Bio-magnetic imaging using highly sensitive quantum magnetometers

This thesis describes the experimental results of highly sensitive quantum magnetometers, known as optically pumped magnetometers (OPMs), for bio-magnetic measurements. First, I show that commercially available OPMs can achieve enhanced spatio-temporal resolution compared to superconducting quantum interference devices (SQUIDs) when recording visual-evoked fields, using a standard visual paradigm. The improved resolution enabled the observation of novel neuronal findings in healthy participants. As OPMs were not originally developed for this neurophysiological application, the technology is not optimised for it, and the product design limits the final performance. In our lab, we developed a modular OPM sensor to surpass these limitations in terms of bandwidth and scalability. I tested the performance of this prototype for bio-magnetic measurements, and validated its use through a series of alpha-rhythm experiments over the visual cortex. Finally, I designed an experiment to explore the possibility of measuring the spinal cord evoked response using both the modular and the commercially available OPMs. Using peripheral nerve stimulations, I demonstrate the importance of the broader bandwidth for spinal cord measurements compared to the brain ones, and thus highlight the suitability of the modular OPM sensor for more sensitive measurements. Preliminary in-vivo spinal cord data using the commercial OPMs show simultaneous evoked fields of the brain and spinal cord.