a novel chemical method of labeling porphyrin compounds , specifically hematoporphyrin derivative , with the radionuclide technetium - 99m producing a radioactive tracer material suitable for biomedical applications . hpd labeled with 99m tc is biologically active in vivo and is preferentially taken up by neoplastic tissues . this provides a simple and specific means of visualizing tumors in man or animal by scintigraphic imaging techniques .