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Denoising low-field MR images with a deep learning algorithm based on simulated data from easily accessible open-source software 使用基于易于访问的开源软件模拟数据的深度学习算法对低场磁共振图像进行降噪。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2025-01-01 DOI: 10.1016/j.jmr.2024.107812
Aram Salehi , Mathieu Mach , Chloe Najac , Beatrice Lena , Thomas O’Reilly , Yiming Dong , Peter Börnert , Hieab Adams , Tavia Evans , Andrew Webb
In this study, we introduce a denoising method aimed at improving the contrast ratio in low-field MRI (LFMRI) using an advanced 3D deep convolutional residual network model. Our approach employs synthetic brain imaging datasets that closely mimic the contrast and noise characteristics of LFMRI scans, addressing the limitation of available in-vivo LFMRI datasets for training deep learning models. In the simulation data, the Relative Contrast Ratio (RCR) increased, and similar improvements were observed in the in-vivo data across different imaging conditions. Comparative evaluations demonstrate that our model performs better than the widely used non-deep learning method, BM4D, in enhancing RCR and maintaining high spatial frequency components in in-vivo data.
在这项研究中,我们引入了一种旨在提高低场MRI (LFMRI)对比度的去噪方法,该方法采用了一种先进的3D深度卷积残差网络模型。我们的方法采用合成脑成像数据集,这些数据集密切模仿LFMRI扫描的对比度和噪声特征,解决了可用的活体LFMRI数据集用于训练深度学习模型的局限性。在模拟数据中,相对对比度(RCR)增加,在不同成像条件下的体内数据中也观察到类似的改善。对比评估表明,我们的模型在增强RCR和保持体内数据的高空间频率成分方面优于广泛使用的非深度学习方法BM4D。
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引用次数: 0
Using machine learning to improve the hard modeling of NMR time series 利用机器学习改进核磁共振时间序列的硬建模。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2025-01-01 DOI: 10.1016/j.jmr.2024.107813
Jan Hellwig , Tobias Strauß , Erik von Harbou , Klaus Neymeyr
Modeling time series of NMR spectra is a useful method to accurately extract information such as temporal concentration profiles from complex processes, e.g. reactions. Modeling these time series by using nonlinear optimization often suffers from high runtimes. On the other hand, using deep learning solves the modeling problem quickly, especially for single spectra with separated peaks. However, the accuracy decreases significantly when peaks overlap or cross. We propose a hybrid approach combining the strengths of both methods while mitigating their drawbacks. This hybrid methods improves on a previous work (Meinhardt et al., 2022) and employs neural networks to predict initial parameters for the optimization algorithm, which only needs to fine-tune the parameters afterwards. We present results for both constructed and experimental data sets and achieve improvements in both runtime and accuracy.
建立核磁共振谱的时间序列模型是一种有效的方法,可以准确地从复杂的过程(如反应)中提取时间浓度分布等信息。使用非线性优化对这些时间序列进行建模通常会遇到高运行时间的问题。另一方面,使用深度学习可以快速解决建模问题,特别是对于具有分离峰的单光谱。然而,当峰值重叠或交叉时,精度显著降低。我们提出了一种混合方法,结合了两种方法的优点,同时减轻了它们的缺点。这种混合方法改进了先前的工作(Meinhardt et al., 2022),并使用神经网络预测优化算法的初始参数,之后只需对参数进行微调。我们提出了构建和实验数据集的结果,并在运行时间和准确性方面取得了改进。
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引用次数: 0
Complete solution for rotating frame relaxation functions during adiabatic pulses 绝热脉冲期间旋转框架松弛函数的完全解。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2025-01-01 DOI: 10.1016/j.jmr.2024.107809
Shalom Michaeli
During adiabatic full passage (AFP) radiofrequency (RF) pulses the relaxation functions are conventionally treated in the Tilting Doubly Rotating Frame (TDRF), or the second rotating frame (SRF) of reference. Such a description is adequate when during the adiabatic passage the magnetization M is perfectly aligned with the time dependent effective magnetic field, B(1)eff(t), leading to T(t) relaxation, or evolves on a plane perpendicular to B(1)eff(t), leading to T(t) relaxation. Time evolution of B(1)eff(t) results in formation of a fictitious magnetic field, which is typically neglected during the AFP pulses operating in adiabatic regime, i.e., given that the adiabatic condition −1(1)(t)/dt|B(1)eff(t) is well satisfied. Here α(1)(t) is the angle between B(1)eff(t) and the axis of quantization of the first rotating frame (FRF) z′, and (1)(t)/dt is the angular velocity. When the fictitious field component cannot be neglected, for the adequate description of relaxation during AFP pulses the solutions for the relaxation functions in a multi-fold rotating frame are necessary. Such a general treatment is currently unavailable for adiabatic RF pulses. Here, we obtain the solution for the relaxation functions in the Tilting Triply Rotating Frame (TTRF) during the Hyperbolic Secant (HS) pulses of the HSn family, HS1 and HS4, where n is the stretching factor. We show that the contribution to the relaxations originating from the non-negligible magnitude of the fictitious field depends on the pulse modulation functions of the AFP pulses and the parameters of the pulses. The corrections to describe the relaxations are given, which may be relevant in specific experimental setups especially for high-resolution NMR.
