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TFLUX is a computer program which simulates radioactive tracer experiments using intact cells under steady-state conditions. It is designed for the naive computer user to use, providing English-like input. An example is described in which compartmentation and flux through the citric acid cycle in Dictyostelium discoideum are simulated.
The use of radioactive tracers in the diagnostic and therapeutic evaluation of the patient with peripheral arterial or venous disease has proven to be clinically useful. Their application has provided a means by which the regional distribution of perfusion at the level of the microcirculation, at rest and under various stresses, can be assessed. Graft patency can be determined simply and repeatedly, and the relative perfusion of "ischemic" ulcers can be used to assess their healing potential. The presence of arteriovenous shunts can be verified, localized, and quantified. Venous thrombi can be detected, and the competence of the venous valvular system and muscle pump as well as the hemodynamics of the venous system can be quantified.
Screening for abnormal capillary filtration in the limbs with radioactive tracers requires the use of molecules of a known hydrodynamic radius. The molecule labeling should be obtained with a pure gamma-emitting radioactive atom, presenting a steady bond with the molecule, in vivo. Indium-111-labeled albumin appears to be the best tracer, and should be injected concurrently with the technetium 99m-labeled erythrocytes. The latter tracer permits assessing volume variations induced by the venous blood return block needed to obtain a capillary pressure increase. A qualitative estimation of lymphatic flow, and screening for abnormal permeability of the lymphatic vessels must be carried out as part of any capillary filtration study protocol.
The status of radioactive tracer studies in cardiovascular diagnosis is summarized. Planning guidelines are suggested for a hospital nuclear medical service including a central nuclear medical facility and satellite units, and resource criteria are given for professional personnel including training and duties, equipment, space, and support system. The administrative organization of a nuclear medical service and case loads are discussed. Guidelines for equipment maintenance and quality controls are described.
Experiments were performed to ascertain the perfusion and drainage of single cephalad channel saphenous venous flaps in dogs. In the first experiment a standard saphenous flap and a single cephalad channel saphenous venous island flap were dissected on contralateral thighs of dogs. A radioactive tracer, 99mTc, was injected into a foreleg vein and its appearance in both flaps was monitored with the use of a static and dynamic scanner. After this experiment, Evans blue, a vital dye, was injected into the foreleg vein of the dog. Five minutes later both flaps were excised and the dye in the flaps was assayed quantitatively. In the third experiment radioactive tracer was injected into the single cephalad channel venous flap subcutaneously and its decay in the flap as well as its uptake in the rest of the body were measured dynamically. The experiments show that the single cephalad channel venous island flap is perfused by and drains through its single cephalad vein. A mathematical model to justify the above conclusion was worked out independently, based on standard values involved in mammalian circulatory mechanisms as in dog and man.
The deposition and clearance of various fibrous materials have been investigated in the rat using radioactive tracer techniques. The materials used include the U.I.C.C. standard reference samples and synthetic mineral fibres. Measurements of total and alveolar deposition were correlated with the AMADs of the radioactive dust samples which ranged from 1 to 2.5 micron. Although total deposition increases steeply over this range, alveolar deposition is relatively constant only increasing from about 10 to 13%. Alveolar deposition is lower than in man, but the maximum in alveolar deposition appears to occur at a similar aerodynamic diameter. Half times of alveolar clearance, measured over a period of several months following single inhalation exposures, were in the range 60-90 days and no significant difference was observed between amphibole and chrysotile asbestos. Autoradiographs of lung sections indicate that alveolar deposition is relatively uniform and occurs right up to the periphery of the lung. Over a period of several months the uniform distribution alters to one in which fibres accumulate in foci which are mainly subpleural. These foci act as centres for the development of nodular fibrosis.
Complete sequencing of the oligosaccharide units of glycoproteins can be performed by conventional physical techniques if nanomole quantities of pure molecules are available. However, isolation of sufficient quantities of a glycoprotein may not be technically feasible (e.g., the analysis of biosynthetic intermediates, or rare molecules). Alternatively, partial structural analyses may answer the biological question at hand. In both instances, radioactive sugars can be used to metabolically label the oligosaccharide units of a glycoprotein, permitting substantial structural characterization. Several aspects of this approach are discussed in this overview, including selection of the labeled precursor, maximization of uptake and incorporation, determinants of the specificity of labeling, and general principles for the release and structural analysis of labeled oligosaccharides. Particular advantages include simplicity, ease of use without sophisticated instrumentation, and the fact that purification to radiometric homogeneity is sufficient. Radioactive tracer techniques cannot replace conventional approaches to sequencing oligosaccharides. However, they do provide a rapid, relatively simple approach to obtaining considerable information from limited amounts of material. For molecules such as short-lived biosynthetic intermediates, there is no substitute for these techniques. This approach has been responsible for the initial identification and characterization of many novel oligosaccharides of biological interest.
