On the Accuracy of Wireless Capsule Endoscope RF and Visual Localization

Wireless capsule endoscope (WCE) has become one of the most popular inspection devices which provides visual investigation of entire gastrointestinal (GI) tract. While the other traditional (wired) endoscopic devices are usually used for colon and stomach inspection. Locating abnormalities such as tumors, polyps and bleedings with wireconnected endoscope in GI tract is simple as long as we could measure the length of the wires inside human body. When WCE is applied, however, this becomes a critical challenge of examination since there is no wires connected to WCE while physicians need to find the exact locations of WCE to identify the position of abnormalities. To locate the WCE accurately, methods have come up in last decade including time of arrival (TOA) based methods, received signal strength (RSS) based methods, phase difference of arrival (PDOA) based methods, electromagnetic methods and video-based tracking methods, etc.. In this thesis, the accuracy of TOA, PDOA and video based localization methods are analyzed. (1) We propose a novel video-based tracking technique based on maximum mutual information, which provides a more accurate measurement of the displacement and rotation of the WCE inside the large intestine. (2) We derive the Cramer-Rao lower bound (CRLB) of TOA ranging using a single tone inside homogeneous tissues to examine the accuracy of three TOA ranging techniques. Then we compare the accuracy of these ranging techniques in non-homogeneous tissues with that in homogeneous tissues. (3) We also apply PDOA based ranging technique exploiting phase difference of two signals. Since the phase difference is taken into consideration, the ranging ambiguity of single tone is eliminated. We evaluate the accuracy of the proposed PDOA ranging technique and compare with that of TOA techniques.