George Jack Hutchinson, Adam Blakey, Nia Jones, Lopa Leach, Neele Dellschaft, Paul Houston, Matthew Hubbard, Reuben O'Dea, Penny Anne Gowland
Purpose
To investigate and explain observed features of the placental DWI signal in healthy and compromised pregnancies using a mathematical model of maternal blood flow.
Methods
Thirteen healthy and nine compromised third trimester pregnancies underwent pulse gradient spin echo DWI MRI, with the results compared to MRI data simulated from a 2D mathematical model of maternal blood flow through the placenta. Both sets of data were fitted to an intravoxel incoherent motion (IVIM) model, and a rebound model (defined within text), which described voxels that did not decay monotonically. Both the in vivo and simulated placentas were split into regions of interest (ROIs) to analyze how the signal varies and how IVIM and rebounding parameters change across the placental width.
Results
There was good agreement between the in vivo MRI data, and the data simulated from the mathematical model. Both sets of data included voxels showing a rebounding signal and voxels showing fast signal decay focused near the maternal side of the placenta. In vivo we found higher in the uterine wall and near the maternal side of the placenta, with the slow diffusion coefficient reduced in all ROIs in compromised pregnancy.
Conclusion
A simulation based entirely on maternal blood explains key features observed in placental DWI, indicating the importance of maternal blood flow in interpreting placental MRI data, and providing potential new metrics for understanding changes in compromised placentas.
目的：利用母体血流数学模型研究和解释健康妊娠和受损妊娠胎盘DWI信号的观察特征。方法：对13例健康孕妇和9例妊娠晚期孕妇进行脉冲梯度自旋回波DWI MRI检查，并将结果与母体胎盘血流二维数学模型模拟的MRI数据进行比较。两组数据都拟合到一个体素内非相干运动（IVIM）模型和一个反弹模型（在文本中定义），该模型描述了没有单调衰减的体素。将活体和模拟胎盘分成感兴趣区域（roi），分析信号如何变化以及IVIM和反弹参数如何在胎盘宽度上变化。结果：体内MRI数据与数学模型模拟数据吻合较好。两组数据都包括显示反弹信号的体素和显示快速信号衰减的体素，这些体素集中在胎盘母体一侧附近。在体内，我们发现子宫壁和胎盘母体一侧附近的ifvim $$ {f}_{IVIM} $$较高，所有ROIs的慢扩散系数D $$ D $$都降低。结论：完全基于母体血液的模拟解释了胎盘DWI观察到的关键特征，表明母体血流在解释胎盘MRI数据中的重要性，并为理解受损胎盘的变化提供了潜在的新指标。
{"title":"The effects of maternal flow on placental diffusion-weighted MRI and intravoxel incoherent motion parameters","authors":"George Jack Hutchinson, Adam Blakey, Nia Jones, Lopa Leach, Neele Dellschaft, Paul Houston, Matthew Hubbard, Reuben O'Dea, Penny Anne Gowland","doi":"10.1002/mrm.30379","DOIUrl":"10.1002/mrm.30379","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>To investigate and explain observed features of the placental DWI signal in healthy and compromised pregnancies using a mathematical model of maternal blood flow.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>Thirteen healthy and nine compromised third trimester pregnancies underwent pulse gradient spin echo DWI MRI, with the results compared to MRI data simulated from a 2D mathematical model of maternal blood flow through the placenta. Both sets of data were fitted to an intravoxel incoherent motion (IVIM) model, and a rebound model (defined within text), which described voxels that did not decay monotonically. Both the in vivo and simulated placentas were split into regions of interest (ROIs) to analyze how the signal varies and how IVIM and rebounding parameters change across the placental width.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>There was good agreement between the in vivo MRI data, and the data simulated from the mathematical model. Both sets of data included voxels showing a rebounding signal and voxels showing fast signal decay focused near the maternal side of the placenta. In vivo we found higher <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>f</mi>\u0000 <mtext>IVIM</mtext>\u0000 </msub>\u0000 </mrow>\u0000 <annotation>$$ {f}_{IVIM} $$</annotation>\u0000 </semantics></math> in the uterine wall and near the maternal side of the placenta, with the slow diffusion coefficient <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>D</mi>\u0000 </mrow>\u0000 <annotation>$$ D $$</annotation>\u0000 </semantics></math> reduced in all ROIs in compromised pregnancy.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>A simulation based entirely on maternal blood explains key features observed in placental DWI, indicating the importance of maternal blood flow in interpreting placental MRI data, and providing potential new metrics for understanding changes in compromised placentas.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1629-1641"},"PeriodicalIF":3.0,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782734/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142751316","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}
Omar Isam Darwish, Pierluigi Di Cio, Ralph Sinkus, Radhouene Neji
Purpose
To demonstrate the feasibility of hepatic 3D MR elastography (MRE) at 0.55 T in healthy volunteers using Hadamard encoding and to study the effects of concomitant fields in the domain of MRE in general.
Methods
Concomitant field effects in MRE are assessed using a Taylor series expansion and an encoding scheme is proposed to study the corresponding effects on 3D MRE at 0.55 T in numerical simulations and in phantom experiments. In addition, five healthy volunteers were enrolled and scanned at 60 Hz mechanical excitation with a Hadamard-encoded 3D MRE sequence at 0.55 T and were also scanned with a reference 3D MRE sequence at 3 T for comparison. The retrieved biomechanical parameters were the magnitude of the complex shear modulus (|G*|), the shear wave speed (Cs), and the loss modulus (G″). Comparison of apparent SNR between 3 T and 0.55 T was performed.
