Detection of brainstem auditory evoked magnetic fields using a SQUID magnetometer with a variable baseline

This study focuses on the detection of ABR magnetic fields using a SQUID magnetometer with a variable baseline. We developed a highly sensitive dc-SQUID system. The SQUID magnetometer has a first-order gradiometer with a variable baseline, i.e., the distance between two co-axial coils. ABR signals, which are generated from a brainstem in a deep part of the brain, are very weak fields. We measured the ABR magnetic fields using three gradiometers which have different baselines: 30 mm, 50 mm and 80 mm. In this experiment, we were able to obtain the best signal-to-noise ratio using the gradiometer with the 50 mm baseline.