Lasers of proper wavelength may be used to excite fluorescence of compounds such as hematoporphyrin derivative (HpD), which preferentially accumulates in malignant tumors over surrounding nonmalignant tissues, after intravenous injection. If the tumors are superficial, the emitted fluorescence light may be imaged or detected by a photomultiplier tube. This forms the basis of a technique for detection of tumors too small to be visible under ordinary light or by x ray. HpD and certain other substances can also absorb light and transfer energy to molecular oxygen present in tissue generating the cytotoxic singlet oxygen. The latter property is the basis for photodynamic therapy of cancer. To predict and control the absorbed dose, it is necessary to determine the concentration of the absorber (HpD) in the tumor and nearby tissue. This may be possible by making quantitative measurements of the fluorescence.

© 1984 Optical Society of America

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