Whole-body gamma counter

Isotope Methods. The isotopes of calcium have relatively short half-lives and are readily counted using liquid scintillation or gamma counters as appropriate to the nuclide. Calcium isotopes may be quantitated in the excreta, blood, tissues or in the whole body. This has made them useful for many nutritional metabolic studies. However, because of safety concerns, radioactive isotopes are cumbersome to work with and many researchers are unwilling to administer them to human beings. This has limited the use of isotopes to those studies in which alternate methods are not available or are imprecise. Methodologies for stable isotopes of calcium, which may be safely used in human being, are becoming available for use in metabolism studies. These will be practical alternatives to radioactive isotopes in the future. 

Gamma Rays (Nuclear-decay y-Rays, 0.5-m.e.v. Photons from Annihilation of Positrons or X-rays). The development of large sodium iodide crystal 7-ray spectrometers (13) has made possible high detection efficiencies (close to 100% for some 7-ray energies). Also, whole-body counters utilizing large cylindrical liquid scintillators provide a detection efficiency of 15% for the 7-rays emitted from potassium-40 in the human body (23). 

Exposure to radium can be determined by use of a whole body counter to measure the presence of gamma radiation emitted by radium (Toohey et al. 1983). Radium levels can also be measured in urine, feces, and other biological media by means of gamma-ray spectroscopy (Lloyd et al. 1983). 

Biomarkers of Exposure and Effect. Currently, human exposure to radium can be assessed by the presence of radioactivity in the body as measured by a whole body counter and in biological fluids such as blood or urine by gamma spectroscopy. 

Radiobioassay is the determination of the kind, quantity, and location of radionuclides in the body by direct measurement (in vivo) or by in vitro analysis of material excreted from the body. Spectral analysis permits rapid analysis of radionuclides that emit gamma rays. Computer systems with data analysis in terms of metabolic models support routine use of bioassay procedures for assessing internally deposited radionuclides. The whole-body counter is an example of an in vivo procedure. 

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