Helmut Dipl Phys Reichenberger

MCG inverse solution: influence of coil size, grid size, number of coils, and SNR

Model studies were used to assess quantitatively the influence of gradiometer coil size, number of measurement points, size of measurement grid and signal-to-noise ratio (SNR) on the accuracy of the inverse solution from a magnetocardiogram. The human torso was modeled by an infinite half-space and the inverse solution was calculated by a moving dipole procedure. The most crucial parameter for inverse solution accuracy is the SNR. Up to a coil radius of 4 cm, the increasing SNR balances the loss due to field averaging, and the inverse solution is improved accordingly. A reasonable number of measurement points is about 15; using more points does not improve the inverse solution appreciably. in multichannel systems, grid size is limited by the size of the dewar. It is found that grid size is not crucial in the inverse solution; optimum size is an area of approximately 200-300 cm/sup 2/.<<ETX>>

Experience with a multichannel system for biomagnetic study

The components of the biomagnetic multichannel system Krenikon are described. The combination of biomagnetically yielded localizations with anatomic images gained from MR or CT is discussed as well as the enhancement of the signal-to-noise ratio by using a correlation technique. The overall localization accuracy is tested with technical phantoms. With volunteers measurements of auditory, visual and somatosensory evoked fields are performed to evaluate the system performance in vivo. Clinical studies were performed mainly with partners from the Universities of Erlangen-Nünberg and Ulm. The data acquisition time typically is 2-10 min which is tolerable both for the patient and the clinical staff. Electric potentials even with invasive electrodes can be recorded simultaneously with the magnetic fields. MEG gives important information for the presurgical diagnosis of epileptic patients and for the understanding of the epilepsy genesis. With MCG, centres of biologic excitation such as ventricular ectopies or accessory bundles in WPW syndrome have been successfully localized.

Design and Operation of a Biomagnetic Multichannel System

This paper describes the design and optimization of the KRENIKON® system for the measurement of magnetic fields of the brain and the heart. Aspects for the configuration of the sensor array are discussed. Special emphasis is given to the suppression of interferences by a combination of magnetic shielding with first-order gradiometers and to the construction of the gradiometer array in foil technology.