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Journal articles on the topic 'Tracer studies'

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Published: 4 June 2021

Last updated: 17 February 2022

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Cobelli, C., G. Toffolo, D. M. Bier, and R. Nosadini. "Models to interpret kinetic data in stable isotope tracer studies." American Journal of Physiology-Endocrinology and Metabolism 253, no. 5 (1987): E551—E564. http://dx.doi.org/10.1152/ajpendo.1987.253.5.e551.

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In contrast to "weightless" radioactive tracers, stable isotope tracers have nonnegligible mass and are naturally present in the system, and the measured variable is a ratio of two isotopic species. These features do not allow stable isotopic tracer data analysis using straightforward analogy with radioactive tracer approaches, even though this practice is common. In this study, we present kinetic variables, models, and measurements for the analysis and interpretation of stable isotope tracer data. Assumptions and mathematical techniques for modeling the data when perturbation is both nonnegligible and negligible are discussed. Emphasis is placed on the rich information content of the dynamic portion of a stable isotope tracer curve and on the role of compartmental and noncompartmental modeling approaches for its interpretation. A presumed and commonly used analogy between the radioactive specific activity and stable isotopic enrichment is shown to be incorrect. We show that the proper analogue of specific activity is the tracer-to-tracee molar ratio. This variable is not a directly measurable one, but a formula is derived that allows its computation from the data. A method for reconstructing the time course in blood of the concentration component due to endogenous synthesis is presented. This allows measurement of the extent of the perturbation in the case where a nonweightless tracer is used. Special attention is given to data analysis originating from a multiple tracer experiment, a configuration necessary for studying more complex systems, e.g., the kinetics of interacting substrates.

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Koeppe, Robert A., David M. Raffel, Scott E. Snyder, Edward P. Ficaro, Michael R. Kilbourn, and David E. Kuhl. "Dual-[11C]Tracer Single-Acquisition Positron Emission Tomography Studies." Journal of Cerebral Blood Flow & Metabolism 21, no. 12 (2001): 1480–92. http://dx.doi.org/10.1097/00004647-200112000-00013.

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The ability to study multiple physiologic processes of the brain simultaneously within the same subject would provide a new means to explore the interactions between neurotransmitter systems in vivo. Currently, examination of two distinct neuropharmacologic measures with positron emission tomography (PET) necessitates performing two separate scans spaced in time to allow for radionuclide decay. The authors present results from a dual-tracer PET study protocol using a single dynamic-scan acquisition where the injections of two tracers are offset by several minutes. Kinetic analysis is used to estimate neuropharmacologic parameters for both tracers simultaneously using a combined compartmental model configuration. This approach results in a large reduction in total study time of nearly 2 hours for carbon-11–labeled tracers. As multiple neuropharmacologic measures are obtained at nearly the same time, interventional protocols involving a pair of dual-tracer scans become feasible in a single PET session. Both computer simulations and actual human PET studies were performed using combinations of three different tracers: [11C]flumazenil, N-[11C]methylpiperidinyl propionate, and [11C]dihydrotetrabenazine. Computer simulations of tracer-injection separations of 10 to 30 minutes showed the feasibility of the approach for separations down to 15 to 20 minutes or less. Dual-tracer PET studies were performed in 32 healthy volunteers using injection separations of 10, 15, or 20 minutes. Model parameter estimates for each tracer were similar to those obtained from previously performed single-injection studies. Voxel-by-voxel parametric images were of good quality for injections spaced by 20 minutes and were nearly as good for 15-minute separations, but were degraded noticeably for some model parameters when injections were spaced by only 10 minutes. The authors conclude that dual-tracer single-scan PET is feasible, yields accurate estimates of multiple neuropharmacologic measures, and can be implemented with a number of different radiotracer pairs.

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Romijn, J. A., D. L. Chinkes, J. M. Schwarz, and R. R. Wolfe. "Lactate-pyruvate interconversion in blood: implications for in vivo tracer studies." American Journal of Physiology-Endocrinology and Metabolism 266, no. 3 (1994): E334—E340. http://dx.doi.org/10.1152/ajpendo.1994.266.3.e334.

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We have evaluated lactate and pyruvate kinetics in whole blood or plasma by the addition of [1-13C]lactate (n = 5) or [1-13C]pyruvate (n = 5) and application of compartmental modeling to the resulting data. Pyruvate and lactate concentrations and tracer-to-tracee ratios were measured at frequent intervals for 45 min. Pyruvate and lactate tracer-to-tracee ratios equilibrated almost completely within 3-4 min in whole blood, whereas there was no isotopic exchange in plasma. The average rate of interconversion between unlabeled lactate and pyruvate was four to five times (pyruvate to lactate) and three to four times (lactate to pyruvate) the net production rate of lactate. We conclude that there is a very rapid interconversion between lactate and pyruvate in blood that has to be considered in the interpretation of in vivo tracer studies.

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Minchin, Peter E. H., and Michael R. Thorpe. "Using the short-lived isotope 11C in mechanistic studies of photosynthate transport." Functional Plant Biology 30, no. 8 (2003): 831. http://dx.doi.org/10.1071/fp03008.

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Tracer techniques have been central in studies of transport in plants. In the case of carbon, the only readily available radioactive tracer has been 14C, although 11C was used for a short time before 14C could be made. Tracers have usually had to be measured by destructive harvesting of the plant, giving a practical limit to the data resolution in both time and space. A major advantage of the short-lived, positron-emitting tracers, of which 11C is one example, is that in vivo measurement is possible, giving detailed time series of tracer data in many locations and opening up powerful new techniques of data analysis. Medical applications of these isotopes have utilised both dynamic imaging and time courses of uptake or washout. Unfortunately, few plant biology laboratories have realised the potential of these techniques, possibly because of the large physics infrastructure needed. In this paper we review the concepts behind the use of these short-lived tracers in plant physiology, and illustrate with several cases where 11C was an essential tool.

