The Radioautographic Method in Biology and Medicine

Abstract

For centuries the chemical elements have been objects of scientific investigation. In 1896 Henri Becquerel discovered that some of the heavier elements were naturally radioactive, emitting alpha, beta and gamma radiation. This emission was studied extensively during the subsequent years. One of the significant advances was the announcement of artificial radioactivity by Curie and Joliot in 1934. It was soon established that all of the known chemical elements possess varying numbers of isotopes, many of which are artificially radioactive, emitting alpha, beta and gamma particles and positrons. The disintegration process is unique, for only one type of emission is known for each radioactive isotope. The radiations emitted by the isotopes may be detected with Geiger counters, spectrometers, ionization chambers or by photographic methods. In 1924 Lacassagne and Lattes reported a modification of the photographic method which has been widely used in biology and medicine. It is simply a method of contact photography for detecting and recording radiations from radioactive isotopes. The photographs obtained are usually called radioautographs but some workers prefer autoradiographs or simply autographs. In the usual applications of this method a solution containing a radioactive isotope is administered to the specimen (or patient) under examination. After a suitable period of time has elapsed portions of the specimens are removed and sectioned. The sections are placed in direct contact with a photographic plate and the combination bound together. Those portions of the specimen containing the radioactive element emit radiations which affect the photographic emulsion in the same manner as ordinary visible light or Xrays. After the development of the photographic plate that region of the emulsion which was adjacent to the radioactive portion of the sample will be darkened. The type and extent of darkening is a measure of the cqncentration of the radioactive material in that portion of the sample in contact with the plate. The radioautographic technique localizes the sources of radiation more closely than any other method of detection now available.