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Figure 1. Overview of the RF shimming procedure. The top panel shows the RF coil used for the experiments, alongside the Tx coil geometry and the electromagnetic simulation results (on Gustav model) yielding the CP mode used for this coil. The bottom panel shows the RF shimming procedure (with approximate duration). First, GRE and tfl_rfmap scans are acquired (4min30s). Second, these images are transferred via ethernet socket from the MRI console onto a separate laptop running Shimming Toolbox and SCT (əs). Third, the spinal cord is automatically segmented to produce a mask that is resampled into the space of the individual coil magnitude and phase images of the tfl_rfmap scan (~5s). Fourth, the RF shim weights are calculated according to the defined constraints for each shim scenario (1min total).

Statement of Need

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Advancing the development of 7T MRI for spinal cord imaging is crucial for the enhanced diagnosis and monitoring of various neurodegenerative diseases [Kearney et al., 2015] and traumas [David et al., 2019]. However, a significant challenge at this field strength is the transmit field inhomogeneity [Collins et al., 2005, Ibrahim et al., 2001, Röschmann, 1987, Yang et al., 2002]. Such inhomogeneity is particularly problematic for imaging the small, deep anatomical structures of the cervical spinal cord , as it can cause uneven signal intensity and elevate the local specific absorption ratio, compromising image quality. This multi-site study explores several radiofrequency (RF) shimming techniques in the cervical spinal cord at 7T.

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Advancing the development of 7T MRI for spinal cord imaging is crucial for the enhanced diagnosis and monitoring of various neurodegenerative diseases [Kearney et al., 2015] and traumas [David et al., 2019]. However, a significant challenge at this field strength is the transmit field inhomogeneity [Collins et al., 2005, Ibrahim et al., 2001, Röschmann, 1987, Yang et al., 2002]. Such inhomogeneity is particularly problematic for imaging the small, deep anatomical structures of the cervical spinal cord , as it can cause uneven signal intensity and elevate the local specific absorption ratio, compromising image quality. This multi-site study explores several radiofrequency (RF) shimming techniques in the cervical spinal cord at 7T.

1     |     Data#

The data can be downloaded from: https://openneuro.org/datasets/ds004906

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1     |     Data

2     |     Overview of processing pipeline#

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During the data acquisition stage, RF shimming was done using the Shimming Toolbox [D'Astous et al., 2023] during the acquisition stage.

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The post-processing pipeline uses the Spinal Cord Toolbox [De Leener et al., 2017].

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During the data acquisition stage, RF shimming was done using the Shimming Toolbox [D'Astous et al., 2023] during the acquisition stage.

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The post-processing pipeline uses the Spinal Cord Toolbox [De Leener et al., 2017].

For each subject:

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Figure 3. B1+ efficiency (A) and CSF/Cord signal ratio from the GRE scan (B) across subjects and across different RF shimming conditions. Data were measured in the spinal cord from C3 to T2 vertebral levels. To match the x-ticks across subjects, the C2-C3 and the T2-T3 intervertebral discs of each subject were aligned with that of the PAM50 template [De Leener et al., 2018], and the curves were linearly scaled.

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Figure 3. B1+ efficiency (A) and CSF/Cord signal ratio from the GRE scan (B) across subjects and across different RF shimming conditions. Data were measured in the spinal cord from C3 to T2 vertebral levels. To match the x-ticks across subjects, the C2-C3 and the T2-T3 intervertebral discs of each subject were aligned with that of the PAM50 template [De Leener et al., 2018], and the curves were linearly scaled.

References#

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Christopher M Collins, Wanzhan Liu, Weston Schreiber, Qing X Yang, and Michael B Smith. Central brightening due to constructive interference with, without, and despite dielectric resonance. J. Magn. Reson. Imaging, 21(2):192–196, February 2005.

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Christopher M Collins, Wanzhan Liu, Weston Schreiber, Qing X Yang, and Michael B Smith. Central brightening due to constructive interference with, without, and despite dielectric resonance. J. Magn. Reson. Imaging, 21(2):192–196, February 2005. doi:https://doi.org/10.1002/jmri.20245.

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Alexandre D'Astous, Gaspard Cereza, Daniel Papp, Kyle M. Gilbert, Jason P. Stockmann, Eva Alonso-Ortiz, and Julien Cohen-Adad. Shimming toolbox: an open-source software toolbox for b0 and b1 shimming in mri. Magnetic Resonance in Medicine, 89(4):1401–1417, 2023. URL: https://onlinelibrary.wiley.com/doi/abs/10.1002/mrm.29528, arXiv:https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.29528, doi:https://doi.org/10.1002/mrm.29528.

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Alexandre D'Astous, Gaspard Cereza, Daniel Papp, Kyle M. Gilbert, Jason P. Stockmann, Eva Alonso-Ortiz, and Julien Cohen-Adad. Shimming toolbox: an open-source software toolbox for b0 and b1 shimming in mri. Magnetic Resonance in Medicine, 89(4):1401–1417, 2023. doi:https://doi.org/10.1002/mrm.29528.