Results
Theoretical analysis, numerical simulations and phantom experiments demonstrated that the effects of concomitant fields in 3D MRE at 0.55 T are negligible. In the healthy volunteer experiments, the mean values of |G*|, Cs, and G″ in the liver were 2.1 ± 0.3 kPa, 1.5 ± 0.1 m/s, and 0.8 ± 0.1 kPa at 0.55 T, respectively, and 2.0 ± 0.2 kPa, 1.5 ± 0.1 m/s, and 0.9 ± 0.1 kPa at 3 T, respectively. Bland–Altman analysis demonstrated good agreement between the biomechanical parameters retrieved at 0.55 T and 3 T. A 2.1-fold relative apparent SNR decrease was observed in 3D MRE at 0.55 T in comparison with 3 T.
Conclusion
Hepatic 3D MRE is feasible at 0.55 T, showing promising initial results in healthy volunteers.
目的：利用 Hadamard 编码证明健康志愿者在 0.55 T 下进行肝脏三维磁共振弹性成像（MRE）的可行性，并研究伴随场对一般 MRE 域的影响：方法：使用泰勒级数展开评估了 MRE 中的并发场效应，并提出了一种编码方案，以便在数值模拟和模型实验中研究 0.55 T 下三维 MRE 的相应效应。此外，还招募了五名健康志愿者，使用哈达玛编码的 0.55 T 三维 MRE 序列在 60 Hz 机械激励下进行扫描，并使用参考的 3 T 三维 MRE 序列进行扫描以进行比较。获取的生物力学参数包括复剪切模量（|G*|）、剪切波速度（Cs）和损耗模量（G″）的大小。对 3 T 和 0.55 T 之间的表观信噪比进行了比较：理论分析、数值模拟和人体模型实验表明，在 0.55 T 的三维 MRE 中，伴随场的影响可以忽略不计。在健康志愿者实验中，肝脏中的|G*|、Cs和G″的平均值在0.55 T时分别为2.1 ± 0.3 kPa、1.5 ± 0.1 m/s和0.8 ± 0.1 kPa，在3 T时分别为2.0 ± 0.2 kPa、1.5 ± 0.1 m/s和0.9 ± 0.1 kPa。Bland-Altman分析表明，在0.55 T和3 T检测到的生物力学参数之间具有良好的一致性。与 3 T 相比，0.55 T 的三维 MRE 的表观信噪比相对降低了 2.1 倍：结论：肝脏三维 MRE 在 0.55 T 下是可行的，在健康志愿者中显示出良好的初步结果。
{"title":"3D MR elastography at 0.55 T: Concomitant field effects and feasibility","authors":"Omar Isam Darwish, Pierluigi Di Cio, Ralph Sinkus, Radhouene Neji","doi":"10.1002/mrm.30377","DOIUrl":"10.1002/mrm.30377","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>To demonstrate the feasibility of hepatic 3D MR elastography (MRE) at 0.55 T in healthy volunteers using Hadamard encoding and to study the effects of concomitant fields in the domain of MRE in general.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>Concomitant field effects in MRE are assessed using a Taylor series expansion and an encoding scheme is proposed to study the corresponding effects on 3D MRE at 0.55 T in numerical simulations and in phantom experiments. In addition, five healthy volunteers were enrolled and scanned at 60 Hz mechanical excitation with a Hadamard-encoded 3D MRE sequence at 0.55 T and were also scanned with a reference 3D MRE sequence at 3 T for comparison. The retrieved biomechanical parameters were the magnitude of the complex shear modulus (|<i>G</i>*|), the shear wave speed (Cs), and the loss modulus (<i>G</i>″). Comparison of apparent SNR between 3 T and 0.55 T was performed.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Theoretical analysis, numerical simulations and phantom experiments demonstrated that the effects of concomitant fields in 3D MRE at 0.55 T are negligible. In the healthy volunteer experiments, the mean values of |<i>G</i>*|, Cs, and G″ in the liver were 2.1 ± 0.3 kPa, 1.5 ± 0.1 m/s, and 0.8 ± 0.1 kPa at 0.55 T, respectively, and 2.0 ± 0.2 kPa, 1.5 ± 0.1 m/s, and 0.9 ± 0.1 kPa at 3 T, respectively. Bland–Altman analysis demonstrated good agreement between the biomechanical parameters retrieved at 0.55 T and 3 T. A 2.1-fold relative apparent SNR decrease was observed in 3D MRE at 0.55 T in comparison with 3 T.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>Hepatic 3D MRE is feasible at 0.55 T, showing promising initial results in healthy volunteers.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1602-1614"},"PeriodicalIF":3.0,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782726/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142716482","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}
Simon Blömer, Lukas Hingerl, Małgorzata Marjańska, Wolfgang Bogner, Stanislav Motyka, Gilbert Hangel, Antoine Klauser, Ovidiu C. Andronesi, Bernhard Strasser
Purpose
Proton (1H)-MRSI via spatial-spectral encoding poses high demands on gradient hardware at ultra-high fields and high-resolutions. Rosette trajectories help alleviate these problems, but at reduced SNR-efficiency because of their k-space densities not matching any desired k-space filter. We propose modified rosette trajectories, which more closely match a Hamming filter, and thereby improve SNR performance while still staying within gradient hardware limitations and without prolonging scan time.
Methods
Analytical and synthetic simulations were validated with phantom and in vivo measurements at 7 T. The rosette and modified rosette trajectories were measured in five healthy volunteers in 6 min in a 2D slice in the brain. An elliptical phase-encoding sequence was measured in one volunteer in 22 min, and a 3D sequence was measured in one volunteer within 19 min. The SNR per-unit-time, linewidth, Cramer-Rao lower bounds (CRLBs), lipid contamination, and data quality of the proposed modified rosette trajectory were compared to the rosette trajectory.