在绝热全通道(AFP)射频(RF)脉冲中,松弛函数通常在倾斜双旋转框架(TDRF)或第二旋转参考框架(SRF)中处理。当在绝热通道中,磁化强度M与时间相关的有效磁场B(1)eff(t)完全对齐,导致T1ρ(t)弛豫,或在垂直于B(1)eff(t)的平面上演变,导致T2ρ(t)弛豫时,这种描述是适当的。B(1)eff(t)的时间演化导致了虚拟磁场的形成,这在绝热状态下工作的AFP脉冲中通常被忽略,也就是说,考虑到|≪B(1)eff(t) /dt的绝热条件,|≪B(1)eff(t)很好地满足。其中α(1)(t)为B(1)eff(t)与第一旋转框架(FRF)量化轴z′之间的夹角,dα(1)(t)/dt为角速度。当虚拟场分量不能忽略时,为了充分描述AFP脉冲中的松弛,需要求解多重旋转框架中的松弛函数。对于绝热射频脉冲,目前还没有这样的一般处理方法。在这里,我们得到了在HSn族、HS1和HS4的双曲割线(Hyperbolic sec割线)脉冲中,倾斜三重旋转框架(TTRF)中的松弛函数的解,其中n为拉伸因子。我们证明了虚构场的不可忽略的大小对弛豫的贡献取决于AFP脉冲的脉冲调制函数和脉冲的参数。给出了描述弛豫的修正,这可能与特定的实验装置有关,特别是高分辨率核磁共振。
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引用次数: 0
Changing the resonant nucleus by altering the static field, compensation of γ and B0 effects in T2 and T2* measurements of porous media 通过改变静场改变共振核,补偿多孔介质T2和T2*测量中的γ和B0效应
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-12-01 DOI: 10.1016/j.jmr.2024.107811
Rheya Rajeev , Naser Ansaribaranghar , Andrés Ramírez Aguilera , Florea Marica , Laura Romero de Zerón , Bruce J. Balcom
Multinuclear 1H, 13C, and 23Na magnetic resonance (MR) has many advantages for studying porous media systems containing hydrocarbons and brine. In recent work, we have explored changing the nucleus measured, keeping the Larmor frequency constant, by changing the static magnetic field B0. Increasing the static B0 field distorts the field in the pore space due to susceptibility mismatch between the matrix and pore fluid. Distortion of the magnetic field in the pore space scales with the applied static field. The gradients that result from the spatial variation of the distorted field will also scale with B0. The equations that describe the inhomogeneous broadening in T2* show that the MR result depends on γB0. The diffusion through internal field gradients effect on T2 depends on the product of γ and G, with G depending on B0.
Increasing the static field to bring a nucleus with lower γ into resonance at the same frequency will result in the products γB0 and γG being constant, and therefore, inhomogeneous broadening and diffusion attenuation effects in porous media are predicted to be constant. We explore the T2* hypothesis with 23Na and 1H measurements of brine in porous reservoir core plugs. We explore the diffusion through internal field gradients effect hypothesis with 1H and 13C measurements of decane saturated glass beads.
