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Accurate, Reliable and Optimized functional MAgnetic resonance imaging at unprecedented field strength for unique exploration of the human brain

Periodic Reporting for period 2 - AROMA (Accurate, Reliable and Optimized functional MAgnetic resonance imaging at unprecedented field strength for unique exploration of the human brain)

Reporting period: 2022-01-01 to 2023-04-30

The objectives of the project are to overcome the fundamental obstacles to leverage the potential of a unique whole-body 11.7 Tesla MRI scanner located at CEA (France). With greater magnetic fields however come greater challenges. The nature of the problems compared to lower field magnets is not new, but they are amplified. As a result, they require innovative actions to fetch and exploit the boost of signal to noise ratio delivered by the magnetic field. The vocation of the instrument is to provide non invasive means to explore the human brain with unprecedented details, i.e. its cognitive functions and associated pathologies. Zooming on the brain or acquiring data with boosted sensitivty could thereby provide knowledge hardly accessible with other modalities. The novel solutions developed in the AROMA project, although they are centered around the 11.7T problems, should have implications for lower field strengh MRI available in the clinic.
The radiofrequency coil used in MR exams is of paramount importance to excite the water magnetization and collect signal to reconstruct images. In this context, the partner in Glasgow in collaboration with CEA has performed electromagnetic simulations to tune different parameters and narrow down the optimal design. After one year, the coil design layout was complete. A 8Tx-8Rx prototype was built and tested at 11.7T to verify the electromagnetic simulations and confirm the transmit efficiency. The final 16Tx-32Rx of the coil was delivered in March 2023. CEA has coordinated the project, continued the commissioning of the 11.7T MRI instrument and the charaterization of the gradient-magnet interactions (acoustics, vibrations, power deposition in the He bath, field monitoring), developed an MR thermometry method to measure non invasively the temperature rise induced by RF pulses and has boosted parallel transmission performance at 7T (while still minimizing the impact on the workflow). An interesting study on SNR versus field strength (3T, 7T, 9.4T 10.5T and 11.7T) on a phantom was performed and published. It confirmed with end of the experimental chain measurements that the SNR potential was well and alive at 11.7T. Collaborative work of DZNE and CEA together gave rise to new and original pulse design methods to implement slab-select acquisitions with parallel transmission universal pulses (e. g. GRE, 3D-EPI and slab-SPACE). The University of Maastricht has kept working on a spiral-VASO implementation. ETH has explored different motion compensation techniques using different methodologies: field sensors, RF trackers and 3D navigators. The 3D navigators now is the solution retained for simplicity and to avoid sensors in the vicinity of the volunteers' heads. New recent work has combined both motion correction with physiological noise correction for field fluctuations induced up to the first order of the spherical harmonics decomposition. DZNE likewise now implements real-time prospective motion correction by using field probe data combined with FID navigators. Skope has designed, produced and tested their first clip on field camera at 11.7T and has kept optimizing its performance with further refinements. Field monitoring has turned to be an invaluable tool for troubleshooting the scanner and has spared the 11.7T users a lot of difficulties. Skope has also supported the entire consortium in their applications (Gradient Impulse Response Function measurements, k-space trajectory monitoring and MR thermometry). The first images acquired at 11.7T on a pumpkin were released Oct 7th 2021, after nearly 20 years of research and development. The project thus has benefitted from great media exposure with interviews for newspapers, radio and national TV. Importantly, filing for authorization to scan human volunteers occured in Dec 2022 towards the French regulatory body (ANSM) and the ethics board. After discussions and requested clarifications, approval was finally granted on Feb 22nd 2023. Although imaging will be performed, this first study, not part of the AROMA project, will mainly consist in studying the biological effects on 20 healthy adult volunteers while exposed to 11.7T. It was an important and necessary first step, and milestone, to later apply for a second approval to scan more volunteers within AROMA, once no adverse effects are first confirmed.
The transmit performance of the RF coil has been tested with a 8 transceiver coil prototype. With two other 11.7T MRI scanners (NIH USA and South Korea), and one possibly in preparation in the UK, the University of Glasgow now has unique experience at that field strength and is a central actor. The PI, Shajan Gunamony, has already been contacted to participate in the UK project. The development of the Pasteur package by CEA and DZNE, with universal pulses, on the software platform of the 7T Siemens Terra could have implications for clinical routine at 7T. More sequences and tools (e.g. slab-select capabilities) have been developped and are unmatched in the industrial sector. The sequences indeed allow solving to a great extent the RF field inhomogeneity problem in the brain, with zero time penalty for the user and no expertise required. It could be a game changer to leverage the potential of 7T scanners in the clinic. The package is available to the community under a C2P agreement and has been dissaminated to about 30 sites worldwide. The tools resulting from ERC proof of concept and FET Open grants, obtaining CE marking for parallel transmission at 7T towards the commercialization of the technology could be the subject of an EIC transition call for proposals. Some support from the European Commission was sought to investigate this possibility but the market of 7T to date was deemed non competitive compared to other high-impact endeavors that are proposed by other EIC-pathfinder consortiums. After years of discussion, Siemens however has finally approached CEA to negotiate some licensing rights. Motion correction is also of paramount importance and to date there is no clear game-changer in the industrial sector. The developments carried out by ETH and DZNE could lead to solutions of interest to the industrials who could benefit from them in their applications at lower fields. It remains to be determined when the tools are published, shared and used by the community whether the developments are worth a commercialization. Finally, the MR thermometry results published by CEA and Skope present the first strong evidence that there could be more heat dissipation in the brain than the theoretical models suggest. It is the first time that the small temperature rises induced by RF fields in MRI could be measured with such precision and accuracy, non invasively, in the human brain and in normal conditions. Such technology thereby could be of use to verify the safety limits used in the mobile phone industry, where the specific absorption rate (SAR) metric remains also the norm for simplicity. Last but not least, the troubleshooting of the scanner demonstrated with the Skope technology has turned already invaluable for experimental devices. After dissemination on the subject, the company should benefit from additional exposure and may sensitize the industrials about the importance of these measurements.More work towards this goal is in progress.