Magnetic Resonance in Medicine最新文献

{"title":"Machine learning-based estimation of respiratory fluctuations in a healthy adult population using resting state BOLD fMRI and head motion parameters.","authors":"Abdoljalil Addeh, Fernando Vega, Amin Morshedi, Rebecca J Williams, G Bruce Pike, M Ethan MacDonald","doi":"10.1002/mrm.30330","DOIUrl":"10.1002/mrm.30330","url":null,"abstract":"<p><strong>Purpose: </strong>External physiological monitoring is the primary approach to measure and remove effects of low-frequency respiratory variation from BOLD-fMRI signals. However, the acquisition of clean external respiratory data during fMRI is not always possible, so recent research has proposed using machine learning to directly estimate respiratory variation (RV), potentially obviating the need for external monitoring. In this study, we propose an extended method for reconstructing RV waveforms directly from resting state BOLD-fMRI data in healthy adult participants with the inclusion of both BOLD signals and derived head motion parameters.</p><p><strong>Methods: </strong>In the proposed method, 1D convolutional neural networks (1D-CNNs) used BOLD signals and head motion parameters to reconstruct the RV waveform for the whole fMRI scan time. Resting-state fMRI data and associated respiratory records from the Human Connectome Project in Young Adults (HCP-YA) dataset are used to train and test the proposed method.</p><p><strong>Results: </strong>Compared to using only BOLD-fMRI data for a CNN input, this approach yielded improvements of 14% in mean absolute error, 24% in mean square error, 14% in correlation, and 12% in dynamic time warping. When tested on independent datasets, the method demonstrated generalizability, even in data with different TRs and physiological conditions.</p><p><strong>Conclusion: </strong>This study shows that the respiratory variations could be reconstructed from BOLD-fMRI data in the young adult population, and its accuracy could be improved using supportive data such as head motion parameters. The method also performed well on independent datasets with different experimental conditions.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1365-1379"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680722/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142558188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revealing membrane integrity and cell size from diffusion kurtosis time dependence.","authors":"Hong-Hsi Lee, Dmitry S Novikov, Els Fieremans, Susie Y Huang","doi":"10.1002/mrm.30335","DOIUrl":"10.1002/mrm.30335","url":null,"abstract":"<p><strong>Purpose: </strong>The nonmonotonic dependence of diffusion kurtosis on diffusion time has been observed in biological tissues, yet its relation to membrane integrity and cellular geometry remains to be clarified. Here we establish and explain the characteristic asymmetric shape of the kurtosis peak. We also derive the relation between the peak time <math> <semantics> <mrow> <msub><mrow><mi>t</mi></mrow> <mrow><mtext>peak</mtext></mrow> </msub> </mrow> <annotation>$$ {t}_{mathrm{peak}} $$</annotation></semantics> </math> , when kurtosis reaches its maximum, and tissue parameters.</p><p><strong>Methods: </strong>The peak shape and its position <math> <semantics> <mrow> <msub><mrow><mi>t</mi></mrow> <mrow><mtext>peak</mtext></mrow> </msub> </mrow> <annotation>$$ {t}_{mathrm{peak}} $$</annotation></semantics> </math> qualitatively follow from the adiabatic extension of the Kärger model onto the case of intra-cellular diffusivity time-dependence. This intuition is corroborated by the effective medium theory-based calculation, as well as by Monte Carlo simulations of diffusion and exchange in randomly and densely packed spheres for various values of permeability, cell fractions and sizes, and intrinsic diffusivity.</p><p><strong>Results: </strong>We establish that <math> <semantics> <mrow> <msub><mrow><mi>t</mi></mrow> <mrow><mtext>peak</mtext></mrow> </msub> </mrow> <annotation>$$ {t}_{mathrm{peak}} $$</annotation></semantics> </math> is proportional to the geometric mean of two characteristic time scales: extra-cellular correlation time (determined by cell size) and intra-cellular residence time (determined by membrane permeability). When exchange is barrier-limited, the peak shape approaches a universal scaling form determined by the ratio <math> <semantics><mrow><mi>t</mi> <mo>/</mo> <msub><mrow><mi>t</mi></mrow> <mrow><mtext>peak</mtext></mrow> </msub> </mrow> <annotation>$$ t/{t}_{mathrm{peak}} $$</annotation></semantics> </math> .</p><p><strong>Conclusion: </strong>Numerical simulations and theory provide an interpretation of a specific feature of kurtosis time-dependence, offering a potential biomarker for in vivo evaluation of pathology by disentangling the functional (permeability) and structural (cell size) integrity in tissues. This is relevant as the time-dependent diffusion cumulants are sensitive to pathological changes in membrane integrity and cellular structure in diseases, such as ischemic stroke, tumors, and Alzheimer's disease.