The nuclei chosen for study: 1H, 13C, and 23Na are the three most important nuclei for studies of fluids (brine and hydrocarbons) in reservoir core plugs. These three nuclei have a common resonance frequency of 33.7 MHz at static fields of 0.79 T, 3.19 T, and 2.99 T, respectively. All three fields are readily achieved with our variable field superconducting magnet.
多核1H, 13C和23Na磁共振(MR)在研究含碳氢化合物和卤水的多孔介质体系方面具有许多优势。在最近的工作中,我们探索了通过改变静态磁场B0来改变被测核,保持拉莫尔频率不变。由于基质和孔隙流体之间的磁化率不匹配,增加静态B0场会扭曲孔隙空间中的场。孔隙空间磁场的畸变随外加静电场的增大而增大。畸变场的空间变化所产生的梯度也将与B0成比例。描述T2*中不均匀展宽的方程表明MR结果依赖于γB0。内场梯度扩散对T2的影响取决于γ和G的乘积,其中G取决于B0。增大静场使具有较低γ的核以相同频率共振,会使产物γ b0和γ g保持恒定,因此预测多孔介质中的非均匀展宽和扩散衰减效应是恒定的。通过对多孔储层岩心塞中盐水的23Na和1H测量,探讨了T2*假说。我们通过对癸烷饱和玻璃微珠的1H和13C测量,探讨了通过内场梯度效应的扩散假说。所选择的核:1H、13C和23Na是研究储层岩心塞中流体(盐水和碳氢化合物)最重要的三个核。这三个原子核在静态场分别为0.79 T、3.19 T和2.99 T时的共共振频率为33.7 MHz。这三个场都很容易实现与我们的变场超导磁体。
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引用次数: 0
A Tribute to a Friend, a Mentor, a Spin Master, and a Mensch – Eriks Kupce 向朋友、导师、旋转大师和男人致敬--埃里克斯-库普斯。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-12-01 DOI: 10.1016/j.jmr.2024.107794
Lewis E. Kay
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引用次数: 0
A compact and mobile stray-field NMR sensor 结构紧凑的移动式杂散场核磁共振传感器
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-11-22 DOI: 10.1016/j.jmr.2024.107798
Belal M.K. Alnajjar , Jürgen Frick , Bernhard Blümich , Jens Anders
In this paper, we introduce a compact, single-sided stray field sensor for NMR relaxometry applications. The sensor consists of four main components: the magnet, the RF coil, the spectrometer, and the translation stage. Our proposed magnet, an improved design of the Profile NMRMOUSE, is designed for low weight, compactness, and magnetic field homogeneity, achieved through various shim strategies using a mixed genetic algorithm. The magnet comprises eight NdFeB blocks, generating a magnetic field of 0.424 T within the sensitive region, positioned 12 mm above the magnet surface. For high spatial resolution measurements, we optimized the sensor performance by using a custom-designed rf coil, providing maximum sensitivity, lateral selectivity, and a dead time of less than 20 µs. Moreover, we utilized 3D-printed structures to precisely align the sensitive slice within the object, using an experimental approach based on CPMG measurements. The presented setup achieved a spatial resolution of 50 µm, with resolution changes proportional to acquisition time. We demonstrate the sensor’s versatility and high resolution with measurements on materials such as cosmetics, elastomers, glue, and wood, verifying the good performance of our design, our alignment strategy, and the measuring scheme.
本文介绍了一种用于核磁共振弛豫测量应用的紧凑型单面杂散场传感器。该传感器由四个主要部件组成:磁铁、射频线圈、光谱仪和平移台。我们提出的磁体是对 Profile NMR-MOUSE 的改进设计,重量轻、结构紧凑、磁场均匀,通过使用混合遗传算法的各种垫片策略实现。磁体由八个钕铁硼块组成,在敏感区域内产生 0.424 T 的磁场,位于磁体表面上方 12 毫米处。为了进行高空间分辨率测量,我们使用定制设计的射频线圈优化了传感器性能,使其具有最高灵敏度和横向选择性,死区时间小于 20 µs。此外,我们还利用 3D 打印结构,采用基于 CPMG 测量的实验方法,在物体内部精确对准敏感切片。所介绍的装置实现了 50 微米的空间分辨率,分辨率的变化与采集时间成正比。我们通过对化妆品、弹性体、胶水和木材等材料的测量,证明了传感器的多功能性和高分辨率,验证了我们的设计、对准策略和测量方案的良好性能。
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引用次数: 0
Optimizing EPR pulses for broadband excitation and refocusing 优化宽带激发和再聚焦的 EPR 脉冲
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-11-19 DOI: 10.1016/j.jmr.2024.107807
Eric R. Lowe , Stefan Stoll , J.P. Kestner
In this paper, we numerically optimize broadband pulse shapes that maximize Hahn echo amplitudes. Pulses are parameterized as neural networks (NN), nonlinear amplitude limited Fourier series (FS), and discrete time series (DT). These are compared to an optimized choice of the conventional hyperbolic secant (HS) pulse shape. A power constraint is included, as are realistic shape distortions due to power amplifier nonlinearity and the transfer function of the microwave resonator. We find that the NN, FS, and DT parameterizations perform equivalently, offer improvements over the best HS pulses, and contain a large number of equivalent optimal maxima, implying the flexibility to include further constraints or optimization goals in future designs.
