Tuberculosis afflicts one third of the population worldwide; more effective therapeutics are urgently needed. However, the slow growth rate of Mycobacterium tuberculosis, the causative agent of tuberculosis, hinders advancement in all areas of TB research. Fluorescent proteins have been widely utilized in real-time imaging of tuberculosis to track disease progression and evaluate therapeutic outcomes in live animals, but the sensitivity of this technique is limited by tissue absorption of fluorescence excitation light, which limits penetration particularly in the visible wavelengths. To circumvent the impact of tissue absorption of excitation light, we have applied a fiber bundle microendoscope to deliver fluorescence excitation light directly into the mouse lung. We have integrated this microendoscope into a whole animal imaging system to enable intravital excitation in the mouse lung combined with whole animal detection. Using the integrated intravital-excitation whole-animal imaging system, we have improved the detection threshold of tdTomato expressing M. bovis BCG strain during pulmonary infection to ~103 colony forming units (CFU). This detection threshold represents a ~3-fold improvement compared to epi-illumination in a whole animal imaging system, which normally detects ~106 CFU within the lungs of a mouse.
Dr. Kristen Maitland is associate professor and associate head in the Department of Biomedical Engineering at Texas A&M University. Her research focuses on the development of optical instrumentation for improved detection and diagnosis of disease, primarily cancer and bacterial infection.
To improve detection of early cancer, Dr. Maitland's lab has developed a multi-scale multi-modal optical imaging system currently being evaluated in a clinical trial. Fluorescence lifetime imaging is used for macroscopic guidance, followed by reflectance confocal microscopic detection of cellular changes associated with precancer development. Technical advances focus on miniaturization of the device and increased scanning speed using a tunable focus lens or spectral encoding of depth.
Dr. Maitland is developing optical sensing and imaging technologies to enable rapid diagnosis of bacterial infection, specifically tuberculosis. Optical fibers are used to excite fluorescence of novel near-infrared optical reporters inside the lung to detect and measure levels of bacterial infection. Fluorescence signal can either be detected from outside the body in small animals or through an optical fiber or fiber microendoscope.