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Radionuclide imaging is one of the most photons, 511 keY). Gamma rays of these important applications of radioactivity in energies are sufficiently penetrating in body nuclear medicine. Radionuclide imaging tissues to be detected from deep-lying organs, laboratories are found in almost every hos-can be stopped efficiently by dense scintilpita!, performing hundreds and even thou-lators, and are shielded adequately with sands of imaging procedures per month in reasonable thicknesses of lead (see Fig. larger institutions. 6-17-soft tissue has similar attenuation In this chapter, we discuss briefly some properties to water). Alpha particles and general aspects of radionuclide imaging, and electrons (~ particles, Auger and conversion we describe the basic principles of the most electrons) are of little use for imaging because widely used imaging device, the gamma they cannot penetrate more than a few camera, also known as the Anger scintilla-millimeters of tissue. Therefore, they cannot tion camera, named after its inventor, Hal escape from within the body and reach an Anger (see Chapter 1, Section C; see also Fig. external radiation detector, except from very 1-3). The performance characteristics of this superficial tissues. Bremsstrahlung (Chapter instrument are discussed in Chapter 14. The 6, Section Al) generated by electron emisuse of the gamma camera for tomographic sions is more penetrating, but the intensity of imaging is described in Chapter 17. this radiation generally is very weak. Imaging system detectors must therefore have good detection efficiency for y rays. It is