Laser excited fluorescence of hematoporphyrin derivative for diagnosis of cancer

Hematoporphyrin derivative (HPD) is selectively retained in malignant tumors for several days after intravenous injection. It fluoresces in the red (600-720 nm) when excited by shorter wavelengths, especially violet (near 400 nm). While fluorescence efficiency is not high, it can be detected at parts per million concentrations when excited by a low-background source such as a krypton ion laser (413 nm), and the fluorescence detected by an image intensifier or photomultiplier tube. We have developed an intensifier based fluorescence imaging system for localization of carcinoma in situ of the lung, aided by digital background subtraction in a video system. A ratio fluorometer and spectrum analyzer have been added for research and for quantitative, noncontact measurements of fluorescence intensity and spectrum of HPD fluorescence and autofluorescence of tissue. Research is continuing to determine the optimum time after injection for best contrast, and the maximum allowable dosage of HPD, limited by the induced temporary photosensitivity of the skin. In diagnosis of epithelial or superficial tumors, the monochromatic radiation and suitability for coupling through fiberoptics, as well as reasonable power (typically 15 mW violet is used) are the principal advantages of the laser.