Improving tip position-estimation performance of gastric tube by compensating geomagnetic field with offset coils

To guide gastric tubes into the stomach correctly, we propose the position-guidance system of a permanent magnet attached to the tip of the tube using high-sensitivity magnetoresistance (MR) sensors placed outside the patient's body. To enhance the sensitivity of the magnetic sensors and improve the position-estimation performance, we employ a small offset coil surrounding the magnetic sensor to compensate the geomagnetic field and evaluate the effect of the geomagnetic field compensation. The results show that the mean value of the position-estimation error with the compensation was less than 10 mm, even when the distance between the permanent magnet and MR sensors is 190 mm, whereas the mean value without the compensation exceeds 10 mm when the distance is greater than 150 mm. This suggests that the proposed compensation method improves the performance and broadens the scope of application for different users, e.g., pregnant or obese patients, of the guide system.