Journal of magnetic resonance最新文献

英文中文

An array of paired folded-end dipoles for whole-brain imaging at 9.4 T 用于 9.4 T 全脑成像的成对折叠端偶极子阵列

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-19 DOI: 10.1016/j.jmr.2024.107791

K.I. Popova , F. Glang , D. Bosch , K. Scheffler , N.I. Avdievich , S.B. Glybovski , G.A. Solomakha

Purpose

To improve transmit B₁⁺ field homogeneity and longitudinal coverage of a human head RF array, we developed a novel eight-element transceiver (TxRx) array using composite elements based on paired folded-end dipoles.

Methods

The developed array consisted of eight pairs of coupled folded-end dipoles. Only one dipole in each pair was driven during transmission, while the other was passively coupled with the active one. The distribution of the transmit B₁⁺ field was numerically optimized by changing the overlap between the dipoles and the value of the reactive lumped element placed in the middle of the passive dipole.

Results

The proposed array of paired folded-end dipoles substantially improved the B₁⁺ homogeneity and longitudinal coverage over the entire brain including the brain stem compared to a single-row folded-end dipole array. The improved whole brain coverage was demonstrated both numerically and experimentally.

Conclusion

As a proof of concept, we developed and characterized both numerically and experimentally a prototype of a single-row eight-element 9.4 T array for human brain imaging consisting of composite array elements based on paired passively-coupled folded-end dipoles. The array improved the transmit magnetic field distribution due to the laterally elongated field pattern created by one active and one passive dipole per channel. As a result, the provided coverage was substantially better than that of an 8-element dipole array consisting of long folded-end dipoles. For the first time, an image of the entire human brain at 9.4 T, covering the brain stem up to the fourth vertebra, was obtained using a simple single row eight-element array.

目的为了改善人体头部射频阵列的发射 B1+ 场均匀性和纵向覆盖范围，我们开发了一种新型八元件收发器（TxRx）阵列，该阵列采用基于成对折叠端偶极子的复合元件。每对偶极子中只有一个在传输过程中被驱动，而另一个则与主动偶极子被动耦合。通过改变偶极子之间的重叠度和置于被动偶极子中间的反应块状元件的值，对发射 B1+ 场的分布进行了数值优化。结果与单排折端偶极子阵列相比，所提出的成对折端偶极子阵列大大提高了 B1+ 的均匀性和对包括脑干在内的整个大脑的纵向覆盖。结论作为概念验证，我们开发了一种用于人脑成像的单排八元件 9.4 T 阵列原型，并对其进行了数值和实验表征，该阵列由基于成对被动耦合折端偶极子的复合阵元组成。由于每个通道由一个有源偶极子和一个无源偶极子形成横向拉长的磁场模式，该阵列改善了发射磁场分布。因此，其覆盖范围大大优于由长折端偶极子组成的 8 元偶极子阵列。利用一个简单的单排八元件阵列，首次在 9.4 T 下获得了整个人脑的图像，覆盖范围从脑干一直到第四节脊椎骨。

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引用次数: 0

“Nutation” of electron spins in biradicals 双拉子中电子自旋的 "突变"。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-18 DOI: 10.1016/j.jmr.2024.107790

Ruslan Zaripov, Ravil Galeev, Kev Salikhov

In this work, the nutation of the spins of unpaired electrons in the nitroxide biradical of bis‑methano[60]fullerene was experimentally studied. Nutation frequencies were found in a wide range of microwave field power. To interpret the obtained results, numerical calculations of the nutation of biradicals were carried out for a set of parameters of the spin–spin interaction of a pair of unpaired electrons and for different values of the Rabi frequency of the microwave field. At comparing numerical results with experimental data, we also used the results of analytical calculations of nutation for some model situations. As a result of the analysis of experimental data on nutation, an estimate of the exchange and dipole–dipole interactions for the studied biradical was obtained. They are consistent with the results obtained from analysis of the shape of the EPR spectrum for a given biradical.

