An autoradiograph is an image on an x-ray film or nuclear emulsion produced by the pattern of decay emissions (e. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. g. , beta particles or gamma rays) from a distribution of a radioactive substance. Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Alternatively, the autoradiograph can also be available as a digital image (digital autoradiography), thanks to the recent development of scintillation gas detectors^[1] or rare earth phosphorimaging systems^[2]. In biology, this technique may be used to determine the tissue localization of a radioactive substance, either introduced into a metabolic pathway, bound to a receptor^{[3] [4]} or enzyme, or hybridized to a nucleic acid^[5]. The film or emulsion is apposed to the labeled tissue section to obtain the autoradiograph (also called an autoradiogram). The auto- prefix indicates that the radioactive substance is within the sample, as distinguished from the case of historadiography or microradiography, in which the sample is X-rayed using an external source. Historadiography is a technique formerly utilized in the fields of Histology and Cellular biology to provide semiquantitative information regarding the density of

The use of radiolabeled ligands to determine the tissue distributions of receptors is termed either in vivo or in vitro receptor autoradiography if the ligand is administered into the circulation (with subsequent tissue removal and sectioning) or applied to the tissue sections, respectively. A radioligand is a Radioactive biochemical substance (in particular a ligand) that is used for diagnosis or for research-oriented study of the receptor In vivo ( Latin: within the living means that which takes place inside an organism. In vitro ( Latin: within the glass refers to the technique of performing a given experiment in a controlled environment outside of a living Organism The ligands are generally labeled with ³H (tritium) or ¹²⁵I. Tritium (ˈtɹɪtiəm symbol or, also known as Hydrogen-3) is a radioactive Isotope of Hydrogen. Iodine-125 (125I is a Radioisotope of Iodine which has uses in Biological assays and in Radiation therapy to treat Prostate cancer The distribution of RNA transcripts in tissue sections by the use of radiolabeled, complementary oligonucleotides or ribonucleic acids ("riboprobes") is called in situ hybridization histochemistry. In situ hybridization (ISH is a type of hybridization that uses a labeled Complementary DNA or RNA strand (i RNA or DNA viral sequences can also be located in this fashion. These probes are usually labeled with ³²P, ³³P, or ³⁵S.

This autoradiographic approach contrasts to techniques such as PET and SPECT where the exact 3-dimensional localization of the radiation source is provided by careful use of coincidence counting, gamma counters and other devices. Positron emission tomography ( PET) is a Nuclear medicine imaging technique which produces a three-dimensional image or map of functional processes in the Single photon emission computed tomography (SPECT or less commonly SPET is a Nuclear medicine tomographic imaging technique using Gamma rays.

References

Additional References

1. Andrew W. Rogers. Techniques of Autoradiography, Elsevier North Holland, 3rd edition, 1979.

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