在本文中,我们通过数值方法优化了能使哈恩回波幅度最大化的宽带脉冲形状。脉冲参数为神经网络(NN)、非线性幅度限制傅里叶级数(FS)和离散时间级数(DT)。这些参数与传统双曲正割(HS)脉冲形状的优化选择进行了比较。由于功率放大器的非线性和微波谐振器的传递函数,还包括功率约束和实际的形状失真。我们发现,NN、FS 和 DT 参数化的性能相当,比最佳 HS 脉冲有所改进,并包含大量等效的最优最大值,这意味着在未来的设计中可以灵活地加入更多的约束条件或优化目标。
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引用次数: 0
Eliminating electromagnetic interference for RF shielding-free MRI via k-space convolution: Insights from MR parallel imaging advances 通过 k 空间卷积消除无射频屏蔽磁共振成像的电磁干扰:磁共振并行成像技术的发展启示。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-11-19 DOI: 10.1016/j.jmr.2024.107808
Yilong Liu , Linfang Xiao , Mengye Lyu , Ruixing Zhu
Recent advances in ultra-low field MRI have attracted attention from both academic and industrial MR communities for its potential in democratizing MRI applications. One of the most striking features on those advances is shielding-free imaging by actively sensing and eliminating the electromagnetic interference (EMI). In this study, we review the analytical approaches for EMI estimation/elimination, and investigate their theoretical basis and relations with parallel imaging reconstruction. We provide further understanding of the existing approaches, formulating EMI estimation as convolution in k-space or multiplication in spectrum-space. We further propose to use tailored convolutional kernel to adaptively fit the varying EMI coupling across the acquisition window. These methods were evaluated with both simulation study and human brain imaging. The results show that using tailored convolutional kernel can achieve more robust performance against system and acquisition imperfections.
超低磁场磁共振成像技术的最新进展吸引了学术界和工业界的关注,因为它具有使磁共振成像应用平民化的潜力。这些进展的最显著特点之一是通过主动感应和消除电磁干扰(EMI)实现无屏蔽成像。在本研究中,我们回顾了电磁干扰估计/消除的分析方法,并研究了它们的理论基础以及与并行成像重建的关系。我们进一步理解了现有的方法,将 EMI 估算表述为 k 空间中的卷积或频谱空间中的乘法。我们还建议使用定制的卷积核来适应整个采集窗口中不断变化的 EMI 耦合。我们通过模拟研究和人脑成像对这些方法进行了评估。结果表明,使用定制的卷积核可以在系统和采集不完善的情况下实现更稳健的性能。
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引用次数: 0
Proton hyperfine couplings and Overhauser DNP 质子高频耦合和奥弗豪斯 DNP。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-11-17 DOI: 10.1016/j.jmr.2024.107797
Michael Mardini , Christy George , Ravi Shankar Palani , Xizi Du , Kong Ooi Tan , Ivan Sergeyev , Yangping Liu , Robert G. Griffin
We have prepared trityl radicals with protons at the positions of the -COOH group in the phenyl rings and examined their EPR spectra, which show large
-
hyperfine couplings, and their dynamic nuclear polarization (DNP) Zeeman field profiles . By assessing these polarizing agents for high-field and Overhauser effect DNP, we gain insight into the roles that these hyperfine couplings and other molecular properties play in the DNP performance of these radicals. Interestingly, we do not observe OE DNP in any of the three molecules we examined. This suggests that hyperfine couplings by themselves are not sufficient to support OE DNP. In this case the electron spin density is 75 % localized on the central carbon atom rather than being distributed uniformly over the aromatic rings. This is in contrast to BDPA where the distribution is delocalized. Our findings do not suggest that any of these radicals are particularly well-suited to high-field DNP. Furthermore, we emphasize that polarizing agents can be extremely sensitive to their solvent environment, even obscuring the intrinsic magnetic properties of the radical.