Results
Using the modified rosette trajectories, an improved k-space weighting function was achieved resulting in an SNR per-unit-time increase of up to 12% compared to rosette's and 23% compared to elliptical phase-encoding, dependent on the two additional trajectory parameters. Similar results were achieved for the theoretical SNR calculation based on k-space densities, as well as when using the pseudo-replica method for simulated, in vivo, and phantom data. The CRLBs of γ-aminobutyric acid and N-acetylaspartylglutamate improved non-significantly for the modified rosette trajectory, whereas the linewidths and lipid contamination remained similar.
Conclusion
By optimizing the shape of the rosette trajectory, the modified rosette trajectories achieved higher SNR per-unit-time and enhanced data quality at the same scan time.
目的：通过空间-光谱编码的质子（1H）-MRSI 对超高场和高分辨率下的梯度硬件提出了很高的要求。轮状轨迹有助于缓解这些问题，但由于其 k 空间密度与任何所需的 k 空间滤波器不匹配，因此 SNR 效率降低。我们提出了修改后的玫瑰花轨迹，它与汉明滤波器更加匹配，从而提高了信噪比性能，同时仍能满足梯度硬件的限制，并且不会延长扫描时间：方法：分析和合成模拟与 7 T 下的模型和活体测量进行了验证。在 6 分钟内对五名健康志愿者的大脑二维切片进行了花环轨迹和改良花环轨迹测量。一名志愿者在 22 分钟内测量了椭圆相位编码序列，一名志愿者在 19 分钟内测量了三维序列。将拟议的修正玫瑰花轨迹与玫瑰花轨迹的单位时间信噪比、线宽、克拉默-拉奥下限（CRLB）、脂质污染和数据质量进行了比较：使用改进后的采样轨迹，改进了 k 空间加权函数，与采样轨迹相比，单位时间信噪比提高了 12%，与椭圆相位编码相比，单位时间信噪比提高了 23%，这取决于两个额外的轨迹参数。基于 k 空间密度的理论信噪比计算，以及对模拟、体内和模型数据使用伪复制方法时，都取得了类似的结果。修改后的莲座轨迹对γ-氨基丁酸和N-乙酰天冬氨酰谷氨酸的CRLB改善不明显，而线宽和脂质污染保持相似：结论：通过优化花环轨迹的形状，改良花环轨迹在相同的扫描时间内获得了更高的单位时间信噪比，并提高了数据质量。
{"title":"Proton-free induction decay MRSI at 7 T in the human brain using an egg-shaped modified rosette K-space trajectory","authors":"Simon Blömer, Lukas Hingerl, Małgorzata Marjańska, Wolfgang Bogner, Stanislav Motyka, Gilbert Hangel, Antoine Klauser, Ovidiu C. Andronesi, Bernhard Strasser","doi":"10.1002/mrm.30368","DOIUrl":"10.1002/mrm.30368","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>Proton (<sup>1</sup>H)-MRSI via spatial-spectral encoding poses high demands on gradient hardware at ultra-high fields and high-resolutions. Rosette trajectories help alleviate these problems, but at reduced SNR-efficiency because of their k-space densities not matching any desired k-space filter. We propose modified rosette trajectories, which more closely match a Hamming filter, and thereby improve SNR performance while still staying within gradient hardware limitations and without prolonging scan time.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>Analytical and synthetic simulations were validated with phantom and in vivo measurements at 7 T. The rosette and modified rosette trajectories were measured in five healthy volunteers in 6 min in a 2D slice in the brain. An elliptical phase-encoding sequence was measured in one volunteer in 22 min, and a 3D sequence was measured in one volunteer within 19 min. The SNR per-unit-time, linewidth, Cramer-Rao lower bounds (CRLBs), lipid contamination, and data quality of the proposed modified rosette trajectory were compared to the rosette trajectory.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Using the modified rosette trajectories, an improved k-space weighting function was achieved resulting in an SNR per-unit-time increase of up to 12% compared to rosette's and 23% compared to elliptical phase-encoding, dependent on the two additional trajectory parameters. Similar results were achieved for the theoretical SNR calculation based on k-space densities, as well as when using the pseudo-replica method for simulated, in vivo, and phantom data. The CRLBs of γ-aminobutyric acid and N-acetylaspartylglutamate improved non-significantly for the modified rosette trajectory, whereas the linewidths and lipid contamination remained similar.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>By optimizing the shape of the rosette trajectory, the modified rosette trajectories achieved higher SNR per-unit-time and enhanced data quality at the same scan time.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1443-1457"},"PeriodicalIF":3.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782714/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142682129","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}
This study leverages the echo planar time-resolved imaging (EPTI) concept in MR fingerprinting (MRF) framework for a new time-resolved MRF (TRMRF) approach, and explores its capability for fast simultaneous quantification of multiple MR parameters including T1, T2, T2*, proton density, off resonance, and B1+.
Methods
The proposed TRMRF method uses the concept of EPTI to track the signal change along the EPI echo train for T2* weighting with a k-t Poisson-based sampling order designed for acquisition. A two-dimensional decomposition algorithm was designed for the image reconstruction, enabling fast and precise subspace modeling. The accuracy of proposed method was evaluated by a T1/T2 phantom. The feasibility was demonstrated through 5 healthy volunteer brain studies.
