INSTITUTE OF PHYSICS PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 50 (2005) 4429–4444 doi:10.1088/0031-9155/50/18/012 Ellipsoidal electrogastrographic forward modelling Andrei Irimia and L Alan Bradshaw Living State Physics Laboratories, Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235-1807, USA Received 25 May 2005, in final form 6 July 2005 Published 7 September 2005 Online at stacks.iop.org/PMB/50/4429 Abstract The theoretical and computational study of the electromagnetic forward and inverse problems in ellipsoidal geometry is important in electrogastrography because the geometry of the human stomach can be well approximated using this idealized body. Moreover, the anisotropies inherent to this organ can be highlighted by the characteristics of the electric potential associated with current dipoles in an ellipsoid. In this paper, we present a forward simulation for the stomach using an analytic expression of the gastric electric potential that employs a truncated expansion of ellipsoidal harmonics; we then demonstrate that an activation front of dipoles propagating along the body of an ellipsoid can simulate gastric electrical activity. In addition to the usefulness of our model, we also discuss its limitations and accuracy. (Some figures in this article are in colour only in the electronic version) 1. Introduction The scientific area of electro- and magnetogastrography (EGG and MGG) has become increasingly important in recent years to both clinicians and biophysicists due to the ever- increasing body of evidence indicating that noninvasive methods of gastrointestinal (GI) disease diagnosis are within sight. Physiologically, electric fields in the human gut are produced by the exchange of ions between cells in the gastric smooth muscle. The movement of these ions creates electric currents that generate magnetic fields; although of the order of pT, these fields can be detected noninvasively using Superconducting QUantum Interference Device (SQUID) magnetometers. SQUIDs are devices equipped with Josephson junctions that are capable of sustaining supercurrents below the critical temperature of the metal of which these junctions are made. Due to their design and certain properties of superconductors, SQUIDs have the ability to measure extremely small changes in magnetic flux, which makes them unrivaled among magnetomers in terms of sensitivity. SQUIDs have been used to measure the weak fields of various human organs, including the brain (electro- and magnetoencephalography), heart (electro- and magnetocardiography (Jenks et al 1997)) and the stomach (EGG and MGG). With over 60 million patients receiving treatment for GI diseases every year just in the US, the importance of early diagnosis and 0031-9155/05/184429+16$30.00 © 2005 IOP Publishing Ltd Printed in the UK 4429