The OPM-MEG project
Fig 1. Prototype of the fixation of the OPMs
The project aims the development of a MEG system based on the atomic optically pumped magnetometers (OPMs).
Conventional MEG systems register the magnetic induction with Superconducting Quantum Interference Devices (SQUIDs). Such systems are extremely expensive both in terms of OPEX and CAPEX due to the need of cooling the sensors with liquid helium. In 2017, the Quspin company issued the first ready-to-use high-sensitive OPMs, which can change the SQUID sensors for MEG measurements. Due to these sensors do not need cooling, usage of them can sufficiently decrease the cost of the MEG system, allowing to make it more susceptible to a wide circle of researchers.
OPMs have also some advantages, which are not related to the price. The construction of the sensors allowing to place them closer to the cortical electric sources, which increases the sensitivity of an OPM-based MEG system. Comparatively small linear size of sensors makes possible the adaptation of the sensitive part of the MEG system with respect to sizes and different shapes of the head. The comparatively small size of the overall OPM-MEG system allows a reduction of the size of the magnetically shielded room (MSR), decreasing consequently its price. In addition, the sensitive axis of the sensor may be changed, which, theoretically, allows to decrease the ill-posedness of the source localization inverse problem.
The possibility of usage of OPMs instead of SQUIDs in the MEG context was shown by several research teams in the world. Such a possibility has also been already checked by the Skoltech research team (see Fig.2).
The experimental setups existing in the world at the moment are the early prototypes. The ready-to-use OPM-MEG system is, however, currently far from being implemented and requires more research on the fields of stability and accuracy, optimal number and placement of the sensors on the head, OPM-oriented numerical methods for localization of the cortical electric sources. The project aims to create the ready-to-use OPM-based MEG system, including all the above.
The high-sensitive OPMs are based on the phenomenon of zero-field resonance, assuming a very low magnetic background. In order to satisfy this requirement, the MSR located at the MEG-center can be used. Also, the system under development needs an accurate and complete comparison with the existing SQUID-based MEG system, one of which is installed in the MEG-center (Elekta Neuromag MEG system).
Fig 2. Figure 2. Mu-rhythm registered with OPMs