A magnetometer system for medical use comprises one or more induction coils for detecting a time varying magnetic field. Each coil has a maximum outer diameter of 10 cm or less, and a configuration such that the ratio of the coil's length to its outer diameter is 0.9 or more, and the ratio of the coil's inner diameter to its outer diameter is 0.6 or more. Each induction coil comprises a magnetic core. The magnetometer system further comprises a detection circuit coupled to each coil and configured to convert a current or voltage generated in the coil by a time varying magnetic field to an output signal for use to analyse the time varying magnetic field.
