Periodic Reporting for period 3 - AROMA (Accurate, Reliable and Optimized functional MAgnetic resonance imaging at unprecedented field strength for unique exploration of the human brain)
Reporting period: 2023-05-01 to 2024-08-31
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 June 2023 but then was converted to 8Tx-31Rx given some encountered transmit problems. 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 cyrostat, 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) for 11.7T preparation. An important discovery arising from the gradient-magnet interaction tests is the impact of 3rd order shim coils, even at lower fields. Unplugging them has proved to be beneficial for layer fMRI at 7T to get rid of so-called fuzzy ripples. An interesting study on SNR versus field strength on a phantom also was performed. It confirmed with end-of-the-chain measurements that the SNR potential was well and alive at 11.7T. DZNE and CEA together developped new pulse design methods to implement slab-select acquisitions with pTx universal pulses. The University of Maastricht has developped a spiral-VASO approach with dedicated workflow and reconstruction pipeline at 7T. ETH has explored different motion compensation techniques using different methodologies. The 3D servo-navigators now is the solution retained for simplicity to avoid sensors in the vicinity of the volunteers' heads. New recent work has combined both motion correction with physiological noise correction up to first order. DZNE likewise now implements real-time prospective motion correction by using field probe data combined with FID navigators. DZNE and ETH have worked together to implement on the Siemens platform the method developped by the latter. It is now operational in Bonn and has been deployed to some extent at 11.7T in NeuroSpin. Skope has designed their 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. 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 in 2021, after nearly 20 years of R&D. Filing for authorization to scan human volunteers occured in Dec 2022 towards the French regulatory body (ANSM) and an ethics board. Twenty healthy volunteers were scanned at 11.7T between July 2023 and February 2024 and no adverse effects were detected. The scans yielded very high resolution T2*-weighted images of excellent quality but also emphasized some challenges like motion and transmit efficiency, to be adressed by the AROMA tools later on. Importantly, this first series of tests was exploratory and necessary to confirm the innocuousness of the 11.7T magnetic field on humans. It is a massive milestone in the life of the project which led to a lot of media attention culminated by congratulations on X of Emmanuel Macron himself. NeuroSpin now seeks a second approval from ANSM to scan again in vivo on a larger scale and to fully deploy the AROMA techniques to complete the project.
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 in preparation in the UK, the University of Glasgow now is a central actor. The PI, Shajan Gunamony, now participates in the british project. The development of the Pasteur package with universal pulses on the software platform of the 7T Siemens Terra could have implications for clinical routine at 7T. More sequences and tools have been developped and are currently unmatched in the industrial sector. Following the work, Siemens has offered funding for a PhD thesis to work on pTx jointly with CEA. Some Philips users have furthermore converted the format of some universal pulses developed on the Siemens platform to make them work on their systems, making the approach even more universal. The sequences allow solving to a great extent the RF field inhomogeneity problem in the brain at 7T, 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 disseminated to about 30 sites worldwide. In this context, the University of Glasgow, DZNE and CEA together applied to an EIC transition grant to commercialize a new 7T RF coil, incorporating in the package universal pulses and SAR management. The market of 7T to date yet was deemed non competitive compared to other high-impact endeavors so that the application was unsuccessful. The impact of the third order shims revealed by the gradient-magnet interaction studies was also new. By shedding light on these problems, one can hope that vendors and gradient coil designers take them more into consideration.
Motion correction is 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 also at lower fields. It remains to be determined 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. Such technology thereby could be of use to verify the safety limits used in the mobile phone industry. Last but not least, the Skope technology has turned already invaluable at 11.7T. The company should thus benefit from additional exposure.
Motion correction is 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 also at lower fields. It remains to be determined 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. Such technology thereby could be of use to verify the safety limits used in the mobile phone industry. Last but not least, the Skope technology has turned already invaluable at 11.7T. The company should thus benefit from additional exposure.