(Semi-)quantitative analysis of reduced nicotinamide adenine dinucleotide fluorescence images of blood-perfused rat heart

In vivo analysis of the metabolic state of tissue by means of reduced nicotinamide adenine dinucleotide (NADH) fluorimetry is disturbed by tissue movements and by hemodynamic and oximetric effects. These factors cause changes in the absorption of ultraviolet (UV) excitation light by the tissue. Many different methods have been used in the literature to compensate measured NADH fluorescence intensities for these effects. In this paper we show on theoretical grounds that the ratio of NADH fluorescence intensity and UV diffuse reflectance intensity provides a (semi-)quantitative measure of tissue NADH concentrations. This result is corroborated by experiments with tissue phantoms in which absorption and back-scattering properties were varied. Furthermore, we have verified the validity of this compensation method in isolated Langendorff-perfused rat heart preparations. In this preparation oximetric effects (of blood and tissue) are the major determinants of the metabolism-dependent UV diffuse reflectance change. Hemodynamic effects accompanying compensatory vasodilation are negligible. Movement artifacts were eliminated by simultaneously recording fluorescence and reflectance images, using a CCD camera with a biprism configuration. The results show that the NADH fluorescence/UV reflectance ratio can be used to monitor the mitochondrial redox state of the surface of intact blood-perfused myocardium.