Journal of magnetic resonance最新文献

{"title":"Using machine learning to improve the hard modeling of NMR time series","authors":"Jan Hellwig ,&nbsp;Tobias Strauß ,&nbsp;Erik von Harbou ,&nbsp;Klaus Neymeyr","doi":"10.1016/j.jmr.2024.107813","DOIUrl":"10.1016/j.jmr.2024.107813","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"370 ","pages":"Article 107813"},"PeriodicalIF":2.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142866467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complete solution for rotating frame relaxation functions during adiabatic pulses","authors":"Shalom Michaeli","doi":"10.1016/j.jmr.2024.107809","DOIUrl":"10.1016/j.jmr.2024.107809","url":null,"abstract":"<div><div>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 <strong>M</strong> is perfectly aligned with the time dependent effective magnetic field, <strong><em>B⁽¹⁾_eff</em></strong><em>(t)</em>, leading to <em>T_1ρ(t)</em> relaxation, or evolves on a plane perpendicular to <strong><em>B⁽¹⁾_eff</em></strong><em>(t)</em>, leading to <em>T_2ρ(t)</em> relaxation. Time evolution of <strong><em>B⁽¹⁾_eff</em></strong><em>(t)</em> 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 <em>|γ⁻¹dα⁽¹⁾(t)/dt|</em> ≪ <em>B⁽¹⁾_eff(t)</em> is well satisfied. Here <em>α⁽¹⁾(t)</em> is the angle between <strong><em>B⁽¹⁾_eff</em></strong><em>(t)</em> and the axis of quantization of the first rotating frame (FRF) <em>z′</em>, and <em>dα⁽¹⁾(t)/dt</em> 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 <em>n</em> 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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"370 ","pages":"Article 107809"},"PeriodicalIF":2.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142792919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Changing the resonant nucleus by altering the static field, compensation of γ and B0 effects in T2 and T2* measurements of porous media","authors":"Rheya Rajeev ,&nbsp;Naser Ansaribaranghar ,&nbsp;Andrés Ramírez Aguilera ,&nbsp;Florea Marica ,&nbsp;Laura Romero de Zerón ,&nbsp;Bruce J. Balcom","doi":"10.1016/j.jmr.2024.107811","DOIUrl":"10.1016/j.jmr.2024.107811","url":null,"abstract":"<div><div>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 <span><math><mrow><mi>γ</mi></mrow></math></span>B₀. The diffusion through internal field gradients effect on T₂ depends on the product of <span><math><mrow><mi>γ</mi></mrow></math></span> and G, with G depending on B₀.</div><div>Increasing the static field to bring a nucleus with lower <span><math><mrow><mi>γ</mi></mrow></math></span> into resonance at the same frequency will result in the products <span><math><mrow><mi>γ</mi></mrow></math></span>B₀ and <span><math><mrow><mi>γ</mi></mrow></math></span>G 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.</div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107811"},"PeriodicalIF":2.0,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142759481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Tribute to a Friend, a Mentor, a Spin Master, and a Mensch – Eriks Kupce","authors":"Lewis E. Kay","doi":"10.1016/j.jmr.2024.107794","DOIUrl":"10.1016/j.jmr.2024.107794","url":null,"abstract":"","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107794"},"PeriodicalIF":2.0,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142684031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A compact and mobile stray-field NMR sensor","authors":"Belal M.K. Alnajjar ,&nbsp;Jürgen Frick ,&nbsp;Bernhard Blümich ,&nbsp;Jens Anders","doi":"10.1016/j.jmr.2024.107798","DOIUrl":"10.1016/j.jmr.2024.107798","url":null,"abstract":"<div><div>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 NMR<span><math><mo>−</mo></math></span>MOUSE, 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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107798"},"PeriodicalIF":2.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimizing EPR pulses for broadband excitation and refocusing","authors":"Eric R. Lowe ,&nbsp;Stefan Stoll ,&nbsp;J.P. Kestner","doi":"10.1016/j.jmr.2024.107807","DOIUrl":"10.1016/j.jmr.2024.107807","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107807"},"PeriodicalIF":2.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Eliminating electromagnetic interference for RF shielding-free MRI via k-space convolution: Insights from MR parallel imaging advances","authors":"Yilong Liu ,&nbsp;Linfang Xiao ,&nbsp;Mengye Lyu ,&nbsp;Ruixing Zhu","doi":"10.1016/j.jmr.2024.107808","DOIUrl":"10.1016/j.jmr.2024.107808","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107808"},"PeriodicalIF":2.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142693981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Proton hyperfine couplings and Overhauser DNP","authors":"Michael Mardini ,&nbsp;Christy George ,&nbsp;Ravi Shankar Palani ,&nbsp;Xizi Du ,&nbsp;Kong Ooi Tan ,&nbsp;Ivan Sergeyev ,&nbsp;Yangping Liu ,&nbsp;Robert G. Griffin","doi":"10.1016/j.jmr.2024.107797","DOIUrl":"10.1016/j.jmr.2024.107797","url":null,"abstract":"<div><div>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 <figure><img></figure> - <figure><img></figure> 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 <span><math><mo>∼</mo></math></span>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107797"},"PeriodicalIF":2.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142684034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"16-channel sleeve antenna array based on passive decoupling method at 14 T","authors":"Youheng Sun ,&nbsp;Miutian Wang ,&nbsp;Jianjun Du ,&nbsp;Wentao Wang ,&nbsp;Gang Yang ,&nbsp;Weimin Wang ,&nbsp;Qiushi Ren","doi":"10.1016/j.jmr.2024.107796","DOIUrl":"10.1016/j.jmr.2024.107796","url":null,"abstract":"<div><div>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 <span><math><msubsup><mrow><mtext>B</mtext></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span> efficiency. The <span><math><msubsup><mrow><mtext>B</mtext></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span> 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 <span><math><msubsup><mrow><mtext>B</mtext></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span> efficiency and better transmission performance.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"369 ","pages":"Article 107796"},"PeriodicalIF":2.0,"publicationDate":"2024-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142693978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Selective enhancement of 1H signal from water and oil in porous media at low field with Overhauser DNP","authors":"Devin M. Morin ,&nbsp;Naser Ansaribaranghar ,&nbsp;Benjamin Nicot ,&nbsp;Derrick Green ,&nbsp;Bruce.J. Balcom","doi":"10.1016/j.jmr.2024.107793","DOIUrl":"10.1016/j.jmr.2024.107793","url":null,"abstract":"<div><div>In porous media MR studies, discriminating between oil and water presents a challenge because MR lifetimes are often similar and spectra overlap. Low saturations might suggest an experimental strategy of increasing the static field for increased sensitivity, but susceptibility effects are exacerbated at higher field. Overhauser dynamic nuclear polarization, effective at low static field, was employed with water and oil-soluble nitroxide to selectively enhance water and oil signals. We employ a home-built 2 MHz ceramic magnet to achieve selective enhancement of water and oil, in bulk, and in a rock core. For imaging, we employ a 705 kHz ceramic magnet with a 4 gauss/cm constant gradient configuration to image the hyperpolarized signal. A rock core flooding experiment was undertaken to highlight the advantages of Overhauser enhancement. A simple phase cycling technique may be employed to cancel the thermally polarized ¹H signal to isolate the enhanced signal of interest.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107793"},"PeriodicalIF":2.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}