Tracer principle

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

Tc-macroaggregated albumin, Tc-albumin microspheres, Tc-albumin minimicrospheres, Tc- erric hydroxide aggregates, Tc-sulfur colloid, Tc-antimony colloid, Tc-phytate 

Bone agents, e.g, polyphosphates, pyrophosphates, diphos-phonates, iminodiphosphonates 

Tc-DTPA, Tc-EDTA, Tc-MIDA (methyliminodiacetic acid), Tc-citrate 

Tc-gluconate, Tc-glucoheptonate, Tc-Fe-ascorbate, Tc-inulin, Tc-mannitol, Tc-dimercaptosuccinic acid 

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TraditionaUy, N uptake rates have been based on the accumulation of N-label in ceUs, defined as a net uptake rake (Bronk et al., 1994), and are calculated based on the tracer principles described above with the extraceUular substrate pool (e.g., NH4+) as the source pool and PN as the target pool ... 

The same year, Hevesy invented the tracer principle, which made it possible to study chemical reactions without disturbing what was being measured. A radioactive indicator (tracer) could be given to a living organism or put in a test tube in amounts so small that there was no effect on the process under study. The tracer was exactly the same chemically as the molecule that it was tracing. 

Radioactive atoms that emit high-energy particles or photons let us keep track of molecules as they take part in chemical reactions. He called these molecules radioindicators. Today we call them radioactive tracers, or radiotracers. The tracer principle became the foundation of a new medical specialty, called atomic medicine, later being called nuclear medicine, and today called molecular imaging. 

In Molecular Imaging (MI) with radiotracers, molecules labeled with radioactive atoms, which undergo the process of radioactive decay are localized and quantified to produce what are cedled molecular images. According to the tracer principle, these molecules are often identical to a natural substance within the body, such as glucose. 

George Hevesy laid the foundation of nuclear medicine, the tracer principle. The emission of photons from radioactive atoms makes it possible to track molecules as they participate in chemical processes anywhere in the human body. Radioactive molecules emit photons that penetrate the body and can tell us what they are doing at all times. 

In 1940, Hamilton and associates in Los Angeles and Hertz and his associates in Boston were the first to measure the uptake of radioactive iodine-128 by the thyroid. This made it possible to diagnose patients with increased or decreased thyroidal function. The names, hyper- and hypothyroidism, reflected the functional basis of the diagnosis. The use of radioiodine to define thyroid disease led to the search for other applications of the radioactive tracer principle. 

The molecular theory of mental illness is based on molecular imaging, which uses the tracer principle to create quantifiable images of the distribution of a radioactive tracer... 

The inherent sensitivity of these techniques, exceeding that of most other chemical or physical methods, the precision of measurements and the increasing commercial availability of radiochemicals may provide a reason for the present extension of radioisotopic methods to application not otherwise strictly dependent on the tracer principle. These include the following assay procedures that are proving to be of great practical convenience. 

Figure 2. Principle of 3 phase flow measurements by the continuous dilution tracer method.

After having proved the principles a dynamic test facility has been constructed. In this facility it is possible to inject 3 tracers in a flownng liquid consisting of air, oil and water. By changing the relative amounts of the different components it is possible to explore the phase diagram and asses the limits for the measurement principle. Experiments have confirmed the accuracy in parameter estimation to be below 10%, which is considered quite satisfactorily for practical applications. The method will be tested on site at an offshore installation this summer. 

Isotopes sufficiently long-Hved for work in weighable amounts are obtainable, at least in principle, for all of the actinide elements through fermium (100) these isotopes with their half-Hves are Hsted in Table 2 (4). Not all of these are available as individual isotopes. It appears that it will always be necessary to study the elements above fermium by means of the tracer technique (except for some very special experiments) because only isotopes with short half-Hves are known. 

A rapid increase in diffusivity in the saturation region is therefore to be expected, as illustrated in Figure 7 (17). Although the corrected diffusivity (Dq) is, in principle, concentration dependent, the concentration dependence of this quantity is generally much weaker than that of the thermodynamic correction factor d ap d a q). The assumption of a constant corrected diffusivity is therefore an acceptable approximation for many systems. More detailed analysis shows that the corrected diffusivity is closely related to the self-diffusivity or tracer diffusivity, and at low sorbate concentrations these quantities become identical. 

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

Detailed Evaluation Detailed evaluation is performed by measuring the capture efficiency, either by using the actual contaminant or by using a tracer gas. (In principle, it is possible to use particles as tracers, but gases are usually used as tracers.) The most reliable evaluation is to use the process-generated contaminant, since there are always problems with a tracer, due to the difficulties of feeding the tracer to the source in the same way and in a similar amount as the generated contaminant. ... 

Tracer methods are not as well standardized as some of the conventional methods. One standard is available, but it comprises radioactive tracers only, which are perhaps not the best alternative for measurements in buildings. In principle, at least three different measurement methods are available the... 

The principle small arms application of military pyrotechnics is in tracer munitions, where they serve as incendiaries, spotters and as fire control. A thorough review of tracer munition design was prepared by Frankford Arsenal (Ref 33) ... 

Figure 1 Schematic sequence of the direct and indirect competitive ELISA. The principle difference is that for direct competitive immunoassay, the well is coated with primary antibody directly, and for indirect competitive immunoassay, the well is coated with antigen. Primary antibody (Y), blocking protein (Y), analyte (T), analyte-tracer ( ), enzyme labeled secondary antibody ), color development ( J)...

Radioactive tracer techniques. In electrochemistry, the procedure is essentially the same as in studies of chemical reactions the electroactive substance or medium (solvent, electrolyte) is labelled, the product of the electrode reaction is isolated and its activity is determined, indicating which part of the electroactive substance was incorporated into a given product or which other component of the electrolysed system participated in product formation. Measurement of the exchange current at an amalgam electrode by means of a labelled metal in the amalgam (see page 262) is based on a similar principle. 

The time variations of the effluent tracer concentration in response to step and pulse inputs and the frequency-response diagram all contain essentially the same information. In principle, any one can be mathematically transformed into the other two. However, since it is easier experimentally to effect a change in input tracer concentration that approximates a step change or an impulse function, and since the measurements associated with sinusoidal variations are much more time consuming and require special equipment, the latter are used much less often in simple reactor studies. Even in the first two cases, one can obtain good experimental results only if the average residence time in the system is relatively long. 

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