Coil Array Research Articles

Design and Dynamic In Vivo Validation of a Multi-Channel Stretchable Liquid Metal Coil Array.

Recent developments in the field of radiofrequency (RF) coils for magnetic resonance imaging (MRI) offer flexible and patient-friendly solutions. Previously, we demonstrated a proof-of-concept single-element stretchable coil design based on liquid metal and a self-tuning smart geometry. In this work, we numerically analyze and experimentally study a multi-channel stretchable coil array and demonstrate its application in dynamic knee imaging. We also compare our flexible coil array to a commonly used commercial rigid coil array. Our numerical analysis shows that the proposed coil array maintains its resonance frequency (<1% variation) and sensitivity (<6%) at various stretching configurations from 0% to 30%. We experimentally demonstrate that the signal-to-noise ratio (SNR) of the acquired MRI images is improved by up to four times with the stretchable coil array due to its conformal and therefore tight-fitting nature. This stretchable array allows for dynamic knee imaging at different flexion angles, infeasible with traditional, rigid coil arrays. These findings are significant as they address the limitations of current rigid coil technology, offering a solution that enhances patient comfort and image quality, particularly in applications requiring dynamic imaging.

Load Design and Waveform Optimization for Near-Field Wireless Powered Communications Using a Coil Array

Load Design and Waveform Optimization for Near-Field Wireless Powered Communications Using a Coil Array

A digital twin for parallel liquid-state nuclear magnetic resonance spectroscopy

One approach to increasing nuclear magnetic resonance measurement sample throughput is to implement multiple, independent detection sites. However, the presence of radio frequency interference poses a challenge in multi-detector systems, particularly in unshielded coil arrays lacking sufficient electrical isolation. This issue can lead to unwanted coupling of inductive coils, resulting in excitation pulse interference and signal transfer among multiple detection sites. Here we propose a theoretical framework that combines electromagnetic simulation with spin-dynamic calculations. This framework enables the evaluation of coil coupling effects, the design of parallel pulse sequences to mitigate inter-channel coupling, and the separation of composite free induction decays obtained from multiple detectors. The parallel pulse compensation scheme was validated by a 2-channel parallel spectroscopy experiment. These results provide valuable insights for the design of parallel nuclear magnetic resonance hardware and for exploring the limits of parallelization capacity within a fixed magnet system.

A scan-specific quality control acquisition for clinical whole-body (WB) MRI protocols

Objective. Image quality in whole-body MRI (WB-MRI) may be degraded by faulty radiofrequency (RF) coil elements or mispositioning of the coil arrays. Phantom-based quality control (QC) is used to identify broken RF coil elements but the frequency of these acquisitions is limited by scanner and staff availability. This work aimed to develop a scan-specific QC acquisition and processing pipeline to detect broken RF coil elements, which is sufficiently rapid to be added to the clinical WB-MRI protocol. The purpose of this is to improve the quality of WB-MRI by reducing the number of patient examinations conducted with suboptimal equipment. Approach. A rapid acquisition (14 s additional acquisition time per imaging station) was developed that identifies broken RF coil elements by acquiring images from each individual coil element and using the integral body coil. This acquisition was added to one centre’s clinical WB-MRI protocol for one year (892 examinations) to evaluate the effect of this scan-specific QC. To demonstrate applicability in multi-centre imaging trials, the technique was also implemented on scanners from three manufacturers. Main results. Over the course of the study RF coil elements were flagged as potentially broken on five occasions, with the faults confirmed in four of those cases. The method had a precision of 80% and a recall of 100% for detecting faulty RF coil elements. The coil array positioning measurements were consistent across scanners and have been used to define the expected variation in signal. Significance. The technique demonstrated here can identify faulty RF coil elements and positioning errors and is a practical addition to the clinical WB-MRI protocol. This approach was fully implemented on systems from two manufacturers and partially implemented on a third. It has potential to reduce the number of clinical examinations conducted with suboptimal hardware and improve image quality across multi-centre studies.

Wireless, customizable coaxially shielded coils for magnetic resonance imaging.

Anatomy-specific radio frequency receive coil arrays routinely adopted in magnetic resonance imaging (MRI) for signal acquisition are commonly burdened by their bulky, fixed, and rigid configurations, which may impose patient discomfort, bothersome positioning, and suboptimal sensitivity in certain situations. Herein, leveraging coaxial cables' inherent flexibility and electric field confining property, we present wireless, ultralightweight, coaxially shielded, passive detuning MRI coils achieving a signal-to-noise ratio comparable to or surpassing that of commercially available cutting-edge receive coil arrays with the potential for improved patient comfort, ease of implementation, and substantially reduced costs. The proposed coils demonstrate versatility by functioning both independently in form-fitting configurations, closely adapting to relatively small anatomical sites, and collectively by inductively coupling together as metamaterials, allowing for extension of the field of view of their coverage to encompass larger anatomical regions without compromising coil sensitivity. The wireless, coaxially shielded MRI coils reported herein pave the way toward next-generation MRI coils.