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Jensen, M. D., P. J. Rogers, M. G. Ellman, and J. M. Miles. "Choice of infusion-sampling mode for tracer studies of free fatty acid metabolism." American Journal of Physiology-Endocrinology and Metabolism 254, no. 5 (1988): E562—E565. http://dx.doi.org/10.1152/ajpendo.1988.254.5.e562.

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To determine the preferred infusion-sampling mode for isotopic studies of free fatty acid (FFA) metabolism, tracer [( 14C]palmitate) was infused into the left ventricle of five anesthetized dogs, and tracee ([3H]palmitate) was infused into three separate peripheral veins of each dog. The [14C]palmitate specific activity (SA) was lower in mixed venous than arterial blood, and [3H]palmitate SA was equal in both sites. The actual infusion rate of [3H]palmitate [2.15 +/- 0.31 X 10(5) disintegrations/min (dpm).kg-1.min-1] could be accurately predicted (2.14 +/- 0.32 X 10(5) dpm.kg-1.min-1) using the known [14C]palmitate infusion rate and the arterial plasma [14C]-to-[3H]palmitate ratio. In contrast, the mixed venous [14C]-to-[3H]palmitate ratio resulted in overestimates (P less than 0.05) of the actual [3H]palmitate infusion rate. In summary, venous tracer infusion with arterial blood sampling for FFA tracer studies provides the most accurate estimates of tracee rate of appearance.

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Cobelli, C., and G. Toffolo. "Constant specific activity input allows reconstruction of endogenous glucose concentration in non-steady state." American Journal of Physiology-Endocrinology and Metabolism 258, no. 6 (1990): E1037—E1040. http://dx.doi.org/10.1152/ajpendo.1990.258.6.e1037.

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In vivo studies on the glucose system often require its perturbation by an exogenous input of glucose, whereas glucose turnover is assessed by infusing a glucose tracer. The constant infusion represents the usual format of tracer administration, but it has no clear advantage other than simplicity. Here we propose a different tracer infusion format. It consists of infusing the tracer in parallel with unlabeled glucose so as to maintain a constant specific activity in the infusate. This protocol does not increase experimental complexity and provides new information on the glucose system in non-steady state by allowing reconstruction of the endogenous component of glucose concentration. This reconstruction only requires very general assumptions, such as tracer-tracee indistinguishability and mass conservation; in particular it is independent of the glucose model structure, i.e., number of compartments and their interconnections. A proof of the result is given for a general nonlinear model of the glucose system. The constant specific activity input is also advantageous for non-steady-state calculations, because it reduces the variation in the measured plasma glucose specific activity. The glucose system has served as the prototype, but the protocol is applicable to other blood-borne substances. The radioactive tracer case has been considered, but the same results apply to stable isotope tracers as well; in this case they also become relevant in a somewhat different context, i.e., kinetic studies in steady state.

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McCarthy, I. D., and S. P. Hughes. "Multiple tracer studies of bone uptake of 99mTc-MDP and 85Sr." American Journal of Physiology-Heart and Circulatory Physiology 256, no. 5 (1989): H1261—H1265. http://dx.doi.org/10.1152/ajpheart.1989.256.5.h1261.

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Multiple tracer outflow dilution studies were performed on the normal canine tibia. In all cases 125I-labeled albumin was used as a vascular tracer. In one series of experiments 99mTc-labeled methylene diphosphonate and [14C]sucrose were used as test tracers, and in a second series 85Sr and 22Na were used. A bolus of three tracers was injected into the tibial nutrient artery, and fractional concentrations appearing in the ipsilateral femoral vein were measured for a period of 5 min. A distributed model, containing parameters for capillary and bone permeability and apparent volumes of distribution of interstitial fluid, was fitted to these data. It was found that there was no discrimination between movement of 85Sr or 22Na from interstitial fluid space into bone. Transcapillary exchange does not appear to be a significant barrier to exchange between blood and bone surfaces.

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Broughton, Alistair, and Andy Shilton. "Tracer studies on an aerated lagoon." Water Science and Technology 65, no. 4 (2012): 611–17. http://dx.doi.org/10.2166/wst.2012.906.

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The city of Palmerston North, New Zealand, has two aerated lagoons as its secondary treatment facility. Interest about treatment efficiency led to an investigation into the hydraulics in the second lagoon to determine if further optimisation was viable. A tracer study using rhodamine WT was undertaken to ascertain the stimulus response output. Samples were also taken at 24 points within the lagoon to determine the tracer concentration profile throughout the lagoon. The mean residence time was determined to be 39.9 h compared with a theoretical residence time of 55.4 h. Peak concentration of the tracer at the outlet occurred at 0.44 of the mean residence time. The results of the tracer study pointed to 28% of volume being dead space. A subsequent sludge survey indicated that 26% of the design volume of the lagoon was filled with sludge. While the curved geometry of the lagoon did not appear to impact the hydraulics the fact that the first aerator is confined in a relatively smaller area will have locally boosted the mixing energy input in this inlet zone. From interpretation of the tracer response and the tracer distribution profiles it appears that the aerators are mixing the influent into the bulk flow effectively in the front end of the lagoon and that there was no evidence of any substantive short-circuiting path of concentrated tracer around to the outlet. The tracer distribution profiles gave direct insight as to how the tracer was being transported within the pond and should be used more often when conducting tracer studies. Comparison with the literature indicated that the lagoon's hydraulic efficiency was on par with a baffled pond system and it would be expected that addition of several baffles to the lagoon would provide minimal further improvement.

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Luca, Liliana, Stefan Ghimişi, and Iulian Popescu. "Studies Regarding the Movement on the Cochleoid." Advanced Materials Research 463-464 (February 2012): 147–50. http://dx.doi.org/10.4028/www.scientific.net/amr.463-464.147.

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There are given details about the cochleoid geometry and there are traced, based on equations, different areas of cochleoid, based on a supporting mechanism. They are shown the laws of variation of the curvature radius and of the tracer point coordinates. It is studied the material point movement on the cochleoid and there are presented relationships and diagrams for speeds and accelerations.

