In Vivo Simultaneous Morphological and Biochemical Optical Imaging of Oral Epithelial Cancer

Abstract

Early detection of cancer is key to reducing morbidity and mortality. Morphological and chemical biomarkers presage the transition from normal to cancerous tissue. We have developed a noninvasive imaging system incorporating optical coherence tomography (OCT) and fluorescence lifetime imaging microscopy (FLIM) into a single optical system for the first time, in order to acquire both sets of biomarkers. OCT can provide morphological images of tissue with high resolution, while FLIM can provide biochemical tissue maps. Coregistered OCT volumes and FLIM images have been acquired simultaneously in an in vivo hamster cheek pouch model of oral cancer. The OCT images indicate morphological biomarkers for cancer including thickening of the epithelial layer and loss of the layered structure. The FLIM images indicate chemical biomarkers including increased nicotinamide adenine dinucleotide and reduced collagen emission. While both sets of biomarkers can differentiate normal and cancerous tissue, we believe their combination will enable the discrimination of benign lesions possessing some of the indicated biomarkers, e.g., scarring or inflammation.

Optical coherence tomography today: speed, contrast, and multimodality

“…189 A spectrometer-based OCT based on a SLD centered at 830 nm provided high-resolution morphological volumetric tissue images with an axial and lateral resolution of 7.3 and 13.4 μm, respectively was combined with a pulsed Q-switched tripled Nd:YAG laser for excitation. The multispectral FLIM based on a direct pulse-recording approach (upon 355 nm laser excitation) provided 2-D superficial maps of the tissue autofluorescence intensity and lifetime at three customizable emission bands with a 100-μm lateral resolution.…”

Extended output phasor representation of multi-spectral fluorescence lifetime imaging microscopy

“…] at λ -th wavelength can be estimated by a Laguerre basis or a multiexponential model [6,8,9]. Similar to the fluorescence decay vector, the multi-spectral fluorescence impulse response vector h k is constructed as…”

“…Being able to measure the fluorescence lifetime at different emission bands would facilitate the identification of the state of the tissue. In this context, multi-spectral FLIM (m-FLIM) is a promising optical diagnosis tool that has been successfully applied to characterize skin and oral cancer [4][5][6], colonic dysplasia [7] and atheroscletoric plaques [8,9], among others pathologies. In time-domain m-FLIM, the sample is excited with a pulse of light and the fluorescence emission intensity decay is recorded over a time-window at different wavelength bands according to the spectral properties of the studied components [9].…”

“…This information can be extracted by considering a linear mixing model at each spatial point and assuming that the multi-spectral end-members are invariant throughout the sample [10,14]. An alternative biochemical characterization of the sample can be achieved by quantifying the average lifetime and normalized intensity per spectral band and pixel in the estimated fluorescence impulse response [6,8,9].…”

“…Both m-FLIM processing approaches [6,[8][9][10]14] can provide quantitative characterization of the sample fluorescence emission, but the required computational power can be prohibited for real-time applications. Moreover, time-resolved m-FLIM measurements are represented by high-dimensional vectors, whose time-domain properties are sometimes difficult to visualize for classification purposes.…”