在这项研究中，我们通过实验研究了双甲氧基[60]富勒烯的亚硝基双自由基中未配对电子自旋的突变。研究发现，在很宽的微波场功率范围内，都能找到突变频率。为了解释所获得的结果，针对一对未成对电子的自旋-自旋相互作用的一组参数以及微波场的不同拉比频率值，对双辐射根的突变进行了数值计算。在将数值结果与实验数据进行比较时，我们还使用了对某些模型情况进行的自转分析计算结果。在分析了换向实验数据后，我们得到了所研究双拉子交换和偶极-偶极相互作用的估计值。这些结果与分析特定双拉子的 EPR 光谱形状所得到的结果是一致的。

引用次数: 0

Rationalising spin relaxation during slice-selective refocusing pulses 合理解释切片选择性再聚焦脉冲期间的自旋弛豫。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-16 DOI: 10.1016/j.jmr.2024.107789

Howard M. Foster , Runchao Li , Yushi Wang , Laura Castañar , Mathias Nilsson , Ralph W. Adams , Gareth A. Morris

Slice-selective refocusing pulses are powerful building blocks in contemporary magnetic resonance experiments, but their use in quantitative applications is complicated by the site-dependent signal loss they introduce. One source of this attenuation is the spin relaxation that occurs during such pulses, which causes losses that depend on the specific longitudinal and transverse relaxation time constants for a given resonance. This dependence is complicated both by any amplitude shaping of the radiofrequency pulse, and by the presence of the spatial encoding pulsed field gradient. The latter causes the net signal measured to be the weighted sum of signal contributions from a continuous range of offsets from resonance. In general, each offset will make a different contribution to the overall signal, and will be attenuated by a different mixture of longitudinal and transverse relaxation that is dictated by the different trajectories that the nuclear magnetisations take during experiments. Despite this complex behaviour, we present evidence from experiments and numerical simulations showing that in practical experimental applications a relatively simple empirical function can be used to accurately predict relaxational attenuation during slice-selective refocusing pulses. This approach may be of practical use in correcting for relaxational losses in quantitative applications of slice-selective pulse methods such as Zangger–Sterk pure shift NMR.

切片选择性再聚焦脉冲是当代磁共振实验的强大组成部分，但由于其带来的与部位相关的信号损失，使其在定量应用中的使用变得复杂。这种衰减的来源之一是脉冲期间发生的自旋弛豫，其造成的损失取决于特定共振的特定纵向和横向弛豫时间常数。射频脉冲的任何振幅整形以及空间编码脉冲场梯度的存在都会使这种依赖性变得复杂。空间编码脉冲场梯度会导致测量到的净信号是来自共振的连续偏移信号的加权和。一般来说，每个偏移都会对整体信号产生不同的贡献，并会被不同的纵向和横向弛豫混合衰减，而这是由核磁化在实验过程中的不同轨迹决定的。尽管这种行为很复杂，但我们从实验和数值模拟中获得的证据表明，在实际实验应用中，可以使用相对简单的经验函数来准确预测切片选择性再聚焦脉冲过程中的弛豫衰减。在定量应用切片选择脉冲方法（如 Zangger-Sterk 纯移位 NMR）时，这种方法可用于校正弛豫损失。

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引用次数: 0

A high-volume resonator for L-band DNP-NMR 用于 L 波段 DNP-NMR 的大容量谐振器。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-15 DOI: 10.1016/j.jmr.2024.107788

Adam R. Altenhof , Qing Yang , Michal Kern , Shaun G. Newman , Jens Anders , Michael W. Malone

DNP-NMR and EPR experiments that operate at or greater than L-band (i.e., ν₀(e⁻) = 1–2 GHz) are typically limited to maximum sample volumes of several hundred µL. These experiments rely on well-known resonator designs for DNP/EPR irradiation such as the loop-gap resonator and Alderman-Grant coil, where their maximum volumes limit further application to imaging experiments and high-throughput screening beyond L-band. Herein, we demonstrate a birdcage (BC) resonator design that can accommodate several mL of sample while operating around 1.5 GHz. The sample volume is maximized by using two identical BC resonators in a stacked configuration. Simulations are used to optimize the BC design and the performance is validated experimentally with liquid-state Overhauser-DNP-NMR experiments. This BC design exploits just the parasitic capacitance of conductive rings and features no fixed tuning capacitors. An enhancement of −77 is achieved on a 10 mM 4-Amino-TEMPO in H₂O sample for a 5 mL sample volume. The associated sample heating is minimal due to the low-E-fields generated and the large sample mass with +3.4 K when driving 100 W for several seconds.