Results
In the phantom studies, T1, T2, and T2* maps of TRMRF correlated strongly with gold-standard methods. The concordance correlation coefficients are 0.9999, 0.9984 and 0.9978, and R2s are 0.9998, 0.9971, and 0.9983. In the in vivo studies, quantitative maps were acquired with 5 healthy volunteers. TRMRF was demonstrated to have comparable results with spiral MRF and gradient-echo EPTI. TRMRF scans using 16, 10, and 6 s per slice were also evaluated to demonstrate the capability of shorter scan times.
Conclusion
A new approach is proposed to exploit the advantage of EPTI in the MRF framework. We demonstrate in phantom and in vivo experiments that T1, T2, T2*, proton density, off resonance, and B1+ can be simultaneously quantified within 6 s/slice by TRMRF.
{"title":"Time-resolved MR fingerprinting for T2* signal extraction: MR fingerprinting meets echo planar time-resolved imaging","authors":"Di Cui, Xiaoxi Liu, Peder E. Z. Larson, Duan Xu","doi":"10.1002/mrm.30381","DOIUrl":"10.1002/mrm.30381","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>This study leverages the echo planar time-resolved imaging (EPTI) concept in MR fingerprinting (MRF) framework for a new time-resolved MRF (TRMRF) approach, and explores its capability for fast simultaneous quantification of multiple MR parameters including T<sub>1</sub>, T<sub>2</sub>, T<sub>2</sub>*, proton density, off resonance, and B<sub>1</sub><sup>+</sup>.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>The proposed TRMRF method uses the concept of EPTI to track the signal change along the EPI echo train for T<sub>2</sub>* weighting with a k-t Poisson-based sampling order designed for acquisition. A two-dimensional decomposition algorithm was designed for the image reconstruction, enabling fast and precise subspace modeling. The accuracy of proposed method was evaluated by a T<sub>1</sub>/T<sub>2</sub> phantom. The feasibility was demonstrated through 5 healthy volunteer brain studies.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>In the phantom studies, T<sub>1</sub>, T<sub>2</sub>, and T<sub>2</sub>* maps of TRMRF correlated strongly with gold-standard methods. The concordance correlation coefficients are 0.9999, 0.9984 and 0.9978, and R<sup>2</sup>s are 0.9998, 0.9971, and 0.9983. In the in vivo studies, quantitative maps were acquired with 5 healthy volunteers. TRMRF was demonstrated to have comparable results with spiral MRF and gradient-echo EPTI. TRMRF scans using 16, 10, and 6 s per slice were also evaluated to demonstrate the capability of shorter scan times.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>A new approach is proposed to exploit the advantage of EPTI in the MRF framework. We demonstrate in phantom and in vivo experiments that T<sub>1</sub>, T<sub>2</sub>, T<sub>2</sub>*, proton density, off resonance, and B<sub>1</sub><sup>+</sup> can be simultaneously quantified within 6 s/slice by TRMRF.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1751-1760"},"PeriodicalIF":3.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142682131","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}
Zhixing Wang, Rajiv Ramasawmy, Ahsan Javed, John P. Mugler III, Craig H. Meyer, Adrienne E. Campbell-Washburn
Purpose
To develop single-slab 3D spiral turbo spin echo (spiral SPACE) for 1-mm3 isotropic whole-brain T2-weighted imaging on a high-performance 0.55T scanner, with high scan efficiency from interleaved spiral-in-out trajectories, variable-flip-angle refocusing radiofrequency (RF) pulses, echo reordering, and concomitant-field compensation.
Methods
A stack-of-spirals (in-out waveforms) turbo-spin-echo acquisition was implemented with T2-weighed contrast. Gradient infidelity was corrected using the gradient impulse response function (GIRF), and concomitant-field compensation was used to correct for phase errors among echoes and during the readout windows. To maintain a long echo train (˜600 ms) within each shot, variable-flip-angle refocusing RF pulses were generated using extended-phase-graph analysis. An echo-reordering scheme provided a smooth signal variation along the echo direction in k-space. Images from spiral SPACE with and without concomitant-field compensation were compared with those from Cartesian SPACE in phantoms and 6 healthy volunteers.
Results
Phantom results demonstrated the improved performance of concomitant-field correction via sequence-based modifications and of GIRF–based trajectory estimation. Volunteer data showed that with concomitant-field correction and echo reordering, system imperfection associated image artifacts and blurring were substantially mitigated in spiral SPACE. Compared with Cartesian SPACE, spiral SPACE had an overall 15%–25% signal-to-noise ratio (SNR) improvement in both white matter and gray matter.
Conclusion
A 3D spiral-in-out SPACE acquisition with variable-flip-angles, concomitant-field compensation, and echo-reordering was demonstrated at 0.55 T, showing promising gains in SNR, compared with Cartesian SPACE.
