Applications of Light Reflectance Sensing in the Gastrointestinal Tract with Ingestible Devices for Disease Diagnosis

Abstract

Disease diagnosis in the gastrointestinal tract can be challenging, often requiring difficult endoscopic procedures or expensive imaging techniques. Pill-sized ingestible sensors represent an alternative method for disease diagnosis in the gastrointestinal tract that is minimally-invasive and cost-effective, thus promoting patient adherence and preventative screening of diseases. In this thesis, I investigate the design of ingestible sensors that emit light and measure light reflectance in the gastrointestinal tract for three applications: the detection of gastric mucosal contact, the diagnosis of upper gastrointestinal bleeding, and the diagnosis of small intestinal ischemia. To enable these applications, I develop arrays of LEDs and photodiodes that monitor the changes in reflectivity of the tissue and changes in color of the tissue. The sensor arrays are fabricated and assembled in ingestible form factors and validated in ex vivo and in vivo experiments with swine. The results demonstrate that the sensing of light reflectance enables accurate differentiation of gastric mucosa versus gastric lumen for the detection of mucosal contact, accurate detection of gastric bleeding even in the presence of red drinks or gastric fluid, and accurate detection of small intestinal ischemia even in the presence of bile and chyme. For the application to diagnose small intestinal ischemia, I present initial mechanical and electrical designs of an ingestible capsule system that activates in the small intestines via the dissolution of a pH-sensitive polymer, then performs duty cycling to enable ischemia detection during the entire small intestinal transit time. I aim to continue the development and validation of these ingestible sensors with the vision of providing minimally-invasive devices to enable cost-effective screening and monitoring of gastrointestinal diseases and conditions.