SQUID measurements of human nerve and muscle near-dc injury-currents using a mechanical modulation of the source position

Near-dc ionic currents arise after injury of nerves. The detection of their concomitant magnetic fields requires new techniques, to be applied in the growing field of biomagnetic measurement technology. The mechanical modulation of the source-to-detector distance enables monitoring of such slowly varying magnetic fields. In this report we describe technical details of the modulation device, including signal processing and system performance. The functionality of the device is demonstrated with an investigation on an in vitro human nerve specimen and with an in vivo investigation, performed with a patient undergoing a diagnostically indicated muscle biopsy.