Journal of magnetic resonance最新文献

{"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 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}

{"title":"Chemical shift prediction in 13C NMR spectroscopy using ensembles of message passing neural networks (MPNNs)","authors":"D. Williamson ,&nbsp;S. Ponte ,&nbsp;I. Iglesias ,&nbsp;N. Tonge ,&nbsp;C. Cobas ,&nbsp;E.K. Kemsley","doi":"10.1016/j.jmr.2024.107795","DOIUrl":"10.1016/j.jmr.2024.107795","url":null,"abstract":"<div><div>This study reports a deep learning approach that utilises message passing neural networks (MPNNs) for predicting chemical shifts in ¹³C NMR spectra of small molecules. MPNNs were trained on two distinct datasets: one with approximately 4000 labelled structures and another with over 40,000. To reduce stochastic variation, an ensemble framework was implemented, which is simple to deploy on multiple nodes of a High-Performance Computing facility.</div><div>The results emphasise the critical role of training set size and diversity. While prediction performance was comparable on test sets drawn from each dataset, the ensemble trained on the larger dataset retained its accuracy when these sets were crossed over, and when applied to a further collection of approximately 12,000 previously unseen structures introduced after all development work had been completed. In contrast, the ensemble trained on the smaller dataset showed a notable decline in generalisation ability. This difference is attributed to the greater diversity of atomic environments captured in the larger dataset.</div><div>The larger dataset also enabled more robust modelling of various error properties, providing a quantitative foundation for spectral assignment and verification. This was achieved in two ways. First, a clear relationship was observed between prediction errors and the frequency of different node feature vectors in the training data, allowing error estimates to be associated with individual nodes based on their type. These estimates can be used as weights in a modified cityblock distance metric when assigning observed to predicted shifts. Second, the mean absolute prediction error calculated at the structure level is well-fitted by a Gaussian kernel cumulative distribution. This enabled a probabilistic assessment of whether the predicted shifts and assigned observations are consistent with originating from the same molecular structure.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107795"},"PeriodicalIF":2.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554889","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":"Implementing a two-stage, shim field-calibrated superconducting shimming method on a 7 T cryogen-free small animal MRI magnet","authors":"Jinhao Liu ,&nbsp;Yaohui Wang ,&nbsp;Miutian Wang ,&nbsp;Wenchen Wang ,&nbsp;Gang Yang ,&nbsp;Weimin Wang ,&nbsp;Qiuliang Wang ,&nbsp;Feng Liu","doi":"10.1016/j.jmr.2024.107787","DOIUrl":"10.1016/j.jmr.2024.107787","url":null,"abstract":"<div><div>Ultrahigh field systems (<span><math><mo>≥</mo></math></span> 7 T) can increase the signal-to-noise ratio of magnetic resonance imaging (MRI), improving imaging performance compared to systems with lower fields. However, these enhancements heavily rely on a high <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> magnetic field homogeneity level, which can be achieved through superconducting shimming. This paper presents a novel two-stage superconducting shimming method designed to achieve precise shimming for a 7 T MRI superconducting magnet. In the initial stage, detailed measurements and fittings were conducted to determine the current polarity and the axial or circumferential positions of the shim fields. Subsequently, an optimization strategy was implemented to determine the optimal shim currents with a flexible target field. The second stage involves an iterative process to fine-tune the current of a specific shim coil, identified as having the most significant impact on field homogeneity. The overall fitness of 99.5% underscores the precision in determining the current polarity and position of the shim fields. Significantly, the calibrated shim system substantially improves the peak-to-peak and Root Mean Square Error (RMSE) field homogeneities from 107.42 ppm and 37.00 ppm to 11.12 ppm and 3.26 ppm, respectively, representing improvements of 89.65% and 91.19%. Furthermore, the simulation results of the fine-tuning stage demonstrate additional enhancements in peak-to-peak field homogeneity, to 9.9 ppm by reducing the current of the Z2 shim coil by 51.3 mA. Additionally, the shimmed magnetic field exhibited high time stability, with a maximum variation of only 27 <span><math><mstyle><mi>µ</mi><mi>T</mi></mstyle></math></span> observed within 48 h. Thus, the proposed two-stage superconducting shimming framework effectively addresses the challenge of imperfect <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> magnetic fields, enhancing peak-to-peak and RMSE field homogeneity. The stepwise optimized approach also mitigates deviations caused by shim-to-shim coupling, demonstrating its efficacy in achieving precise shimming in ultrahigh-field MRI systems.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107787"},"PeriodicalIF":2.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142549766","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":"Neural net analysis of NMR spectra from strongly-coupled spin systems","authors":"James H. Prestegard ,&nbsp;Geert-Jan Boons ,&nbsp;Pradeep Chopra ,&nbsp;John Glushka ,&nbsp;John H. Grimes Jr. ,&nbsp;Bernd Simon","doi":"10.1016/j.jmr.2024.107792","DOIUrl":"10.1016/j.jmr.2024.107792","url":null,"abstract":"<div><div>Extracting parameters such as chemical shifts and coupling constants from proton NMR spectra is often a first step in using spectra for compound identification and structure determination. This can become challenging when scalar couplings between protons are comparable in size to chemical shift differences (strongly coupled), as is often the case with low-field (bench top) spectrometers. Here we explore the potential utility of AI methods, in particular neural networks, for extracting parameters from low-field spectra. Rather than seeking large experimental sets of spectra for training a network, we chose quantum mechanical simulation of sets, something that is possible with modern software packages and computer resources. We show that application of a network trained on 2-D J-resolved spectra and applied to a spectrum of iduronic acid, shows some promise, but also meets with some obstacles. We suggest that these may be overcome with improved pulse sequences and more extensive simulations.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107792"},"PeriodicalIF":2.0,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142526881","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}