3-D Tracking System For The Micro Medical Devices In The Human Body Based On The Hall Effect Sensor Array And OpenGL Technology

As a significant trend of the medical diagnosis, the noninvasive technology has been revolutionized by the modern engineering technologies. Recently, a new non-invasive technique, the MEMS Medical Capsule has been developed which shows brilliant potential in the application of disease area observation, local drug release and wireless monitoring of the gastrointestinal parameters. Up to now, many MEMS Medical Capsules are available commercially, such as M2A, ESO-PILL NORIKA3 to name but a few. In clinical use, when the capsule is swallowed, it is critical for the doctor to precisely track the movement and location of the capsule in order to organize an effective diagnosis scheme. Thus how to wirelessly track the capsule inside human body has become an area of interest.So far, some methods have been implemented to wirelessly track a MEMS Medical Capsule, such as Magnetic Marker Monitoring (MMM), ECT, Digital X-ray Gastrointestinal Tract. However, the MMM technology is based on the DC-SQUID which is hampered by the high cost of practical use. The harmful radiation exposure is the weakness of both the X-ray imaging and ECT. Moreover, the low trace observability of X-Ray sets anther obstacle for easy application of capsule tracking. To provide a low-cost, harmless and easy-to-operate method, the magnetic tracking technique was early developed by Donald G. Polvani et al (1998), whose patent presented the sketch of magnetic positioning system including the foundation of algorithms on paper. V.Schlageter, et al (2001,2002) described a magnetic sensing technique with the Hall Sensor array. They introduced a real-time sensing hardware, which is, however, not wearable. Based on the research aforementioned, we develop a wearable tracking system based on the Hall Effect and Quiescent Magnetic field. This system is composed of a wearable vest and the software interface. The Hall Effect sensing modules detect the magnetic field signals of a tiny magnet assembled in the capsule, then the signals are collected by a USB data collecting card and transferred to a workstation where data procession and calculation are accomplished, finally the location of the capsule is presented in the three-dimension software interface.To accomplish the real-time data collection and reduce the noise, some effective multi-channel data collecting and processing solutions are implemented. Several trial tests have been performed with relatively accurate expectation to justify the precision of the system. The results of the volunteer experiments compared with the X-ray image of the small intestine demonstrate that this system can effectively trace the motion of the capsule inside the twisted intestine.To limit the electromagnetic interference, the classic low passing circuit and a digital signal filter have been developed which restrain the electromagnetic noise effectively. However, the earth itself is a huge magnet with the same distributional characteristic of magnetic filed as our tiny magnet inside the capsule which can not be reduced by the methods implemented for the electromagnetic noise reduction. To eliminate the earth magnetic interference in a low cost and effective way, a method designated by the Magnetic Interference Level Labeling is developed.The Ideal Magnetic Dipole Model also leads to the detecting error; we discussed the limitation of the model when the magnetic source locates not far from the detection sensor.From the results of the experiments, we can see the trace reported by the system precisely reflects the actual traveling path of the capsule. The relative locating error of the system was approximately around 10%. Thus conclusively, the results of this trial test demonstrate that the system is qualified to locate the trace of the capsule. The volunteer experiments have been tested for clinic use, the results of which indicate that the trace basically represents the distribution of the small intestine even though it highly twists. Meanwhile, the results also reflect this system effectively reduces the interference from the earth magnetic field which eases the practical use considerably.To improve the system accuracy and the observation quality, we focus on the efforts to decrease the systematic error, reduce the noise and make the mathematical model more accurate.The mathematical model of the tracking algorithm was simply based on the magnetic dipole when the magnetic source located far from the sensing module. However, in reality the magnetic dipole model is limited when the capsule moves close to the sensing module which leads to the low precision. Therefore the optimization of the mathematical model of the tracking algorithm is the main focus for further study.