A spatiotemporal dipole simulation of biomagnetic fields from gastric electrical activity

We simulated the magnetic fields from electrical activity of gastric smooth muscle using current dipoles with fixed location and time-varying moments. Dipoles were assigned frequencies, phases, and magnitudes characteristic of the known spatial properties of cellular oscillators in gastric smooth muscle. Additionally, we simulated cellular uncoupling by introducing random phase differences. We calculated extracorporeal magnetic fields from these source configurations for a multichannel SQUID magnetometer. Autoregressive spectral analysis was applied to determine frequency characteristics of both normal and uncoupled gastric magnetic fields. For normal muscle, propagation of gastric electrical activity was evident in time-sequenced isocontour plots of magnetic field strength, which were used to determine propagation velocity and direction. Uncoupled smooth muscle was less coordinated and absence of propagation or retrograde propagation was indicated in time-sequenced isocontour plots. The noninvasive measurement of gastric magnetic fields allows quantitative determination of the state of health of gastric smooth muscle.