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Gergely David, Siawoosh Mohammadi, Allan R Martin, Julien Cohen-Adad, Nikolaus Weiskopf, Alan Thompson, and Patrick Freund. Traumatic and nontraumatic spinal cord injury: pathological insights from neuroimaging. Nat. Rev. Neurol., 15(12):718–731, December 2019.

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Gergely David, Siawoosh Mohammadi, Allan R Martin, Julien Cohen-Adad, Nikolaus Weiskopf, Alan Thompson, and Patrick Freund. Traumatic and nontraumatic spinal cord injury: pathological insights from neuroimaging. Nat. Rev. Neurol., 15(12):718–731, December 2019. doi:https://doi.org/10.1038/s41582-019-0270-5.

4(1,2)
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Benjamin De Leener, Simon Lévy, Sara M. Dupont, Vladimir S. Fonov, Nikola Stikov, D. Louis Collins, Virginie Callot, and Julien Cohen-Adad. Sct: spinal cord toolbox, an open-source software for processing spinal cord \MRI\ data. NeuroImage, 145, Part A():24 – 43, 2017. URL: http://www.sciencedirect.com/science/article/pii/S1053811916305560, doi:https://doi.org/10.1016/j.neuroimage.2016.10.009.

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Benjamin De Leener, Simon Lévy, Sara M. Dupont, Vladimir S. Fonov, Nikola Stikov, D. Louis Collins, Virginie Callot, and Julien Cohen-Adad. Sct: spinal cord toolbox, an open-source software for processing spinal cord \MRI\ data. NeuroImage, 145, Part A():24 – 43, 2017. doi:https://doi.org/10.1016/j.neuroimage.2016.10.009.

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Tamer S Ibrahim, Robert Lee, Amir M Abduljalil, Brian A Baertlein, and Pierre-Marie L Robitaille. Dielectric resonances and B1 field inhomogeneity in UHF MRI: computational analysis and experimental findings. 2001. Accessed: 2020-8-10.

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Tamer S Ibrahim, Robert Lee, Amir M Abduljalil, Brian A Baertlein, and Pierre-Marie L Robitaille. Dielectric resonances and b1 field inhomogeneity in uhfmri: computational analysis and experimental findings. Magnetic Resonance Imaging, 19(2):219–226, 2001. doi:https://doi.org/10.1016/S0730-725X(01)00300-9.

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Hugh Kearney, David H Miller, and Olga Ciccarelli. Spinal cord MRI in multiple sclerosis–diagnostic, prognostic and clinical value. Nat. Rev. Neurol., 11(6):327–338, June 2015.

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Hugh Kearney, David H Miller, and Olga Ciccarelli. Spinal cord MRI in multiple sclerosis–diagnostic, prognostic and clinical value. Nat. Rev. Neurol., 11(6):327–338, June 2015. doi:https://doi.org/10.1038/nrneurol.2015.80.

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P Röschmann. Radiofrequency penetration and absorption in the human body: limitations to high-field whole-body nuclear magnetic resonance imaging. Med. Phys., 14(6):922–931, November 1987.

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P Röschmann. Radiofrequency penetration and absorption in the human body: limitations to high-field whole-body nuclear magnetic resonance imaging. Med. Phys., 14(6):922–931, November 1987. doi:https://doi.org/10.1118/1.595995.

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Qing X Yang, Jinghua Wang, Xiaoliang Zhang, Christopher M Collins, Michael B Smith, Haiying Liu, Xiao-Hong Zhu, J Thomas Vaughan, Kamil Ugurbil, and Wei Chen. Analysis of wave behavior in lossy dielectric samples at high field. Magn. Reson. Med., 47(5):982–989, May 2002.

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Qing X Yang, Jinghua Wang, Xiaoliang Zhang, Christopher M Collins, Michael B Smith, Haiying Liu, Xiao-Hong Zhu, J Thomas Vaughan, Kamil Ugurbil, and Wei Chen. Analysis of wave behavior in lossy dielectric samples at high field. Magn. Reson. Med., 47(5):982–989, May 2002. doi:https://doi.org/10.1002/mrm.10137.

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Benjamin De Leener, Vladimir S. Fonov, D. Louis Collins, Virginie Callot, Nikola Stikov, and Julien Cohen-Adad. Pam50: unbiased multimodal template of the brainstem and spinal cord aligned with the icbm152 space. NeuroImage, 165:170–179, 2018. URL: https://www.sciencedirect.com/science/article/pii/S1053811917308686, doi:https://doi.org/10.1016/j.neuroimage.2017.10.041.

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Benjamin De Leener, Vladimir S. Fonov, D. Louis Collins, Virginie Callot, Nikola Stikov, and Julien Cohen-Adad. Pam50: unbiased multimodal template of the brainstem and spinal cord aligned with the icbm152 space. NeuroImage, 165:170–179, 2018. doi:https://doi.org/10.1016/j.neuroimage.2017.10.041.