autoradiograph

(ô'tō-rā'dē-ō-grăf')
n.
An image recorded on a photographic film or plate produced by the radiation emitted from a specimen, such as a section of tissue, that has been treated or injected with a radioactively labeled isotope or that has absorbed or ingested such an isotope. Also called autoradiogram.

autoradiographic au'to·ra'di·o·graph'ic adj.
autoradiography au'to·ra'di·og'ra·phy (-ŏg'rə-fē) n.

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A photographic technique used to localize a radioactive substance within a solid specimen; also known as radioautography.

A photographic emulsion is placed in contact with the object to be tested and is left for several hours, days, or weeks, depending on the suspected concentration of the radioactive material to be measured. The emulsion, which is a gel containing silver halide, is then developed, fixed, and washed as in the usual photographic process. At sites where the emulsion was close enough to the radioactive substance, it appears dark because of the presence of silver grains. When the number of grains is insufficient to darken the film to the unaided eye, the film may be examined with the aid of a microscope. The individual silver grains may then be seen. The pattern formed by the grains depends on the type of radiation and the nature of the photographic emulsion. Alpha particles produce short, straight rows or tracks of grains. Beta particles as well as x-rays and gamma rays, which affect film by producing beta particles, produce tortuous tracks whose lengths and grain densities depend on the energy of the beta particles. Low-energy particles produce shorter tracks with higher grain densities. Very low energy particles like those from tritium (3-hydrogen) may produce only a single grain very close to the site of decay.

Autoradiography can be used to detect, and measure semiquantitatively, the radioactive materials in almost any object that can be placed in contact with film or photographic emulsion in some form. However, in biological research the object may be (1) a whole plant or animal that can be flattened against a film; (2) the cut surface of a plant or animal, or one of its organs; (3) thin sections of tissues or cells; (4) squashed or otherwise flattened cells; (5) surface films produced by spreading on water the protein monolayers containing DNA or ribonucleic acid (RNA) that are picked up on grids for electron microscopy; (6) sheets of paper or other materials on which radioactive substances have been separated by chromatography or electrophoresis; or (7) acrylamide gels in which DNA, RNA, or proteins have been separated by electrophoresis. See also Radiography.

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The phenomenon was discovered accidentally by Henri Becquerel (1852-1908) in 1896, when he left a specimen of potassium uranyl sulphate in contact with a photographic plate. Its modern applications are mainly in medicine. For example, the iodine distribution in the thyroid gland can be mapped by injecting radioiodine and making an autoradiogram of a biopsy, or the phosphorus distribution in a leaf can be ascertained by growing it in a cultural medium containing radiophosphorus. In both cases the specimen is left for an appropriate time on a sheet of X-ray film.

— Graham Saxby

or autoradiogram

the image produced by autoradiography.

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The film produced by autoradiography.

(ô′tōrādē-og′rəfē)
n

1. a photographic recording of radiation from radioactive material, obtained by placing the surface of the radioactive material in close proximity to a photographic emulsion. n 2. the use of radioactive substances introduced into tissue followed by the placement of a photographic plate on the surface of the tissue preparation, usually employed in cytology and histology.

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