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1329-1347"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142546254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical shift-encoded multishot EPI for navigator-free prostate DWI.","authors":"Yiming Dong, David Atkinson, Kirsten Koolstra, Matthias J P van Osch, Peter Börnert","doi":"10.1002/mrm.30334","DOIUrl":"10.1002/mrm.30334","url":null,"abstract":"<p><strong>Purpose: </strong>DWI is an important contrast for prostate MRI to enable early and accurate detection of cancer. This study introduces a Dixon 3-shot-EPI protocol with structured low-rank reconstruction for navigator-free DWI. The aim is to overcome the limitations of single-shot EPI (ssh-EPI), such as geometric distortions and fat signal interference, while addressing the motion-induced phase variations of multishot EPI and simultaneously allowing water/fat separation.</p><p><strong>Methods: </strong>DWI data were acquired from 7 healthy volunteers using both Dixon 3-shot EPI and standard fat-suppressed ssh-EPI with similar scan times for comparison. Two readers evaluated image quality using a 5-point Likert scale regarding different aspects. The ADC values were quantitatively compared between protocols. To show feasibility in a clinical setting, the protocol was applied to two patients.</p><p><strong>Results: </strong>From the reader scores, Dixon 3-shot EPI significantly reduced geometric distortion compared with ssh-EPI (p < 0.01), with no significant differences in edge definition, SNR, or overall image quality. There was no significant difference in ADC values between the two protocols. However, the Dixon multishot-EPI protocol offered advantages such as self-referenced B₀ map-driven distortion correction, greater flexibility in imaging parameters, and superior fat suppression. In the patient data, the lesion could be clearly identified in both protocols and on the associated ADC maps.</p><p><strong>Conclusion: </strong>The proposed Dixon 3-shot-EPI protocol shows promise as an alternative to ssh-EPI for prostate DWI, providing reduced geometric distortions and improved fat suppression. It addresses common DWI issues based on EPI and enhances scanning flexibility, indicating potential for optimized imaging.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1059-1076"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680737/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Toward quantitative CEST imaging of glutamate in the mouse brain using a multi-pool exchange model calibrated by ¹H-MRS.","authors":"Cécile Maguin, Eloïse Mougel, Julien Valette, Julien Flament","doi":"10.1002/mrm.30353","DOIUrl":"10.1002/mrm.30353","url":null,"abstract":"<p><strong>Purpose: </strong>To develop a CEST quantification model to map glutamate concentration in the mouse brain at 11.7 T, overcoming the limitations of conventional glutamate-weighted CEST (gluCEST) contrast (magnetization transfer ratio with asymmetric analysis).</p><p><strong>Methods: </strong>¹H-MRS was used as a gold standard for glutamate quantification to calibrate a CEST-based quantitative pipeline. Joint localized measurements of Z-spectra at B₁ = 5 μT and quantitative ¹H-MRS were carried out in two voxels of interest in the mouse brain. A six-pool Bloch-McConnell model was found appropriate to fit experimental data. Glutamate exchange rate was estimated in both regions with this dedicated multi-pool fitting model and using glutamate concentration determined by ¹H-MRS.</p><p><strong>Results: </strong>Glutamate exchange rate was estimated to be ˜1300 Hz in the mouse brain. Using this calibrated value, maps of glutamate concentration in the mouse brain were obtained by pixel-by-pixel fitting of Z-spectra at B₁ = 5 μT. A complementary study of simulations, however, showed that the quantitative model has high sensitivity to noise, and therefore, requires high-SNR acquisitions. Interestingly, fitted [Glu] seemed to be overestimated compared to ¹H-MRS measurements, although it was estimated with simulations that the model has no intrinsic fitting bias with our experimental level of noise. The hypothesis of an unknown proton-exchanging pool contributing to gluCEST signal is discussed.</p><p><strong>Conclusion: </strong>High-resolution mapping of glutamate in the brain was made possible using the proposed calibrated quantification model of gluCEST data. Further studying of the in vivo molecular contributions to gluCEST signal could improve modeling.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1394-1410"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680732/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142503165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"¹²⁹Xe Image Processing Pipeline: An open-source, graphical user interface application for the analysis of hyperpolarized ¹²⁹Xe MRI.","authors":"Abdullah S Bdaiwi, Matthew M Willmering, Joseph W Plummer, Riaz Hussain, David J Roach, Juan Parra-Robles, Peter J Niedbalski, Jason C Woods, Laura L Walkup, Zackary I Cleveland","doi":"10.1002/mrm.30347","DOIUrl":"10.1002/mrm.30347","url":null,"abstract":"<p><strong>Purpose: </strong>Hyperpolarized ¹²⁹Xe MRI presents opportunities to assess regional pulmonary microstructure and function. Ongoing advancements in hardware, sequences, and image processing have helped it become increasingly adopted for both research and clinical use. As the number of applications and users increase, standardization becomes crucial. To that end, this study developed an executable, open-source ¹²⁹Xe image processing pipeline (XIPline) to provide a user-friendly, graphical user interface-based analysis pipeline to analyze and visualize ¹²⁹Xe MR data, including scanner calibration, ventilation, diffusion-weighted, and gas exchange images.