Beat Pilot Tone (BPT): Simultaneous MRI and RF motion sensing at arbitrary frequencies.

To introduce a simple system exploitation with the potential to turn MRI scanners into general-purpose radiofrequency (RF) motion monitoring systems. Inspired by Pilot Tone (PT), this work proposes Beat Pilot Tone (BPT), in which two or more RF tones at arbitrary frequencies are transmitted continuously during the scan. These tones create motion-modulated standing wave patterns that are sensed by the receiver coil array, incidentally mixed by intermodulation in the receiver chain, and digitized simultaneously with the MRI data. BPT can operate at almost any frequency as long as the intermodulation products lie within the bandwidth of the receivers. BPT's mechanism is explained in electromagnetic simulations and validated experimentally. Phantom and volunteer experiments over a range of transmit frequencies suggest that BPT may offer frequency-dependent sensitivity to motion. Using a semi-flexible anterior receiver array, BPT appears to sense cardiac-induced body vibrations at microwave frequencies ( 1.2 GHz). At lower frequencies, it exhibits a similar cardiac signal shape to PT, likely due to blood volume changes. Other volunteer experiments with respiratory, bulk, and head motion show that BPT can achieve greater sensitivity to motion than PT and greater separability between motion types. Basic multiple-input multiple-output ( MIMO) operation with simultaneous PT and BPT in head motion is demonstrated using two transmit antennas and a 22-channel head-neck coil. BPT may offer a rich source of motion information that is frequency-dependent, simultaneous, and complementary to PT and the MRI exam.

A Stepwise Control of Multiple Magnetic Millirobots for Flow Manipulation Applications

Small‐scale magnetic robots are extensively recognized as promising untethered devices that can be controlled externally for numerous microscale applications. This study is proposed to address the independent control of multiple magnetic millirobots using an array of electromagnetic coils. Herein, each of the fabricated magnetic millirobots is magnetized with a dissimilar magnetization profile. Further, these millirobots are independently controlled using the mentioned magnetization strategy in addition to the supply of controlled current to each electromagnetic coil. To explore the physics of this combined stepwise approach in controlling the millirobots, theoretical and numerical investigations are carried out that further ensure the practical significance for broad applications. For demonstration purposes, three different shear‐induced flow manipulation experiments, including the particle manipulation task, fluid color transition task, and micromixing task, are conducted using more than one millirobot with distinct motions. A maximum of three millirobots controlled with different motions are employed in the micromixing task, and further, it is observed to achieve nearly 80% mixing efficiency within 45 s. The presented work with the introduced actuation system and motion control strategies can strengthen the existing methods of small‐scale robots for various applications, particularly for tasks that demand multiple millirobots.

Coil Array Technique With Maximum Tolerance to 2-D Misalignment for Wireless Power Transfer Systems

Coil Array Technique With Maximum Tolerance to 2-D Misalignment for Wireless Power Transfer Systems

Extended curvature birdcage coil design for localized magnetic field in 9.4 T MRI for multiple mouse imaging

Magnetic resonance imaging (MRI) for preclinical analysis is useful for testing medical procedures, therapies, and drug development. Preclinical MRI uses small animals, such as mice, for multiple studies. Preclinical studies are often needed to control target mouse models with different parameters; thus, performing simultaneous MRIs is desired to reduce study time and provide a fair comparison. In this study, we propose a variation of a birdcage coil that is capable of providing the same field intensity for each mouse compared to a traditional birdcage coil configuration. The arrangement of the proposed birdcage coil produces a uniform and strongly localized magnetic |B1|-field in each of the four target mice. The design involves rotating the legs of the birdcage coil so that the current distribution produces a uniform field inside each mouse. Electromagnetic simulations were performed to validate the proposed design. The proposed design exhibited a better field intensity than the reference linear, circularly polarized mode birdcage coils and an eight-channel loop array coil. The proposed customized birdcage coil arrangement promises a better field intensity and uniformity across multiple mouse imaging using 9.4 T preclinical MRI scanners.

A birdcage transmit, 24-channel conformal receive array coil for sensitive 31P magnetic resonance spectroscopic imaging of the human brain at 7 T.

