arXiv subjects

Xiaoliang Zhang

Publications and source records attributed to Xiaoliang Zhang.

At least 19 recordsLinked to original sources

arXiv2025

A Dual-Tuned Concentric Multimodal RF Coil for 7T 1H/31P MRSI: Concurrently Enhancing B1 Efficiency Over Single-Tuned References

This study presents the design, simulation, and experimental validation of a dual-tuned concentric multimodal surface coil for 7T 1H/31P magnetic resonance spectroscopic imaging (MRSI), developed to significantly enhance 31P B1 efficiency while improving 1H performance. The coil architecture utilizes two interleaved sets of three concentric loop resonators. Intra-nucleus electromagnetic coupling within each three-loop set generates a spectrum of eigenmodes; the operational modes for 1H and 31P were specifically selected because their co-directed current distributions reinforce the magnetic field at the center, yielding B1 patterns that resemble those of conventional single-loop surface coils but with superior efficiency. Full-wave electromagnetic simulations and bench measurements on a fabricated prototype were conducted to characterize the multimodal resonance behavior, scattering parameters, B1 distribution, and 10-g local SAR, using size-matched conventional single-tuned loops as references. The results confirmed that the design reproducibly generated the predicted eigenmode ordering with sufficient spectral separation to prevent interference from parasitic or undesired modes. Notably, the multimodal design achieved an 83% boost in 31P B1 efficiency and a 21% boost in 1H B1 efficiency at the coil center compared to same-sized single-tuned references. Sufficient inter-nuclear decoupling was achieved to prevent signal leakage between channels, and simulations with a human head model confirmed that the peak 10-g local SAR remained comparable to conventional designs. These findings demonstrate that this multimodal concentric design offers a robust and highly efficient solution for multinuclear MRSI at ultrahigh fields, effectively mitigating the sensitivity limitations of X-nuclei without compromising proton-based imaging capabilities.

physics.med-ph↗

arXiv2025

Predicting the Thermal Conductivity Collapse in SWCNT Bundles: The Interplay of Symmetry Breaking and Scattering Revealed by Machine-Learning-Driven Quantum Transport

We combine machine learning (ML)-based neuroevolution potentials (NEP) with anharmonic lattice dynamics and the Boltzmann transport equation (ALD-BTE) to achieve a quantitative and mode-resolved description of thermal transport in individual (10, 0) zigzag single-walled carbon nanotubes (SWCNTs) and their bundles. Our analysis reveals a dual mechanism behind the drastic suppression of thermal conductivity in bundles: first, the breaking of rotational symmetry in isolated SWCNTs dramatically enhances the scattering rates of symmetry-sensitive phonon modes, such as the twist (TW) mode. Second, the emergence of new inter-tube phonon modes introduces abundant additional scattering channels across the entire frequency spectrum. Crucially, the incorporation of quantum Bose-Einstein (BE) statistics is essential to accurately capture these phenomena, enabling our approach to quantitatively reproduce experimental observations. This work establishes the combination of ML-driven interatomic potentials and ALD-BTE as a predictive framework for nanoscale thermal transport, effectively bridging the gap between theoretical models and experimental measurements.

cond-mat.mes-hall↗

arXiv2025

Multimodal concentric surface coils for enhanced sensitivity in MR imaging

This study presents the design, simulation, and experimental validation of a novel multimodal concentric surface coil for MR imaging, developed to achieve higher B1 field efficiency while maintaining low SAR for enhanced imaging performance. The coil comprises multiple electromagnetically coupled concentric resonators of varying sizes. The resonant frequency of a desired mode is tuned to 127 MHz, as an example, to demonstrate the performance of the proposed technique at 3 Tesla. Fullwave electromagnetic simulations of the proposed design and bench tests of fabricated prototypes were conducted to evaluate the coil's B1 field efficiency and distribution, multimodal resonance behavior, scattering parameters, and SAR performance. Inductive Current Elimination or magnetic wall decoupling was implemented to enhance channel isolation in a multi channel configuration to demonstrate the feasibility of applying this multimodal technique to RF array design and parallel imaging. Experimental results show that the proposed concentric coil achieves higher B1 field efficiency and reduced SAR compared to a conventional surface coil of the same size operating at 3 Tesla. Bench measurements on the prototypes confirmed successful tuning and impedance matching, with measured S11 and S21 parameters validating the effectiveness of the decoupling strategy. B1 mapping experiments further demonstrated efficient RF power delivery across multiple planes. These findings suggest that the proposed multimodal concentric coil has the potential to serve as a promising alternative to conventional surface coils for high performance MR imaging, offering enhanced RF efficiency, reduced SAR, and the ability to construct multichannel RF arrays.

