Human body radioactivity applications

Henshaw DL (1989) Application of sohd state nuclear track detectors to measurements of natural alpha-radioactivity in human body tissues. Nucl Tracks Radiat Meas 16(4) 253-270 Int J Radiat Appl lustrum Part D... 

The effect of radiation (see Chap. 23 in this Volume) emitted by the radioactive tracers on a chemical or biological system under study is also usually negligible. The amount of a radioactive tracer necessary for an experiment is normally so small that no detectable radiolysis occurs in the system. However, in long-term storage of radiation-sensitive compounds, one must be cautious of the effect of radiation. And, of course, in application to human body, careful consideration is necessary on the effects of radiation during and after the experiment (see Chap. 47 of Vol. 5). 

It is astonishing to note that technetium has an important medical application. In 1954 E. J. Baumann and his co-workers [28.10] injected a solution, containing a Tc isotope into rats with tumors. After two hours the Tc concentration in the tumors was 11-30 times higher than in the blood. Since 1964 a diagnostic technique is used in which the isotope 9 Tc with a half-life of six hours is injected in the human body. The radioactive isotope is absorbed in tumors that can later be locaHzed by radioactive detection. The selection of " Tc is justified by the fact that the half-Hfe is low and that the isotope is not a 3-emitter. The isotope can thus perform its medical function with minimal secondary effects for the patient. 

Most of the forementioned studies which examined the influence of various dietary fiber on the bioavailability of calcium by human subjects have depended upon the comparative measurements of calcium content of diets and calcium contents of stools and urine. As reviewed by Allen (3), calcium balance studies have distinct limitations relative to accuracy and precision. However, their ease of application and cost, laboratory equipment requirements, and real (or perceived) safety in comparison to available radioactive or stable isotope methods continue to make their use popular. In calcium balance studies, calcium absorption is assumed to be the difference between calcium excretion in the feces and calcium intake. Usually this is expressed as a percent of the calcium intake. This method assumes that all fecal calcium loss is unabsorbed dietary calcium which is, of course, untrue since appreciable amounts of calcium from the body are lost via the intestinal route through the biliary tract. Hence, calcium absorption by this method may underestimate absorption of dietary calcium but is useful for comparative purposes. It has been estimated that bile salts may contribute about 100 g calcium/day to the intestinal calcium contents. Bile salt calcium has been found to be more efficiently absorbed through the intestinal mucosa than is dietary calcium (20) but less so by other investigators (21). 

In considering tests that might be applicable to humans, as opposed to experimental mammals, some limitations will be obvious. No test is acceptable that requires administration of hazardous materials, such as radioactive compounds or other known chemical mutagens. Biologic materials are limited to body fluids, such as blood and urine, and cells, such as blood cells, hair follicles, and sperm. These strictures rule out some useful tests that are applied to other organisms and to cell cultures. 

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