Design and Development of New Radiopharmaceuticals

The major factors in the design of a new radiopharmaceutical for radioisotope scintigraphy are the photon energy of the radionuclide, the ability to incorporate the radionuclide insuitable chemical and biological form, the radiation dose to the patient, and the cost of production of the radiopharmaceutical. In this laboratory, the radionuclides, indium-113m and ytterbium-169, and technetium-99m, have been incorporated into a variety of radiopharmaceuticals. These include particles suitable for lung and liver studies, chelates for brain and kidney studies, and ionic forms for blood pool imaging. Studies in experimental animals and man indicate that these agents offer certain advantages over previously available radiopharmaceuticals. By providing larger numbers of photons, they permit more precise temporal and spatial resolution. The longer half-life of the tin-113 parent radionuclide from which indium-113m can be eluted makes indium-113m readily available, even at sites distant from the source of production. The tin-indium generator system need be purchased only every five months rather than weekly as in the case of the widely used molybdenum-technetium system. The ytterbium-radionuclide in the chemical form of a chelate is particularly useful as an inexpensive agent that provides high photon yields for renal and brain imaging. The rapid and complete biological excretion results in low radiation dose while the longer physical half-life greatly extends the shelf-life. (author)