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Joshi, Aniket D., Robert A. Koeppe, Jeffrey A. Fessier, and Michael R. Kilbourn. "Signal Separation and Parameter Estimation in Noninvasive Dual-Tracer PET Scans using Reference-Region Approaches." Journal of Cerebral Blood Flow & Metabolism 29, no. 7 (2009): 1346–57. http://dx.doi.org/10.1038/jcbfm.2009.53.

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This is the first study to report results from a noninvasive dual-tracer positron emission tomography (PET) in humans not requiring arterial sampling, in which two radiotracers were injected closely in time within the same scan. These studies yield near simultaneous information on two different neuropharmacological systems, providing better characterization of a subject's neurologic condition. The noninvasive dual-tracer approach described in this study is based on the primary assumption that an appropriate bolus plus constant infusion protocol brings the reference tissue of the first radiotracer to steady state before injection of the second tracer. Two methods for separation of time-activity curves (TACs) and parameter estimation were investigated, namely (1) an extrapolation method, in which TACs of the first tracer were extrapolated over total scan duration followed by subtraction from dual-tracer TACs and (2) a simultaneous fitting method, in which reference-region models for both tracers were fitted simultaneously to dual-tracer TACs. Combinations of two reversible tracers ([11C]flumazenil and [11C]dihydrotetrabenazine) or one reversible and one irreversible tracer ([11C] N-methylpiperidinyl propionate) were used. After the dual-tracer scan, a single-tracer (ST) scan using one of the tracers was obtained for comparison of the dual-tracer results. Both approaches provided parameter estimates with intersubject regions-of-interest means typically within 10% of those obtained from ST scans without an appreciable increase in variance.

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Bychkov, E. "Tracer Diffusion Studies of Chalcogenide Glasses." Defect and Diffusion Forum 194-199 (April 2001): 909–18. http://dx.doi.org/10.4028/www.scientific.net/ddf.194-199.909.

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Salbu, B. "Radioactive tracer techniques in speciation studies." Environmental Technology Letters 8, no. 1-12 (1987): 381–92. http://dx.doi.org/10.1080/09593338709384497.

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Preston, Tom. "Existing and Emerging Technologies for Measuring Stable Isotope Labelled Retinol in Biological Samples: Isotope Dilution Analysis of Body Retinol Stores." International Journal for Vitamin and Nutrition Research 84, Supplement 1 (2014): 30–39. http://dx.doi.org/10.1024/0300-9831/a000186.

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This paper discusses some of the recent improvements in instrumentation used for stable isotope tracer measurements in the context of measuring retinol stores, in vivo. Tracer costs, together with concerns that larger tracer doses may perturb the parameter under study, demand that ever more sensitive mass spectrometric techniques are developed. GCMS is the most widely used technique. It has high sensitivity in terms of sample amount and uses high resolution GC, yet its ability to detect low isotope ratios is limited by background noise. LCMSMS may become more accessible for tracer studies. Its ability to measure low level stable isotope tracers may prove superior to GCMS, but it is isotope ratio MS (IRMS) that has been designed specifically for low level stable isotope analysis through accurate analysis of tracer:tracee ratios (the tracee being the unlabelled species). Compound-specific isotope analysis, where GC is interfaced to IRMS, is gaining popularity. Here, individual 13C-labelled compounds are separated by GC, combusted to CO2 and transferred on-line for ratiometric analysis by IRMS at the ppm level. However, commercially-available 13C-labelled retinol tracers are 2 - 4 times more expensive than deuterated tracers. For 2H-labelled compounds, GC-pyrolysis-IRMS has now become more generally available as an operating mode on the same IRMS instrument. Here, individual compounds are separated by GC and pyrolysed to H2 at high temperature for analysis by IRMS. It is predicted that GC-pyrolysis-IRMS will facilitate low level tracer procedures to measure body retinol stores, as has been accomplished in the case of fatty acids and amino acids. Sample size requirements for GC-P-IRMS may exceed those of GCMS, but this paper discusses sample preparation procedures and predicts improvements, particularly in the efficiency of sample introduction.

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Rydock, James P., and Brian K. Lamb. "A Continuous Fast-Response Dual-Tracer Analyzer for Halogenated Atmospheric Tracer Studies." Journal of Atmospheric and Oceanic Technology 11, no. 5 (1994): 1262–72. http://dx.doi.org/10.1175/1520-0426(1994)011<1262:acfrdt>2.0.co;2.

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Patterson, Kristine Y., and Claude Veillon. "Stable Isotopes of Minerals as Metabolic Tracers in Human Nutrition Research." Experimental Biology and Medicine 226, no. 4 (2001): 271–82. http://dx.doi.org/10.1177/153537020122600403.

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Enriched stable isotopes used as tracers have proven to be valuable in studies of the absorption and metabolism of minerals. Unlike radioisotopes, they can be used in high-risk population groups such as infants, children, and pregnant or lactating women. Estimates of mineral absorption can be made from the oral administration of a single tracer or from two tracers, one given orally and the other intravenously (IV). It is possible to determine the metabolism of the mineral with modeling based on the amount of the tracer or tracers in different biological samples. One of the key decisions in studies of this type is determining which enriched isotope and what amount to use. An example is given of calculations to estimate and compare the amounts of tracers needed for an absorption study. Methods for calculating the amounts of tracer in oral and IV doses are presented, and limits of detection and quantitation are discussed in terms of percent of enrichment and related to isotope ratio measurement precision. A general review of the use of mass spectrometric instruments for quantifying various stable isotopes is given.

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Fu, B. M., F. E. Curry, and S. Weinbaum. "A diffusion wake model for tracer ultrastructure-permeability studies in microvessels." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 6 (1995): H2124—H2140. http://dx.doi.org/10.1152/ajpheart.1995.269.6.h2124.

