Novel Parallel-Transmit Head/Neck RF Array Coils for Ultra-High Field MRI at 7T, 9.4T, and 11.7T.

• Applicants: Dr. Nikolai Avdievich, Ph.D.; Professor Dr. Harald Quick
• Subject Area: Medical Physics, Biomedical Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530130666

In ultra-high field (UHF) neuro-magnetic resonance imaging (MRI) research there is increased interest in imaging fine structures and function beyond the brain. Detailed investigation of the interconnections between the brain and the cervical spine (C-spine) is considered an important next step in UHF neuro-MRI. While UHF MRI inherently provides high signal-to-noise-ratio (SNR) to support structural and functional MRI with high resolution, there is no radiofrequency (RF) coil available that provides simultaneous RF signal coverage for the head/neck region. The most widely used commercial 7-Tesla (7T) RF head coil covers the cerebrum but provides only poor coverage below the cerebellum. The same limitations apply for UHF neuro-MRI at 9.4T and 11.7T, the MRI systems with the highest magnetic field strength available for human MRI. In this project, two German and a French research site that all employ UHF MRI systems have joined forces to overcome this limitation and to develop three 16-channel (ch) transmit (Tx)/64-ch receive (Rx) RF array coils for human head/neck UHF neuro-MRI at 7T, 9.4T, and 11.7T. We will optimize signal coverage, the parallel Tx (pTx) performance and SNR of the arrays. Further, we will investigate various sets of 16 Tx elements including loops and dipoles and their combinations positioned in two or three rows surrounding the subject and covering the volume of interest. Tx array development will include a comparison of a common double-layer Transmit-only/Receive-only (ToRo) setup consisting of two nested Tx and Rx arrays, with a novel hybrid single-layer RF array coil consisting of a combination of transceiver (TxRx) elements with Rx-only elements. The hybrid design can substantially simplify the RF coil structure to render it more reliable and safer. To improve central SNR, we will also consider combining loops and dipoles in designing the Rx arrays. To provide additional B0-shimming, local B0 shim loops will be incorporated into the RF coil structure. Although the RF coils will be used at three different field strength and resonance frequencies, we aim at unifying the mechanical and electrical design of the RF arrays as far as possible to maximize synergies in this German-French consortium. As an important precondition, all three UHF MRI systems are from the same manufacturer, use the latest generation pTx RF system, and share the same software and sequences. RF simulations, pTx-optimization, computer-aided design of the housings, safety evaluations, and the use of pTx pulses will all be performed in interactive collaboration. All three UHF sites synergistically provide their unique expertise in this process and at the same time are responsible to adapting the RF head/neck coils to the respective field strength and MRI system. Eventually, head/neck subject scanning on all MRI systems will be performed to provide intraindividual evaluation and comparison of UHF head/neck neuro-MRI performance at 7T, 9.4T, and 11.7T.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Dr. Frank Mauconduit, Ph.D.