Submission to IEEE Reviews in Biomedical Engineering

1 One of the significant challenges in Capsule Endoscopy (CE) is to precisely determine the pathologies 2 location. The localization process is primarily estimated using the received signal strength from sensors in 3 the capsule system through its movement in the gastrointestinal (GI) tract. Consequently, the wireless 4 capsule endoscope (WCE) system requires improvement to handle the lack of the capsule instantaneous 5 localization information and to solve the relatively low transmission data rate challenges. Furthermore, 6 the association between the capsule’s transmitter position, capsule location, signal reduction and the 7 capsule direction should be assessed. These measurements deliver significant information for the 8 instantaneous capsule localization systems based on TOA (time of arrival) approach, PDOA (phase 9 difference of arrival), RSS (received signal strength), electromagnetic, DOA (direction of arrival) and 10 video tracking approaches are developed to locate the WCE precisely. The current article introduces the 11 acquisition concept of the GI medical images using the endoscopy with a comprehensive description of 12 the endoscopy system components. Capsule localization and tracking are considered to be the most 13 important features of the WCE system, thus the current article emphasizes the most common localization 14 systems generally, highlighting the DOA-based localization systems and discusses the required 15 significant research challenges to be addressed. 16