Quantum Sensing the Brain Without Need for Cryogenics
(PhysicsWorld) A collaborative research team at the University of Nottingham’s Sir Peter Mansfield Imaging Centre and the Wellcome Centre for Human Neuroimaging at University College London, funded by the UK National Quantum Technologies programme and Wellcome is developing quantum enabled magnetic field sensors that offer sensitivity without the need for cyrogenics.
For many years the only viable option for imaging brain function on the superconducting quantum interference device (SQUID) – a cryogenic sensor that relies on quantum tunnelling through an insulating gap between two superconductors (the Josephson effect). The tunnelling current is a function of magnetic flux through the SQUID.
To maintain their superconductivity, SQUIDs must be cooled to –269 °C, which limits the design and deployment of MEG scanners. First, because they operate at such low temperatures, a thermally insulating gap must be maintained between the sensor and the patient’s head to prevent injury. Because magnetic field decays with distance squared, this gap limits sensitivity to the brain’s magnetic field. Second, cryogenics mean that sensors must be fixed in position above the head inside a cryogenic dewar, which means that if a patient moves their head relative to the scanner, the quality of the data goes down drastically. Just a 5 mm shift can render data useless, and many people cannot tolerate this environment. The fixed nature of the sensors also results in a one-size-fits-all helmet. This is a significant barrier to scanning young children and babies, since the helmet is much too large. Finally, the complex combination of SQUID sensors, control electronics and cryogenics makes MEG expensive.
Recent commercialization by the US company QuSpin has made optically pumped magnotometers (MEG( robust, easy to use and readily available, while miniaturization has made the most recent generation small and lightweight (similar to a Lego brick in both size and weight). Based on this new design, our team has integrated OPMs into a working prototype MEG device. Because they are so small and don’t need cryogenics, OPMs can be mounted directly on the surface of a human head, increasing sensitivity by removing the thermally insulating gap and getting the sensor closer to the brain.
Based on this new design, the team has integrated optically pumped magnetometers into a working prototype MEG device. This also allows the sensor array to move with the head, making the MEG measurement resilient to subject motion. Flexibility of OPM placement means an array can adapt to any head size, enabling babies and children as well as adults to be scanned with the same system. The lack of complex cryogenics also means that OPM-based MEG systems are ostensibly cheaper to produce and run. This technology therefore allows MEG to evolve, making systems more practical, more powerful, significantly cheaper and consequently much more suitable for clinical use.