A Study of Capsule Endoscopy Orientation Estimation Using Received Signal Strength Katjana Krhac 1 , Kamran Sayrafian 2 , Mehdi Alasti 3 , Kamya Yekeh Yazdandoost 4 , Dina Simunic 1 1 Faculty of Electrical Engineering and Computing, University of Zagreb, Croatia 2 Information Technology Laboratory, National Institute of Standards & Technology, USA 3 AdGen Telecom Group, USA 4 Department of Electrical Engineering and Automation, Aalto University, Finland Abstract— Comprehensive study of wireless communication for ingestible electronics is a very challenging task. To initiate the study on wireless capsule endoscopy, an innovative immersive platform containing an enhanced 3D human body model has been developed. This platform allows for flexible placement of a capsule inside the gastrointestinal (GI) tract and multiple receivers around the abdomen area. It is shown that any directionality (or equivalently null) in the antenna radiation pattern can be exploited to sense changes in the orientation of the capsule through observation of the S21 vector at a set of on-body receivers. Two methodologies i.e. complex cross-correlation and Minkowski distance were used to assess capsule orientation estimation with respect to a reference position. The study was performed within the Ultra-Wide Band frequency range as this technology is considered to be an attractive candidate for the next generation of wireless capsule endoscopy. Keywords—Wireless Capsule Endoscopy; Orientation Estimation; Ultra-Wide Band; Correlation Coefficient I. INTRODUCTION Endoscopy procedure plays a significant part in nearly all GI-related diseases as well as a crucial role in clinical research. It is estimated that more than 20 million GI endoscopies are performed each year in the United States [1]. A Wireless Capsule Endoscopy (WCE) is an ingestible capsule equipped with a miniaturized video camera. It provides a minimally-invasive alternative imaging technology for the entire Gastrointestinal (GI) tract of the human body. WCE is the only painless, and effective diagnostic technology for various diseases such as obscure gastrointestinal bleeding, tumors, cancer, Crohn’s disease, and celiac disease. The breakthrough impact of WCE in medicine is that they allow observation of abnormalities in the entire 5 m to 7 m length of the small intestine from locations that are not accessible by today’s conventional endoscopy or colonoscopy technology. Eighteen years after the first invention of this technology, positioning and mapping metrology science in this area is still in its infancy. As a result, doctors receive clear pictures of abnormalities such as bleeding and tumors inside the GI-tract, but they have no way to determine their precise locations within the body or the relative distance of the abnormality from an anatomic landmark such as the pylorus or the ileocecal valve. This is due to lack of knowledge about location and orientation of a capsule at the time when an image is taken. Lack of such critical information necessitates follow-on use of expensive and invasive testing such as deep enteroscopy, CT enterography, or even surgery to determine the site of the tumor, lesion, or bleeding. The elasticity of the GI tract and looped and folded nature of some its components (e.g., small intestine) along with variable speed and irregular motion pattern of a WCE pose several unique metrology challenges for this problem. Since, the next generation of endoscopy capsules are expected to deliver higher quality images or even videos as well as more diagnosis and therapeutic functionality, in this study, Ultra-Wideband (UWB) technology has been considered for the wireless communication links between the transmitter antenna inside the capsule and the receiver’s nodes located on the body. Despite the high attenuation, higher bandwidth (i.e. data rate) and lower complexity of the transceiver makes UWB an attractive candidate for future WCE. To the best of the authors’ knowledge, previous investigation of capsule position estimation or orientation in the literature has not considered unlicensed UWB frequency band. Recent publications and research activities on WCE is mostly focused on developing accurate position estimation methodologies [2,3,4,5,6]; however, as the miniaturized camera in these capsules do not have a wide view angle, knowledge of the capsule orientation inside the Gastrointestinal tract could also be a valuable information for the physicians who review the transmitted images. This adds another layer of complexity to the already challenging localization problem for such capsules. Previous research on the detection (or control) of capsule orientation involved using magnetic field [4]. In this paper, a preliminary study of orientation estimation using the received signal strength by a set of receivers located on the patient’s abdomen area is presented. Another challenge in studying localization or orientation estimation of a WCE is the platform that is