Journal of magnetic resonance最新文献_第7页

Using solid-state MRI and a double-tuned RF coil to quantify bone matrix and mineral densities in rat bones 使用固态MRI和双调谐射频线圈量化大鼠骨骼中的骨基质和矿物质密度

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-01 Epub Date: 2025-06-20 DOI: 10.1016/j.jmr.2025.107925

Victor B. Kassey , Matthias Walle , Diana Yeritsyan , Daniel V. Kassey , Yaotang Wu , Brian D. Snyder , Edward K. Rodriguez , Jerome L. Ackerman , Ara Nazarian

Quantitative information on the composition of bone, specifically the content of calcium phosphate mineral and organic matrix, is essential for accurate diagnosis of metabolic bone diseases such as osteoporosis, osteomalacia, and renal osteodystrophy, as well as for differentiating among these conditions. Conventional MRI fails to provide this information because these substances are solid and, therefore, yield no signal in conventional MRI scans, which typically employ spin or gradient echoes. In this report, we show how phosphorus and proton solid-state MRI yield the desired compositional information in bone specimens with ZTE and WASPI pulse sequences, respectively, coupled with the use of a two-port double-tuned solenoidal RF coil.

Electrical network simulations and construction details of the RF coil are detailed. Electrical performance was simulated using QUCS software to find the circuit component values that minimize reflected power and maximize interport isolation. Phantoms of known composition, as well as ex vivo femurs from normal, low bone density, and vitamin D-deficient rats, were included in the study. A simple correction for B₁ inhomogeneity was applied to achieve quantitative accuracy in the image intensity values.

Bone matrix and mineral densities derived from MRI strongly correlated (R² = 0.84) with chemical analysis, demonstrating the ability to measure compositional differences relevant to osteoporosis and osteomalacia.

骨组成的定量信息，特别是磷酸钙矿物和有机基质的含量，对于准确诊断代谢性骨疾病（如骨质疏松症、骨软化症和肾性骨营养不良）以及区分这些疾病至关重要。传统的MRI无法提供这些信息，因为这些物质是固体的，因此在传统的MRI扫描中无法产生信号，而传统的MRI扫描通常使用自旋或梯度回波。在本报告中，我们展示了磷和质子固态MRI如何分别使用ZTE和WASPI脉冲序列在骨标本中产生所需的成分信息，并结合使用双端口双调谐螺线管射频线圈。详细介绍了射频线圈的电气网络仿真和结构细节。利用QUCS软件对电路的电气性能进行了模拟，以找出使反射功率最小和使接口隔离最大化的电路元件值。已知成分的幻影，以及正常、低骨密度和维生素d缺乏大鼠的离体股骨，都被纳入研究。对B1非均匀性进行了简单的校正，以实现图像强度值的定量精度。MRI得出的骨基质和矿物质密度与化学分析高度相关（R2 = 0.84），证明了测量骨质疏松症和骨软化症相关成分差异的能力。

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引用次数: 0

Accurate image reconstruction from reduced data in pulsed electron paramagnetic resonance imaging 脉冲电子顺磁共振成像中简化数据的精确图像重建

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-01 Epub Date: 2025-06-23 DOI: 10.1016/j.jmr.2025.107920

Zheng Zhang , Boris Epel , Buxin Chen , Dan Xia , Emil Y. Sidky , Howard Halpern , Xiaochuan Pan

Objective:

We investigate and develop algorithms for reconstructing effective probe-density images, and then for obtaining oxygen-concentration images, from data of a subject collected at sparse views (SVs) or over a limited-angular range (LAR) for possibly achieving fast pulsed electron paramagnetic resonance imaging (EPRI). We refer to the effective probe-density image simply as the EPR image in the work.

Methods:

The reconstruction problem of EPR images from SV or LAR data in pulsed EPRI is formulated as an optimization program that includes a constraint either on the total variation (TV) or on the directional-TVs (DTVs) of the EPR image. Two algorithms, referred to as TV and DTV algorithms, are developed then for reconstruction of EPR images, respectively, from SV and LAR data through solving the respective optimization programs. Oxygen-concentration image is estimated subsequently from the EPR images reconstructed.