目的：在高性能 0.55T 扫描仪上开发用于 1 mm3 各向同性全脑 T2 加权成像的单板三维螺旋涡轮自旋回波（螺旋 SPACE），通过交错螺旋进出轨迹、可变翻转角度重新聚焦射频（RF）脉冲、回波重排和同场补偿实现高效扫描：方法：采用 T2 权衡对比，进行螺旋堆叠（进出波形）涡轮自旋回波采集。利用梯度脉冲响应函数（GIRF）校正梯度失真，并利用共场补偿校正回波间和读出窗期间的相位误差。为了在每个镜头内保持长回波序列（˜600 ms），使用扩展相位图分析法生成了可变翻转角度的再聚焦射频脉冲。回波重排方案提供了沿 k 空间回波方向的平滑信号变化。在人体模型和 6 名健康志愿者身上比较了螺旋 SPACE 和笛卡尔 SPACE（带或不带共场补偿）的图像：结果：模型结果表明，通过基于序列的修改和基于 GIRF 的轨迹估计，共场校正的性能有所提高。志愿者的数据显示，通过共场校正和回波重排，在螺旋 SPACE 中，与系统不完善相关的图像伪影和模糊现象大大减少。与笛卡尔 SPACE 相比，螺旋 SPACE 在白质和灰质中的信噪比（SNR）总体提高了 15%-25%：与笛卡尔 SPACE 相比，在 0.55 T 条件下采用可变翻转角度、同时场补偿和回声重排的三维螺旋-进-出 SPACE 采集显示出了良好的信噪比提升效果。
{"title":"Variable-flip-angle 3D spiral-in-out turbo spin-echo imaging using concomitant gradient compensation and echo reordering at 0.55 T","authors":"Zhixing Wang, Rajiv Ramasawmy, Ahsan Javed, John P. Mugler III, Craig H. Meyer, Adrienne E. Campbell-Washburn","doi":"10.1002/mrm.30380","DOIUrl":"10.1002/mrm.30380","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>To develop single-slab 3D spiral turbo spin echo (spiral SPACE) for 1-mm<sup>3</sup> isotropic whole-brain T<sub>2</sub>-weighted imaging on a high-performance 0.55T scanner, with high scan efficiency from interleaved spiral-in-out trajectories, variable-flip-angle refocusing radiofrequency (RF) pulses, echo reordering, and concomitant-field compensation.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>A stack-of-spirals (in-out waveforms) turbo-spin-echo acquisition was implemented with T<sub>2</sub>-weighed contrast. Gradient infidelity was corrected using the gradient impulse response function (GIRF), and concomitant-field compensation was used to correct for phase errors among echoes and during the readout windows. To maintain a long echo train (˜600 ms) within each shot, variable-flip-angle refocusing RF pulses were generated using extended-phase-graph analysis. An echo-reordering scheme provided a smooth signal variation along the echo direction in k-space. Images from spiral SPACE with and without concomitant-field compensation were compared with those from Cartesian SPACE in phantoms and 6 healthy volunteers.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Phantom results demonstrated the improved performance of concomitant-field correction via sequence-based modifications and of GIRF–based trajectory estimation. Volunteer data showed that with concomitant-field correction and echo reordering, system imperfection associated image artifacts and blurring were substantially mitigated in spiral SPACE. Compared with Cartesian SPACE, spiral SPACE had an overall 15%–25% signal-to-noise ratio (SNR) improvement in both white matter and gray matter.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>A 3D spiral-in-out SPACE acquisition with variable-flip-angles, concomitant-field compensation, and echo-reordering was demonstrated at 0.55 T, showing promising gains in SNR, compared with Cartesian SPACE.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1741-1750"},"PeriodicalIF":3.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782727/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142682150","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}
Jian Hu, Martin S. Craig, Silvin P. Knight, Celine De Looze, James F. Meaney, Rose Anne Kenny, Xin Chen, Michael A. Chappell
Purpose
One possible contributing factor for cerebral blood flow (CBF) decline in normal aging is the increase in partial volume effects due to brain atrophy, as cortical thinning can exacerbate the contamination of gray-matter (GM) voxels by other tissue types. This work investigates CBF changes in normal aging of a large elderly cohort aged 54 to 84 and how correction for partial volume effects that would accommodate potential changes in GM might affect this.
Methods
The study cohort consisted of 474 participants aged 54 to 84 years using pseudo-continuous arterial spin labeling MRI. A volumetric pipeline and a surface-based pipeline were applied to measure global and regional perfusion. Volumetric regions of interest (ROIs) included GM, cerebral white matter, vascular territories, and the brain atlas from the UK Biobank. The cortical parcellation was using Desikan–Killiany atlas. Non–partial volume effect correction (PVEc) and PVEc GM-CBF changes with aging were modeled using linear regressions.
Results
Global GM CBF decreased by 0.17 mL/100 g/min per year with aging before PVEc (p < 0.05) and was 0.18 mL/100 g/min after PVEc (p < 0.05). All cortical parcels exhibited CBF decreases with age before PVEc. After PVEc, seven parcels retained decreasing trends. However, GM CBF demonstrated increase with age after PVEc in three parcels.
Conclusion
Although decreases in global perfusion are observed with aging before PVEc, perfusion variations appear to be more regionally selective after PVEc. This supports the understanding that variation in cerebral perfusion with age observed with imaging is influenced by regional changes in anatomy that can be accommodated with PVEc, but perfusion variation is still observable even after PVE is accounted for.
