Biomagnetic research in gastroenterology

Humans rely on their gastrointestinal system for providing the body with a constant supply of nutrients, water and electrolytes. The food must be digested (reduced physically and chemically to a molecular level) to be absorbed in the small intestine. Since both digestion and absorption depend on diffusion the flow of nutrients along the small intestine (GI transit) must be compatible with the rates of both these processes. GI transit depends on motions of the intestine walls, caused by contractions and relaxations (motor activity) of the muscle layers, which in turn are governed by electrical signals. So far in the clinical routine, GI transit has been studied by methods based on X-rays and radioisotopes, and motor activity by means of pressure recordings obtained by catheters passed by mouth or nostrils. Moreover, electrical activity recordings present important drawbacks. The use of magnetic measurements to study the gastrointestinal tract can be divided in two categories, one concerned with magnetic fields produced intrinsically by the electric currents of organs and the other with magnetic fields produced by magnetic materials that are ingested. In the first group, magnetic measurements are used to detect electric currents associated with the gastrointestinal tract. In the second group, the fields produced by ingested magnetic markers (MM) or tracers (MT) can be measured at the surface of the torso, allowing determination of the position, time course, quantity and state of order yielding information about the gastrointestinal motility. Biomagnetic techniques in some cases can represent an alternative, and in others a unique way to study the gastrointestinal tract. It is interesting to note that the scenario provided by GI applications of biomagnetism integrate all the possible fields yet measured in humans: those from electric current as in the brain and heart, those from paramagnetic substances as in the case of the liver and, finally, magnetic fields produced by ferromagnetic particles as in the case of magnetic markers and tracers. There is hope that in the future more information about the GI tract or even more comfortable exams would be possible by biomagnetic means. The past achievements were described in the 8 and 10 International Conferences on Biomagnetism [1,2] and in Andrä et al [3]. In the following sections, a survey of the work performed by some groups in the area will be reviewed and updated, concluding with some possible problems to be tacked by biomagnetic means.