Optical absorption of untreated and laser-irradiated tissues

Abstract

Room temperature absorption spectra of thin, slices of rat tissue, freshly harvested, have been measured in the ultra-violet to near infra-red range and compared with light absorption in a blood sample. Absorption of various tissue materials showed two strong bands peaking at 430 and 1940 nm with two weak absorption bands at 550 and 1450 nm. Blood shows reduced absorption at all of these wavelengths, but the spectra are strikingly similar to those of solid tissue. Absorption spectra taken from kidney which had been irradiated at 430 nm from a nitrogen laser-pumped tunable dye laser showed a definite decrease in absorption with exposure time at 430 nm with an increase in absorption at 440 nm. This band, the Soret absorption band, is characteristic of deoxygenated haemoglobin. The observed decrease in absorption may be due to photochemical reactions involving these haemoglobin derivatives or due to thermo-mechanical shock effects.