Figure 1. Scanning fiber endoscope optics and fluorescence spectrometry of major structural constituents of atherosclerotic plaques.

a, The scanning fiber endoscope excites tissues by scanning blue (424nm), green (488nm) and red lasers (642nm) in a spiral pattern. Backscattered (reflectance) light and fluorescent signal is collected by a ring of optical fibers located in the periphery of the scanner housing and shaft, and conducted to a computer for image generation. b, The optical system can be mounted in 2.1mm (left) or 1.2mm (right) endoscopes. c–h, Fluorescence spectrometry of representative samples of histology-proven tunica media (red dot), fibrous cap (blue dot), necrotic core (green dot), and thrombus (fuchsia dot) were collected with a fiber-coupled spectrophotometer from (c) normal arterial walls, (d) fibroatheroma, and (e) ruptured plaque with associated thrombus after excitation with scanning fiber endoscope lasers [(f) λex=424nm; (g) 488nm; (h) 642nm]. i, By spreading out the excitation wavelengths of the 3 lasers over the visible and near-infrared spectrum of light, multimodal scanning fiber endoscopy has the capability to excite tissue autofluorescence for spectral biochemical analysis and provide a broad, non-overlapping range of colors for multiplexed molecular images. h, Molecular probes labeled with red dyes are particularly convenient for endovascular use, based on the negligible autofluorescence excited at 642nm that enables higher target-to-background ratios. i, In addition, the extinction coefficient of hemoglobin (Hb) is greatly reduced in the red and near-infra red spectrum, which translates into lower attenuation of fluorescence signal through tissue and blood. On the opposite end of the visible spectrum, the extinction coefficient of hemoglobin (Hb) is at its peak, which translates into high absorption at 424nm. The hemoglobin-related light extinction results in a void in autofluorescence detection, turning hemoglobin into a physiological negative contrast in spectral imaging.