Abstract

In general, the medical community has accommodated for the need to post-procedurally fix, embed, section and stain tissue biopsies to diagnose disease. However, histopathology is a time-consuming and inefficient practice: delaying diagnosis and preventing real-time, closed-loop decision making. Further, the need for invasive biopsy and the limited amount of tissue actually examined lead to sampling bias such that the presence of disease can never be fully ruled out. A technique capable of making equivalent observations of cellular structure and molecular characteristics rapidly, and in situ could significantly improve patient care and cost. Several variations of optical tools for in vivo microscopy of tissue have already been developed. Optical coherence tomography (OCT), for instance is one of few techniques already used clinically. However, although OCT provides impressive penetration depth through layered tissues, it relies on optical reflectance from structural variations in the tissue, which prevents cellular level resolution and molecularly specific contrast. On the other hand, confocal laser microendoscopy (CLE) allows for molecularly specific diagnosis of tissues, similar to high resolution ex vivo confocal microscopy of stained histological samples. Though many implementations of CLE have been developed, current versions suffer from small fields of view, slow imaging speeds and fixed or limited depth scanning capabilities, limiting their practicality for screening large areas of tissue and layered tissues. Despite the lack of practical implementations available, in vivo confocal fluorescence imaging has been shown to have high sensitivity in disease typing and grading. 95% of doctors polled in one study agreed that CLE should be used in the detection of Barrett’s Esophagus. Another 87% agreed that CLE is more accurate than ERCP with brush cytology and/or forceps biopsy, which is the standard of care for determining malignant biliary strictures [1. In general, fluorescence imaging of tissues in vivo can provide the contrast needed to distinguish normal from diseased tissue in a variety of tissue surfaces, ranging from the gastrointestinal tract to the lungs [2. Furthermore, the molecular specificity of fluorescence imaging may allow visualization of molecular disease biomarkers before structural changes become visible through traditional white light endoscopy and OCT. Fluorophores that target known disease biomarkers are an active field of research and will augment fluorescence imaging as the next generation of dyes is developed. Given the promising sensitivity of fluorescence imaging, there is a need for high speed, volumetric implementations which allow rapid, cellular-level examination of tissues both in situ and in fresh biopsies.

© 2016 Optical Society of America