Keywords: RF Arrays & Systems, RF Arrays & Systems, X-nuclear array coil

Motivation: ³¹P MRSI provides a valuable tool for metabolic imaging of human brain, and is crucial for studying neuroenergetics and neurological diseases, however, faces the low SNR challenge. 

Goal(s): To construct a dual-tuned 8-channel ³¹P/¹H transceiver array head coil with excellent performance for both proton structural MRI and ³¹P MRSI at 7T.

Approach: We constructed an 8-ch ³¹P/¹H transceiver array coil based on the novel double tuned and double matched (DODO) coil element, and compared its performance with the ³¹P/¹H TEM volume coil.

Results: The 8-ch ³¹P/¹H transceiver array coil shows significantly higher performance compared to ³¹P/¹H TEM volume coil.

Impact: We developed an 8-ch ³¹P/¹H transceiver array coil with excellent performance based on the DODO coil design. This technology has broad applications for in vivo human brain ³¹P MRSI studies and can be adapted to other multinuclear array coil designs.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: The poultry industry utilizes MRI to assess egg quality, especially to identify fertilized eggs. Image quality across eggs should be similar and with efficient filling factor.

Goal(s): The goal is to design a specialized coil for MRI that can efficiently and accurately scan multiple eggs , providing the same image quality for each egg.

Approach: The proposed coil has a multiloop structure. We used electromagnetic simulations to compute the magnetic field and compared the proposed coil with a volume and individual loop coils.

Results: Validated through simulations and MR images, the coil displayed the scalability and, enabling the imaging of multiple eggs

Impact: The proposed coil design  shows better egg per area filling factor efficiency and uniform image quality for each egg and also scalability for high-throughput egg screening. This design promises to enhance multiple egg imaging quality control in the poultry industry.

Keywords: High-Field MRI, High-Field MRI, Flexible coils, SAR efficiency, Coupling, Non-uniform current distribution

Motivation: At Ultra-High-Field, non-uniform currents have the potential to boost efficiency of loop coils at depth. However, possible advantages of non-uniform current naturally arising from short wavelength at Ultra-High-Field have not been investigated yet.

Goal(s): To characterize the impact of non-uniform currents on SAR efficiency for different coil geometries and coil orientations relative to the main magnetic field, and evaluate the feasibility of using such coils

Approach: Analysis was performed using simulations and experiments

Results: A 62x280mm elongated loop provided higher SAR efficiency than a conventional loop, or a dipole, at depth, with flexibility. low coupling, similar SNR and transmit efficiency than a dipole.

Impact: An elongated design of loops provided higher performance than conventional loops and dipoles in terms of SAR efficiency at depth, with flexibility, and low coupling. Results in this work provide a new avenue to explore in flexible coil design.

Keywords: RF Arrays & Systems, High-Field MRI, non-human primate, RF antenna, Dipole

Motivation: Imaging the brains of non-human primates (NHPs) at ultra-high field (UHF) is challenging, especially for whole-brain functional imaging in awake NHPs where high SNR is needed.

Goal(s): To design a dedicated system that overcomes challenges associated with UHF imaging and enhances signal-to-noise ratio (SNR) for high-quality NHP brain imaging.

Approach: We developed a 6-dipole parallel-transceive array, and a 16-loop receive array, optimized through electromagnetic simulations. We implemented preamplifier-decoupled dipoles to reduce coupling issues.

Results: The system showed good preamplifier-decoupling levels. Our dipoles’ implementation reduced experimental noise matching issues and EM simulations shows an SNR improvement.

Impact: Our 6pTx/22Rx antenna should improve awake NHP brain imaging at UHF, including transceive preamplifier-decoupled dipoles, designed for a specific imaging setup.

Keywords: RF Arrays & Systems, RF Arrays & Systems, g-factors

Motivation: Driven by the potential of the highly flexible twisted pair coil in creating unique sensitivity patterns for optimal acceleration.

Goal(s): To compare geometry factors of the twisted pair and conventional copper coils, exploring effective arrangements for various coil shapes.

Approach: Simulations of eight-element arrays containing circular and elongated coils; assessing geometry factors and the impact of random coil placements.

Results: Findings emphasize similar geometry factors between the twisted pair and conventional coils. Moreover, random coil setups around a phantom do not inherently improve geometry factors.

Impact: A comparison between twisted pair and conventional coils shows similar performance in g-factors. The flexibility of the twisted pair can be used to improve the g-factor but more work is required in finding the optimal shape of these coils.

Keywords: RF Arrays & Systems, RF Arrays & Systems, 3T 13C applications, low field transmit array design

Motivation: Tackle the coupling issue among the coil elements in phased array design at low field, so as to use phased array as transceiver at low fields for good transmit efficiency, receive sensitivity profile, and acceleration performance.

