Use of a 3-D Wireless Power Transfer Technique as a Method for Capsule Localization

Capsule endoscopy has been heralded as a technological milestone in the diagnosis and therapeutics of gastrointestinal (GI) pathologies. The location and position of the capsule within the GI tract are important information for subsequent surgical intervention or local drug delivery. Accurate information of capsule location is therefore required during endoscopy. Although radio frequency (RF)-based, magnetic tracking and video localization have been investigated in the past, the complexity of those systems and potential inaccuracy in the localization data necessitate the scope for further research. This article proposes the dual use of a wireless power transfer (WPT) configuration as a method to enable the determination of the location of an endoscopic capsule. Measurements conducted on a homogeneous agar-based liquid phantom predict a maximum error of 12% between the calculated and measured trajectories of the capsule in a working volume of 100 mm $\times 100$ mm $\times 100$ mm

Design of an Electromagnetic Coil Array for Wireless Endoscope Capsule Localization

Wireless capsule endoscopy is a technique that visualizes mucosa of gastrointestinal tract. The first wireless capsule endoscope was developed in 2001, and since then, the tech-nology has been in constant development. With its reduced amount of discomfort, ability to visualize the whole gastrointestinal tract and many interesting future prospects, capsule en-doscopy is challenging the conventional procedure, in which a camera module at the end of a tube is inserted to the gastrointestinal tract. In general, the method can be used to diagnose many diseases, such as cancers, Celiac disease and Crohn’s disease. In order to achieve all the future prospects of the technology, for example, active steering of the capsule, biopsy and drug-delivery with the capsule, challenge of detecting the cap-sule’s position and orientation inside human needs to be overcome. Therefore, the localiza-tion challenge is considered in this thesis. The aim is to select an optimal method for localiza-tion based on current research, and to model and develop a prototype that could be utilized in capsule localization. The designed sensor array is evaluated with the help of finite element method -based modelling, sensitivity analysis and practical experiments. Based on the studied literature, an active magnetic field strength -based localization tech-nique was selected for further analysis. According to the literature, the method provides high accuracy and could also be utilized in other purposes, for example, wireless charging and ac-tive locomotion of the capsule. In addition, the method does not suffer from attenuation of the fields within a human body. Therefore, theoretical basis of the magnetic field strength -based localization was presented, and four electromagnetic coil arrays were designed for sensitivity analysis. Contrary to many developed arrays seen in the literature review, all the designed systems were planar, in order to develop a system that could be fitted, for instance, inside a hospital bed. Based on the sensitivity analysis, an array with relatively large sensitivity and optimal number of measurement channels was selected for practical study. In addition, pos-sible markers that could be fitted inside a regular sized endoscopic capsule were numerically modelled. It was found that a resonated solenoid marker with ferrite core causes the largest voltage compared to other modelled targets, and therefore it was constructed for experi-ments. The whole array was built and equipped with electronics and measurement devices to be able to perform testing. Two channels of the array were selected for example measurements, and the results were analysed and compared with modelled values and sensitivity patterns. The system was tested at multiple different heights and positions, and the effect of changing the marker’s orientation with respect to the array was analysed. It was found that the system gives a reasonable response when the marker is oriented along the excitation magnetic field. With this orientation, it was possible to measure significant voltages caused by the marker even at distance of 25 cm from the array. However, when the marker was oriented so that the excitation field could not properly excite it, the measured voltages got smaller. In addition, at certain orientation, the measured voltages did not seem reliable because voltage caused by the marker could not been discriminated from the noise of the system. The study indicates that the method is suitable for localization of resonated solenoid sample with ferrite core, but further improvements are needed to make the system work at each position and orientation of the marker. In addition, an inversion algorithm that estimates marker’s position and orien-tation based on the measured voltage needs to be integrated to the system

Localization and Tracking of Intestinal Paths for Wireless Capsule Endoscopy

Wireless capsule endoscopy (WCE) is a non-invasive technology used for visual inspection of the human gastrointestinal (GI) tract. Localization of the capsule is a vital component of the system, as this enables physicians to identify the position of abnormalities. Several approaches exist that use the received signal strength (RSS) of the radio frequency (RF) signals for localization. However, few of these utilize the sparseness of the signals. Due to intestinal motility, the capsule positions will change with time. The distance travelled by the capsule in the intestine, however, remains more or less constant with time. In this thesis, a compressive sensing (CS) based localization algorithm is presented, that utilize signal sparsity in the RSS measurements. Different L1-minimization algorithms are used to find the sparse location vector. The performance is evaluated by electromagnetic (EM) simulations performed on a human voxel model, using narrow-band (NB) and ultra wide-band (UWB) signals. From intestinal positions, the distance the capsule has travelled is estimated by use of Kalman- and particle filters. It was found that localization accuracy of a few millimeters is possible under ideal conditions, when the RSS measurements are generated from a path loss model. When using path loss data from the EM simulations, localization accuracy on the order of 20-30 mm was achievable for NB signals. Use of UWB signals resulted in localization errors between 35-60 mm, depending on frequency range and bandwidth. From generated intestinal positions, the travelled distance was estimated with a minimum accuracy of a few millimeters, when using a VNL Kalman filter and moderate amounts of observation noise. The results are found from a limited amount of data. In order to increase the confidence in the presented results, the performance of the localization algorithm and the filters should be evaluated with a larger number of datasets