Laser-induced autofluorescence measurement of the brain was performed to assess its spectroscopic properties and to distinguish brain tumors from the normal tissues. The excitation-induced emission spectra were plotted on a 2-dimensional map, the excitation-emission matrix, to determine the excitation wavelengths most sensitive for the spectroscopic identification of brain tumors. The excitation-emission matrices of various types of human brain tumors and normal brain samples lead to the selection of three fluorescence peaks at 470, 520, and 630 nm, corresponding excitation light at 360, 440, and 490 nm, respectively for comparing the autofluorescence signatures of brain tissue. The fluorophores most likely related to each of these peaks are NAD(P)H, various flavins, and porphyrins, respectively. In vivo studies of rat gliomas showed that "NAD(P)H", "flavin", and "porphyrin" fluorescence were lower in gliomas than in normal brain. This finding suggests that there are certain relationship between brain tissue autofluorescence intensity and metabolic activity. In vitro human normal brain tissue fluorescence signals were lower in gray matter than in white matter and "NAD(P)H" fluorescence were lower in all measured human brain tumors than in normal brain. "Flavin" and "porphyrin" fluorescence in the neoplastic tissues was lower or higher than normal tissue depending on their nature. In conclusion, the fluorescence spectroscopic diagnostic system might be able to distinguish brain tumors from the normal brain tissue. The results of this study need to be verified and the investigation extended to human brain tumors in the operating room.
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