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Tissue that has undergone significant yet unknown amount of ischemic injury is frequently encountered in organ
transplantation and trauma clinics. With no reliable real-time method of assessing the degree of injury incurred in tissue,
surgeons generally rely on visual observation which is subjective. In this work, we investigate the use of optical
spectroscopy methods as a potentially more reliable approach. Previous work by various groups was strongly suggestive
that tissue autofluorescence from NADH obtained under UV excitation is sensitive to metabolic response changes. To
test and expand upon this concept, we monitored autofluorescence and light scattering intensities of injured vs. uninjured
rat kidneys via multimodal imaging under 355 nm, 325 nm, and 266 nm excitation as well as scattering under 500 nm
illumination. 355 nm excitation was used to probe mainly NADH, a metabolite, while 266 nm excitation was used to
probe mainly tryptophan to correct for non-metabolic signal artifacts. The ratio of autofluorescence intensities derived
under these two excitation wavelengths was calculated and its temporal profile was fit to a relaxation model. Time
constants were extracted, and longer time constants were associated with kidney dysfunction. Analysis of both the
autofluorescence and light scattering images suggests that changes in microstructure tissue morphology, blood
absorption spectral characteristics, and pH contribute to the behavior of the observed signal which may be used to obtain
tissue functional information and offer predictive capability.
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