Dynamic recording of the lateral distribution of biomagnetic fields

The measurement of magnetic fields of centimeter-sized objects with high magnetic-field, lateral and temporal resolution is of great interest for physical and biomedical research. Using current measurement technologies based on SQUID arrays, the resolution is limited by technological factors such as the sensor size and the sensor-target-distance due to the cryogenic cooling. Optically pumped magnetometers (OPM) allow for first measurements of magnetic fields with a millimeter resolution. However, these measurements are currently performed sequentially by scanning the object of interest. This prevents a synchronous measurement of the magnetic field with high spatial and temporal resolution. In this project, we want to develop new methods and technologies that allow for the measurement of magnetic fields of centimeter-sized objects with lateral resolutions in the range of millimeters, a magnetic field resolution in the range of picoteslas, and a bandwidth of 100 Hz. The measurements should be feasible at external magnetic fields of about 50μT, the typical strength of the earth’s magnetic field in our latitudes, without the need of costly magnetic shielding. To realize this objective, novel optically pumped magnetometers need to be developed. This requires both the development of a new mode of operation for optically pumped magnetometers, which, for the first time, allows for the parallel dynamic recording of two-dimensional magnetic fields, as well as the adaptation of integrated optical absorption cells to the requirements arising from the new mode of operation and the targeted lateral resolution. In addition, new methods for solving the magnetic inverse problem are to be developed, which allow on the one hand to adjust the parameters of the measurement system and on the other hand to reconstruct the sources of the magnetic field inside the examinated object. The recording system and the reconstruction algorithms are to be validated against measurements with special technical phantoms. The realization of this innovative measurement system opens up a variety of applications. An important example is the measurement of biomagnetic fields in animal experimental research. The measurement of magnetocardiograms of small animals (e.g. mice) with high spatial and temporal resolution could e.g. be used for monitoring the effect of drugs with high throughput rates. The measurement of magnetoencephalograms of small animals is of high interest for neuroscientific research on epileptic activity, for which intracortical currents need to be reconstructed with high spatial resolution due to the small size of cortical areas in small animals. The technological basis for both applications should be established with the development of the magnetic measurement system and the corresponding inverse imaging methods in this project.