我们制备了质子位于苯基环中-COOH 基团位置的三苯甲基自由基,并研究了它们的 EPR 光谱(显示出较大的超线性耦合)及其动态核极化(DNP)泽曼场剖面。通过评估这些极化剂的高场和奥弗霍瑟效应 DNP,我们深入了解了这些超线性耦合和其他分子特性在这些自由基的 DNP 性能中所起的作用。有趣的是,在我们研究的三种分子中,我们没有观察到 OE DNP。这表明超精细耦合本身不足以支持 OE DNP。在这种情况下,电子自旋密度的 75% 都集中在中心碳原子上,而不是均匀地分布在芳香环上。这与 BDPA 形成鲜明对比,在 BDPA 中,电子自旋分布是分散的。我们的研究结果并不表明这些自由基中的任何一种特别适合高场 DNP。此外,我们还强调,极化剂对其溶剂环境极为敏感,甚至会掩盖自由基的内在磁性。
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引用次数: 0
16-channel sleeve antenna array based on passive decoupling method at 14 T 基于无源去耦方法的 16 通道套筒天线阵列,14 T。
IF 2 3区 化学 Q3 BIOCHEMICAL RESEARCH METHODS Pub Date : 2024-11-16 DOI: 10.1016/j.jmr.2024.107796
Youheng Sun , Miutian Wang , Jianjun Du , Wentao Wang , Gang Yang , Weimin Wang , Qiushi Ren
At ultra-high fields, especially at 14 T, head coil arrays face significant challenges with coupling between elements. Although passive decoupling methods can reduce this coupling, the decoupling elements can cause destructive interference to the RF field of the head array, thus reducing the B1+ efficiency. The B1+ loss due to this effect can be even higher than that due to inter-element coupling. In this study, we develop a novel passive decoupling method to improve the performance of head coil arrays at 14 T. Specifically, passive dipole antennas were utilized to decouple the 16-channel sleeve antenna array, with their positioning optimized to minimize destructive interference with the array’s RF field by increasing their distance from the active antennas. We used electromagnetic simulations to optimize the position of the passive dipoles to obtain the best performance of the array. In addition, we introduced a 16-channel dipole antenna array to compare the array performance when evaluating the sleeve antenna array performance using a human body model. We also constructed the optimized sleeve antenna array and measured its S-parameters to verify the effectiveness of the decoupling strategy. Our results show that the improved passive decoupling method can well reduce the destructive interference of the decoupling elements to the RF field. The sleeve antenna array developed under this method exhibits higher B1+ efficiency and better transmission performance.
在超高场,尤其是 14 T 时,头部线圈阵列面临着元件间耦合的巨大挑战。虽然无源去耦方法可以减少这种耦合,但去耦元件会对磁头阵列的射频场造成破坏性干扰,从而降低 B1+ 效率。这种效应造成的 B1+ 损耗可能比元件间耦合造成的损耗还要高。具体来说,我们利用无源偶极子天线对 16 通道套筒天线阵列进行去耦,并对其位置进行了优化,通过增大其与有源天线的距离,最大限度地减少对阵列射频场的破坏性干扰。我们利用电磁模拟来优化无源偶极子的位置,以获得阵列的最佳性能。此外,我们还引入了一个 16 通道偶极子天线阵列,以便在使用人体模型评估套筒天线阵列性能时对阵列性能进行比较。我们还构建了优化的套筒天线阵列,并测量了其 S 参数,以验证去耦策略的有效性。结果表明,改进的无源去耦方法可以很好地降低去耦元件对射频场的破坏性干扰。采用这种方法开发的套筒天线阵列具有更高的 B1+ 效率和更好的传输性能。
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引用次数: 0
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Journal of magnetic resonance
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