New pTx HF antennas for head/neck ultra-high field MRI at 7T, 9.4T and 11.7T

In UHF MRI, there is increasing interest in investigating the finest structures and functional processes beyond the brain. The detailed examination of the connections between the brain and the cervical spine is considered an important next step in UHF neuro MRI. While UHF MRI provides an inherently high signal-to-noise ratio (SNR) for high-resolution structural and functional MRI, there is no radiofrequency (RF) coil available today that provides RF signal coverage of the head and neck region. The most commonly used commercial 7 Tesla (7T) RF head coil covers the cerebrum, but has limited coverage below the cerebellum. The same limitations apply to UHF neuro MRI at 9.4T and 11.7T magnetic field strength, the most powerful MRI systems available to date.

In this cooperation project funded by the DFG and the French ANR (DFG Project number 530130666), two German (Erwin L. Hahn Institute for MRI, Essen (ELH) and Max Planck Institute for Biological Cybernetics, Tübingen (MPI)) and one French UHF MRI research group (CEA Paris-Saclay) are joining forces to overcome this limitation and develop three 16-channel transmit (Tx)/64-channel receive (Rx) RF array coils for head/neck UHF neuro MRI at 7T, 9.4T and 11.7T. The aim is to optimize signal coverage, parallel transmission (pTx) and SNR. In addition, variants of 16 Tx elements with loops and dipoles surrounding the head/neck region are investigated. The development of the Tx arrays includes a comparison of conventional two-layer Tx-only/Rx-only (ToRo) arrays with a new hybrid array consisting of transceiver (TxRx) and Rx-only elements. The hybrid design can simplify the structure of the RF array and improve reliability and safety. To increase the SNR in the center, combinations of loops and dipoles are considered as Rx elements. To enable additional B0 shimming, local B0 shim coils are integrated into the coil design.

Although the RF coils are to be used at three different field strengths and resonant frequencies, the mechanical and electrical design of the RF arrays will be standardized as far as possible in order to exploit maximum synergies in this Franco-German consortium. Important basic requirements are that all three UHF MRI systems are from the same manufacturer (Siemens), use the latest version of the pTx RF system and have the same software and sequences. The RF simulations, the pTx optimization, the computer-aided design of the coil housings, the safety tests and the application of pTx pulses are carried out in interactive cooperation.

Finally, subjects will be examined on all three MRI systems in order to investigate the UHF neuro-MRI performance of the new RF head/neck coils at 7T, 9.4T and 11.7T and to enable an intra-individual field strength comparison.