Abstract:

Neuromagnetic imaging is a relatively new diagnostic tool for examination of electrical activities in the nervous system. It is based on the non-invasive detection of extremely weak magnetic fields around the human body with superconducting quantum interference device (SQUID) detectors. Often the equivalent current dipole model is used to describe the centre of the electrical activity. New current density reconstruction methods enable the imaging of the spatial extent and structure of neuronal activities. For practical use in medical diagnosis a combination of the abstract neuromagnetic images with MR or CT images is required in order to match the functional activity with anatomy and morphology. The neuromagnetic images can be overlaid onto three-dimensional morphological images with spatially arbitrarily selectable slices. The matching of both imaging modalities is discussed. On the basis of the detection of auditory evoked magnetic fields, neuromagnetic images are reconstructed with linear estimation theory algorithms. The MR images are used as a priori information of the volume conductor geometry and allow an attachment of functional and morphological properties.

Abstract:

A 19-channel SQUID system for biomagnetic measurements has been developed. This system differs from standard instruments in its modular approach. Various gradiometers can be coupled to the SQUIDs, the cryogenic system allows the exchange of single channels and the electronics is based on a cassette system. Problems with thermal insulation, vibrations of the gradiometers and tilted gradiometer geometries are discussed and solutions are presented.

Abstract:

Ziel dieses neuen medizinischen Diagnoseverfahren ist es, mit sog. supraleitenden Quanten-Intererenz-Detektoren (SQUIDs), die durch neuronale Ströme im Gehirn hervorgerufen magnetischen Felder außerhalb des menschlichen Kopfes zu messen, um so ein Bild von der Funktion des Gehirns zu erstellen.

Abstract:

A modular low-noise seven-channel SQUID-magnetometer for biomagnetic measurements was developed. The DC-SQUIDs are prepared by thin film technology based on the materials NbN-MgO-NbN, and show a flux noise below 10 μΦ0/√Hz. The signal is picked up with first-order wire-wound gradiometers of 2-cm diameter and coupled to the SQUIDs by integrated coupling coils. Individual channels can be replaced from the system, and various gradiometers can be used giving a flexible modular system. The electronics are based on the flux-locked-loop method extended by a bias modulation technique to reduce 1/f noise. The overall system noise is below 20 fT/√Hz. Biomagnetic measurements on auditory evoked fields have been carried out

Abstract:

Foreign Patent Documents from GermanyThe invention relates to a method of reconstructing the spatial current distribution in a biological object, at least one component of the magnetic field produced by the current sources being measured at a number of points outside the object, after which the current distribution at the volume elements situated within the object is reconstructed from the measuring values. In order to improve the accuracy of reconstruction, in a representation containing the morphological structure of the object the surfaces are specified on which the current sources are presumably present, the reconstruction being limited to the volume elements which are situated on these surfaces