在 L 波段或更高波段（即 ν0(e-) = 1-2 GHz）运行的 DNP-NMR 和 EPR 实验通常仅限于几百微升的最大样品量。这些实验依赖于众所周知的 DNP/EPR 辐照谐振器设计，如环隙谐振器和奥尔德曼-格兰特线圈，它们的最大体积限制了成像实验和 L 波段以上高通量筛选的进一步应用。在这里，我们展示了一种鸟笼（BC）谐振器设计，它可以容纳几毫升样品，同时工作频率在 1.5 GHz 左右。通过在堆叠配置中使用两个相同的 BC 谐振器，最大限度地增加了样品体积。模拟用于优化 BC 设计，液态 Overhauser-DNP-NMR 实验验证了其性能。这种 BC 设计只利用了导电环的寄生电容，没有固定的调谐电容。在 5 mL 样品体积下，在 10 mM 4-Amino-TEMPO in H2O 样品上实现了 -77 的增强。由于产生的电场较低，且样品质量较大，在 100 W 的功率下持续数秒后，样品的加热温度为 +3.4 K，因此相关的样品加热温度极低。

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引用次数: 0

Frequency-independent dual-tuned cable traps for multi-nuclear MRI and MRS 用于多核 MRI 和 MRS 的频率无关双调谐电缆陷阱

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-10 DOI: 10.1016/j.jmr.2024.107786

Yijin Yang , Ming Lu , Xinqiang Yan

Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) of non-proton nuclei (X-nuclei) typically require additional proton imaging for anatomical reference and B₀ shimming. Therefore, two RF systems exist, necessitating cable traps to block the unwanted common-mode current at both Larmor frequencies of ¹H and X-nuclei. This study introduces a frequency-independent dual-tuned cable trap that combines a standard solenoid cable trap with a float solenoid trap to independently tune high and low frequencies without compromising performance. The methods involved theoretical analysis, electromagnetic simulations, and bench tests. Two design approaches were evaluated: a float cable trap for ¹H, a non-float cable trap for X-nuclei, and vice versa. Results showed that the design with the float trap for X-nuclei and non-float for ¹H had superior performance, with high common-mode current suppression ability at both frequencies. Bench tests confirmed these findings, demonstrating effectiveness across various static fields and X-nuclei. The proposed frequency-independent dual-tuned cable trap provides a compact and efficient solution for multinuclear MRI and MRS, enhancing safety, image quality, and flexibility.

非质子核（X-核）的磁共振成像（MRI）和磁共振波谱分析（MRS）通常需要额外的质子成像来进行解剖学参考和 B0 偏移。因此，存在两个射频系统，需要电缆陷阱来阻断 1H 核和 X 核两种拉莫尔频率下不需要的共模电流。本研究介绍了一种与频率无关的双调谐电缆陷波器，它结合了标准电磁电缆陷波器和浮动电磁陷波器，可在不影响性能的情况下独立调谐高频和低频。研究方法包括理论分析、电磁模拟和台架试验。对两种设计方法进行了评估：用于 1H 核的浮动电缆陷波器和用于 X 核的非浮动电缆陷波器，反之亦然。结果表明，X 核采用浮动电缆陷波器，1H 核采用非浮动电缆陷波器的设计性能优越，在两种频率下都具有很高的共模电流抑制能力。工作台测试证实了这些发现，证明了在各种静态场和 X 核中的有效性。所提出的频率无关双调谐电缆阱为多核 MRI 和 MRS 提供了一种紧凑高效的解决方案，提高了安全性、图像质量和灵活性。

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引用次数: 0

Homonuclear J-couplings and heteronuclear structural constraints 同核 J耦合和异核结构约束。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-09 DOI: 10.1016/j.jmr.2024.107785

Edward P. Saliba , Ravi Shankar Palani, Robert G. Griffin

In magic angle spinning (MAS) experiments involving uniformly ¹³C/¹⁵N labeled proteins, ¹³C–¹³C and ¹³C–¹⁵N dipolar recoupling experiments are now routinely used to measure direct dipole–dipole couplings that constrain distances and torsion angles and determine molecular structures. When the distances are short (<4 Å), the direct couplings dominate the evolution of the spin system, and the ¹³C–¹³C and ¹³C–¹⁵N J-couplings (scalar couplings) are ignored. However, for structurally interesting >4 Å distances, the dipolar and J-couplings are generally of comparable magnitude, and the variation in J must be included in order to optimize the precision of the experiment. This problem is circumvented in cases with well resolved spectra by using frequency-selective dipolar recoupling methods where the effects of J-couplings are refocused. However, for larger molecules with more spectral crowding, the requisite pulse length to achieve selectivity becomes long and leads to unacceptable sensitivity losses during the pulse or the spectral overlap precludes selective excitation. In this paper, we address this problem with two approaches aimed at facilitating higher precision internuclear distance measurements in systems that are not fully resolved. Namely, (1) we describe an approach for high precision measurements of specific J-couplings using the in-phase anti-phase (IPAP) sequence which is integrated into a non-selective dipolar recoupling technique and (2) we utilize the measured J-couplings to implement a double quantum filter experiment capable of providing the resolution necessary for frequency selective dipolar recoupling techniques without resorting to multidimensional spectroscopy. We illustrate these methods using a 7-peptide segment from the amyloidogenic Sup-35p protein, U-¹³C/¹⁵N-GNNQQNY, where we have measured 25 of the 27 possible one bond ¹³C–¹³C J-couplings.