Results:

Using numerical studies with simulated data of a digital phantom and also with real data of a physical phantom and a mouse model, we demonstrate the potential of the TV and DTV algorithms that yield, respectively, from SV and LAR data, numerically accurate EPR and oxygen-concentration images.

Conclusion:

The TV and DTV algorithms developed can yield numerically accurate EPR and oxygen-concentration images, respectively, from SV and LAR data in pulsed EPRI.

Significance:

The work may yield insights into the design of scans with minimized scanning time, thus potentially enabling basic and preclinical in vivo studies with fast pulsed EPRI.

目的：研究和开发从稀疏视图（SVs）或有限角范围（LAR）采集的受试者数据中重建有效探针密度图像，然后获得氧浓度图像的算法，从而可能实现快速脉冲电子顺磁共振成像（EPRI）。在本文中，我们将有效探针密度图像简称为EPR图像。方法：将脉冲EPRI中SV或LAR数据的EPR图像重建问题制定为一个优化程序，该程序包括对EPR图像的总变差（TV）或方向电视（dtv）的约束。然后，通过求解各自的优化程序，分别开发了两种算法，即TV和DTV算法，用于从SV和LAR数据重建EPR图像。随后从重构的EPR图像中估计氧浓度图像。结果：通过对数字幻影的模拟数据以及物理幻影和小鼠模型的真实数据进行数值研究，我们展示了TV和DTV算法的潜力，分别从SV和LAR数据产生数值精确的EPR和氧浓度图像。结论：所开发的TV和DTV算法可以分别从脉冲EPRI的SV和LAR数据中获得数值精确的EPR和氧浓度图像。意义：这项工作可能会对最小化扫描时间的扫描设计产生见解，从而有可能实现快速脉冲EPRI的基础和临床前体内研究。

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引用次数: 0

Towards complete suppression of diagonal peaks in solid-state MAS NMR homonuclear chemical shift correlation spectra 固态MAS核磁共振同核化学位移相关谱对角峰的完全抑制

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-01 Epub Date: 2025-06-25 DOI: 10.1016/j.jmr.2025.107926

Shengyu Zhang , Yuchen Li , Yansheng Ye , Fang Tian , Xinhua Peng , Riqiang Fu

The feasibility of applying the spin-echo based diagonal peak suppression method in solid-state MAS NMR homonuclear chemical shift correlation experiments is demonstrated. A complete phase cycling is designed to generate sine- and cosine-modulations of the chemical shift difference between the spin-diffused signals, enabling the quadrature detection in the indirect dimension. Meanwhile, all signals not involved in polarization transfer are refocused at the center of the indirect dimension. A data processing algorithm is developed to extract and suppress these spin-echo refocused signals without affecting nearby spin-diffused cross peaks. The processed spectrum is then converted into a conventional two-dimensional homonuclear chemical shift correlation spectrum, free of diagonal peaks. The effectiveness of this method is illustrated using a uniformly ¹³C-labeled Fmoc-leucine sample and a sample of human Atg8 homolog LC3B, directly conjugated to the amino headgroup of phosphatidylethanolamine (PE) lipids in liposomes.

论证了基于自旋回波对角峰抑制方法应用于固态MAS核磁共振同核化学位移相关实验的可行性。设计了一个完整的相位循环，以产生自旋扩散信号之间的化学位移差的正弦和余弦调制，从而实现间接维度的正交检测。同时，所有不参与极化转移的信号都被重新聚焦在间接维的中心。为了在不影响附近自旋扩散交叉峰的情况下提取和抑制这些自旋回波重聚焦信号，提出了一种数据处理算法。然后将处理后的光谱转换为传统的二维同核化学位移相关光谱，没有对角峰。使用统一的13c标记的fmoc -亮氨酸样品和人类at8同源物LC3B样品，直接偶联到脂质体中磷脂酰乙醇胺（PE）脂质的氨基头基，证明了该方法的有效性。