{"title":"Regional changes in cerebral perfusion with age when accounting for changes in gray-matter volume","authors":"Jian Hu, Martin S. Craig, Silvin P. Knight, Celine De Looze, James F. Meaney, Rose Anne Kenny, Xin Chen, Michael A. Chappell","doi":"10.1002/mrm.30376","DOIUrl":"10.1002/mrm.30376","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>One possible contributing factor for cerebral blood flow (CBF) decline in normal aging is the increase in partial volume effects due to brain atrophy, as cortical thinning can exacerbate the contamination of gray-matter (GM) voxels by other tissue types. This work investigates CBF changes in normal aging of a large elderly cohort aged 54 to 84 and how correction for partial volume effects that would accommodate potential changes in GM might affect this.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>The study cohort consisted of 474 participants aged 54 to 84 years using pseudo-continuous arterial spin labeling MRI. A volumetric pipeline and a surface-based pipeline were applied to measure global and regional perfusion. Volumetric regions of interest (ROIs) included GM, cerebral white matter, vascular territories, and the brain atlas from the UK Biobank. The cortical parcellation was using Desikan–Killiany atlas. Non–partial volume effect correction (PVEc) and PVEc GM-CBF changes with aging were modeled using linear regressions.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Global GM CBF decreased by 0.17 mL/100 g/min per year with aging before PVEc (<i>p</i> < 0.05) and was 0.18 mL/100 g/min after PVEc (<i>p</i> < 0.05). All cortical parcels exhibited CBF decreases with age before PVEc. After PVEc, seven parcels retained decreasing trends. However, GM CBF demonstrated increase with age after PVEc in three parcels.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>Although decreases in global perfusion are observed with aging before PVEc, perfusion variations appear to be more regionally selective after PVEc. This supports the understanding that variation in cerebral perfusion with age observed with imaging is influenced by regional changes in anatomy that can be accommodated with PVEc, but perfusion variation is still observable even after PVE is accounted for.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1807-1820"},"PeriodicalIF":3.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782718/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142682130","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}
Zijing Dong, Timothy G. Reese, Hong-Hsi Lee, Susie Y. Huang, Jonathan R. Polimeni, Lawrence L. Wald, Fuyixue Wang
Purpose
To overcome the major challenges in diffusion MRI (dMRI) acquisition, including limited SNR, distortion/blurring, and susceptibility to motion artifacts.
Theory and Methods
A novel Romer-EPTI technique is developed to achieve SNR-efficient acquisition while providing distortion-free imaging, minimal spatial blurring, high motion robustness, and simultaneous multi-TE imaging. It introduces a ROtating-view Motion-robust supEr-Resolution technique (Romer) combined with a distortion/blurring-free Echo Planar Time-resolved Imaging (EPTI) readout. Romer enhances SNR through simultaneous multi-thick-slice acquisition with rotating-view encoding, while providing high motion-robustness via a high-fidelity, motion-aware super-resolution reconstruction. Instead of EPI, the in-plane encoding is performed using EPTI readout to prevent geometric distortion, T2/T2*-blurring, and importantly, dynamic distortions that could introduce additional blurring/artifacts after super-resolution reconstruction due to combining volumes with inconsistent geometries. This further improves effective spatial resolution and motion robustness. Additional developments include strategies to address slab-boundary artifacts, achieve minimized TE and optimized readout for additional SNR gain, and increase robustness to strong phase variations at high b-values.
Results
Using Romer-EPTI, we demonstrated distortion-free whole-brain mesoscale in-vivo dMRI at both 3T (500-μm isotropic [iso] resolution) and 7T (485-μm iso resolution) for the first time. Motion experiments demonstrated the technique's motion robustness and its ability to obtain high-resolution diffusion images in the presence of subject motion. Romer-EPTI also demonstrated high SNR gain and robustness in high b-value (b = 5000 s/mm2) and time-dependent dMRI.
Conclusion
The high SNR efficiency, improved image quality, and motion robustness of Romer-EPTI make it a highly efficient acquisition for high-resolution dMRI and microstructure imaging.
{"title":"Romer-EPTI: Rotating-view motion-robust super-resolution EPTI for SNR-efficient distortion-free in-vivo mesoscale diffusion MRI and microstructure imaging","authors":"Zijing Dong, Timothy G. Reese, Hong-Hsi Lee, Susie Y. Huang, Jonathan R. Polimeni, Lawrence L. Wald, Fuyixue Wang","doi":"10.1002/mrm.30365","DOIUrl":"10.1002/mrm.30365","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>To overcome the major challenges in diffusion MRI (dMRI) acquisition, including limited SNR, distortion/blurring, and susceptibility to motion artifacts.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Theory and Methods</h3>\u0000 \u0000 <p>A novel Romer-EPTI technique is developed to achieve SNR-efficient acquisition while providing distortion-free imaging, minimal spatial blurring, high motion robustness, and simultaneous multi-TE imaging. It introduces a ROtating-view Motion-robust supEr-Resolution technique (Romer) combined with a distortion/blurring-free Echo Planar Time-resolved Imaging (EPTI) readout. Romer enhances SNR through simultaneous multi-thick-slice acquisition with rotating-view encoding, while providing high motion-robustness via a high-fidelity, motion-aware super-resolution reconstruction. Instead of EPI, the in-plane encoding is performed using EPTI readout to prevent geometric distortion, <i>T</i><sub>2</sub>/<i>T</i><sub>2</sub>*-blurring, and importantly, dynamic distortions that could introduce additional blurring/artifacts after super-resolution reconstruction due to combining volumes with inconsistent geometries. This further improves effective spatial resolution and motion robustness. Additional developments include strategies to address slab-boundary artifacts, achieve minimized TE and optimized readout for additional SNR gain, and increase robustness to strong phase variations at high <i>b</i>-values.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Using Romer-EPTI, we demonstrated distortion-free whole-brain mesoscale in-vivo dMRI at both 3T (500-μm isotropic [iso] resolution) and 7T (485-μm iso resolution) for the first time. Motion experiments demonstrated the technique's motion robustness and its ability to obtain high-resolution diffusion images in the presence of subject motion. Romer-EPTI also demonstrated high SNR gain and robustness in high <i>b</i>-value (<i>b</i> = 5000 s/mm<sup>2</sup>) and time-dependent dMRI.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>The high SNR efficiency, improved image quality, and motion robustness of Romer-EPTI make it a highly efficient acquisition for high-resolution dMRI and microstructure imaging.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1535-1555"},"PeriodicalIF":3.0,"publicationDate":"2024-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782731/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142648438","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}
Mert Şişman, Thanh D. Nguyen, Alexandra G. Roberts, Dominick J. Romano, Alexey V. Dimov, Ilhami Kovanlikaya, Pascal Spincemaille, Yi Wang
Purpose
Myelin quantification is used in the study of demyelination in neurodegenerative diseases. A novel noninvasive MRI method, Microstructure-Informed Myelin Mapping (MIMM), is proposed to quantify the myelin volume fraction (MVF) from a routine multi-gradient echo sequence (mGRE) using a multiscale biophysical signal model of the effects of microstructural myelin and iron.