In this report we describe a radionuclide procedure designed to evaluate the migration of a particulate radioactive tracer from the vagina to the peritoneal cavity and ovaries, as well as the determination of the patency of the pathways between these two extremes of the female reproductive system. 99mTc-labelled human albumin microspheres (99mTc-HAM) were deposited in the posterior fornices of 24 patients a day before they were to undergo different gynaecological operations. During this period sequential images were obtained and after the operation radioactivity levels in the removed organs and tissues were counted with a scintillation detector. In 14 out of 21 cases, the ovaries and fallopian tubes were counted separately from the uterus. Nine were positive (radioactivity levels were sufficiently high in the tubes and ovaries) and 5 were negative (no substantial radioactivity levels could be detected in either the tubes or the ovaries). The 5 negative results all occurred in patients with proved tubal damage as a result of previous infection. All the results were either true positive or true negative, providing evidence of migration, or obstruction, of 99mTc-HAM from the vagina through the uterus and tubes to the peritoneal cavity and ovaries.
Examination of the input-output events in functioning organs by the use of the impulse-response function (IRF) for a radioactive tracer is gaining more and more ground in nuclear medicine. This study summarizes the development of deconvolution analysis, laying special stress on the 'model-free' approach. System linearity and time invariance are discussed, and means of eliminating noise in IRFs originating from the input and organ-time-activity curves are outlined. Typical IRFs are illustrated by flow diagrams, time-domain curves, and their representation by Laplace transforms. The cases of nondiffusible and diffusible tracers as well as parenchymally extracted and transported substances are discussed. Methods for the derivation of models and for the calculation of physiologically important parameters from the IRFs are suggested.
Cross-contamination between a hospital's vacuum and compressed air systems was demonstrated using xenon-133 as a tracer. A xenon-133 bolus was introduced to the vacuum system in the intensive care unit. Calculations based on the amount of radioactive tracer recovered from the compressed air outlet at the same location as that at which the tracer was introduced indicated that 17% of the tracer had entered the compressed air system. The contamination was caused because the vacuum and compressed air systems were located in the same machine room. This could conceivably provide a route for respiratory tract contamination in patients receiving ventilatory assistance with air-oxygen mixtures.
The Inter-Society Commission for Heart Disease Resources report concerning optimal resource guidelines for radioactive tracer studies of the heart and circulation is described. This report is an overview of the status of cardiovascular radionuclide diagnostic studies as well as a guideline to the hospital resources (physical and human) required for a high-quality nuclear medicine laboratory dealing with this area of study. These guidelines are directed to physicians and hospital administrators who are currently responsible for planning and organizing nuclear medicine programs or who anticipate a future need for such services in their community.
The reassociation kinetics have been measured for radioactive Escherichia coli DNAs (tracers) of various average single-strand lengths reassociated alone and in the presence of excess unlabeled DNA (driver) of two different average lengths. Hydroxylapatite binding was used to follow the reaction time course. The length-dependence of the rate constant determined in the tracer self-reassociation reactions is in agreement with the square-root dependence previously determined (Wetmur, J. G., & Davisond, N. (1968) J. Mol. Biol. 31, 349-370) using optical methods to follow the time course. However, for the driver-tracer reactions, where the radioactive DNA reassociates largely with DNA of a different average length, the dependence of the rate constant upon average tracer length is increased and approaches an L to the first power dependence. In 0.18 M Na+, the variation of the rate constant for tracer reassociation with the lengths of the reassociating strands has been shown to fit the simple equation k = (9.0077).(L T 0.55 + 1/L D 0.55), where k is the observed rate constant in L mol-1 s-1 and L(T)and L(D) are the weight average tracer and driver lengths, respectively, in nucleotides. This dependence suggests that the rate of nucleation of two free strands is proportional to the sum of the reciprocals of the hydrodynamic radii of the two strands.
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Transport of radioactive leucine was used to demonstrate cerebellar projections from the external cuneate nucleus (NCE) and from adjacent portions of the main cuneate nucleus (NC), of the spinal trigeminal nucleus (N.tr.sp.V) and of the vestibular nuclei. Projections from NCE and NC in part terminate over exclusive regions and in part overlap. After injections limited to NCE, labeling is found in all regions of the anterior lobe and lobule VI, in vermal lobules VII, VIII, and IX, and in medial regions of central folia of the paramedian lobule. Afferents from NC are observed in intermediate and lateral regions of lobules IV-VI, in lobules VIII and IX, in medial portions of crura I and II, and in lateral parts of central folia of the paramedian lobule as well as in its rostral folia. Afferents from N.tr.sp.V are distributed in lateral regions of lobules II-VI, in the rostral folium of lobule IX, in medial parts of crura I and II, and in rostral folia of the paramedian lobule. Afferents from the vestibular nuclei are present in vermal lobules VII, IX, and X and in the paramedian lobule. Projections from NCE are bilateral with ipsilateral predominance, whereas those from NC and N.tr.sp.V are ipsilateral. Projections from NCE are generally much denser than those from the other nuclei. Throughout the projection area, afferents from NCE are distributed in greater amounts in folia close to the medullary core and are much less dense near the surface. Afferents from the other nuclei do not show surface-to-depth density differences.
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A simple and inexpensive unit for the collection of excreta from individual mice was designed. The results of experiments in which counts of collected radioactive excreta were made closely approximated those previously obtained using a whole-body gamma counter.
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