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We developed a time-dependent diffusion model for analyzing the concentration profiles of low-molecular-weight tracers in the interendothelial clefts of the capillary wall that takes into account the three-dimensional time-dependent filling of the surrounding tissue space. The model provides a connecting link between two methods to investigate transvascular exchange: electron-microscopic experiments to study the time-dependent wake formed by low-molecular-weight tracers (such as lanthanum nitrate) on the tissue side of the junction strand discontinuities in the interendothelial cleft of frog mesentery capillaries (R. H. Adamson and C. C. Michel. J. Physiol. Lond. 466: 303-327, 1993) and confocal-microscopic experiments to measure the spread of low-molecular-weight fluorescent tracers in the tissue space surrounding these microvessels (R. H. Adamson, J. F. Lenz, and F. E. Curry, Microcirculation 1: 251-265, 1994). We show that the interpretation of the presence of tracer as an all-or-none indication of a pathway across the junctional strand is likely to be incorrect for small solutes. Large-pore pathways, in which the local tracer flux densities are high, reach a threshold concentration for detection and are likely to be detected after relatively short perfusion times, whereas distributed small-pore pathways may not be detected until the tissue concentrations surrounding the entire vessel approach threshold concentrations. The analysis using this approach supports the hypothesis advanced by Fu et al. (J. Biomech. Eng. 116: 502-513, 1994) that the principal pathways for water and solutes of < 1.0 nm diameter across the interendothelial cleft may be different and suggests new experiments to test this hypothesis.

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Rosenblatt, J., D. Chinkes, M. Wolfe, and R. R. Wolfe. "Stable isotope tracer analysis by GC-MS, including quantification of isotopomer effects." American Journal of Physiology-Endocrinology and Metabolism 263, no. 3 (1992): E584—E596. http://dx.doi.org/10.1152/ajpendo.1992.263.3.e584.

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In metabolic tracer studies it is frequently useful to infuse tracers that are differently labeled variants of the same molecule. These tracers are known as isotopomers. Analysis of the enrichment of each isotopic analogue can be accomplished by gas chromatography-mass spectrometry (GC-MS). However, the raw GC-MS data must be corrected to give the information required. This paper addresses how to transform the raw GC-MS data, consisting of relative abundance ratios at specific ion masses, into relative molar ratios of tracer and tracee molecules. Several correction factors are necessary. First, the background must be measured and corrected for, since it is always present in the sample. Second, the abundances in the spectrum of the labeled molecule are different from those in the unlabeled molecule, and this proportionality "skew" is corrected. A third correction factor accounts for the overlapping spectra of two or more isotopomers that cannot be measured independently. The final correction removes the "double vision" effect that may appear in some spectra due to the presence of (M - H)+ species.

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Hötzl, H., W. Käss, and B. Reichert. "Application of Microbial Tracers in Ground Water Studies." Water Science and Technology 24, no. 2 (1991): 295–300. http://dx.doi.org/10.2166/wst.1991.0077.

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In situ tracing experiments have proved to be reliable tools to get direct information on subsurface flow direction and flow parameters. Beside dyes, salts, radioisotopes and drift bodies, microbes can be used as tracers. In several comparative experiments carried out in porous and karst aquifers by the International Association of Tracer Hydrology (ATH) the microbial markers (bacteria and bacteriophages) have shown promising results. They are especially suitable to explain and model the subsurface transport of microorganisms.

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Shilton, Andy N., and Julius N. Prasad. "Tracer studies of a gravel bed wetland." Water Science and Technology 34, no. 3-4 (1996): 421–25. http://dx.doi.org/10.2166/wst.1996.0459.

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Current rational design methods for subsurface flow wetlands idealise these systems as plug flow reactors. This assumption ignores the existence of longitudinal dispersion, short-circuiting, stagnant zones and so on. This paper reports on a series of three tracer experiments performed on a gravel bed wetland with a design hydraulic retention time of four days in order to study its hydraulic characteristics. The results present the hydraulic retention time distributions. The first tracer run using a single point inlet source had a mean time of 2.71 days. The second and third had the influent distributed across their width using an inlet manifold and yielded mean retention times of 3.47 and 3.41 days respectively. Further interpretation of these results indicates that the current plug flow assumption used in design can result in over estimation of treatment efficiency.

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Agunwamba, Jonah C. "Reduction of sampling time in tracer studies." Water Environment Research 69, no. 3 (1997): 343–49. http://dx.doi.org/10.2175/106143097x125542.

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Halnan, K. E. "No evidence of harm from tracer studies." BMJ 311, no. 6998 (1995): 192. http://dx.doi.org/10.1136/bmj.311.6998.192c.

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Sandomirski, K., S. Martin, G. Maret, H. Stark, and T. Gisler. "Highly birefringent colloidal particles for tracer studies." Journal of Physics: Condensed Matter 16, no. 38 (2004): S4137—S4144. http://dx.doi.org/10.1088/0953-8984/16/38/027.

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Cordova-Fraga, T., J. J. Bernal-Alvarado, G. Gutierrez-Juarez, M. Sosa, and M. Vargas-Luna. "Gastric activity studies using a magnetic tracer." Physiological Measurement 25, no. 5 (2004): 1261–70. http://dx.doi.org/10.1088/0967-3334/25/5/015.

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Hibbs, David E., Kenneth L. Parkhill, and John S. Gulliver. "Sulfur Hexafluoride Gas Tracer Studies in Streams." Journal of Environmental Engineering 124, no. 8 (1998): 752–60. http://dx.doi.org/10.1061/(asce)0733-9372(1998)124:8(752).

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Russell, Stewart. "Advantage of predictive modeling in tracer studies." American Journal of Physiology-Endocrinology and Metabolism 300, no. 1 (2011): E252. http://dx.doi.org/10.1152/ajpendo.00537.2010.

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Bauer, F., E. Bilz, and A. Freyer. "C-14 tracer studies on zeolite catalysis." Czechoslovak Journal of Physics 56, S4 (2006): D417—D423. http://dx.doi.org/10.1007/s10582-006-0532-5.

