Tracer tissues, damaged

Because exposure to radiation is a health risk, the administration of radioactive isotopes must be monitored and controlled carefully. Isotopes that emit alpha or beta particles are not used for Imaging, because these radiations cause substantial tissue damage. Specificity for a target organ is essential so that the amount of radioactive material can be kept as low as possible. In addition, an Isotope for medical Imaging must have a decay rate that is slow enough to allow time to make and administer the tracer compound, yet fast enough rid the body of radioactivity in as short a time as possible. 

In preclinical studies, histopathology has traditionally been the primary method of demonstrating GI injury. While this remains the most reliable way to detect and characterize tissue damage at the conclusion of a study, the need for realtime detection remains. The literature abounds on biomarkers of GI disease, though most are nonspecific and/or insensitive. The field is improving, however, and we describe several biomarkers here that have some possible or demonstrated utility in preclinical species. Many orally administered probe tests, such as the sucrose breath test, are not considered to have utility in preclinical studies due to the requirement for radioactive tracers and are therefore not covered. 

It is necessary to provide evidence that these conqtounds are taken up by the plants and that damage to the plants can be directly associated with the presence of these conqtounds in plant tissues or organs. Tracer-labeled phenolic acids can best serve these investigations. Several crucial questions must be answered in order to derive a realistic assessment of plant damage and, furthermore, to devise means to alleviate such damage in the field. For instance, does damage occur at or on the root surface, or is the chemical(s)... 

Making metastable technetium-99 is an expensive business. A cheaper, common alternative tracer is iodine-131, which emits a gamma ray when it decays. But the iodine isotope also releases beta particles that can damage tissues, making it less attractive as an imaging agent. 

Alpha decay involves the loss of a particle equivalent to a helium nucleus. Alpha (oe) particles, being large and positively charged, do not penetrate far in hving tissue, but they do cause ionization damage and this makes them generally unsuitable for tracer studies. 

The use of cobalt radiation treatments for cancerous tumors was described in Example 26-3. Several other nuclides are used as radioactive tracers in medicine. Radioisotopes of an element have the same chemical properties as stable isotopes of the same element, so they can be used to label the presence of an element in compounds. A radiation detector can be used to follow the path of the element throughout the body. Modern computer-based techniques allow construction of an image of the area of the body where the radioisotope is concentrated. Salt solutions containing "iNa can be injected into the bloodstream to follow the flow of blood and locate obstructions in the circulatory system. Thallium-201 tends to concentrate in healthy heart tissue, whereas technetium-99 concentrates in abnormal heart tissue. The two can be used together to survey damage from heart disease. 

Overall, dietary protein requirements represent the amount of protein that is required to support net protein synthesis (growth, repair of damaged tissues, lactation, pregnancy, muscle hypertrophy, enzyme synthesis), amino acid oxidation, and the inefficiency inherent in the amino add recycling process. The two methods of determining protein requirements are the NBAL method and those using isotope tracers. 

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