在涉及均匀 13C/15N 标记蛋白质的魔角旋光（MAS）实验中，13C-13C 和 13C-15N 偶极再偶联实验现在已被常规用于测量直接偶极-偶极耦合，从而约束距离和扭转角并确定分子结构。当距离较短时（13C-13C 和 13C-15N J耦合（标量耦合）被忽略。然而，对于具有结构意义的大于 4 Å 的距离，偶极耦合和 J 耦合的量级通常相当，为了优化实验精度，J 的变化必须包括在内。在光谱解析度较高的情况下，可以通过使用频率选择性偶极再偶联方法来规避这一问题，在这种方法中，J 偶联的影响被重新聚焦。然而，对于具有更多光谱拥挤的较大分子，实现选择性所需的脉冲长度变得很长，导致脉冲期间出现不可接受的灵敏度损失，或者光谱重叠排除了选择性激发。在本文中，我们通过两种方法来解决这一问题，旨在促进在未完全解析的系统中进行更高精度的核间距测量。即：(1) 我们描述了一种利用同相反相（IPAP）序列高精度测量特定 J 偶合的方法，该方法被集成到非选择性偶极再耦合技术中；(2) 我们利用测量到的 J 偶合来实施双量子滤波器实验，该实验能够提供频率选择性偶极再耦合技术所需的分辨率，而无需诉诸多维光谱学。我们使用淀粉样蛋白 Sup-35p 蛋白的一个 7 肽段 U-13C/15N-GNNQQNY 来说明这些方法，我们测量了 27 个可能的单键 13C-13C J 耦合中的 25 个。

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引用次数: 0

Simultaneous multinuclear MRI via a single RF channel 通过单个射频通道同时进行多核磁共振成像

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-09 DOI: 10.1016/j.jmr.2024.107782

Mohammad Rasool Vaezi K., Jan G. Korvink, Mazin Jouda

Magnetic resonance imaging (MRI) stands as one of the most powerful noninvasive and non-destructive imaging techniques, finding extensive utility in medical and industrial applications. Its ability to acquire signals from multiple nuclei grants it additional levels of strength by providing multi-dimensional datasets of the object under test. However, this typically requires dedicated hardware to detect each nucleus. In this paper, we report on the use of a digital lock-in amplifier to perform simultaneous multi-nuclear MRI with a single physical radio frequency (RF) channel. While we showcase this concept by demonstrating the results of fully parallel (TX and RX) ¹H and ¹⁹F MRI images, we emphasize that it is not limited to two nuclei but can accommodate more nuclei with no extra cost on the hardware or scan time. The scalability is virtually unlimited, constrained only by the processing speed of the digital unit. Furthermore, we demonstrate that the quality of parallel imaging with SNR of 54 is comparable to the commercial single channel with SNR of 43. Thus with no reduction in imaging quality, the proposed concept promises a tremendous reduction in scan time, system complexity, and hardware costs.

磁共振成像（MRI）是最强大的非侵入性和非破坏性成像技术之一，在医疗和工业应用中有着广泛的用途。磁共振成像能够从多个核获取信号，提供被测物体的多维数据集，因而具有更强的优势。然而，这通常需要专用硬件来检测每个核。在本文中，我们报告了使用数字锁相放大器通过单个物理射频 (RF) 通道同时进行多核磁共振成像的情况。我们通过演示完全并行（TX 和 RX）的 1H 和 19F MRI 图像结果来展示这一概念，同时我们强调，它并不局限于两个核，而是可以容纳更多的核，而无需额外的硬件成本或扫描时间。可扩展性几乎是无限的，仅受数字单元处理速度的限制。此外，我们还证明，信噪比为 54 的并行成像质量与信噪比为 43 的商用单通道成像质量相当。因此，在不降低成像质量的情况下，所提出的概念有望大大减少扫描时间、系统复杂性和硬件成本。