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Bauer, F., E. Bilz, and A. Freyer. "C-14 tracer studies on zeolite catalysis." Czechoslovak Journal of Physics 56, no. 1 (2006): D417—D423. http://dx.doi.org/10.1007/s10582-006-1047-9.

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TACHIBANA, HIROYUKI, TAKESHI MATSUMOTO, YASUO OGASAWARA, TAKAO KODAMA, and FUMIHIKO KAJIYA. "QUANTITATIVE DOUBLE-TRACER DIGITALRADIOGRAPHY BASED ON DESMETHYLIMIPRAMINE DEPOSITION: APPLICATION TO STUDIES ON MYOCARDIAL PERFUSION HETEROGENEITY." Journal of Mechanics in Medicine and Biology 03, no. 03n04 (2003): 261–73. http://dx.doi.org/10.1142/s0219519403000776.

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Desmethylimipramine (DMI), an α2-adrenergic antagonist, is a nearly ideal deposition tracer for evaluating the myocardial flow distribution with the least artifactual effects on microcirculation. Myocardial retentions of tritium- and iodine-125-labeled DMI (HDMI, IDMI) were confirmed to be satisfactory; the retentions of IDMI and HDMI at 1 min were 95 and 91% respectively in isolated Tyrode-perfused rabbit hearts (n=6) at a perfusion rate of 8.1 ml/min/g, and 98 and 96% respectively, in blood-perfused rat hearts (n=4) at a perfusion rate of 3.1 ml/min/g. Using these tracers combined with subtraction digitalradiography, it allowed the assessing of changes of myocardial flow distribution with 400×400 μ m 2 resolution. In blood-perfused rat hearts (n=4), the validity of this method was verified by the strong cross-correlation between regional densities of two tracers injected simultaneously (r=0.94) and the regression line having a slope close to one. Furthermore, in Tyrode-perfused rabbit hearts, the flow distributions were evaluated before and after decreasing perfusion rate moderately by 34% (n=7) and severely by 70% (n=7). Severe flow reduction increased the coefficient of variation of tracer density (CV) significantly from 19 to 25%, but CV did not change with moderate flow reduction (20 vs. 19%). Regional densities of two tracers were cross-correlated still substantially under severe low-flow perfusion (r=0.84). Accordingly, flow differences between originally high- and low-flow regions were enlarged under severe flow reduction. In conclusion, double-tracer digitalradiography based on the DMI deposition will be a potent method for the analysis of flow heterogeneity at microvascular levels.

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Hoerr, R. A., D. E. Matthews, D. M. Bier, and V. R. Young. "Leucine kinetics from [2H3]- and [13C]leucine infused simultaneously by gut and vein." American Journal of Physiology-Endocrinology and Metabolism 260, no. 1 (1991): E111—E117. http://dx.doi.org/10.1152/ajpendo.1991.260.1.e111.

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In amino acid tracer kinetic studies of the fed state, ingested amino acid may be taken up during its initial transit through splanchnic tissues and thus not enter the plasma compartment where tracer is infused. To investigate this possibility, adult human subjects received simultaneous intravenous (iv) and intragastric (ig) leucine tracer infusions, first during a postabsorptive (PA) 4-h primed continuous ig infusion of L-[1-13C]-leucine and L-[5,5,5-2H3]leucine iv, followed on a separate day by a fed infusion, in which an ig infusion of a liquid formula was started 2 h before the tracer infusion and continued throughout the tracer study. Subjects were accustomed to a constant experimental diet supplying 1.5 g protein.kg-1.day-1 and 41-45 kcal.kg-1.day-1 for 7 and 12 days before the PA and fed studies, respectively. For the PA study, plasma enrichment for the ig tracer was 3.34 +/- 0.27 (SE) mol + excess and for the iv tracer it was 4.18 +/- 0.10 (P less than 0.02). Enrichments of alpha-keto-isocaproic acid (KIC) were 3.24 +/- 0.16 (ig) and 3.02 +/- 0.14 (iv), respectively [not significant (NS)]. For the fed study, plasma leucine enrichment for the ig tracer was 2.15 +/- 0.14 and for the iv tracer was 2.84 +/- 0.09 (P less than 0.02). KIC enrichments were 2.02 +/- 0.08 (ig) and 2.24 +/- 0.08 (iv), respectively (NS). In the PA study, the ratio of the plasma leucine enrichments for the ig and iv tracers was 0.80 +/- 0.06 and in the fed experiment, 0.76 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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Basu, Rita, Barbara Di Camillo, Gianna Toffolo, et al. "Use of a novel triple-tracer approach to assess postprandial glucose metabolism." American Journal of Physiology-Endocrinology and Metabolism 284, no. 1 (2003): E55—E69. http://dx.doi.org/10.1152/ajpendo.00190.2001.

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Numerous studies have used the dual-tracer method to assess postprandial glucose metabolism. The present experiments were undertaken to determine whether the marked tracer nonsteady state that occurs with the dual-tracer approach after food ingestion introduces error when it is used to simultaneously measure both meal glucose appearance (Ra meal) and endogenous glucose production (EGP). To do so, a novel triple-tracer approach was designed: 12 subjects ingested a mixed meal containing [1-13C]glucose while [6-3H]glucose and [6,6-2H2]glucose were infused intravenously in patterns that minimized the change in the plasma ratios of [6-3H]glucose to [1-13C]glucose and of [6,6-2H2]glucose to endogenous glucose, respectively. Ra meal and EGP measured with this approach were essentially model independent, since non-steady-state error was minimized by the protocol. Initial splanchnic glucose extraction (ISE) was 12.9% ± 3.4%, and suppression of EGP (EGPS) was 40.3% ± 4.1%. In contrast, when calculated with the dual-tracer one-compartment model, ISE was higher ( P < 0.05) and EGPS was lower ( P < 0.005) than observed with the triple-tracer approach. These errors could only be prevented by using time-varying volumes different for Ra meal and EGP. Analysis of the dual-tracer data with a two-compartment model reduced but did not totally avoid the problems associated with marked postprandial changes in the tracer-to-tracee ratios. We conclude that results from previous studies that have used the dual-tracer one-compartment model to measure postprandial carbohydrate metabolism need to be reevaluated and that the triple-tracer technique may provide a useful approach for doing so.