Goal(s): Design and build a 3T ¹³C/¹H 8-channel array for hyperpolarized ¹³C MRSI and steady-state ¹³C MRS after oral uptake of ¹³C labelled glucose

Approach: Use a novel cable trap decoupling mechanism to decouple the coil elements in the 3T ¹³C 8-channel array

Results: Workbench and experiment results show that the coil elements are decoupled very well with each other.

Impact: This innovative research on mitigating coil element coupling in low-field phased array designs empowers low-field MRI applications. Enhanced transmit efficiency, receive sensitivity and acceleration performance offer improved diagnostic quality, benefiting scientists, clinicians, and patients.

Keywords: New Devices, Spectroscopy

Motivation: Quantification of magnetic resonance spectroscopy (MRS) spectra requires sufficient SNR to detect changes in metabolic state. At ultra-high field, low concentration metabolite require length scan times to obtain sufficient SNR.

Goal(s): To use a novel metasurface design to enhance the B₁^- receive sensitivity in phantom and in vivo brain proton spectroscopy data at 7T, resulting in increased SNR without additional scan time.

Approach: Receive sensitivity enhancement was measured in phantom and in vivo experiments with and without the metasurface present.

Results: The metasurfaces enhanced phantom spectral SNR by an average of 58%, while in vivo spectral SNR was improved on average by 38%. 

Impact: The work impacts 7T spectroscopy techniques by improving the inherent receive sensitivity, yielding higher SNR spectra. Future work will focus on demonstrating this application in patent populations to reduce scan times and enhance the signal from low concentration metabolites.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Simultaneous functional imaging of the brain and spinal cord can offer valuable insights into the interactions and processing pathways between these organs

Goal(s): The goal is to build an transmit array and receive array for 7T the brain and spinal cord MRI.

Approach: The approach uses corner-fed self-decoupling for transmit array and center-fed self-decoupling for receive array.

Results: A 20-channel modular self-decoupled transmit array and 32-channel overlapped receive array were fabricated. Both arrays exhibit excellent matching performance, acceptable decoupling, and high detuning ability. Thanks to the self-decoupling technology, both arrays are splitable which simplifies the setup and allows for easier access by subjects.

Impact: The proposed device will solve the hardware issue and permit studies of healthy subjects to improve our understanding of the resting-state connectivity and interaction between the brain and spinal cord, compensating impaired sensory, motor, or autonomic functions in neurological disorders.

Keywords: RF Arrays & Systems, High-Field MRI, Hybrid & Novel Systems Technology, RF Array, Parallel Imaging

Motivation: Increased sensitivity and sufficient image coverage is demanded for more efficient and comprehensive extremity imaging. 

Goal(s): Our goal is to exploit multiple-row quadrature RF coil array configuration to increase detection/transmission sensitivity and image coverage for human knee imaging at 7T. 

Approach: Due to the increase of the channel count in a multiple-row configuration, it is technically challenging to attain adequate decoupling between quadrature elements of the array. We address this issue by using a double cross magnetic wall decoupling.

Results: The use of double cross magnetic wall decoupling have proven to be an efficient decoupling method. 

Impact: The feasibility of this work is a substantial achievement in the multichannel RF hardware engineering, poised to enhance MR imaging technology, especially in high-field applications, where multiple-row quadrature RF coil array configuration can significantly impact image quality and overall efficiency.   

Keywords: RF Arrays & Systems, MSK, Sodium, Ultra-High Field, Knee

Motivation: Overcome the limitations of current sodium/proton knee coil configurations using a flexible RF coil array system

Goal(s): Acceptance testing of a 32 channel (16 proton and 16 sodium) RF coil array and demonstrate applicability for sodium and proton MRI of the knee.

Approach: 8 hexagonal modules (4 coils each) were assembled in a volumetric configuration, with sodium and proton MRI quality assessed for phantom and human knee imaging.

Results: High quality sodium volumetric images of the knee were obtained while anatomical proton images were achieved using a standard TSE sequence with additional GRAPPA acceleration and without repositioning

Impact: A 32 channel modular array has been demonstrated to be an effective and flexible solution for both proton and sodium MRI of the knee. Sodium sensitivity was optimised while maintaining proton performance sufficient to acquire accelerated high quality anatomical images.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: The use of MLCs has shown the potential to improve the SNR at short distance as compared to an equivalent SLC.

Goal(s): Evaluation of the performances of a 8-channels MLC-array for head imaging at 7T.