physics.med-ph↗

arXiv2025

Spin Phonon Coupling and Relaxation time in Lu(II) compound with 9.2GHz clock transition

Electron spin qubits operating at atomic clock transitions exhibit exceptionally long coherence times, making them promising candidates for scalable quantum information applications. In solid-state systems, interactions between qubits and lattice phonons are known to play a critical role in spin relaxation (T1) and decoherence (T2). In this work, we perform first-principles calculations on a Lu(II) complex spin qubit featuring a prominent clock transition. By employing advanced electronic structure methods, we quantitatively evaluate the influence of phonons on the hyperfine interaction, which serves as the primary spin-lattice coupling mechanism. Treating these phonon-induced variations as first-order perturbations, we apply the Redfield master equation to compute both T1 and T2, along with their temperature dependencies. For T1, we adopt a second quantization formalism to describe phonon interactions, while T2 is evaluated by explicitly integrating acoustic phonon contributions across the full Brillouin zone. Our results reproduce the experimentally observed magnetic field dependence of T2, including the coherence peak near 0.43 T, though the absolute values of T1 and T2 differ by one to two orders of magnitude. Analysis reveals that T1 is primarily governed by longitudinal phonons, whereas T2 is most strongly influenced by mid-wavelength, mid-energy acoustic modes. These findings provide a quantitative demonstration of the clock transition protective effect on spin qubit coherence and offer a transferable computational framework for evaluating spin-phonon interactions in other molecular spin qubits.

cond-mat.mtrl-sci↗

arXiv2025

Electronic structure of compressively strained thin film La$_2$PrNi$_2$O$_7$

The discovery of superconductivity in the bulk nickelates under high pressure is a major advance in physics. The recent observation of superconductivity at ambient pressure in compressively strained bilayer nickelate thin films has now enabled direct characterization of the superconducting phase through angle resolved photoemission spectroscopy (ARPES). Here we present an in-situ ARPES study of compressively strained La$_2$PrNi$_2$O$_7$ films grown by oxide molecular beam epitaxy, and the ozone treated counterparts with an onset T$_c$ of 40 K, supplemented with results from pulsed laser deposition films with similar T$_c$. We resolve a systematic strain-driven electronic band shift with respect to that of bulk crystals, in qualitative agreement with density functional theory (DFT) calculations. However, the strongly renormalized flat 3$d_{z2}$ band shifts a factor of 5-10 smaller than anticipated by DFT. Furthermore, it stays ~70 meV below the Fermi level, contradicting the expectation that superconductivity results from the high density of states of this band at the Fermi level. We also observed a non-trivial k$_z$ dispersion of the cuprate-like 3$d_{x2-y2}$ band. Combined with results from both X-ray diffraction and DFT, we suggest that the strained films are under ~5 GPa effective pressure, considerably larger than the naïve expectation from the DFT relaxed structure. Finally, the ~70 meV energy position is intriguingly close to the collective mode coupling more prominently seen in thin films, in the energy range of both oxygen related phonons and the maximum of the spin excitation spectrum.

cond-mat.supr-con↗

arXiv2025

Discrete Dielectric Coatings for Length Control and Tunability of Half-Wave Dipole Antennas at 300 MHz Magnetic Resonance Imaging Applications

This study presents a novel discretely dielectric material-coated (DDMC) dipole antenna design for ultra-high-field (UHF) MRI applications. This design improves frequency tuning, lowers electric field intensity, and reduces SAR by including discrete high-permittivity dielectric coatings at both ends of the dipole. The DDMC dipole's performance was compared to that of a fractionated dipole design using metrics such as inter-element coupling, B1 field distribution, and SNR. Simulations and experimental results showed that the DDMC dipole provided superior B1 field uniformity with significantly reduced B1 variation along the dipole conductor while reducing SAR, making it a safer and more efficient option for MR signal excitation and reception in UHF MR imaging. Furthermore, with its improved electromagnetic decoupling performance, the multichannel array made from the proposed DDMC dipoles shows promise for improving parallel imaging and imaging quality in UHF MRI, with future work focusing on material optimization and scalability for multi-channel arrays.