Theory and Methods
In MIMM, the effects of myelin are modeled based on the Hollow Cylinder Fiber Model accounting for anisotropy, while iron is considered as an isotropic paramagnetic point source. This model is used to create a dictionary of mGRE magnitude signal evolution and total voxel susceptibility using finite elements of size 0.2 μm. Next, voxel-by-voxel stochastic matching pursuit between acquired mGRE data (magnitude+QSM) and the pre-computed dictionary generates quantitative MVF and iron susceptibility maps. Dictionary matching was evaluated under three conditions: (1) without fiber orientation (basic), (2) with fiber orientation obtained using DTI, and (3) with fiber orientation obtained using an atlas (atlas). MIMM was compared with the three-pool complex fitting (3PCF) using T2-relaxometry myelin water fraction (MWF) map as reference.
Results
The DTI MIMM and atlas MIMM approaches were equally effective in reducing the overestimation of MVF in certain white matter tracts observed in the basic MIMM approach, and they both showed good agreement with T2-relaxometry MWF. MIMM MVF reduced myelin overestimation of globus pallidus observed in 3PCF MWF.
Conclusion
MIMM processing of mGRE data can provide MVF maps from routine clinical scans without requiring special sequences.
{"title":"Microstructure-Informed Myelin Mapping (MIMM) from routine multi-echo gradient echo data using multiscale physics modeling of iron and myelin effects and QSM","authors":"Mert Şişman, Thanh D. Nguyen, Alexandra G. Roberts, Dominick J. Romano, Alexey V. Dimov, Ilhami Kovanlikaya, Pascal Spincemaille, Yi Wang","doi":"10.1002/mrm.30369","DOIUrl":"10.1002/mrm.30369","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>Myelin quantification is used in the study of demyelination in neurodegenerative diseases. A novel noninvasive MRI method, Microstructure-Informed Myelin Mapping (MIMM), is proposed to quantify the myelin volume fraction (MVF) from a routine multi-gradient echo sequence (mGRE) using a multiscale biophysical signal model of the effects of microstructural myelin and iron.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Theory and Methods</h3>\u0000 \u0000 <p>In MIMM, the effects of myelin are modeled based on the Hollow Cylinder Fiber Model accounting for anisotropy, while iron is considered as an isotropic paramagnetic point source. This model is used to create a dictionary of mGRE magnitude signal evolution and total voxel susceptibility using finite elements of size 0.2 μm. Next, voxel-by-voxel stochastic matching pursuit between acquired mGRE data (magnitude+QSM) and the pre-computed dictionary generates quantitative MVF and iron susceptibility maps. Dictionary matching was evaluated under three conditions: (1) without fiber orientation (basic), (2) with fiber orientation obtained using DTI, and (3) with fiber orientation obtained using an atlas (atlas). MIMM was compared with the three-pool complex fitting (3PCF) using T2-relaxometry myelin water fraction (MWF) map as reference.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>The DTI MIMM and atlas MIMM approaches were equally effective in reducing the overestimation of MVF in certain white matter tracts observed in the basic MIMM approach, and they both showed good agreement with T2-relaxometry MWF. MIMM MVF reduced myelin overestimation of globus pallidus observed in 3PCF MWF.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>MIMM processing of mGRE data can provide MVF maps from routine clinical scans without requiring special sequences.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1499-1515"},"PeriodicalIF":3.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142648383","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}
Kylie Yeung, Kher Lik Ng, Jordan J. McGing, Aaron Axford, Sarah Birkhoelzer, Ayaka Shinozaki, Mattia Ricchi, Noemi Sgambelluri, Fulvio Zaccagna, Rebecca Mills, Andrew J. M. Lewis, Jennifer J. Rayner, Zack Ravetz, Lise Berner, Kenneth Jacob, Anthony McIntyre, Marianne Durrant, Oliver J. Rider, Rolf F. Schulte, Fergus V. Gleeson, Damian J. Tyler, James T. Grist
Purpose
The purpose of this work is to validate a simple and versatile integrated variable flip angle (VFA) method for mapping B1 in hyperpolarized MRI, which can be used to correct signal variations due to coil inhomogeneity.
Theory and Methods
Simulations were run to assess performance of the VFA B1 mapping method compared to the currently used constant flip angle (CFA) approach. Simulation results were used to inform the design of VFA sequences, validated in four volunteers for hyperpolarized xenon-129 imaging of the lungs and another four volunteers for hyperpolarized carbon-13 imaging of the human brain. B1 maps obtained were used to correct transmit and receive inhomogeneity in the images.
Results
Simulations showed improved performance of the VFA approach over the CFA approach with reduced sensitivity to T1. For xenon-129, the B1 maps accurately reflected the variation of signal depolarization, but in some cases could not be used to correct for coil receive inhomogeneity due to a lack of transmit-receive reciprocity resulting from suboptimal coil positioning. For carbon-13, the B1 maps showed good agreement with a separately acquired B1 map of a phantom and were effectively used to correct coil-induced signal inhomogeneity.
Conclusion
A simple, versatile, and effective VFA B1 mapping method was implemented and evaluated. Inclusion of the B1 mapping method in hyperpolarized imaging studies can enable more robust signal quantification.