</p><p><strong>Methods: </strong>The customizable XIPline is designed in MATLAB to analyze data from all three major scanner platforms. Calibration data is processed to calculate optimal flip angle and determine¹²⁹Xe frequency offset. Data processing includes loading, reconstructing, registering, segmenting, and post-processing images. Ventilation analysis incorporates three common algorithms to calculate ventilation defect percentage and novel techniques to assess defect distribution and ventilation texture. Diffusion analysis features ADC mapping, modified linear binning to account for ADC age-dependence, and common diffusion morphometry methods. Gas exchange processing uses a generalized linear binning for data acquired using 1-point Dixon imaging.</p><p><strong>Results: </strong>The XIPline workflow is demonstrated using analysis from representative calibration, ventilation, diffusion, and gas exchange data.</p><p><strong>Conclusion: </strong>The application will reduce redundant effort when implementing new techniques across research sites by providing an open-source framework for developers. In its current form, it offers a robust and adaptable platform for ¹²⁹Xe MRI analysis to ensure methodological consistency, transparency, and support for collaborative research across multiple sites and MRI manufacturers.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1220-1237"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680735/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142558186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Repeatability of diffusion kurtosis tensor parameters in muscles of the lower legs.","authors":"Ethan Mathew, Richard Dortch, Bruce Damon, Sudarshan Ragunathan, C Chad Quarles","doi":"10.1002/mrm.30344","DOIUrl":"10.1002/mrm.30344","url":null,"abstract":"<p><strong>Purpose: </strong>The aim of this study was to provide measurements from and investigate the repeatability of diffusion kurtosis tensor parameters in the muscles of the lower legs.</p><p><strong>Methods: </strong>Test-retest acquisition of a kurtosis tensor sequence was performed in 13 healthy volunteers. Quantitative kurtosis tensor parameters were derived, and repeatability of each parameter was evaluated by muscle group and over the whole muscle through intraclass correlation coefficient (ICC) and within-subject coefficient of variation (wsCV). Bland-Altman analysis was also conducted. Differences in parameter values by muscle group were investigated through an analysis of variance.</p><p><strong>Results: </strong>Axial kurtosis and radial kurtosis values from the test data were 0.63 ± 0.04 and 0.70 ± 0.05, respectively. Kurtosis tensor parameters from all muscle groups and over the whole muscle had wsCV below 15%. ICC for the parameters from most muscle groups was above 85%, with the lowest ICC over the whole muscle being 88.39%. The medial gastrocnemius and extensor digitorum longus showed highest repeatability. Mean, axial, and radial diffusivity had higher wsCV despite being lower-order terms than kurtosis.</p><p><strong>Conclusion: </strong>This study sought to examine the repeatability of diffusion kurtosis tensor-derived parameters in the legs and verify that they could potentially be used as longitudinal imaging metrics. wsCV values from test-retest data indicated high repeatability throughout all examined muscle groups. There were minimal differences in kurtosis and diffusivity parameters between muscle groups in this healthy volunteer cohort.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1306-1313"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11682918/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142623004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Parallel transmit hybrid pulse design for controlled on-resonance magnetization transfer in R₁ mapping at 7T.","authors":"David Leitão, Raphael Tomi-Tricot, Philippa Bridgen, Pierluigi Di Cio, Patrick Liebig, Rene Gumbrecht, Dieter Ritter, Sharon Giles, Joseph V Hajnal, Shaihan J Malik","doi":"10.1002/mrm.30333","DOIUrl":"10.1002/mrm.30333","url":null,"abstract":"&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;This work proposes a \"hybrid\" RF pulse design method for parallel transmit (pTx) systems to simultaneously control flip angle and root-mean-squared &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mo&gt;+&lt;/mo&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {mathrm{B}}_1^{+} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; ( &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; ). These pulses are generally only designed for flip angle, however, this can lead to uncontrolled &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; , which then leads to variable magnetization transfer (MT) effects. We demonstrate the hybrid design approach for quantitative imaging where both flip angle and &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; are important.