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引用次数: 0

Finite element modeling of Rb-129Xe spin-exchange optical pumping and optimized Rb source distribution 铷- 129xe自旋交换光泵浦的有限元建模及优化铷源分布

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-05-30 DOI: 10.1016/j.jmr.2025.107889

Jimmy E. Ball, Jim M. Wild, Graham Norquay

Rubidium (Rb) vapor density (

[Rb]

) is a key parameter in xenon-129 polarization (

P_{Xe}

) build up in spin-exchange optical pumping. In practice,

[Rb]

within the cell often falls below saturation levels and is spatially heterogeneous leading to system underperformance. In this study, finite element modeling was performed to investigate the role of Rb source distribution in heterogeneous in-cell

[Rb]

, and to optimize a Rb presaturator to achieve homogeneous

[Rb]

and reduce the flow rate dependence of

[Rb]

. Lower than expected

P_{Xe}

in previous iterations of our polarizer can be attributed to sub-saturation

[Rb]

due to the small surface area of the Rb source in the main cell body and the absence of upstream Rb vapor presaturation, leading to lower than desired

P_{Xe}

. We found that increasing the surface area of the Rb source in the main cell body does not effectively reduce

[Rb]

heterogeneity. Instead, achieving a more uniform distribution of

[Rb]

necessitates the use of a sufficiently long presaturator at a given gas flow rate, increasing

P_{Xe}

. We also report discrepancy between modeled and experimentally measured laser absorption, highlighting limitations of the existing optical pumping model and suggesting directions for future model revisions and the investigation of currently unexplored areas.

铷（Rb）蒸气密度（[Rb]）是自旋交换光泵浦中氙-129极化（PXe）形成的关键参数。实际上，单元内的[Rb]通常低于饱和水平，并且在空间上不均匀，导致系统性能不佳。本研究通过有限元建模研究了Rb源分布在非均质胞内[Rb]中的作用，并对Rb预饱和器进行了优化，以实现均匀[Rb]并降低对[Rb]流量的依赖。在我们之前的偏振器迭代中，低于预期的PXe可归因于亚饱和[Rb]，这是由于主胞体中Rb源的小表面积和上游Rb蒸气压力的缺乏，导致PXe低于预期。我们发现，增加主细胞体Rb源的表面积并不能有效降低[Rb]的异质性。相反，要实现[Rb]的更均匀分布，就需要在给定的气体流速下使用足够长的预热器，从而增加PXe。我们还报告了模型和实验测量的激光吸收之间的差异，突出了现有光泵模型的局限性，并为未来的模型修订和目前未开发区域的研究提出了方向。

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引用次数: 0

Probing rare and short-lived conformational states in nucleic acids using off-resonance carbonyl and guanidino carbon R1ρ relaxation dispersion 利用非共振羰基和鸟嘌呤碳R1ρ弛豫色散探测核酸的稀有和短寿命构象态

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-05-29 DOI: 10.1016/j.jmr.2025.107910

Supriya Pratihar , Yeongjoon Lee , Ainan Geng , Shibani Bhattacharya , Hashim M. Al-Hashimi