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Schröter, Jennifer, Daniel Rieger, Christian Stassen, et al. "ICON-ART 2.1: a flexible tracer framework and its application for composition studies in numerical weather forecasting and climate simulations." Geoscientific Model Development 11, no. 10 (2018): 4043–68. http://dx.doi.org/10.5194/gmd-11-4043-2018.

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Abstract. Atmospheric composition studies on weather and climate timescales require flexible, scalable models. The ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) provides such an environment. Here, we introduce the most up-to-date version of the flexible tracer framework for ICON-ART and explain its application in one numerical weather forecast and one climate related case study. We demonstrate the implementation of idealised tracers and chemistry tendencies of different complexity using the ART infrastructure. Using different ICON physics configurations for weather and climate with ART, we perform integrations on different timescales, illustrating the model's performance. First, we present a hindcast experiment for the 2002 ozone hole split with two different ozone chemistry schemes using the numerical weather prediction physics configuration. We compare the hindcast with observations and discuss the confinement of the vortex split using an idealised tracer diagnostic. Secondly, we study AMIP-type integrations using a simplified chemistry scheme in conjunction with the climate physics configuration. We use two different simulations: the interactive simulation, where modelled ozone is coupled back to the radiation scheme, and the non-interactive simulation that uses a default background climatology of ozone. Additionally, we introduce changes of water vapour by methane oxidation for the interactive simulation. We discuss the impact of stratospheric ozone and water vapour variations in the interactive and non-interactive integrations on the water vapour tape recorder, as a measure of tropical upwelling changes. Additionally we explain the seasonal evolution and latitudinal distribution of the age of air. The age of air is a measure of the strength of the meridional overturning circulation with young air in the tropical upwelling region and older air in polar winter downwelling regions. We conclude that our flexible tracer framework allows for tailor-made configurations of ICON-ART in weather and climate applications that are easy to configure and run well.

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Wolfe, Robert R., Sanghee Park, Il-Young Kim, et al. "Quantifying the contribution of dietary protein to whole body protein kinetics: examination of the intrinsically labeled proteins method." American Journal of Physiology-Endocrinology and Metabolism 317, no. 1 (2019): E74—E84. http://dx.doi.org/10.1152/ajpendo.00294.2018.

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Intrinsically labeled dietary proteins have been used to trace various aspects of digestion and absorption, including quantifying the contribution of dietary protein to observed postprandial amino acid and protein kinetics in human subjects. Quantification of the rate of appearance in peripheral blood of an unlabeled (tracee) amino acid originating from an intrinsically labeled protein (exogenous Ra) requires the assumption that there is no dilution of the isotope enrichment of the protein-bound amino acid in the gastrointestinal tract or across the splanchnic bed. It must also be assumed that the effective volume of distribution into which the tracer and tracee appear can be reasonably estimated by a single value and that any recycling of the tracer is minimal and thus does not affect calculated rates. We have assessed these assumptions quantitatively using values from published studies. We conclude that the use of intrinsically labeled proteins as currently described to quantify exogenous Ra systematically underestimates the true value. When used with the tracer-determined rates of amino acid kinetics, underestimation of exogenous Ra from the intrinsically labeled protein method likely translates to incorrect conclusions regarding protein breakdown, including the effect of a protein meal and the anabolic impact of the speed of digestion and absorption of amino acids. Estimation of exogenous Ra from the bioavailability of ingested protein has some advantages as compared with the intrinsically labeled protein method. We therefore conclude that the bioavailability method for estimating exogenous Ra is preferable to the intrinsically labeled protein method.

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Dimitrova, Tsvetelina, Frank Repmann, and Dirk Freese. "Preparation of 15N-labeled Potassium Ferrocyanide for Tracer Studies." Environment and Pollution 6, no. 2 (2017): 41. http://dx.doi.org/10.5539/ep.v6n2p41.

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Isotopic labels are widely used to trace the fate and cycling of common environmental contaminants. Many of the labeled materials are not available commercially and, depending on the complexity of the substance, the label and the enrichment level, custom syntheses are costly. A simple, straightforward, and cost effective method for the preparation of a highly enriched, 15N-labeled potassium ferrocyanide (K4[Fe(C15N)6]*3H2O) has been developed to meet the requirements of related tracer experiments and minimize their costs. In this case, the 15N label was used to quantify iron cyanide detoxification (biodegradation and/or transformation) within soil-plant-systems. 15N-labeled potassium cyanide (KC15N) and a ferrous iron salt have been used for the synthesis. Extensive qualitative and quantitative analyses showed a product, entirely identical in its functional and elemental components to commercial non-labeled K4[Fe(CN)6]*3H2O and in its 15N enrichment to the KC15N used for its synthesis. To investigate their behavior and fate in various environmental compartments, other labeled iron or metal cyanide complexes might be synthesized in analogous manner.

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Endres, Christopher J., and Richard E. Carson. "Assessment of Dynamic Neurotransmitter Changes with Bolus or Infusion Delivery of Neuroreceptor Ligands." Journal of Cerebral Blood Flow & Metabolism 18, no. 11 (1998): 1196–210. http://dx.doi.org/10.1097/00004647-199811000-00006.