{"title":"Evaluation of an integrated variable flip angle protocol to estimate coil B1 for hyperpolarized MRI","authors":"Kylie Yeung, Kher Lik Ng, Jordan J. McGing, Aaron Axford, Sarah Birkhoelzer, Ayaka Shinozaki, Mattia Ricchi, Noemi Sgambelluri, Fulvio Zaccagna, Rebecca Mills, Andrew J. M. Lewis, Jennifer J. Rayner, Zack Ravetz, Lise Berner, Kenneth Jacob, Anthony McIntyre, Marianne Durrant, Oliver J. Rider, Rolf F. Schulte, Fergus V. Gleeson, Damian J. Tyler, James T. Grist","doi":"10.1002/mrm.30378","DOIUrl":"10.1002/mrm.30378","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>The purpose of this work is to validate a simple and versatile integrated variable flip angle (VFA) method for mapping B<sub>1</sub> in hyperpolarized MRI, which can be used to correct signal variations due to coil inhomogeneity.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Theory and Methods</h3>\u0000 \u0000 <p>Simulations were run to assess performance of the VFA B<sub>1</sub> mapping method compared to the currently used constant flip angle (CFA) approach. Simulation results were used to inform the design of VFA sequences, validated in four volunteers for hyperpolarized xenon-129 imaging of the lungs and another four volunteers for hyperpolarized carbon-13 imaging of the human brain. B<sub>1</sub> maps obtained were used to correct transmit and receive inhomogeneity in the images.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Simulations showed improved performance of the VFA approach over the CFA approach with reduced sensitivity to T<sub>1</sub>. For xenon-129, the B<sub>1</sub> maps accurately reflected the variation of signal depolarization, but in some cases could not be used to correct for coil receive inhomogeneity due to a lack of transmit-receive reciprocity resulting from suboptimal coil positioning. For carbon-13, the B<sub>1</sub> maps showed good agreement with a separately acquired B<sub>1</sub> map of a phantom and were effectively used to correct coil-induced signal inhomogeneity.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>A simple, versatile, and effective VFA B<sub>1</sub> mapping method was implemented and evaluated. Inclusion of the B<sub>1</sub> mapping method in hyperpolarized imaging studies can enable more robust signal quantification.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 4","pages":"1615-1628"},"PeriodicalIF":3.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11782732/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142648332","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}
Simon Weinmüller, Jonathan Endres, Nam Dang, Rudolf Stollberger, Moritz Zaiss
Purpose
The complex signal decay during the transient FLASH MRI readout can lead to artifacts in magnitude and phase images. We show that target-driven optimization of individual RF flip angles and phases can realize near-ideal signal behavior and mitigate artifacts.
Methods
The differentiable end-to-end optimization framework MR-zero is used to optimize RF trains of the FLASH sequence. We focus herein on minimizing deviations from the ideally spoiled signal by using a mono-exponential Look–Locker target. We first obtain the transient FLASH signal decay substructure, and then minimize the deviation to the Look–Locker decay by optimizing the individual (i) flip angles, (ii) RF phases, and (iii) flip angles and RF phases. Comparison between measurement and simulation is performed using Pulseq in 1D and 2D.
Results
We were able to reproduce the complex substructure of the transient FLASH signal decay. All three optimization objectives can bring the real FLASH signal closer to the ideal case, with best results when both flip angles and RF phases are adjusted jointly. This solution outperformed all tested conventional quadratic RF cyclings in terms of (i) matching the Look–Locker target signal, (ii) phase stability, (iii) point spread functions ideality, (iv) robustness against parameter changes, and (v) magnitude and phase image quality. Other target functions for the signal could as well be realized, yet their response is not as general as for the Look–Locker target and needs to be optimized for a specific context.
Conclusion
Individual flip angle and RF phase optimization improves the transient signal decay of FLASH MRI sequences.
{"title":"MR-zero meets FLASH – controlling the transient signal decay in gradient- and RF-spoiled gradient echo sequences","authors":"Simon Weinmüller, Jonathan Endres, Nam Dang, Rudolf Stollberger, Moritz Zaiss","doi":"10.1002/mrm.30318","DOIUrl":"10.1002/mrm.30318","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>The complex signal decay during the transient FLASH MRI readout can lead to artifacts in magnitude and phase images. We show that target-driven optimization of individual RF flip angles and phases can realize near-ideal signal behavior and mitigate artifacts.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>The differentiable end-to-end optimization framework MR-zero is used to optimize RF trains of the FLASH sequence. We focus herein on minimizing deviations from the ideally spoiled signal by using a mono-exponential Look–Locker target. We first obtain the transient FLASH signal decay substructure, and then minimize the deviation to the Look–Locker decay by optimizing the individual (i) flip angles, (ii) RF phases, and (iii) flip angles and RF phases. Comparison between measurement and simulation is performed using Pulseq in 1D and 2D.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>We were able to reproduce the complex substructure of the transient FLASH signal decay. All three optimization objectives can bring the real FLASH signal closer to the ideal case, with best results when both flip angles and RF phases are adjusted jointly. This solution outperformed all tested conventional quadratic RF cyclings in terms of (i) matching the Look–Locker target signal, (ii) phase stability, (iii) point spread functions ideality, (iv) robustness against parameter changes, and (v) magnitude and phase image quality. Other target functions for the signal could as well be realized, yet their response is not as general as for the Look–Locker target and needs to be optimized for a specific context.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>Individual flip angle and RF phase optimization improves the transient signal decay of FLASH MRI sequences.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18065,"journal":{"name":"Magnetic Resonance in Medicine","volume":"93 3","pages":"942-960"},"PeriodicalIF":3.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11680739/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142648431","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}
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