam induced interactions with matter in liquid cells and opens new pathways to fabricate nanostructures with tailored architectures and chemistries via shape-controlled nanolithographic patterning from liquid-phase precursors.

Field-stepped direct detection electron paramagnetic resonance

The widest scan that had been demonstrated previously for rapid scan EPR was a 155G sinusoidal scan. As the scan width increases, the voltage requirement across the resonating capacitor and scan coils increases dramatically and the background signal induced by the rapidly changing field increases. An alternate approach is needed to achieve wider scans. A field-stepped direct detection EPR method that is based on rapid-scan technology is now reported, and scan widths up to 6200G have been demonstrated. A linear scan frequency of 5.12kHz was generated with the scan driver described previously. The field was stepped at intervals of 0.01 to 1G, depending on the linewidths in the spectra. At each field data for triangular scans with widths up to 11.5G were acquired. Data from the triangular scans were combined by matching DC offsets for overlapping regions of successive scans. This approach has the following advantages relative to CW, several of which are similar to the advantages of rapid scan. (i) In CW if the modulation amplitude is too large, the signal is broadened. In direct detection field modulation is not used. (ii) In CW the small modulation amplitude detects only a small fraction of the signal amplitude. In direct detection each scan detects a larger fraction of the signal, which improves the signal-to-noise ratio. (iii) If the scan rate is fast enough to cause rapid scan oscillations, the slow scan spectrum can be recovered by deconvolution after the combination of segments. (iv) The data are acquired with quadrature detection, which permits phase correction in the post processing. (v) In the direct detection method the signal typically is oversampled in the field direction. The number of points to be averaged, thereby improving the signal-to-noise ratio, is determined in post processing based on the desired field resolution. A degased lithium phthalocyanine sample was used to demonstrate that the linear deconvolution procedure can be employed with field-stepped direct detection EPR signals. Field-stepped direct detection EPR spectra were obtained for Cu2+ doped in Ni(diethyldithiocarbamate)2, Cu2+ doped in Zn tetratolylporphyrin, perdeuterated tempone in sucrose octaacetate, vanadyl ion doped in a parasubstituted Zn tetratolylporphyrin, Mn2+ impurity in CaO, and an oriented crystal of Mn2+ doped in Mg(acetylacetonate)2(H2O)2.

Multilayer Scanning Coil Detector for Improved Detection of Surface Pathogen Contamination

This paper presents an investigation into improved pathogen detection on food and food contact surfaces using a multilayer scanning coil detector combined with wireless magnetoelastic (ME) biosensors. In contrast to our previous studies of surface pathogen detection where a single-layer planar coil was employed, a more sensitive detector with a multi-layer coil design was investigated in this work. The two-fold roles of the coil detector are: (1) the application of an alternating magnetic field for the excitation of the ME sensor’s vibration and (2) detection of the resultant magnetic flux changes induced by the vibrating sensor. Surface pathogen detection can then be realized when the sensor comes into contact and binds specifically with the pathogen of interest, causing the sensor’s resonant frequency to decrease. For surfaces with large roughness and curvatures (e.g., leafy greens and cantaloupes), a long stand-off distance (distance between the sensor and detector) may be required. Hence, enhancement in the excitation power and sensitivity of coil detector with a multilayer design is a key to improving the system’s detection capabilities. Furthermore, smaller ME biosensors with higher mass sensitivity can also be measured with this sensitive multilayer coil detector. Several design parameters, including the number of layers, width, height, and spacing of coil turns, were studied. Coils were fabricated using standard microelectronic fabrication techniques (photolithograpy, electroplating, etching and sputtering) and tested.Both theoretical calculations and experimental data showed that the above coil geometric parameters have a significant impact on the signal amplitude and stand-off distance. Finally, with the newly fabricated multilayer coil detector, simultaneous measurement of multiple biosensors on spinach leaf surfaces was demonstrated. This multilayer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.