physics.med-ph↗

arXiv2025

A coupled planar transmit RF array for ultrahigh field spine MR imaging

Ultrahigh-field MRI, such as those operating at 7 Tesla, enhances diagnostic capabilities but also presents unique challenges, including the need for advanced RF coil designs to achieve an optimal signal-to-noise ratio and transmit efficiency, particularly when imaging large samples. In this work, we introduce the coupled planar array, a novel technique for high-frequency, large-size RF coil design with enhanced the RF magnetic field (B1) efficiency and transmit performance for ultrahigh-field spine imaging applications. This array comprises multiple resonators that are electromagnetically coupled to function as a single multimodal resonator. The field distribution of its highest frequency mode is suitable for spine imaging applications. Based on the numerical modeling and calculation, a prototype of the coupled planar array was constructed and its performance was evaluated through comprehensive numerical simulations, rigorous RF measurements, empirical tests, and a comparison against a conventional surface coil with the same size and geometry. The results of this study demonstrate that the proposed coupled planar array exhibits superior performance compared to conventional surface coils in terms of B1 efficiency for both transmit (B1+) and receive (B1-) fields, specific absorption rate (SAR), and the ability to operate at high frequencies. This study suggests a promising and efficient approach to the design of high-frequency, large-size RF coils for spine MR imaging at ultrahigh magnetic fields.

physics.med-ph↗

arXiv2025

Structural and Electronic Evolution of Bilayer Nickelates Under Biaxial Strain

The discovery of high-Tc superconductivity around 80K in bilayer nickelate La3Ni2O7 under high pressure has expanded the family of high-Tc superconductors above the nitrogen boiling temperature. Recent studies have further shown that ambient pressure superconductivity with a Tc exceeding 40K can be achieved in compressively strained La3Ni2O7 thin films, offering a tunable platform for investigating the pairing mechanism in high-Tc nickelates. A comprehensive understanding of the structural and electronic properties of bilayer nickelate under epitaxial strain is essential to advance this active field. In this work, we employ first-principles calculations to systematically explore the entire rare-earth (Re) series of bilayer nickelates Re3Ni2O7 in the realistic orthorhombic Amam phase under various compressive and tensile strain conditions. We highlight the materials properties change when strain is applied, and compare these results with those observed under high pressure. Our findings show that 2.5\% compressive strain increases the apical Ni-O-Ni bond angle toward 180 degree, and causes the Ni $d_{z^2}$ bands to move away from the Fermi level. The tight-binding parameters for the 2.5\% compressively strained La3Ni2O7 are quite similar to those of the unstrained material, except that the on-site energy difference between the Ni $d_{z^2}$ and $d_{x^2-y^2}$ orbitals increases by about 50 percent. Notably, the absence of the $d_{z^2}$ bands at the Fermi energy under compressive strain contrasts sharply with the electronic structure in the high-pressure {\it Fmmm} phase, suggesting that the presence of $d_{z^2}$ bands at the Fermi energy may not be a requisite for superconductivity.

cond-mat.supr-con↗

arXiv2024

Altermagnetism and Strain Induced Altermagnetic Transition in Cairo Pentagonal Monolayer

Altermagnetism, a recently discovered class of magnetic order characterized by vanishing net magnetization and spin-splitting band structures, has garnered significant research attention. In this work, we introduce a novel two-dimensional system that exhibits $g$-wave altermagnetism and undergoes a strain-induced transition from $g$-wave to $d$-wave altermagnetism. This system can be realized in an unconventional monolayer Cairo pentagonal lattice, for which we present a realistic tight-binding model that incorporates both magnetic and non-magnetic sites. Furthermore, we demonstrate that non-trivial band topology can emerge in this system by breaking the symmetry that protects the spin-polarized nodal points. Finally, \emph{ab initio} calculations on several candidate materials, such as FeS$_2$ and Nb$_2$FeB$_2$, which exhibit symmetry consistent with the proposed tight-binding Hamiltonian, are also presented. These findings open new avenues for exploring spintronic devices based on altermagnetic systems.