Chemical exchange-based NMR techniques provide powerful approaches for characterizing lowly-populated and short-lived conformational states in nucleic acids. Among possible probes, the nucleobase carbonyl and guanidino carbons stand out due to the sensitivity of their chemical shifts to hydrogen bonding and keto–enol tautomerization. However, chemical exchange measurements targeting these carbon nuclei have not yet been reported in studies of nucleic acids. Here, we present an experiment for measuring off-resonance R_1ρ relaxation dispersion for guanine-C2, guanine-C6, thymine/uracil-C2, and thymine/uracil-C4 carbons in uniformly ¹³C/¹⁵N labeled nucleic acids. We demonstrate the utility of the experiment by characterizing chemical exchange in a G•T mismatch in duplex DNA between a dominant wobble conformation and two lowly-populated, short-lived, and rapidly interconverting Watson–Crick-like tautomeric states (G^enol•T ⇌ G•T^enol) implicated in DNA replicative errors. The population and exchange rate deduced from the guanine-C6, guanine-C2, and thymine-C4 off-resonance R_1ρ relaxation dispersion profiles were in excellent agreement with counterparts obtained from R_1ρ measurements on proton-bound carbon and nitrogen nuclei. The carbon chemical shifts of the minor state were downfield shifted relative to the wobble ground state, consistent with (G)C6 = O···HO-C4(T^enol) and (G^enol)C6-OH···O=C4(T) hydrogen bonding in the Watson-Crick-like tautomeric state. As a second application, we did not detect any exchange contribution to uracil-C2 and uracil-C4 R_1ρ profiles measured for a U·U mismatch in RNA, consistent with isomerization between two alternative wobble conformations occurring on the sub-microsecond timescale. These results establish carbonyl and guanidino carbons as valuable probes for chemical exchange measurements of micro-to-millisecond motions in nucleic acids.

基于化学交换的核磁共振技术为表征核酸中低密度和短寿命的构象状态提供了强有力的方法。在可能的探针中，核碱基羰基和胍基碳因其化学转变对氢键和酮-烯醇互变异构的敏感性而脱颖而出。然而，针对这些碳核的化学交换测量尚未在核酸研究中报道。在这里，我们提出了一个实验测量非共振R1ρ弛豫色散的鸟嘌呤- c2，鸟嘌呤- c6，胸腺嘧啶/尿嘧啶- c2和胸腺嘧啶/尿嘧啶- c4碳在均匀13C/15N标记的核酸。我们通过表征双工DNA中G•T不匹配的化学交换，在一个主要的摆动构象和两个低密度的、短寿命的、快速相互转换的沃森-克里克样互变异构态（Genol•T + G•Tenol）之间进行了实验，证明了该实验的效用。从鸟嘌呤- c6、鸟嘌呤- c2和胸腺嘧啶- c4非共振R1ρ弛豫色散谱中得到的居群和交换率与质子结合碳核和氮核的R1ρ测量结果非常吻合。次要态的碳化学位移相对于摆动基态向下移动，与(G)C6 = O··O-C4（Tenol）和（Genol）C6- oh··O=C4(T)在沃森-克里克样互变异构态中的氢键一致。作为第二个应用，我们没有检测到任何交换对uracil-C2和uracil-C4 R1ρ谱的贡献，用于测量RNA中的U·U错配，这与发生在亚微秒时间尺度上的两种可选摆动构象之间的异构化一致。这些结果建立了羰基和胍基碳作为有价值的探针的化学交换测量的微至毫秒运动的核酸。

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引用次数: 0

Reduction of radiofrequency induced implant heating via flexible metasurface shielding at 7 T 通过柔性超表面屏蔽在7 T下减少射频诱导的植入物加热

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-06-02 DOI: 10.1016/j.jmr.2025.107918

Paul S. Jacobs , Wyger M. Brink , Pradnya Narvekar , Neil E. Wilson , Anshuman Swain , Neeraj Panchal , Samir Mehta , Mark A. Elliott , Ravinder Reddy

Passive implanted devices are commonly contraindicated at ultra-high field MRI due to the risk of radiofrequency heating. Mitigation of this risk has come in many forms, such as modifying implant materials or creating novel radiofrequency coils. These methods require substantial involvement from manufacturers and may not benefit patients with existing implants. In this study, a tailored metasurface design is demonstrated to improve implant safety at 7 T by shielding the local B₁⁺ field. A prototype metasurface was designed and implemented with a unit cell size of 15 mm using discrete capacitors of 30 pF values. Phantom and human body model simulations were used to validate differences in the SAR distribution with and without the metasurface. Fiber optic temperature probes were used to measure temperature increase across two representative orthopedic screws placed inside a tissue mimicking phantom during a high-SAR sequence. Phantom and in-vivo imaging were performed to assess the metasurface effect on image quality. With the metasurface, an average maximum temperature decrease of 0.50 °C or 34.9 % near the implant was observed. RF field simulations yielded similar decreases in SAR for the phantom (40.7 %) and substantial decreases for the in-vivo leg model (97 %). Phantom image SNR showed a global 8.5 % decrease with the metasurface while in-vivo images showed a 4.8 % decrease in SNR, with the region in its immediate vicinity experiencing substantial signal drop. These results demonstrate the feasibility of a metasurface designed to substantially reduce local RF induced heating with only minor degradation of image quality. Future work will focus on refinement of the metasurface design and further in-vivo testing.