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Theory and methods: &lt;/strong&gt;A dual cost function optimization is performed containing the normalized mean squared errors of the flip angle and &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; distributions weighted by a parameter &lt;math&gt; &lt;semantics&gt;&lt;mrow&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;/mrow&gt; &lt;annotation&gt;$$ lambda $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; . Simulations were conducted to study the behavior of both properties when simultaneously optimizing them. In vivo experiments on a 7T MRI system with an 8-channel pTx head coil were carried out to study the effect of the hybrid design approach on variable flip angle &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;R&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt;&lt;/msub&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {mathrm{R}}_1 $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; (= 1/T&lt;sub&gt;1&lt;/sub&gt;) mapping.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;Simulations showed that both flip angle and &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; can be homogenized simultaneously without detriment to either when compared to an individual optimization. By homogenizing flip angle and &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msubsup&gt;&lt;mi&gt;B&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt; &lt;mi&gt;rms&lt;/mi&gt;&lt;/msubsup&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {B}_1^{mathrm{rms}} $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; , &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;R&lt;/mi&gt; &lt;mn&gt;1&lt;/mn&gt;&lt;/msub&gt; &lt;/mrow&gt; &lt;annotation&gt;$$ {mathrm{R}}_1 $$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; maps were more uniform (coefficient of variation 6.6% vs. 13.0%) compared to those acquired with pulses that only homogenized flip angle.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;The proposed hybrid design homogenizes on-resonance MT effects while homogenizing the flip angle distribution, with only a small detriment in the latter compared to a pulse that just homogenizes f","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1090-1103"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680742/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"<ArticleTitle xmlns:ns0=\"http://www.w3.org/1998/Math/MathML\">Bilateral orthogonality generative acquisitions method for homogeneous <ns0:math> <ns0:mrow><ns0:msubsup><ns0:mi>T</ns0:mi> <ns0:mn>2</ns0:mn> <ns0:mo>*</ns0:mo></ns0:msubsup> </ns0:mrow> </ns0:math> images using parallel transmission at 7 T.","authors":"Çelik Boğa, Anke Henning","doi":"10.1002/mrm.30329","DOIUrl":"10.1002/mrm.30329","url":null,"abstract":"<p><strong>Purpose: </strong>The novel bilateral orthogonality generative acquisitions method has been developed for homogeneous <math> <semantics> <mrow><msubsup><mi>T</mi> <mn>2</mn> <mo>*</mo></msubsup> </mrow> <annotation>$$ {mathrm{T}}_2^{ast } $$</annotation></semantics> </math> images without the effects of transmit field inhomogeneity using a parallel-transmission (pTx) system at 7 T.</p><p><strong>Theory and methods: </strong>A new method has been introduced using four low-angle gradient-echo (GRE) acquisitions to obtain homogeneous <math> <semantics> <mrow><msubsup><mi>T</mi> <mn>2</mn> <mo>*</mo></msubsup> </mrow> <annotation>$$ {mathrm{T}}_2^{ast } $$</annotation></semantics> </math> contrast by removing the effects of transmit field inhomogeneity in the pTx system. First, two input images are obtained in circularly polarized mode and another mode in which the first transmit channel or channel group have an additional transmit phase of π. The last two acquisitions are single-channel acquisitions for a dual-channel system or single-channel group acquisitions for more than two channels. The introduced method is demonstrated in dual-channel and eight-channel pTx systems using phantom and whole-brain in vivo experiments. Noise performance of the proposed method is also tested against the ratio of two GRE acquisitions and the TIAMO (time-interleaved acquisitions of modes) method.</p><p><strong>Results: </strong>Th new method results in more homogeneous <math> <semantics> <mrow><msubsup><mi>T</mi> <mn>2</mn> <mo>*</mo></msubsup> </mrow> <annotation>$$ {mathrm{T}}_2^{ast } $$</annotation></semantics> </math> contrast in the final images than the compared methods, particularly in the low-intensity regions of circularly polarized-mode images for the images obtained via ratio of the two GRE acquisitions.</p><p><strong>Conclusion: </strong>The introduced method is easy to implement, robust, and provides homogeneous <math> <semantics> <mrow><msubsup><mi>T</mi> <mn>2</mn> <mo>*</mo></msubsup> </mrow> <annotation>$$ {mathrm{T}}_2^{ast } $$</annotation></semantics> </math> images of the whole brain using pTx systems with any number of channels, compared with the ratio of the two GRE images and the TIAMO method.