A nested phosphorus and proton coil array for brain magnetic resonance imaging and spectroscopy

Abstract

A dual-nuclei radiofrequency coil array was constructed for phosphorus and proton magnetic resonance imaging and spectroscopy of the human brain at 7 Tesla. An eight-channel transceive degenerate birdcage phosphorus module was implemented to provide whole-brain coverage and significant sensitivity improvement over a standard dual-tuned loop coil. A nested eight-channel proton module provided adequate sensitivity for anatomical localization without substantially sacrificing performance on the phosphorus module. The developed array enabled phosphorus spectroscopy, a saturation transfer technique to calculate the global creatine kinase forward reaction rate, and single-metabolite whole-brain imaging with 1.4 cm nominal isotropic resolution in 15 min (2.3 cm actual resolution), while additionally enabling 1 mm isotropic proton imaging. This study demonstrates that a multi-channel array can be utilized for phosphorus and proton applications with improved coverage and/or sensitivity over traditional single-channel coils. The efficient multi-channel coil array, time-efficient pulse sequences, and the enhanced signal strength available at ultra-high fields can be combined to allow volumetric assessment of the brain and could provide new insights into the underlying energy metabolism impairment in several neurodegenerative conditions, such as Alzheimer’s and Parkinson’s diseases, as well as mental disorders such as schizophrenia.

Double‐tuned 31P/1H human head array with high performance at both frequencies for spectroscopic imaging at 9.4T

“…Commonly, to simplify decoupling and placement of multiple elements of a DT array, 1 H loops are moved away from the subject and positioned in a second layer . Alternatively, they are made substantially smaller than X‐nuclei loops and are located inside of them . Both methods decrease loading of 1 H loops and, thus, compromise the Tx‐performance and SNR of the DT array at 1 H frequency .…”

“…There are several previously reported DT UHF head array coil designs . To the best of our knowledge, a 4‐layer DT array coil consisting of 2 double‐layer ToRo‐setups (both X‐nuclei and 1 H) has never yet been reported due to its high complexity.…”

“…To the best of our knowledge, a 4‐layer DT array coil consisting of 2 double‐layer ToRo‐setups (both X‐nuclei and 1 H) has never yet been reported due to its high complexity. Commonly, DT human head array coils consist of 2 or 3 layers . The double‐layer design contains 2 TxRx volume coils or TxRx arrays.…”

An eight‐channel sodium/proton coil for brain MRI at 3 T

“…Although a conventional degenerate mode birdcage has the potential for desirable excitation and reception properties, it is, in practice, difficult to achieve complete degeneracy because of the coupling between non‐adjacent neighbor elements . Although coupling can be dampened by strong tissue loading in high‐frequency implementations, we observed resonance frequency splitting at 32.6 MHz. By tilting the rungs away from the z ‐direction, the shared triangular vertices provided a means to decouple nearest and next‐nearest neighbor coils using local lumped elements (Figure ).…”

Reducing signal‐to‐noise ratio degradation due to coil coupling in a receiver array for 35Cl MRI at 9.4 T: A comparison of matching and decoupling strategies

“…However, other nuclei such as chlorine ( 35 CI) are of interest despite their lower SNR ( 35 Cl provides approximately 20 times less signal than 23 Na and 23 Na 12 000 times less signal than 1 H) due to the additional diagnostic information they can provide. Next to different spectroscopic methods, 35 Cl MRI has been found in previous preclinical and clinical studies to provide further insights into cellular metabolism . Although the SNR limitation has been mitigated in several studies by the use of ultrahigh field scanners (21 T, 9.4 T, 7 T), further gains can be obtained from using purpose‐built radio frequency (RF) setups.…”