由于射频加热的风险，被动式植入装置通常禁止在超高场MRI中使用。减轻这种风险的方法有很多，比如修改植入材料或制造新型射频线圈。这些方法需要制造商的大量参与，并且可能对现有植入物的患者没有好处。在这项研究中，量身定制的超表面设计被证明可以通过屏蔽局部B1+场来提高7 T时种植体的安全性。设计并实现了一个原型超表面，其单元尺寸为15 mm，使用30 pF值的分立电容器。通过模拟和人体模型模拟来验证有和没有超表面时SAR分布的差异。在高sar序列中，使用光纤温度探头测量放置在模拟组织内的两个具有代表性的骨科螺钉的温度升高。幻影和活体成像评估超表面效应对图像质量的影响。在超表面下，种植体附近的平均最高温度下降了0.50°C或34.9%。射频场模拟对假体的SAR也有类似的降低（40.7%），对活体腿模型的SAR也有明显的降低（97%）。幻影图像的信噪比在超表面上整体下降了8.5%，而活体图像的信噪比下降了4.8%，其邻近区域的信号明显下降。这些结果证明了设计一种超表面的可行性，该超表面可以大大减少局部射频引起的加热，而图像质量只有轻微的下降。未来的工作将集中在改进超表面设计和进一步的体内测试上。

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引用次数: 0

Evaluating the effect of 1H decoupling on 19F longitudinal relaxation and signal line shape in 5-Fluorotryptophan 评价1H解耦对5-氟色氨酸19F纵向弛豫和信号线形状的影响

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-05-21 DOI: 10.1016/j.jmr.2025.107899

Yuki Toyama , Koh Takeuchi , Ichio Shimada

Fluorine 19 (¹⁹F) in aromatic rings serves as a useful spin probe for studying the structure, dynamics, and intermolecular interactions of biomolecules and small-molecule ligands. Although ¹⁹F NMR involving aromatic ¹⁹F probes has a number of applications, quantitative relaxation analyses of these probes remain challenging due to the complexity of ¹H-¹⁹F spin interaction networks. In this study, we investigated ¹H-¹⁹F spin interactions in the 5-fluorotryptophan system, focusing on the effects of ¹H decoupling on ¹⁹F relaxation properties and line shape. We demonstrate that ¹H decoupling significantly slows down the ¹⁹F magnetization recovery process, leading to reduced sensitivity particularly in large proteins. In addition, ¹H decoupling effectively eliminates cross-correlations between ¹⁹F chemical shift anisotropy and ¹H-¹⁹F dipole-dipole interactions, resolving the asymmetric line shape of the aromatic ¹⁹F signal. Through experimental and theoretical analyses of the ¹H-coupled ¹⁹F spin system, we propose a model that explains these relaxation behaviors. Our results offer practical guidelines for optimizing ¹H decoupling schemes in aromatic ¹⁹F probes, thereby expanding the utility of ¹⁹F NMR.