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To describe the effect of endogenous dopamine on [11C]raclopride binding, we previously extended the conventional receptor ligand model to include dynamic changes in neurotransmitter concentration. Here, we apply the extended model in simulations of neurotransmitter competition studies using either bolus or bolus-plus-infusion (B/I) tracer delivery. The purpose of this study was (1) to develop an interpretation of the measured change in tracer binding in terms of underlying neurotransmitter changes, and (2) to determine tracer characteristics that maximize sensitivity to neurotransmitter release. A wide range of kinetic parameters was tested based on existing reversible positron emission tomography tracers. In simulations of bolus studies, the percent reduction in distribution volume (Δ V) caused by a neurotransmitter pulse was calculated. For B/I simulations, equilibrium was assumed, and the maximum percent reduction in tissue concentration (Δ C) after neurotransmitter release was calculated. Both Δ V and Δ C were strongly correlated with the integral of the neurotransmitter pulse. The values of Δ V and Δ C were highly dependent on the kinetic properties of the tracer in tissue, and Δ V could be characterized in terms of the tissue free tracer concentration. The value of Δ V was typically maximized for binding potentials of ~3 to 10, with Δ C being maximized at binding potentials of ~1 to 2. Both measures increased with faster tissue-to-blood clearance of tracer and lower nonspecific binding. These simulations provide a guideline for interpreting the results of neurotransmitter release studies and for selecting radiotracers and experimental design.

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McDougall, Trevor J., Sjoerd Groeskamp, and Stephen M. Griffies. "On Geometrical Aspects of Interior Ocean Mixing." Journal of Physical Oceanography 44, no. 8 (2014): 2164–75. http://dx.doi.org/10.1175/jpo-d-13-0270.1.

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Abstract The small-slope approximation to the full three-dimensional diffusion tensor of epineutral diffusion gives exactly the same tracer flux as the commonly used projected nonorthogonal diffusive flux of layered ocean models and of theoretical studies. The epineutral diffusion achieved by this small-slope approximation is not exactly in the direction of the correct epineutral tracer gradient. That is, the use of the small-slope approximation leads to a very small flux of tracer in a direction in which there is no epineutral gradient of tracer. For (the tracer) temperature or salinity, the difference between the correct epineutral gradient and the small-slope approximation to it is proportional to neutral helicity. The authors also make the point that small-scale turbulent mixing processes act to diffuse tracers isotropically (i.e., the same in each spatial direction) and hence it is strictly a misnomer to call this process “dianeutral diffusion” or “vertical diffusion.” This realization also has implications for the diffusion tensor.

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Schwesig, D., and A. Bergmann. "Use of anthropogenic gadolinium as a tracer for bank filtrate in drinking water wells." Water Supply 11, no. 6 (2011): 654–58. http://dx.doi.org/10.2166/ws.2011.097.

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Knowledge of the amount of bank filtrate in raw water is crucial for drinking water suppliers using water wells in close proximity to rivers, in particular if those rivers are strongly affected by anthropogenic activities, e.g. receiving effluents from waste water treatment plants. Analysis of organic micropollutants as tracer compounds is costly and time-consuming, and results may be biased by processes such as sorption, degradation or even by other input pathways such as land use activities. In this study, the use of gadolinium (Gd) as an alternative conservative tracer to indicate the amount of bank filtrate in raw water from drinking water wells close to rivers was investigated. In two case studies in Germany and Luxembourg, river water and water from drinking water wells at several distances from the rivers was sampled and analysed for anthropogenic Gd as well as for some of the organic trace pollutants conventionally used as tracer compounds. The amount of bank filtrate as calculated from Gd was compared with the estimates derived by conventional tracers and by hydrological flux modelling. The results indicated that the measurement of Gd may provide a promising alternative to monitor infiltration of river water in ground water used for production of drinking water.

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Ellis, J. B., D. M. Revitt, P. Lister, C. Willgress, and A. Buckley. "Experimental studies of sewer exfiltration." Water Science and Technology 47, no. 4 (2003): 61–67. http://dx.doi.org/10.2166/wst.2003.0221.

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The effects of joint openings and in-pipe sediment on exfiltration losses in an experimental sewer are reported and the influence of flow and head on loss rates are also evaluated. Exfiltration rates tend to be exponential with changes in head for clean-water tests but exhibit power functions when the pipe is subject to sedimentation. In-pipe sediment leads to an effective sealing of joints especially if the invert deposits are both organic in nature and contain saturated adhesive material such as shredded toilet tissue. Simple tracer techniques are described to quantify exfiltration losses and the potential effects of tracer adsorption by in-pipe solids are evaluated.

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Calabria, Ferdinando, Robert Pichler, Mario Leporace, et al. "68Ga/64Cu PSMA Bio-Distribution in Prostate Cancer Patients: Potential Pitfalls for Different Tracers." Current Radiopharmaceuticals 12, no. 3 (2019): 238–46. http://dx.doi.org/10.2174/1874471012666190515090755.

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Background:68Ga-PSMA is a widely useful PET/CT tracer for prostate cancer imaging. Being a transmembrane protein acting as a glutamate carboxypeptidase enzyme, PSMA is highly expressed in prostate cancer cells. PSMA can also be labeled with 64Cu, offering a longer half-life and different resolution imaging. Several studies documented bio-distribution and pitfalls of 68Ga-PSMA as well as of 64Cu- PSMA. No data are reported on differences between these two variants of PSMA. Our aim was to evaluate physiological distribution of these two tracers and to analyze false positive cases.Methods:We examined tracer bio-distribution in prostate cancer patients with negative 68Ga-PSMA PET/CT (n=20) and negative 64Ga-PSMA PET/CT (n=10). A diagnostic pitfall for each tracer was documented.Results:Bio-distribution of both tracers was similar, with some differences due to renal excretion of 68Ga- PSMA and biliary excretion of 64Cu-PSMA. 68Ga-PSMA uptake was observed in sarcoidosis while 64Cu- PSMA uptake was recorded in pneumonitis.Discussion:Both tracers may present similar bio-distribution in the human body, with similar uptake in exocrine glands and high intestinal uptake. Similarly to other tracers, false positive cases cannot be excluded in clinical practice.Conclusion:The knowledge of difference in bio-distribution between two tracers may help in interpretation of PET data. Diagnostic pitfalls can be documented, due to the possibility of PSMA uptake in inflammation. Our results are preliminary to future studies comparing diagnostic accuracies of 68Ga-PSMA and 64Cu-PSMA.

