Calibration-free parallel transmission of the cervical, thoracic, and lumbar spinal cord at 7T

Aigner, C.S.; Sánchez Alarcon, M.F.; D'Astous, A.; Alonso-Ortiz, E.; Cohen-Adad, J.; Schmitter, S.

Calibration-free parallel transmission of the cervical, thoracic, and lumbar spinal cord at 7T

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Item Type:	Article
Title:	Calibration-free parallel transmission of the cervical, thoracic, and lumbar spinal cord at 7T
Creators Name:	Aigner, C.S., Sánchez Alarcon, M.F., D'Astous, A., Alonso-Ortiz, E., Cohen-Adad, J. and Schmitter, S.
Abstract:	PURPOSE: To address the limitations of spinal cord imaging at ultra-high field (UHF) due to time-consuming parallel transmit (pTx) adjustments. This study introduces calibration-free offline computed universal shim modes that can be applied seamlessly for different pTx RF coils and spinal cord target regions, substantially enhancing spinal cord imaging efficiency at UHF. METHODS: A library of channel-wise relative B(+)(1) maps for the cervical spinal cord (six datasets) and thoracic and lumbar spinal cord (nine datasets) was constructed to optimize transmit homogeneity and efficiency for these regions. A tailored B0 shim was optimized for the cervical spine to enhance spatial magnetic field homogeneity further. The performance of the universal shims was validated using absolute saturation based B(+)(1) mapping and high-resolution 2D and 3D multi-echo gradient-recalled echo (GRE) data to assess the image quality. RESULTS: The proposed universal shims demonstrated a 50% improvement in B(+)(1) efficiency compared to the default (zero phase) shim mode. B(+)(1) homogeneity was also improved by 20%. The optimized universal shims achieved performance comparable to subject-specific pTx adjustments, while eliminating the need for lengthy pTx calibration times, saving about 10 min per experiment. CONCLUSION: The development of universal shims represents a significant advance by eliminating time-consuming subject-specific pTx adjustments. This approach is expected to make UHF spinal cord imaging more accessible and user-friendly, particularly for non-pTx experts.
Keywords:	7 Tesla, Calibration-Free, Parallel Transmission, Spinal Cord, Universal Pulse
Source:	Magnetic Resonance in Medicine
ISSN:	0740-3194
Publisher:	Wiley
Volume:	92
Number:	4
Page Range:	1496-1510
Date:	October 2024
Official Publication:	https://doi.org/10.1002/mrm.30137
PubMed:	View item in PubMed

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