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引用次数: 0

Optimization of 15N–13C double-resonance NMR experiments under low temperature magic angle spinning dynamic nuclear polarization conditions 低温魔角旋转动态核极化条件下 15N-13C 双共振核磁共振实验的优化。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-02 DOI: 10.1016/j.jmr.2024.107783

C. Blake Wilson, Robert Tycko

Dynamic nuclear polarization (DNP) enhanced magic angle spinning (MAS) solid-state NMR carried out at 25 K enables rapid acquisition of multi-dimensional ¹³C–¹⁵N correlation spectra for protein structure studies and resonance assignment. Under commonly used DNP conditions, solvent deuteration reduces ¹H–¹⁵N cross polarization (CP) efficiencies, necessitates more careful optimization, and requires longer high-power ¹⁵N radio-frequency pulses. The sensitivity of 2D heteronuclear correlation experiments is potentially impaired. Here we show that 2D ¹⁵N-¹³C experiments based on ¹³C-¹⁵N transferred echo double resonance (TEDOR) methods outperform 2D experiments based on CP transfers in a fully deuterated solvent, and are competitive with CP-based experiments when the solvent is only partially deuterated. Additionally, we show that optimization of TEDOR-based 2D experiments is simpler than optimization of CP-based experiments under 25 K MAS conditions.

在 25 K 温度下进行动态核偏振（DNP）增强型魔角旋转（MAS）固态核磁共振可快速获取多维 13C-15N 相关光谱，用于蛋白质结构研究和共振分配。在常用的 DNP 条件下，溶剂氘化会降低 1H-15N 交叉极化 (CP) 效率，因此需要进行更仔细的优化，并需要更长的高功率 15N 射频脉冲。二维异核相关实验的灵敏度可能会受到影响。在这里，我们展示了基于 13C-15N 转移回波双共振（TEDOR）方法的二维 15N-13C 实验优于在完全氚化溶剂中基于 CP 转移的二维实验，并且在溶剂仅部分氚化时与基于 CP 的实验具有竞争力。此外，我们还表明，在 25 K MAS 条件下，基于 TEDOR 的二维实验的优化比基于 CP 的实验的优化更简单。

引用次数: 0

In Memoriam: Professor Vladimír Sklenář (April 16, 1951 – April 13, 2024) 悼念弗拉迪米尔-斯克雷纳日教授（1951 年 4 月 16 日 - 2024 年 4 月 13 日）。

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-10-02 DOI: 10.1016/j.jmr.2024.107784

Ad Bax , Juli Feigon

引用次数: 0

Peculiarities in Rabi oscillations for fast-relaxing electron spins 快速松弛电子自旋拉比振荡的特殊性

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2024-09-26 DOI: 10.1016/j.jmr.2024.107781

Antonio Barbon , Grigory A. Rusetsky , Sveva Linarello , Roman Strzelczyk , Ryhor Fedaruk

Rabi oscillations (transient nutations) are a phenomenon that has proven itself well in EPR for identifying electron spin quantum numbers and electron-spin transitions. They are successfully applied when the Rabi frequency significantly exceeds the spin relaxation rates and therefore does not depend on these rates. However, the short transverse relaxation time, being comparable to or even shorter than the dead time of EPR spectrometers, makes it difficult to observe Rabi oscillations and their frequency depends not only on the intensity of the short microwave pulse, but also on its shape and relaxation rates. Two techniques are considered that are suitable for this case, in which Rabi oscillations are detected by monitoring the FID amplitude as a function of pulse duration or microwave field amplitude. We describe the FID-detected Rabi oscillations analytically or numerically for rectangular or shaped pulses, respectively. The description is confirmed by EPR experiments using DPPH as a model sample.

拉比振荡（瞬态螺母振荡）是一种在 EPR 中被证明可以很好地识别电子自旋量子数和电子自旋跃迁的现象。当拉比频率大大超过自旋弛豫速率，因而不依赖于自旋弛豫速率时，拉比振荡就能成功应用。然而，由于横向弛豫时间较短，与 EPR 光谱仪的死区时间相当甚至更短，因此很难观察到拉比振荡，其频率不仅取决于短微波脉冲的强度，还取决于其形状和弛豫速率。我们考虑了两种适用于这种情况的技术，即通过监测 FID 振幅与脉冲持续时间或微波场振幅的函数关系来检测拉比振荡。我们分别对矩形或异形脉冲的 FID 检测到的拉比振荡进行了分析或数值描述。以 DPPH 为模型样品进行的 EPR 实验证实了这一描述。

引用次数: 0

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