Small Amounts Of Tracer Research Articles

CFD Simulation of Liquid–Liquid Two-Phase Hydrodynamics and Axial Dispersion Analysis for a Non-Pulsed Disc and Doughnut Solvent Extraction Column

ABSTRACTA two-phase computational fluid dynamics (CFD) simulation for a non-pulsed disc and doughnut solvent extraction column has been developed with commercial CFD software FLUENT. Simulated hydrodynamic results including phase distribution, velocity fields, and holdup are given, which enables predicted holdup to be compared with experimental data. Average absolute relative deviation (AARD) of experimental data and CFD prediction in this study is found to be 10.8%, which is comparable to the estimated error in the experimental data and the predictions from traditional correlations in the literature. To estimate the extent of axial dispersion, a species transport model is used for the continuous phase with a small amount of tracer introduced in the continuous phase, when Sauter mean diameter of the dispersed phase is set to be 3.5 mm. A two-point monitoring method is used to estimate a Peclet number. The tracer concentration distribution in the two-dimensional distance–time space is interpreted with MATLAB along with the experimental measurement. The simulated Peclet numbers are compared with column experiments, and in general the simulation underestimates the experimental data by 60%. Introducing a modified drag law improves the predictions. This work shows that CFD can successfully model the performance of a non-pulsed disc and doughnut solvent extraction column.

Usefulness of 11C-Choline Positron Emission Tomography for Genital Chlamydial Infection Assessment in a Balb/c Murine Model

The aim of this study is to explore the feasibility of 11C-Choline PET in the assessment of the degree of inflammation in the Chlamydia muridarum genital infection model. Forty female Balb/c mice received 2.5 mg of medroxyprogesterone acetate i.m. 9 and 2 days prior to the infection: 21 mice were infected by C. muridarum into the vaginal vault, 12 mice were treated with inactivated chlamydiae, and 7 mice were SPG buffer-treated as negative controls. Three healthy control mice were not treated with progesterone. Mice in each category were randomly subdivided in two groups: (1) sacrificed at 5, 10, 15, and 20 days for histological analysis and (2) undergoing 11C-Choline PET at days 5, 10, and 20 post-infection (20 MBq of 11C-Choline, uptake time of 10 min, acquisition through a small-animal PET tomograph for 15 min). Infected animals showed a significantly higher standardized uptake value than both controls and animals inoculated with heat-inactivated chlamydiae in each PET scan (P<0.05). All organs of the infected animals had scores of inflammation ranging between 2 and 3 at day 5, decreasing to 1-2 at day 20. This preliminary result demonstrated that 11C-Choline PET can highlight a specific proliferation mechanism of inflammatory cells induced by C. muridarum, thanks to a very high sensitivity in detecting very small amounts of tracer in inflammatory cells.

Incorporation and intracellular hydrolysis of 131 I-albumin injected in rat testis.

A method of cell separation by enzymatic attack and filtration was applied after injecting the testes. The results indicated that in the case of the interstitial injections, the fraction rich in interstitial cells captures from 30 to 50 times more RISA than that rich in germinal cells, and from 10 to 20 times more than that rich in Sertoli cells. Following the intratubular injection, radioactivity incorporation was greatly reduced and there were no differences in RISA (radioactivity/mg of protein) among the cell fractions. It was concluded that Sertoli cells do not have in its apical side a phagocytic activity comparable to that of the interstitial macrophages and possibly they incorporate only a small amount of tracer by a process of moderate pinocytosis.

Tracer Study of Mixing and Transport in the Upper Hudson River with Multiple Dams

In October 2001, ∼0.2mol of SF6 was injected into the upper Hudson River, a modified natural channel with multiple dams, at Ft. Edward, N.Y. The tracer was monitored for 7 days as it moved ∼50km downriver. The longitudinal evolution of the tracer distribution was used to estimate one-dimensional advection (9.0±0.2kmd-1) and dispersion (17.3±4.0m2s-1) along the river axis. Comparison of these results to tracer studies on channels without dams suggests that dams reduce longitudinal dispersion below the value expected in a natural channel with the same discharge. SF6 loss through air–water gas exchange along the river and at two dams (10.7m combined height) was estimated by observing decay in peak concentration. Losses at dams (approximately 50% per dam) were dominant. The estimated gas exchange at dams was compared to a simple model adapted from those available in literature. Small amounts of tracer were trapped in a canal segment (∼5km long) that parallels the river, where advection and dispersion were sha...

