Pub Date : 2024-11-01DOI: 10.1016/j.jmr.2024.107793
Devin M. Morin , Naser Ansaribaranghar , Benjamin Nicot , Derrick Green , Bruce.J. Balcom
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.
{"title":"Selective enhancement of 1H signal from water and oil in porous media at low field with Overhauser DNP","authors":"Devin M. Morin , Naser Ansaribaranghar , Benjamin Nicot , Derrick Green , 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 <sup>1</sup>H 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}
Pub Date : 2024-11-01DOI: 10.1016/j.jmr.2024.107795
D. Williamson , S. Ponte , I. Iglesias , N. Tonge , C. Cobas , E.K. Kemsley
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.
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.
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.
{"title":"Chemical shift prediction in 13C NMR spectroscopy using ensembles of message passing neural networks (MPNNs)","authors":"D. Williamson , S. Ponte , I. Iglesias , N. Tonge , C. Cobas , 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 <sup>13</sup>C 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}
Pub Date : 2024-11-01DOI: 10.1016/j.jmr.2024.107787
Jinhao Liu , Yaohui Wang , Miutian Wang , Wenchen Wang , Gang Yang , Weimin Wang , Qiuliang Wang , Feng Liu
Ultrahigh field systems ( 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 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 observed within 48 h. Thus, the proposed two-stage superconducting shimming framework effectively addresses the challenge of imperfect 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.
{"title":"Implementing a two-stage, shim field-calibrated superconducting shimming method on a 7 T cryogen-free small animal MRI magnet","authors":"Jinhao Liu , Yaohui Wang , Miutian Wang , Wenchen Wang , Gang Yang , Weimin Wang , Qiuliang Wang , 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}
Pub Date : 2024-10-22DOI: 10.1016/j.jmr.2024.107792
James H. Prestegard , Geert-Jan Boons , Pradeep Chopra , John Glushka , John H. Grimes Jr. , Bernd Simon
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.
{"title":"Neural net analysis of NMR spectra from strongly-coupled spin systems","authors":"James H. Prestegard , Geert-Jan Boons , Pradeep Chopra , John Glushka , John H. Grimes Jr. , 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}
Pub Date : 2024-10-19DOI: 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。
{"title":"An array of paired folded-end dipoles for whole-brain imaging at 9.4 T","authors":"K.I. Popova , F. Glang , D. Bosch , K. Scheffler , N.I. Avdievich , S.B. Glybovski , G.A. Solomakha","doi":"10.1016/j.jmr.2024.107791","DOIUrl":"10.1016/j.jmr.2024.107791","url":null,"abstract":"<div><h3>Purpose</h3><div>To improve transmit B<sub>1</sub><sup>+</sup> 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.</div></div><div><h3>Methods</h3><div>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 B<sub>1</sub><sup>+</sup> 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.</div></div><div><h3>Results</h3><div>The proposed array of paired folded-end dipoles substantially improved the B<sub>1</sub><sup>+</sup> 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.</div></div><div><h3>Conclusion</h3><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107791"},"PeriodicalIF":2.0,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142526880","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}
Pub Date : 2024-10-18DOI: 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.
{"title":"“Nutation” of electron spins in biradicals","authors":"Ruslan Zaripov, Ravil Galeev, Kev Salikhov","doi":"10.1016/j.jmr.2024.107790","DOIUrl":"10.1016/j.jmr.2024.107790","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107790"},"PeriodicalIF":2.0,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142515399","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}
Pub Date : 2024-10-16DOI: 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.
{"title":"Rationalising spin relaxation during slice-selective refocusing pulses","authors":"Howard M. Foster , Runchao Li , Yushi Wang , Laura Castañar , Mathias Nilsson , Ralph W. Adams , Gareth A. Morris","doi":"10.1016/j.jmr.2024.107789","DOIUrl":"10.1016/j.jmr.2024.107789","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107789"},"PeriodicalIF":2.0,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142515402","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}
Pub Date : 2024-10-15DOI: 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。
{"title":"A high-volume resonator for L-band DNP-NMR","authors":"Adam R. Altenhof , Qing Yang , Michal Kern , Shaun G. Newman , Jens Anders , Michael W. Malone","doi":"10.1016/j.jmr.2024.107788","DOIUrl":"10.1016/j.jmr.2024.107788","url":null,"abstract":"<div><div>DNP-NMR and EPR experiments that operate at or greater than L-band (<em>i.e.,</em> ν<sub>0</sub>(e<sup>−</sup>) = 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 H<sub>2</sub>O sample for a 5 mL sample volume. The associated sample heating is minimal due to the low-<em>E</em>-fields generated and the large sample mass with +3.4 K when driving 100 W for several seconds.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107788"},"PeriodicalIF":2.0,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142515400","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}
Pub Date : 2024-10-10DOI: 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。
{"title":"Frequency-independent dual-tuned cable traps for multi-nuclear MRI and MRS","authors":"Yijin Yang , Ming Lu , Xinqiang Yan","doi":"10.1016/j.jmr.2024.107786","DOIUrl":"10.1016/j.jmr.2024.107786","url":null,"abstract":"<div><div>Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) of non-proton nuclei (X-nuclei) typically require additional proton imaging for anatomical reference and B<sub>0</sub> shimming. Therefore, two RF systems exist, necessitating cable traps to block the unwanted common-mode current at both Larmor frequencies of <sup>1</sup>H 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 <sup>1</sup>H, 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 <sup>1</sup>H 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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107786"},"PeriodicalIF":2.0,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142432878","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}
Pub Date : 2024-10-09DOI: 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.
{"title":"Homonuclear J-couplings and heteronuclear structural constraints","authors":"Edward P. Saliba , Ravi Shankar Palani, Robert G. Griffin","doi":"10.1016/j.jmr.2024.107785","DOIUrl":"10.1016/j.jmr.2024.107785","url":null,"abstract":"<div><div>In magic angle spinning (MAS) experiments involving uniformly <sup>13</sup>C/<sup>15</sup>N labeled proteins, <sup>13</sup>C–<sup>13</sup>C and <sup>13</sup>C–<sup>15</sup>N 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 <sup>13</sup>C–<sup>13</sup>C and <sup>13</sup>C–<sup>15</sup>N 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-<sup>13</sup>C/<sup>15</sup>N-GNNQQNY, where we have measured 25 of the 27 possible one bond <sup>13</sup>C–<sup>13</sup>C J-couplings.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"368 ","pages":"Article 107785"},"PeriodicalIF":2.0,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142515401","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}
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