芳香环中的氟19 （19F）是研究生物分子和小分子配体的结构、动力学和分子间相互作用的有用自旋探针。尽管涉及芳香19F探针的19F核磁共振有许多应用，但由于1H-19F自旋相互作用网络的复杂性，这些探针的定量松弛分析仍然具有挑战性。在本研究中，我们研究了5-氟色氨酸体系中1H-19F自旋相互作用，重点研究了1H解耦对19F弛豫性质和线形的影响。我们证明，1H解耦显著减缓了19F磁化恢复过程，导致敏感性降低，特别是在大蛋白质中。此外，1H去耦有效地消除了19F化学位移各向异性与1H-19F偶极子-偶极子相互作用之间的相互关联，解决了芳香19F信号的不对称线形。通过对h耦合的19F自旋系统的实验和理论分析，我们提出了一个解释这些弛豫行为的模型。我们的结果为优化芳香19F探针的1H解耦方案提供了实用指南，从而扩大了19F NMR的实用性。

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引用次数: 0

Effects of insufficient 31P pulse amplitudes on 13C-detected 31P13C rotational-echo double-resonance measurements in solid state NMR 固态核磁共振中31P脉冲幅值不足对13c检测31P13C旋转回波双共振测量的影响

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-01 Epub Date: 2025-05-28 DOI: 10.1016/j.jmr.2025.107908

Motahareh G. Larimi, Robert Tycko

We investigate the effects of insufficient ³¹P pulse amplitudes on ¹³C-detected ³¹P¹³C Rotational-Echo Double-Resonance (REDOR) measurements in a 17.5 T magnetic field. Experimental REDOR data on two compounds show that normalized REDOR difference signals

Δ S / S_{0}

are suppressed when the amplitudes of ³¹P π pulse trains are not very large compared with the ³¹P chemical shift anisotropies. This behavior is explained theoretically by an analysis of the effects of imperfections in π pulse rotations due to the orientation-dependent and time-dependent resonance offsets under magic-angle spinning in REDOR measurements. We show that effects of the same pulse imperfections can be observed directly by measurements of an effective relaxation time

{T_{1}}^{eff}

for longitudinal ³¹P spin polarization under identical π pulse trains.

我们研究了在17.5 T磁场中，31P脉冲幅度不足对13c探测到的31P13C旋转回波双共振（REDOR）测量的影响。两种化合物的实验REDOR数据表明，当31P π脉冲序列的幅度不是很大时，归一化REDOR差分信号ΔS/S0被抑制。从理论上解释了这种行为，分析了在REDOR测量中，由于魔角旋转下的方向相关和时间相关的共振偏移，π脉冲旋转中的缺陷的影响。通过测量相同π脉冲序列下纵向31P自旋极化的有效弛豫时间T1eff，可以直接观察到相同脉冲缺陷的影响。

引用次数: 0

Strong field gradients enable NMR-based diffusion measurements for K+, Mg2+, Cl−, and SO42− ions in biomolecular solutions 强场梯度使核磁共振为基础的扩散测量K+， Mg2+， Cl−和SO42−离子在生物分子溶液

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-07-01 Epub Date: 2025-04-30 DOI: 10.1016/j.jmr.2025.107890

Tianzhi Wang , Daniel Arcos , F. David Doty , B. Montgomery Pettitt , Junji Iwahara

NMR-based diffusion measurements of potassium (K⁺), magnesium (Mg²⁺), chloride (Cl⁻), and sulfate (SO₄²⁻) ions have been challenging even though these ions are biologically important. For these ions, the gyromagnetic ratios of the NMR-active nuclei, ³⁹K, ²⁵Mg, ³⁵Cl, and ³³S, are less than 1/10 of the ¹H gyromagnetic ratio, causing a low sensitivity in NMR detection and a low efficiency in NMR dephasing needed for diffusion measurements. These nuclei also undergo rapid longitudinal and transverse NMR relaxation via the quadrupolar mechanism, severely limiting the effectiveness of NMR-based diffusion measurements. Interactions with biomolecules promote the NMR relaxation of these ions, hindering measurements of the ion diffusion. We demonstrate that, despite these challenges, diffusion of K⁺, Mg²⁺, Cl⁻, and SO₄²⁻ ions in biomolecular solutions can be measured accurately and precisely through use of appropriately designed high-field NMR probe hardware that can generate strong field gradients >1000 G/cm. The NMR-based diffusion coefficients measured at 17.6 T for these ions in the absence of biomolecules agreed well with conductivity-based values in the literature. This consistency supports that ion diffusion along the magnetic field is unaffected by the Lorentz force acting on the ions, as previously predicted. Our data on ion diffusion in solutions of proteins and DNA illuminate the effect of electrostatic interactions on the apparent diffusion coefficients of ions. Thus, high-field NMR probe hardware that can generate strong field gradients opens a new avenue to characterize the dynamic behavior of various ions around biomolecules and their effect on biomolecular electrostatics.