Evaluating Brain Death with Positron Emission Tomography: Case Report on Dynamic Imaging of 18F‐Fluorodeoxyglucose Activity after Intravenous Bolus Injection

A dynamic positron emission tomography (PET) study of the head was performed over 1 hour after the intravenous bolus administration of 18F-fluorodeoxyglucose (18F-FDG) to a 18-year-old patient with the clinical diagnosis of brain death. This dynamic PET study was performed on the seventh day after a severe posttraumatic closed-head injury. No intracerebral uptake or retention of tracer was noted, consistent with a diffuse absence of brain metabolism. A small amount of tracer was noted to slowly rise over time within the sagittal sinus, indicating that visualization of sagittal sinuses on technetium 99m-diethylene-triaminepentaacetic acid planar images could provide a falsely negative scintigraphic evaluation for the presence of brain death. It is concluded that PET FDG imaging may be a useful technique in evaluating patients for brain death.

A simple technique for introducing anterograde and retrograde tracers into the vestibular and cochlear sensory organs.

The standard method for labeling the afferent and efferent innervation of the cochlear and vestibular sensory organs is by microinjection of tracer substances into the labyrinth. Injection of small amounts of tracer often result in incomplete and inconsistent labeling, but large injections can cause spurious labeling of brainstem structures due to diffusion from perilymph to cerebrospinal fluid. Effective labeling with minimal artifact can, however, be achieved by a relatively simple method involving placement of a tracer-saturated pledglet of gelatin sponge in the round window after rupture of its membrane. The gelatin sponge simultaneously acts as a continuous-release vehicle for the tracer and prevents reflux of perilymph and tracer into the middle ear cavity. Use of this technique produces labeling with a degree of intensity and anatomic detail that rivals that seen with more complicated methods of tracer placement.

Is there a dopaminergic projection from the A11 catecholamine cell group to the amygdala?

The dopaminergic nature of the pathway from the subparafascicular thalamic nucleus and its adjacent region to the amygdala was reexamined by means of retrograde fluorescent tracers coupled with tyrosine hydroxylase (TH) immunofluorescence. After injecting a small amount of tracer into the amygdala, retrogradely labeled cells were found in the subparafascicular thalamic nucleus and its adjacent periventricular region. TH immunofluorescence showed that these labeled cells completely lacked TH immunoreactivity. Similar results were obtained when a larger amount of tracer was applied to the amygdala. The present study, in contrast to the previous report describing the dopaminergic innervation of the amygdala by the cells in and around the subparafascicular area (A11 catecholamine cell group), indicates that the A11 cell group does not contribute to a dopaminergic input to the amygdala.

Evidence for a blood-thymus barrier using electron-opaque tracers.

In order to verify the existence of a blood-thymus barrier to circulating macromolecules, the permeability of the vessels of the thymus was analyzed in young adult mice using electron opaque tracers of different molecular dimensions (horseradish peroxidase, cytochrome c, catalase, ferritin, colloidal lanthanum). Results show that although blood-borne macromolecules do penetrate the thymus, their parenchyma] distribution is limited to the medulla of the lobe by several factors: (a) the differential permeability of the various segments of the vascular tree; (b) the spatial segregation of these segments within the lobe; (c) the strategic location of parenchymal macrophages along the vessels. The cortex is exclusively supplied by capillaries, which have impermeable endothelial junctions. Although a small amount of tracer is transported by plasmalemmal vesicles through the capillary endothelium, this tracer is promptly sequestrated by macrophages stretched out in a continuous row along the cortical capillaries and it does not reach the intercellular clefts between cortical lymphocytes and reticular cells. The medulla contains all the leaky vessels, namely postcapillary venules and arterioles. Across the walls of the venules, large quantities of all injected tracers escape through the clefts between migrating lymphocytes and endothelial cells; also the arterioles have a small number of endothelial junctions which are permeable to peroxidase, but do not allow passage of tracers of higher molecular weight. The tracers released by the leaky vessels penetrate the intercellular clefts of the medulla, but they never reach the cortical parenchyma, even at long time intervals after the injection. Therefore, a blood-thymus barrier to circulating macromolecules does exist, but is limited to the cortex. Medullary lymphocytes are freely exposed to blood-borne substances.

Brain scanning in the diagnosis of intracranial abscess.

Radioisotope brain scanning was found to give positive results in 16 of the 18 patients with brain abscess, and in all 6 patients with subdural abscess. Abnormal uptake was also seen in patients with cerebritis, meningitis, cavernous sinus thrombophlebitis, and abscess of the scalp. A study based on tissue-counting for radioactive content revealed a high uptake in the capsule of an abscess and a very small amount of tracer in the purulent material in the first several hours after the radiopharmaceutical injection.