Hypericin Fluorescence Imaging of Oral Cancer: From Endoscopy to Real-time 3-Dimensional Endomicroscopy

Oral cancers are conventionally diagnosed using white light endoscopy and histopathology. However, oral lesions can be difficult to visualize under white light. Fluorescence imaging can complement current techniques by highlighting lesional areas. Hypericin is a plant-based photosensitizer that can be used for photodynamic therapy and fluorescence diagnostic imaging of cancer. We present hypericin fluorescence imaging techniques that can be used as minimally invasive techniques for diagnostic imaging of oral lesions and discuss their applications from endoscopy to real-time 3-dimensional (3D) endomicroscopy. Fluorescence endoscopy provides a macro view of the lesions while endomicroscopy provides details at the microscopic level. In endoscopy, digitized images were analyzed to extract the red to blue (RIB) intensity ratio, which was found to be a good image parameter to discriminate between normal, hyperplastic and malignant oral tissue, with sensitivity and specificity levels of over 90%. Further development to interface the endoscope to a real-time image analysis system can enable same-day diagnosis in the clinic. An endomicroscope enables fluorescence imaging at the microscopic level and can highlight morphological differences between normal and lesion tissue. We are further developing an embedded computing system interfaced to an endomicroscope for real-time 3D fluorescence visualization of tumors. A Field Programmable Gated Array and a special control circuit have been programmed to synchronize cross-sectional image grabbing and Z-depth scanning and automate acquisition of confocal image stacks, termed datasets. Real-time volume rendering of datasets was tested on a PC equipped with a Graphics Processing Unit. The results demonstrate the potential of the endomicroscope-embedded computing system for real-time visualization of 3D structures in the oral cavity. We anticipate that a real-time 3D endomicroscopy system can complement white light and fluorescence endoscopy in a clinical setting by providing morphological details not visible by using endoscopy alone.