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Purpose: Advancing the development of 7 T MRI for spinal cord imaging is crucial for the enhanced diagnosis and monitoring of various neurodegenerative diseases and traumas. However, a significant challenge at this field strength is the transmit field inhomogeneity. 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 multisite study explores several RF shimming techniques in the cervical spinal cord. Methods: Data were collected from 5 participants between two 7 T sites with a custom 8Tx/20Rx parallel transmission coil. We explored two radiofrequency (RF) shimming approaches from an MRI vendor and four from an open‐source toolbox, showcasing their ability to enhance transmit field and signal homogeneity along the cervical spinal cord. Results: The circularly polarized (CP), coefficient of variation (CoV), and specific absorption rate (SAR) efficiency shim modes showed the highest B1+ efficiency, and the vendor‐based "patient" and "volume" modes showed the lowest B1+ efficiency. The coefficient of variation method produced the highest CSF/spinal cord contrast on T2*‐weighted scans (ratio of 1.27 ± 0.03), and the lowest variation of that contrast along the superior–inferior axis. Conclusion: The study's findings highlight the potential of RF shimming to advance 7 T MRI's clinical utility for central nervous system imaging by enabling more homogenous and efficient spinal cord imaging. Additionally, the research incorporates a reproducible Jupyter Notebook, enhancing the study's transparency and facilitating peer verification. [ABSTRACT FROM AUTHOR]

Phosphorus (31P) magnetic resonance spectroscopic imaging (MRSI) can serve as a critical tool for more direct quantification of brain energy metabolism, tissue pH, and cell membrane turnover. However, the low concentration of 31P metabolites in biological tissue may result in low signal‐to‐noise ratio (SNR) in 31P MRS images. In this work, we present an innovative design and construction of a 31P radiofrequency coil for whole‐brain MRSI at 7 T. Our coil builds on current literature in ultra‐high field 31P coil design and offers complete coverage of the brain, including the cerebellum and brainstem. The coil consists of an actively detunable volume transmit (Tx) resonator and a custom 24‐channel receive (Rx) array. The volume Tx resonator is a 16‐rung high‐pass birdcage coil. The Rx coil consists of a 24‐element phased array composed of catered loop shapes and sizes built onto a custom, close‐fitting, head‐shaped housing. The Rx array was designed to provide complete coverage of the head, while minimizing mutual coupling. The Rx configuration had a mean S11 reflection coefficient better than −20 decibels (dB) when the coil was loaded with a human head. The mean mutual coupling (S21) among Rx elements, when loaded with a human head, was −16 dB. In phantom imaging, the phased array produced a central SNR that was 4.4‐fold higher than the corresponding central SNR when operating the 31P birdcage as a transceiver. The peripheral SNR was 12‐fold higher when applying the optimized phased array. In vivo 3D 31P MRSI experiments produced high‐quality spectra in the cerebrum gray and white matter, as well as in the cerebellum. Characteristic phosphorus metabolites related to adenosine triphosphate metabolism and cell membrane turnover were distinguishable across all brain regions. In summary, our results demonstrate the potential of our novel coil for accurate, whole‐brain 31P metabolite quantification. [ABSTRACT FROM AUTHOR]

Phosphorus ( 31 P) magnetic resonance spectroscopic imaging (MRSI) can serve as a critical tool for more direct quantification of brain energy metabolism, tissue pH, and cell membrane turnover. However, the low concentration of 31 P metabolites in biological tissue may result in low signal-to-noise ratio (SNR) in 31 P MRS images. In this work, we present an innovative design and construction of a 31 P radiofrequency coil for whole-brain MRSI at 7 T. Our coil builds on current literature in ultra-high field 31 P coil design and offers complete coverage of the brain, including the cerebellum and brainstem. The coil consists of an actively detunable volume transmit (Tx) resonator and a custom 24-channel receive (Rx) array. The volume Tx resonator is a 16-rung high-pass birdcage coil. The Rx coil consists of a 24-element phased array composed of catered loop shapes and sizes built onto a custom, close-fitting, head-shaped housing. The Rx array was designed to provide complete coverage of the head, while minimizing mutual coupling. The Rx configuration had a mean S 11 reflection coefficient better than -20 decibels (dB) when the coil was loaded with a human head. The mean mutual coupling ( S 21 ) among Rx elements, when loaded with a human head, was -16 dB. In phantom imaging, the phased array produced a central SNR that was 4.4-fold higher than the corresponding central SNR when operating the 31 P birdcage as a transceiver. The peripheral SNR was 12-fold higher when applying the optimized phased array. In vivo 3D 31 P MRSI experiments produced high-quality spectra in the cerebrum gray and white matter, as well as in the cerebellum. Characteristic phosphorus metabolites related to adenosine triphosphate metabolism and cell membrane turnover were distinguishable across all brain regions. In summary, our results demonstrate the potential of our novel coil for accurate, whole-brain 31 P metabolite quantification., (© 2024 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)