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1043-1058"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680731/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142391629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Large improvement in RF magnetic fields and imaging SNR with whole-head high-permittivity slurry helmet for human-brain MRI applications at 7 T.","authors":"Soo Han Soon, Xin Li, Matt Waks, Xiao-Hong Zhu, Hannes M Wiesner, Navid P Gandji, Qing X Yang, Michael T Lanagan, Wei Chen","doi":"10.1002/mrm.30350","DOIUrl":"10.1002/mrm.30350","url":null,"abstract":"<p><strong>Purpose: </strong>To optimize the design and demonstrate the integration of a helmet-shaped container filled with a high-permittivity material (HPM) slurry with RF head coil arrays to improve RF coil sensitivity and SNR for human-brain proton MRI.</p><p><strong>Methods: </strong>RF reception magnetic fields ( <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>-</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{-} $$</annotation></semantics> </math> ) of a 32-channel receive-only coil array with various geometries and permittivity values of HPM slurry helmet are calculated with electromagnetic simulation at 7 T. A 16-channel transmit-only coil array, a 32-channel receive-only coil array, and a 2-piece HPM slurry helmet were constructed and assembled. RF transmission magnetic field ( <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>+</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{+} $$</annotation></semantics> </math> ), <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>-</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{-} $$</annotation></semantics> </math> , and MRI SNR maps from the entire human brain were measured and compared.</p><p><strong>Results: </strong>Simulations showed that averaged <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>-</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{-} $$</annotation></semantics> </math> improvement with the HPM slurry helmet increased from 57% to 87% as the relative permittivity (ε_r) of HPM slurry increased from 110 to 210. In vivo experiments showed that the average <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>+</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{+} $$</annotation></semantics> </math> improvement over the human brain was 14.5% with the two-piece HPM slurry (ε_r ≈ 170) helmet, and the average <math> <semantics> <mrow><msubsup><mi>B</mi> <mn>1</mn> <mo>-</mo></msubsup> </mrow> <annotation>$$ {mathrm{B}}_1^{-} $$</annotation></semantics> </math> and SNR were improved 63% and 34%, respectively, because the MRI noise level was increased by the lossy HPM.</p><p><strong>Conclusion: </strong>The RF coil sensitivity and MRI SNR were largely improved with the two-piece HPM slurry helmet demonstrated by both electromagnetic simulations and in vivo human head experiments at 7 T. The findings demonstrate that incorporating an easily producible HPM slurry helmet into the RF coil array significantly enhances human-brain MRI SNR homogeneity and quality at ultrahigh field. Greater SNR improvement is anticipated using the less lossy HPM and optimal design.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1205-1219"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680740/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142503162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phase contrast MRI with minimized background phase errors.","authors":"Michael Loecher, Daniel B Ennis","doi":"10.1002/mrm.30336","DOIUrl":"10.1002/mrm.30336","url":null,"abstract":"<p><strong>Purpose: </strong>Phase contrast MRI (PC-MRI) is used clinically to measure velocities in the body, but systematic background phase errors caused by magnetic field imperfections corrupt the velocity measurements with offsets that limit clinical utility. This work aims to minimize systematic background phase errors in PC-MRI, thereby maximizing the accuracy of velocity measurements.</p><p><strong>Methods: </strong>The MRI scanner's background phase errors from eddy currents and mechanical oscillations were modeled using the gradient impulse response function (GIRF). Gradient waveforms were then numerically optimized using the GIRF to create pulse sequences that minimize the background phase errors. The pulse sequences were tested in a static phantom where the predicted response could be compared directly to the measured background velocity. The optimized acquisitions were then tested in human subjects, where flow rates and background errors were compared to conventional PC-MRI.</p><p><strong>Results: </strong>When using the GIRF-optimized gradient waveforms, the predicted background phase was within 0.6 [95% CI = -3.4, 5.4] mm/s of the measured background phase in a static phantom. Excellent agreement was seen for in vivo blood flow values (flow rate agreement <math> <semantics> <mrow><msup><mi>r</mi> <mn>2</mn></msup> </mrow> <annotation>$$ {r}^2 $$</annotation></semantics> </math> = 0.96), and the background phase was reduced by 78.8 <math> <semantics><mrow><mo>±</mo></mrow> <annotation>$$ pm $$</annotation></semantics> </math> 18.7%.</p><p><strong>Conclusion: </strong>This work shows that using a GIRF to model the effects of magnetic field imperfections combined with numerically optimized gradient waveforms enables PC-MRI waveforms to be designed to produce a minimal background phase in the most time-efficient manner. The methodology could be adapted for other MRI sequences where similar magnetic field errors affect measurements.</p>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":" ","pages":"1104-1116"},"PeriodicalIF":3.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}