Pub Date : 2025-01-01DOI: 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.
{"title":"Denoising low-field MR images with a deep learning algorithm based on simulated data from easily accessible open-source software","authors":"Aram Salehi , Mathieu Mach , Chloe Najac , Beatrice Lena , Thomas O’Reilly , Yiming Dong , Peter Börnert , Hieab Adams , Tavia Evans , Andrew Webb","doi":"10.1016/j.jmr.2024.107812","DOIUrl":"10.1016/j.jmr.2024.107812","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"370 ","pages":"Article 107812"},"PeriodicalIF":2.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142796632","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 : 2025-01-01DOI: 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。
{"title":"Using machine learning to improve the hard modeling of NMR time series","authors":"Jan Hellwig , Tobias Strauß , Erik von Harbou , 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}
Pub Date : 2025-01-01DOI: 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 T1ρ(t) relaxation, or evolves on a plane perpendicular to B(1)eff(t), leading to T2ρ(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 |γ−1dα(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 dα(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.
{"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<sup>(1)</sup><sub>eff</sub></em></strong><em>(t)</em>, leading to <em>T<sub>1ρ</sub>(t)</em> relaxation, or evolves on a plane perpendicular to <strong><em>B<sup>(1)</sup><sub>eff</sub></em></strong><em>(t)</em>, leading to <em>T<sub>2ρ</sub>(t)</em> relaxation. Time evolution of <strong><em>B<sup>(1)</sup><sub>eff</sub></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<sup>−1</sup>dα<sup>(1)</sup>(t)/dt|</em> ≪ <em>B<sup>(1)</sup><sub>eff</sub>(t)</em> is well satisfied. Here <em>α<sup>(1)</sup>(t)</em> is the angle between <strong><em>B<sup>(1)</sup><sub>eff</sub></em></strong><em>(t)</em> and the axis of quantization of the first rotating frame (FRF) <em>z′</em>, and <em>dα<sup>(1)</sup>(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}
Pub Date : 2024-12-01DOI: 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 B0. The diffusion through internal field gradients effect on T2 depends on the product of and G, with G depending on B0.
Increasing the static field to bring a nucleus with lower into resonance at the same frequency will result in the products B0 and 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.
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.
{"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 , Naser Ansaribaranghar , Andrés Ramírez Aguilera , Florea Marica , Laura Romero de Zerón , Bruce J. Balcom","doi":"10.1016/j.jmr.2024.107811","DOIUrl":"10.1016/j.jmr.2024.107811","url":null,"abstract":"<div><div>Multinuclear <sup>1</sup>H, <sup>13</sup>C, and <sup>23</sup>Na 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 B<sub>0</sub>. Increasing the static B<sub>0</sub> 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 B<sub>0</sub>. The equations that describe the inhomogeneous broadening in T<sub>2</sub>* show that the MR result depends on <span><math><mrow><mi>γ</mi></mrow></math></span>B<sub>0</sub>. The diffusion through internal field gradients effect on T<sub>2</sub> depends on the product of <span><math><mrow><mi>γ</mi></mrow></math></span> and G, with G depending on B<sub>0</sub>.</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>B<sub>0</sub> 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 T<sub>2</sub>* hypothesis with <sup>23</sup>Na and <sup>1</sup>H measurements of brine in porous reservoir core plugs. We explore the diffusion through internal field gradients effect hypothesis with <sup>1</sup>H and <sup>13</sup>C measurements of decane saturated glass beads.</div><div>The nuclei chosen for study: <sup>1</sup>H, <sup>13</sup>C, and <sup>23</sup>Na 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}
Pub Date : 2024-12-01DOI: 10.1016/j.jmr.2024.107794
Lewis E. Kay
{"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}
Pub Date : 2024-11-22DOI: 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。
{"title":"A compact and mobile stray-field NMR sensor","authors":"Belal M.K. Alnajjar , Jürgen Frick , Bernhard Blümich , 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}
Pub Date : 2024-11-19DOI: 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.
{"title":"Optimizing EPR pulses for broadband excitation and refocusing","authors":"Eric R. Lowe , Stefan Stoll , 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}
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。
{"title":"Eliminating electromagnetic interference for RF shielding-free MRI via k-space convolution: Insights from MR parallel imaging advances","authors":"Yilong Liu , Linfang Xiao , Mengye Lyu , 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}
Pub Date : 2024-11-17DOI: 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.
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Pub Date : 2024-11-16DOI: 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 efficiency. The 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 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。
{"title":"16-channel sleeve antenna array based on passive decoupling method at 14 T","authors":"Youheng Sun , Miutian Wang , Jianjun Du , Wentao Wang , Gang Yang , Weimin Wang , 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}
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