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Romanski, S. A., Rita M. Nelson, and Michael D. Jensen. "Meal fatty acid uptake in human adipose tissue: technical and experimental design issues." American Journal of Physiology-Endocrinology and Metabolism 279, no. 2 (2000): E447—E454. http://dx.doi.org/10.1152/ajpendo.2000.279.2.e447.

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The adipose tissue uptake of dietary fat has been studied using fatty acid radiotracers incorporated into a meal, followed by adipose tissue biopsies. A number of experimental design issues, including the use of isotopic tracers to measure meal fatty acid oxidation and plasma appearance of tracer, as well as the heterogeneity of adipose tissue fatty acid uptake, have been addressed. We examined these questions in a study of 24 volunteers (12 men and 12 women) who consumed a meal containing [3H]triolein and [14C]triolein. Slight differences in the purity of [3H]triolein vs. [14C]triolein were found, which could affect the apparent adipose tissue uptake of meal fatty acids. The adipose tissue triglyceride specific activity from bilateral biopsy sites agreed well, implying that a unilateral biopsy is satisfactory for measuring tracer uptake. Meal fatty acid oxidation measured using [3H]triolein and [14C]triolein was well correlated ( r = 0.79, P < 0.0001). The peak tracer appearance in plasma chylomicrons occurred 1 h after the ingestion of a second, unlabeled meal. Our findings have implications for the experimental design of future meal fatty acid tracer/adipose tissue biopsy studies.

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Chernokozhev, D. A., K. I. Kuznetsova, R. R. Gazimov, A. S. Zasedatelev, and M. S. Khozyaiov. "MODERN METHODOLOGICAL POSSIBILITIES OF THE TRACER METHOD FOR ASSESSING THE COVERAGE OF AN OIL RESERVOIR BY FLOODING." BULLETIN of Russian Academy of Natural Sciences 21 (April 2021): 24–28. http://dx.doi.org/10.52531/1682-1696-2021-21-1-24-28.

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The article presents the results of modeling tracer studies of the process of flooding of an oil reservoir. As a result of the studies, the dependences on the time of the change in the volume occupied by the injected water were obtained. Formulas are given that allow us to calculate the values of the coefficient of coverage of the reservoir area by flooding as a whole and the contribution of each injection well to flooding. The technology is implemented by continuously pumping the tracer into the injection well. Continuous injection of different tracers into different injection wells allows for operational monitoring of oil field development

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Ives, K. J., and O. Hoyer. "Tracer studies of the hydraulics of tapered flocculation." Water Science and Technology 37, no. 10 (1998): 69–77. http://dx.doi.org/10.2166/wst.1998.0379.

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A pilot plant, with a flow capacity of 600 m3/h, was constructed as a tapered (diminishing velocity gradients) flocculation system. The flowthrough patterns of a series of 4 tanks and a transfer channel were evaluated hydraulically using an alkali (NaOH) as a tracer, using pH probes. Ideally, the tanks, containing stirrers, and the channel should have plug flow conditions. The actual conditions were affected by the inlet and outlet arrangements, and directions of rotations of the stirrers. By creating a high steady-state plateau of pH11, the subsequent decrease of pH when the alkali was cut off gave a measure of the flow regime in each tank and the channel. By adjustment of the inlet and outlet weirs and slots, the stirrers and the insertion of baffles, a best design was derived allowing for compromises among the units. It was shown that an adjustment to optimise one tank or channel affected the performance of both upstream and downstream units.

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Bychkov, E. "Tracer diffusion studies of ion-conducting chalcogenide glasses." Solid State Ionics 136-137, no. 1-2 (2000): 1111–18. http://dx.doi.org/10.1016/s0167-2738(00)00516-6.

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Aoyama, Michio, Pavel P. Povinec, and Joan-Albert Sanchez-Cabeza. "The Southern Hemisphere Ocean Tracer Studies (SHOTS) project." Progress in Oceanography 89, no. 1-4 (2011): 1–6. http://dx.doi.org/10.1016/j.pocean.2010.12.002.

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Botto, Robert E. "Solid 13C NMR tracer studies to probe coalification." Energy & Fuels 1, no. 2 (1987): 228–30. http://dx.doi.org/10.1021/ef00002a017.

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Eisenreich, Wolfgang, Ernst Kupfer, Wolfgang Weber, and Adelbert Bacher. "Tracer Studies with Crude U-13C-Lipid Mixtures." Journal of Biological Chemistry 272, no. 2 (1997): 867–74. http://dx.doi.org/10.1074/jbc.272.2.867.

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Barrett, P. Hugh R., and David M. Foster. "Design and analysis of lipid tracer kinetic studies." Current Opinion in Lipidology 7, no. 3 (1996): 143–48. http://dx.doi.org/10.1097/00041433-199606000-00006.

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Boufadel, Michel C., Makram T. Suidan, and Albert D. Venosa. "Tracer Studies in Laboratory Beach Simulating Tidal Influences." Journal of Environmental Engineering 132, no. 6 (2006): 616–23. http://dx.doi.org/10.1061/(asce)0733-9372(2006)132:6(616).

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Cabrera, M. L., and D. E. Kissel. "Review and simplification of calculations in15N tracer studies." Fertilizer Research 20, no. 1 (1989): 11–15. http://dx.doi.org/10.1007/bf01055396.

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Atkinson, A., D. P. Moon, D. W. Smart, and R. I. Taylor. "Tracer diffusion studies in NiO bicrystals and polycrystals." Journal of Materials Science 21, no. 5 (1986): 1747–57. http://dx.doi.org/10.1007/bf01114735.

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HAPPEL, J. "Modeling transient tracer studies in plug-flow reactors." Journal of Catalysis 123, no. 1 (1990): 12–20. http://dx.doi.org/10.1016/0021-9517(90)90153-b.

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