Phosphorus (31P) magnetic resonance spectroscopic imaging (MRSI) can serve as a critical tool for more direct quantification of brain energy metabolism, tissue pH, and cell membrane turnover. However, the low concentration of 31P metabolites in biological tissue may result in low signal-to-noise ratio (SNR) in 31P MRS images. In this work, we present an innovative design and construction of a 31P radiofrequency coil for whole-brain MRSI at 7 T. Our coil builds on current literature in ultra-high field 31P coil design and offers complete coverage of the brain, including the cerebellum and brainstem. The coil consists of an actively detunable volume transmit (Tx) resonator and a custom 24-channel receive (Rx) array. The volume Tx resonator is a 16-rung high-pass birdcage coil. The Rx coil consists of a 24-element phased array composed of catered loop shapes and sizes built onto a custom, close-fitting, head-shaped housing. The Rx array was designed to provide complete coverage of the head, while minimizing mutual coupling. The Rx configuration had a mean reflection coefficient better than -20 decibels (dB) when the coil was loaded with a human head. The mean mutual coupling ( ) among Rx elements, when loaded with a human head, was -16 dB. In phantom imaging, the phased array produced a central SNR that was 4.4-fold higher than the corresponding central SNR when operating the 31P birdcage as a transceiver. The peripheral SNR was 12-fold higher when applying the optimized phased array. In vivo 3D 31P MRSI experiments produced high-quality spectra in the cerebrum gray and white matter, as well as in the cerebellum. Characteristic phosphorus metabolites related to adenosine triphosphate metabolism and cell membrane turnover were distinguishable across all brain regions. In summary, our results demonstrate the potential of our novel coil for accurate, whole-brain 31P metabolite quantification.

Free-breathing high-resolution respiratory-gated radial stack-of-stars magnetic resonance imaging of the upper abdomen at 7 T.

Ultrahigh field magnetic resonance imaging (MRI) (≥ 7 T) has the potential to provide superior spatial resolution and unique image contrast. Apart from radiofrequency transmit inhomogeneities in the body at this field strength, imaging of the upper abdomen faces additional challenges associated with motion-induced ghosting artifacts. To address these challenges, the goal of this work was to develop a technique for high-resolution free-breathing upper abdominal MRI at 7 T with a large field of view. Free-breathing 3D gradient-recalled echo (GRE) water-excited radial stack-of-stars data were acquired in seven healthy volunteers (five males/two females, body mass index: 19.6-24.8 kg/m2) at 7 T using an eight-channel transceive array coil. Two volunteers were also examined at 3 T. In each volunteer, the liver and kidney regions were scanned in two separate acquisitions. To homogenize signal excitation, the time-interleaved acquisition of modes (TIAMO) method was used with personalized pairs of B1 shims, based on a 23-s Cartesian fast low angle shot(FLASH) acquisition. Utilizing free-induction decay navigator signals, respiratory-gated images were reconstructed at a spatial resolution of 0.8 × 0.8 × 1.0 mm3. Two experienced radiologists rated the image quality and the impact of B1 inhomogeneity and motion-related artifacts on multipoint scales. The images of all volunteers showcased effective water excitation and were accurately corrected for respiratory motion. The impact of B1 inhomogeneity on image quality was minimal, underscoring the efficacy of the multitransmit TIAMO shim. The high spatial resolution allowed excellent depiction of small structures such as the adrenal glands, the proximal ureter, the diaphragm, and small blood vessels, although some streaking artifacts persisted in liver image data. In direct comparisons with 3 T performed for two volunteers, 7-T acquisitions demonstrated increases in signal-to-noise ratio of 77% and 58%. Overall, this work demonstrates the feasibility of free-breathing MRI in the upper abdomen at submillimeter spatial resolution at a magnetic field strength of 7 T.

Weft insertion guideway design based on high-temperature superconducting levitation

Abstract Wide-width weaving machines typically employ the method of increasing the shuttle’s initial speed to achieve a broader weft insertion. However, this approach not only leads to issues such as significant equipment vibrations, high noise levels, increased energy consumption, and reduced lifespan but also has limitations in achieving substantial increases in the fabric width. The article proposes a wide-width weft insertion method based on high-temperature superconducting magnetic levitation technology. It utilizes the levitation characteristics of high-temperature superconducting shuttles in a permanent magnet array’s magnetic field to levitate the shuttle. The shuttle is then propelled by a traveling wave magnetic field generated by an array of electromagnetic coils, enabling wide-width weft insertion. Based on the required thrust values and weaving speed for the shuttle insertion process, the structural parameters of the weft insertion guideway were calculated. A superconducting suspended weft insertion structure was designed, and a mathematical model between the weft insertion guideway and the shuttle was established. Subsequently, a simulation model of the weft insertion guideway was created using Simulink, and the model was simulated, verified, and analyzed using the field-oriented control algorithm. The simulation results indicate that the operating speed of the levitated shuttle and the driving force for weft insertion meet the requirements for high-speed wide-width weaving.

