Comparison of the amplitude/intensity function of the auditory evoked N1m and N1 components.

This study compared the intensity dependence of the auditory evoked N1 and N1m components in 10 healthy subjects. The evoked responses were recorded simultaneously at 33 channels for the auditory evoked potentials (AEP) and with a 37-channel magnetometer for the auditory evoked fields (AEF). They were satisfactorily modeled by a tangential and a radial dipole per hemisphere for the N1 component and a tangential dipole in the left hemisphere for the N1m component. The tangential dipoles showed different dipole characteristics. The amplitude of the AEP rose significantly with increasing stimulus intensity whereas the amplitudes of the AEF tended to plateau between the highest intensities. The magnetic dipole shifted to the surface of the skull with higher stimulus intensity whereas the electric tangential dipole moved to the center of the skull. The latencies decreased with increasing stimulus intensity.

High-resolution monitoring of the gastrointestinal transit of a magnetically marked capsule.

The purpose of this study was to demonstrate that it is possible to continuously monitor the gastrointestinal transit of magnetically marked, solid, oral dosage forms with multichannel biomagnetic measuring equipment and by magnetic source imaging (MSI) methods. For the investigations presented, a sucrose pellet was coated with powdered magnetite (Fe3O4) in poly(methyl methacrylate). Then, the pellet was enclosed in a capsule prepared from silicone rubber and magnetized to obtain a net magnetic dipole moment. After ingestion of the capsule, its magnetic field distribution over the abdomen was recorded for several time intervals with a 37-channel superconducting quantum interference device (SQUID) magnetometer. At each time point, the position of the capsule within the gastrointestinal tract was calculated from the measured field distribution, assuming a magnetic dipole model. The data presented here demonstrate that with this noninvasive method of magnetic marker monitoring it is possible to investigate the gastrointestinal transit of a solid oral dosage form with a temporal resolution in the order of milliseconds and a spatial resolution within a range of millimeters.