Use of fluorescence spectral ratios to determine dosimetry during coronary laser angioplasty

This paper determines the usefulness of simple spectral ratios of UV-induced florescence from intracoronary targets during laser angioplasty. UV-laser excited fluorescence of coronary obstructions (97% ± 3 stenosis) were obtained by means of percutaneous contact of guide wires and 14-fiber catheters for laser angioplasty in 21 patients. Analysis of these 243 clinical and an additional 250 in vitro spectra was performed with ratios of fluorescence intensities (FI) at 382 mn and 439 nm, where oxyHb absorption is constant but tissue types differ, and 417 nm. The ratio FI382nm/FI439nm gave reliable indexes of the underlying tissue type (3.0 ± 0.2 for fibrous plaque and 1.1 ± 0.2 for smooth muscle) as the blood layer varied up to 40 μm. The values of FI417nm, FI382nm + FI439nm, and their ratio could be used to determine the blood layer thickness ± 1 μm from 0 to 40 μm and the fraction of fiber area sensing tissue