Optimized Design of Passive Array Coils for High-Efficiency and Anti-Misalignment WPT System

Optimized Design of Passive Array Coils for High-Efficiency and Anti-Misalignment WPT System

Three-row MRI receive array with remote circuitry to preserve radiation transparency

Objective. Up to this point, 1.5 T linac-compatible coil array layouts have been restricted to one or two rows of coils because of the desire to place radiation-opaque circuitry adjacent to the coils and outside the window through which the linac beam travels. Such layouts can limit parallel imaging performance. The purpose of this work was to design and build a three-row array in which remotely located circuits permitted a central row of coils while preserving the radiolucent window. Approach. The remote circuits consisted of a phase shifter to cancel the phase introduced by the coaxial link between the circuit and coil, followed by standard components for tuning, matching, detuning, and preamplifier decoupling. Tests were performed to compare prototype single-channel coils with remote or local circuits, which were followed by tests comparing two and three-row arrays . Main results. The single-channel coil with the remote circuit maintained 85% SNR at depths of 30 mm or more as compared to a coil with local circuit. The three-row array provided similar SNR as the two-row array, along with geometry factor advantages for parallel imaging acceleration in the head–foot direction. Significance. The remote circuit strategy could potentially support future MR-linac arrays by allowing greater flexibility in array layout compared to those confined by local circuits, which can be leveraged for parallel imaging acceleration.

Minimizing electric fields and increasing peripheral nerve stimulation thresholds using a body gradient array coil.

To demonstrate the performance of gradient array coils in minimizing switched-gradient-induced electric fields (E-fields) and improving peripheral nerve stimulation (PNS) thresholds while generating gradient fields with adjustable linearity across customizable regions of linearity (ROLs). A body gradient array coil is used to reduce the induced E-fields on the surface of a body model by modulating applied currents. This is achieved by performing an optimization problem with the peak E-field as the objective function and current amplitudes as unknown variables. Coil dimensions and winding patterns are fixed throughout the optimization, whereas other engineering metrics remain adjustable. Various scenarios are explored by manipulating adjustable parameters. The array design consistently yields lower E-fields and higher PNS thresholds across all scenarios compared with a conventional coil. When the gradient array coil generates target gradient fields within a 44-cm-diameter spherical ROL, the maximum E-field is reduced by 10%, 18%, and 61% for the X, Y, and Z gradients, respectively. Transitioning to a smaller ROL (24 cm) and relaxing the gradient linearity error results in further E-field reductions. In oblique gradients, the array coil demonstrates the most substantial reduction of 40% in the Z-Y direction. Among the investigated scenarios, the most significant increase of 4.3-fold is observed in the PNS thresholds. Our study demonstrated that gradient array coils offer a promising pathway toward achieving high-performance gradient coils regarding gradient strength, slew rate, and PNS thresholds, especially in scenarios in which linear magnetic fields are required within specific target regions.

Energy Efficient and Adaptive Design for Wireless Power Transfer in Electric Vehicles

Wireless power transfer (WPT) has the potential to revolutionise global transportation and to catalyse the rise of the market for electric vehicles (EVs) by providing a compelling alternative to the conventional ways of charging that involve the use of cables. Nevertheless, coil misalignment, which is caused by the behaviours of drivers who park their vehicles, is a substantial challenge since it has a detrimental impact on power transfer efficiency (PTE). This work presents a unique coil design that is coupled with adaptive hardware in order to improve power transfer efficiency (PTE) in magnetic resonant coupling waste power transfer (WPT) systems and reduce the impacts of coil misalignment, which is a significant impediment that is preventing the broad implementation of WPT for electric vehicles (EVs). Simulation with ADS was used to validate the effectiveness of the new design, which exhibited a high degree of congruence with the theoretical analysis. In addition, receiver and transmitter circuitry that was specifically constructed for the purpose of simulating real-world vehicle and parking bay settings was utilised. This allowed for the collecting of PTE data in a controlled environment that was on a smaller scale. Experiments showed that there was a significant thirty percent improvement in the power transfer efficiency (PTE) at the centre of the coil array, and an astonishing ninety percent improvement was recorded when the array was misaligned by three quarters of its radius. When compared to single coil designs that serve as benchmarks, the suggested new coil array displays improved property transfer efficiency (PTE).