基于核磁共振的钾离子（K+）、镁离子（Mg2+）、氯离子（Cl−）和硫酸盐离子（SO42−）的扩散测量一直具有挑战性，尽管这些离子在生物学上很重要。对于这些离子，核磁共振活性核（39K、25Mg、35Cl和33S）的回旋磁比小于1H回旋磁比的1/10，导致核磁共振检测灵敏度低，扩散测量所需的核磁共振减相效率低。这些核也通过四极性机制经历快速的纵向和横向核磁共振弛豫，严重限制了核磁共振扩散测量的有效性。与生物分子的相互作用促进了这些离子的核磁共振弛豫，阻碍了离子扩散的测量。我们证明，尽管存在这些挑战，但通过使用适当设计的高场核磁共振探针硬件，可以准确地测量生物分子溶液中K+， Mg2+， Cl−和SO42−离子的扩散，该探针硬件可以产生1000 G/cm的强场梯度。在没有生物分子的情况下，这些离子在17.6 T下的核磁共振扩散系数与文献中基于电导率的值很好地一致。这种一致性支持离子沿磁场扩散不受作用在离子上的洛伦兹力的影响，正如先前预测的那样。我们在蛋白质和DNA溶液中离子扩散的数据阐明了静电相互作用对离子表观扩散系数的影响。因此，可以产生强场梯度的高场核磁共振探针硬件为表征生物分子周围各种离子的动态行为及其对生物分子静电的影响开辟了新的途径。

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引用次数: 0

Improve robustness to mismatched sampling rate: An alternating deep low-rank approach for exponential function reconstruction and its biomedical magnetic resonance applications 提高对错配采样率的鲁棒性：指数函数重建的交替深度低秩方法及其生物医学磁共振应用

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-07-01 Epub Date: 2025-05-15 DOI: 10.1016/j.jmr.2025.107898

Yihui Huang , Zi Wang , Xinlin Zhang , Jian Cao , Zhangren Tu , Meijin Lin , Lv Li , Xianwang Jiang , Di Guo , Xiaobo Qu

Undersampling accelerates signal acquisition at the expense of introducing artifacts. Removing these artifacts is a fundamental problem in signal processing and this task is also called signal reconstruction. Through modeling signals as the superimposed exponential functions, deep learning has achieved fast and high-fidelity signal reconstruction by training a mapping from the undersampled exponentials to the fully sampled ones. However, the mismatch, such as undersampling rates (25 % vs. 50 %), anatomical region (knee vs. brain), and contrast configurations (PDw vs. T₂w), between the training and target data will heavily compromise the reconstruction. To overcome this limitation, we propose Alternating Deep Low-Rank (ADLR), which combines deep learning solvers and classic optimization solvers. Experimental validation on the reconstruction of synthetic and real-world biomedical magnetic resonance signals demonstrates that ADLR can effectively alleviate the mismatch issue and achieve lower reconstruction errors than state-of-the-art methods.

欠采样以引入伪影为代价加速信号采集。去除这些伪影是信号处理中的一个基本问题，这项任务也被称为信号重建。通过将信号建模为叠加的指数函数，深度学习通过训练从欠采样指数到全采样指数的映射，实现了快速高保真的信号重建。然而，训练数据和目标数据之间的不匹配，如采样不足率（25% vs 50%）、解剖区域（膝盖vs大脑）和对比配置（PDw vs T2w），将严重影响重建。为了克服这一限制，我们提出了交替深度低秩（ADLR），它结合了深度学习求解器和经典优化求解器。对合成和真实生物医学磁共振信号的重建实验验证表明，ADLR可以有效地缓解不匹配问题，实现比现有方法更低的重建误差。

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