A Novel Marker Design for Magnetic Marker Monitoring in the Human Gastrointestinal Tract

Magnetic marker monitoring (MMM) is a technique to determine the motility of the gastrointestinal tract and to observe the dissolution of pharmaceutical compounds. Today's magnetic markers usually consist of magnetized magnetite. Because of their weak magnetic fields, highly sensitive sensor systems are required. For a wider class of applications, stronger markers and more flexible measurement setups are necessary. In this paper, a novel marker design is introduced. This marker comprises one permanent magnet and a compartment of iron powder in a magnetically unstable configuration. During dissolution of the pharmaceuticals, the powder is redistributed around the magnet, thereby altering the externally measured magnetic induction. Based on this design, magnetically marked tablets and capsules were prepared and their magnetic field during dissolution was observed. Magnetic induction values were between 16 and 0.2 μT at distances of 5-30 cm, which is considerably higher compared to the pico-Tesla range of conventional markers. During dissolution, the magnetic induction decreased by between 14% and 27%. These values could be confirmed in detailed finite element method simulations. In conclusion, the present results indicate that our novel marker design is well suited for MMM with more flexible sensor technologies, such as magnetoresistive sensors.