Wearable Coaxially-Shielded Metamaterial for Magnetic Resonance Imaging.

Recent advancements in metamaterials have yielded the possibility of a wireless solution to improve signal-to-noise ratio (SNR) in magnetic resonance imaging (MRI). Unlike traditional closely packed local coil arrays with rigid designs and numerous components, these lightweight, cost-effective metamaterials eliminate the need for radio frequency cabling, baluns, adapters, and interfaces. However, their clinical adoption is limited by their low sensitivity, bulky physical footprint, and limited, specific use cases. Herein, a wearable metamaterial developed using commercially available coaxial cable, designed for a 3.0T MRI system is introduced. This metamaterial inherits the coaxially-shielded structure of its constituent cable, confining the electric field within and mitigating coupling to its surroundings. This ensures safer clinical adoption, lower signal loss, and resistance to frequency shifts. Weighing only 50g, the metamaterial maximizes its sensitivity by conforming to the anatomical region of interest. MRI images acquired using this metamaterial with various pulse sequences achieve an SNR comparable or even surpass that of a state-of-the-art 16-channel knee coil. This work introduces a novel paradigm for constructing metamaterials in the MRI environment, paving the way for the development of next-generation wireless MRI technology.

Vehicle Position Detection Based on Machine Learning Algorithms in Dynamic Wireless Charging.

Dynamic wireless charging (DWC) has emerged as a viable approach to mitigate range anxiety by ensuring continuous and uninterrupted charging for electric vehicles in motion. DWC systems rely on the length of the transmitter, which can be categorized into long-track transmitters and segmented coil arrays. The segmented coil array, favored for its heightened efficiency and reduced electromagnetic interference, stands out as the preferred option. However, in such DWC systems, the need arises to detect the vehicle's position, specifically to activate the transmitter coils aligned with the receiver pad and de-energize uncoupled transmitter coils. This paper introduces various machine learning algorithms for precise vehicle position determination, accommodating diverse ground clearances of electric vehicles and various speeds. Through testing eight different machine learning algorithms and comparing the results, the random forest algorithm emerged as superior, displaying the lowest error in predicting the actual position.

A Wireless Power Transfer Mattress Based System for Perpetually Operating Physiological Monitoring Wearables.

This article presents a novel wireless power mattress-based system architecture tailored to guarantee continuous energy for in-home environment healthcare wearables intended to be used in the context of patients who would benefit from long-term monitoring of specific physiological biomarkers. The design demonstrates that it is possible to transfer over 20 mW at a primary-secondary distance of 20.7 cm, whilst still keeping within all FCC/ICNIRP safety regulations, using the proposed simplified beamforming-controlled power transfer multi-input single-output system. Compared with other beamforming-controlled based works, the proposed design used non-coupling coil arrays, significantly reducing the algorithmic complexity. An on-chip wireless power charger system was also designed to provide high-efficiency power storage (89.3% power conversion efficiency and 83.9% power charge efficiency), guaranteeing wearables can continuously maintain their functionality. In contrast with conventional NiMh chargers, this work proposes a trimming function that makes it compatible with batteries of varying capacities. It also employs a four-stage charge loop to ensure safety and sustainability during the charging process. Overall, this work shows that by relying on wireless power transfer, it is, in principle, possible to create a safe wearable that could enable continuous monitoring of certain healthcare biomarkers with little or zero maintenance burden for the patients or carers.

Evolution of a Combined UV/Vis and NMR Setup with Fixed Pathlengths for Mass-limited Samples.

The investigation of reaction mechanisms is a complex task that usually requires the use of several techniques. To obtain as much information as possible on the reaction and any intermediates - possibly invisible to one technique - the combination of techniques is a solution. In this work we present a new setup for combined UV/Vis and NMR spectroscopy and compare it to an established alternative. The presented approach allows a versatile usage of different commercially-available components like mirrors and fiber bundles as well as different fixed pathlengths according to double transmission or single transmission measurements. While a previous approach is based on a dip-probe setup for conventional NMR probes, the new one is based on a micro-Helmholtz coil array (LiquidVoxel™). This makes the use of rectangular cuvettes possible, which ensure well-defined pathlengths allowing for quantification of species. Additionally, very low quantities of compound can be analyzed due to the microfabrication and small cuvette size used. As proof-of-principle this new setup for combined UV/Vis and NMR spectroscopy is used to examine a well-studied photochromic system of the dithienylethene compound class. A thorough comparison of the pros and cons of the two setups for combined UV/Vis and NMR measurements is performed.