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Abstract

There are disclosed an instrument and method for using near IR to discriminate between healthy and diseased tissue, using, e.g., a catheter and a spectrophotometer. Near IR is passed at certain wavelengths to suspected tissue, and reflected light is analyzed to determine the absorbance, and preferably the second derivative thereof. From identification of the absorption spectra of known diseased and known healthy tissue, a relation has been established to determine the following correlation equation for determining the predictive value of y: y=Co+C.sub.1 A(.lambda..sub.1)+C.sub.2 A(.lambda..sub.2) wherein A(.lambda..sub.1)+A(.lambda..sub.2) are the second derivatives for the absorbance at the two selected wavelengths. For blood cholesterol esters and plaque, .lambda..sub.1 is preferably 1714.5 and .lambda..sub.2 is preferably 1678.5 nm. Solving for the coefficients Co, C.sub.1 and C.sub.2, it has been shown that values of y less than -8.0 represent diseased tissue, which should be treated. Ablation laser treatment is described as one mode of treatment.

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