cond-mat.str-el↗

arXiv2024

Near-Field Coupling Coil System: A Novel Radiofrequency Coil Solution for MRI

The performance of radiofrequency (RF) coils has a significant impact on the quality and speed of magnetic resonance imaging (MRI). Consequently, rigid coils with attached cables are commonly employed to achieve optimal SNR performance and parallel imaging capability. However, since the adoption of MRI in clinical imaging, both patients and doctors have long suffered from the poor examination experience and physical strain caused by the bulky housings and cumbersome cables of traditional coils. This paper presents a new architectural concept, the Near-Field Coupling (NFC) coil system, which integrates a pickup coil array within the magnet with an NFC coil worn by the patient. In contrast to conventional coils, the NFC coil system obviates the necessity for bed-mounted connectors. It provides a lightweight, cost-effective solution that enhances patient comfort and supports disposable, custom designs for the NFC coils. The paper also derives the SNR expression for the NFC coil system, proposes two key design principles, and demonstrates the system's potential in SNR and parallel imaging through an implementation case.

physics.med-ph↗

arXiv2024

Superconducting and low temperature RF Coils for Ultra-Low-Field MRI: A Study on SNR Performance

This study incorporates electromagnetic simulations to assess the performance of multi-turn solenoid coils for ultra-low field MR imaging with various conductor materials (superconducting material, low-temperature copper, and room-temperature copper) across different human samples (elbow, knee, and brain). At 70 mT, superconducting materials performed significantly better than both room-temperature and low-temperature copper. The high Q-factor of the superconducting material indicates lower energy loss, which is useful for MR imaging. Furthermore, B1+ field efficiency increased significantly with superconducting materials, indicating superior performance. SNR evaluations revealed that materials with higher conductivity significantly improve SNR, which is critical for producing high-quality MR images. These results show that superconducting and low-temperature copper materials can significantly improve MR imaging quality at ultra-low fields, which has important implications for coil design and optimization.

physics.med-ph↗

arXiv2024

Quantitative Evaluation of Microstrip, Dipole, and L/C Loop pTx Arrays for UHF MR Imaging

Ultra-high field MRI (7T+) unlocks a new era of brain research with superior resolution and signal-to-noise. Capturing intricate neural activity and detailed soft tissue pathology, this technology, coupled with advanced RF coil arrays, holds immense potential for clinical diagnosis and discovery. For high-field body imaging, microstrip resonators and dipole arrays for high-field body imaging show promise due to high-frequency operation and improved decoupling. Microstrip arrays excel in compactness, reduced radiation loss, and customizable lengths. Dipole arrays excel in deeper body penetration. Shorter wavelengths at ultrahigh fields can cause image inhomogeneity and elevated SAR. Multichannel transmit arrays address these issues. This research compares three common array types (L/C loop, microstrip, dipole) using CST Studio simulations to evaluate electric/magnetic fields and decoupling. This can guide RF array selection for ultrahigh field MRI.

physics.med-ph↗

arXiv2024

Ultrashort echo time and zero echo time MR imaging and their applications at high magnetic fields: A literature survey

UTE (Ultrashort Echo Time) and ZTE (Zero Echo Time) sequences have been developed to detect short T2 relaxation signals coming from regions that are unable to be detected by conventional MRI methods. Due to the high dipole-dipole interactions in solid and semi-solid tissues, the echo time generated is simply not enough to produce a signal using conventional imaging method, often leading to void signal coming from the discussed areas. By the application of these techniques, solid and semi-solid areas can be imaged which can have a profound impact in clinical imaging. High and Ultra-high field strength (UHF) provides a vital advantage in providing better sensitivity and specificity of MR imaging. When coupled with the UTE and ZTE sequences, the image can recover void signals as well as a much-improved signal quality. To further this strategy, secondary data from various research tools was obtained to further validate the research while addressing the drawbacks to this approach. It was found that UTE and ZTE sequences coupled with some techniques such as qualitative imaging and new trajectories are very crucial for accurate image depiction of the areas of the musculoskeletal system, neural system, lung imaging and dental imaging.

physics.med-ph↗

arXiv2023

Multimodal surface coils for low-field MR imaging

Leveraging the potential of low-field Magnetic Resonance Imaging (MRI), our study introduces the multimodal surface RF coil, a design tailored to overcome the limitations of conventional coils in this context. The inherent challenges of low-field MRI, notably suboptimal signal-to-noise ratio (SNR) and the need for specialized RF coils, are effectively addressed by our novel design. The multimodal surface coil is characterized by a unique assembly of resonators, optimized for both B1 efficiency and low-frequency tuning capabilities, essential for low-field applications. This paper provides a thorough investigation of the conceptual framework, design intricacies, and bench test validation of the multimodal surface coil. Through detailed simulations and comparative analyses, we demonstrate its superior performance in terms of B1 field efficiency, outperforming conventional surface coils.

