Microendoscopy for molecular imaging inside the human lung

Abstract

One of the greatest challenges facing modern medicine is the inexorable rise of multidrug-resistant infections. In addition to better antibiotic stewardship, this challenge demands improved methods of diagnosis and treatment. Pulmonary diseases, which are responsible for a significant burden of disease and death worldwide, are among the conditions for which diagnosis must be improved. Little is currently known about the processes that drive lung disease. The ability to accurately diagnose and stratify patients would thus help clinicians overcome one of the main challenges presented by patients with severe respiratory diseases in the intensive care unit (ICU), and would help prevent the overuse of antibiotics. In conjunction with flexible bronchoscopy, which is routinely used in the ICU, microendoscopy can be used for in vivo examination of the lung. In this process, a narrow optical-fiber imaging bundle is inserted through the working channel of a bronchoscope, thus allowing images to be obtained from deep within the lung. Single-color confocal microendoscopy has previously been evaluated for distal lung imaging (generally with green fluorescence).1 Tissue autofluorescence will, however, often mask disease targets at this excitation wavelength (488nm). As a result, there is a pressing need to shift fluorescence microendoscopy into the red and near-IR region, where autofluorescence is much weaker. The lack of tools and approaches that can be used to interrogate the biology of the distal human lung in situ has been a significant hurdle in developing and evaluating new treatments of pulmonary infection and inflammation. Driven by this requirement, we are hoping to empower clinicians to perform a molecular optical biopsy with immediate bedside results. To this end, we are developing camera-based solutions2 that provide a robust and economical route to multicolor fluorescence detection. Our initial two-color widefield fluorescence microendoscopy system3 (see Figure 1) comprises off-the-shelf commercial components. Light from two LEDs (with center Figure 1. System diagram of our two-color fluorescence system. Two LEDs (with center wavelengths of 470 and 625nm) are combined with a dichroic mirror. Illumination from these LEDs is sent to the microscope objective via the emission filter and another two-band dichroic mirror. Fluorescence that is returned from the imaging bundle is then focused onto the color CMOS camera via a tube lens with a focal length of 200mm.