Approach: Electromagnetic simulation was used to evaluate and compare the SNR, noise-covariance matrix and g-maps obtained with the MLC-array and with an equivalent array of SLC.

Results: As compared to the SLC-array, the MLC-array achieves an increased SNR in a relatively large peripheral ring and a reduced maximum g-factor.

Impact: Array of MLC represents a valuable strategy for array developpement at high field that can be employed to improve the SNR or reduce the number of  channels.

Keywords: RF Arrays & Systems, New Devices

Motivation: Advancements in array coil technology may not yield proportional gains in temporal SNR when physiological fluctuations are the primary noise source.

Goal(s): We constructed a highly dense array covering the visual cortex and evaluated its noise characteristics and performance as a function of resolution.

Approach: We evaluated image SNR and temporal SNR in vivo at 7 Tesla and produced BOLD activation maps using a visual paradigm.

Results: The improvement in image SNR with decreased resolution was significantly higher than the improvement in temporal SNR. This suggests physiological noise dominance at the lower resolution.

Impact: The image and temporal SNR offered by the visual coil allows for sub-millimeter resolution. Insight into the transition between thermal and physiologically noise dominated regimes will aid in reducing the risk of false positives in fMRI using this dense array.

Keywords: RF Arrays & Systems, RF Arrays & Systems, RF Rx array, Hybrid RF and shimming, Multi-coil shimming

Motivation: Multi-coil (MC) B0 shimming provides unrivaled brain shimming, yet early proof-of-concept implementations with preexisting RF hardware suffered from coupling and reduced sensitivity.

Goal(s): The design and realization of integrated MC/RF hardware for dynamic MC technique (DYNAMITE) B0 shimming of the human brain at 3T at full RF sensitivity.

Approach: We experimentally validate previously derived theoretical strategies for the minimization of MC-to-RF coupling and design integrated MC/RF hardware for MRI of the human brain.

Results: Great agreement was found between direct coupling measurements and simulated magnetic field flux, which was used in our previous work as a proxy of coupling due to mutual inductance.

Impact: Once the hardware construction and implementation with clinical MRI protocols is complete, the novel MC/RF setup is expected to improve diagnostic imaging in brain areas suffering from inhomogeneous B0 conditions.

Keywords: Safety, Safety

Motivation: Brain MRI with shoulder implants are often contraindicated at 7T with head coils due to possibility of radiofrequency (RF)-induced heating. Such implants are not uncommon in older adults; contraindication results in increasing proportion of elderly to be denied high-field scans. Assessing heating safety of MRI at 7T with implants is of significance.

Goal(s): To measure shoulder implant heating during MRI at 7T with pTx head coils and assess safety thereof.

Approach: Temperature of a reverse total shoulder implant was measured with fluoroptic sesnors during MRI at Siemens 7T Terra with pTX head coil.

Results: No significant heating (>1°C) of the implant was observed.

Impact: Findings from this study may enable brain scanning individuals with shoulder implant at 7T, thus making improved image quality a possibility.

Keywords: High-Field MRI, RF Arrays & Systems

Motivation: Labeling efficiency in pCASL suffers from an inferior drop-off in B1+ leading to low SNR perfusion-weighted images which can affect CBF quantification.

Goal(s): To assess the feasibility of pCASL in healthy volunteers using a custom-built head and neck coil at 7T.    

Approach: Volunteers were scanned with pCASL on two coils: a normal head coil and a head and neck coil with circularly polarized shim weights, and the results were compared in terms of CBF and tSNR.

Results: pCASL in healthy volunteers using a novel neurovascular coil at 7T gave an average GM/WM CBF ratio of 1.51, comparable to a conventional head coil.

Impact: This proof-of-concept study shows the feasibility of pCASL using a novel 8TxRx56Rx neurovascular (head and neck) coil at 7T and compares the performance against a conventional 8Tx64Rx head coil.

Keywords: High-Field MRI, Modelling, 9.4T RF coil LFMS TMS

Motivation: Recently, The research methods of transcranial magnetic stimulation(TMS)/fMRI in ultra-high fields are receiving increasing attention.

Goal(s): However, as the magnetic field strength increases, the interference problem between the TMS coil and the radio frequency（RF） coil will also become increasingly apparent.

Approach: We designed two types of TMS coils and 9.4T human RF  coil using the target field method, and evaluated the impact between the TMS coil and the RF coil using electromagnetic simulation based on the human head model.

Results: We have established a method for evaluating the interaction between RF coils and TMS coils in ultra-high fields.

Impact: Our work explores the combined use of TMS/fMRI in ultra-high fields, providing a non-invasive and precise approach for the microscopic study of brain nerve activity under  TMS, and also providing a basis for the regulation of brain nerves.