physics.med-ph↗

arXiv2023

Electric Field and SAR Reduction in High Impedance RF Arrays by Using High Permittivity Materials for 7T MR Imaging

Higher frequencies and shorter wavelengths present significant design issues at ultra-high fields, making multi-channel array setup a critical component for ultra-high field MR imaging. The requirement for multi-channel arrays, as well as ongoing efforts to increase the number of channels in an array, are always limited by the major issue known as inter-element coupling. This coupling affects the current and field distribution, noise correlation between channels, and frequency of array elements, lowering imaging quality and performance. To realize the full potential of UHF MRI, we must ensure that the coupling between array elements is kept to a minimum. High-impedance coils allow array systems to completely realize their potential by providing optimal isolation while requiring minimal design modifications. These minor design changes, which demand the use of low capacitance on the conventional loop to induce elevated impedance, result in a significant safety hazard that cannot be overlooked. High electric fields are formed across these low capacitance lumped elements, which may result in higher SAR values in the imaging subject, depositing more power and, ultimately, providing a greater risk of tissue heating-related injury to the human sample. We propose an innovative method of utilizing high-dielectric material to effectively reduce electric fields and SAR values in the imaging sample while preserving the B1 efficiency and inter-element decoupling between the array elements to address this important safety concern with minimal changes to the existing array design comprising high-impedance coils.

physics.med-ph↗

arXiv2023

Coupled stack-up volume RF coils for low-field MR imaging

The advent of low field open magnetic resonance imaging (MRI) systems has greatly expanded the accessibility of MRI technology to meet a wide range of patient needs. However, the inherent challenges of low-field MRI, such as limited signal-to-noise ratios and limited availability of dedicated RF coil, have prompted the need for innovative coil designs that can improve imaging quality and diagnostic capabilities. In response to these challenges, we introduce the coupled stack-up volume coil, a novel RF coil design that addresses the shortcomings of conventional birdcage in the context of low field open MRI. The proposed coupled stack-up volume coil design utilizes a unique architecture that optimizes both transmit/receive efficiency and RF field homogeneity and offers the advantage of a simple design and construction, making it a practical and feasible solution for low field MRI applications. This paper presents a comprehensive exploration of the theoretical framework, design considerations, and experimental validation of this innovative coil design. Through rigorous analysis and empirical testing, we demonstrate the superior performance of the coupled stack-up volume coil in achieving improved transmit/receive efficiency and more uniform magnetic field distribution compared to traditional birdcage coils.

physics.med-ph↗

arXiv2023

Dual-tuned Coaxial-transmission-line RF coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields

$Objective:$ Information on the metabolism of tissues in both healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging ($^{13}$C-HPMRI) and deuterium metabolic imaging ($^2$H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios ($γ_{13C}$ = 10.7 MHz/T; $γ_{2H}$ = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil. $ Methods:$ Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters. $Results:$ Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the $^{13}$C and $^2$H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned $^1$H/$^{13}$C and $^1$H/$^2$H RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained. $Conclusion:$ The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging. $Significance:$ The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.

physics.med-ph↗

arXiv2023

Self-supervised Deep Unrolled Reconstruction Using Regularization by Denoising

Deep learning methods have been successfully used in various computer vision tasks. Inspired by that success, deep learning has been explored in magnetic resonance imaging (MRI) reconstruction. In particular, integrating deep learning and model-based optimization methods has shown considerable advantages. However, a large amount of labeled training data is typically needed for high reconstruction quality, which is challenging for some MRI applications. In this paper, we propose a novel reconstruction method, named DURED-Net, that enables interpretable self-supervised learning for MR image reconstruction by combining a self-supervised denoising network and a plug-and-play method. We aim to boost the reconstruction performance of Noise2Noise in MR reconstruction by adding an explicit prior that utilizes imaging physics. Specifically, the leverage of a denoising network for MRI reconstruction is achieved using Regularization by Denoising (RED). Experiment results demonstrate that the proposed method requires a reduced amount of training data to achieve high reconstruction quality among the state-of-art of MR reconstruction utilizing the Noise2Noise method.

eess.IV↗