Fluorescence studies of hematoporphyrin derivative in normal and malignant rat tissue

Laser-induced fluorescence in rat tissue was studied during the uptake and clearing period of i.v.-injected hematoporphyrin derivative. A malignant rat tumor and normal tissue of 20 different kinds from the tumor-bearing animals were investigated. A pulsed nitrogen laser (337 nm) was used in conjunction with an optical multichannel analyzer system, in which the whole fluorescence light distribution was captured for each laser pulse. Several of the organs exhibited an initial and a delayed intensity peak in the characteristic hematoporphyrin derivative laser-induced fluorescence intensity (630 nm) that might be interpreted as due to intracellular transformations of different chemical components of the hematoporphyrin derivative preparation. By dividing the background-free 630-nm signal by the blue fluorescence intensity, a dimensionless quantity is obtained that could have many advantages in practical endoscopic laser-induced fluorescence work. This ratio was also shown to exhibit a larger contrast between tumor and surrounding tissue. The ratio between the two red fluorescence peaks was also found to be useful for discriminating tumor from normal tissue. A combination of the two ratios was shown to be particularly valuable for tumor discrimination.