SQUID (superconducting quantum interference device) magnetometers have been used to study the magnetic activity associated with spike discharges occurring in interictal periods in patients with temporal lobe epilepsy. Magnetic field maps associated with specific spike discharges were obtained from measurements made with the SQUID at various locations on the skull. Improved mathematical models, which accounted for the head shape of the patient, the orientation of the SQUID, and volume current contributions, were developed to calculate the predicted magnetic field maps. Good agreement was obtained between the experimental clinical maps and those predicted by the model. The model also provided close agreement with the EEG profiles to permit comparison of the localizing accuracy of both the EEG and MEG techniques. A small implantable current dipole source flap was constructed, evaluated, and preliminary clinical data collected. This permits a source to be placed at a known location for evaluation purposes. SQUID instrumentation has been improved with the addition of a shielded room, a gantry support system, and a space digitizer.
