Topic
Transient equilibrium
About: Transient equilibrium is a research topic. Over the lifetime, 17 publications have been published within this topic receiving 593 citations.
Papers
TL;DR: An infusion protocol consisting of bolus plus continuous infusion of CF was designed and applied and has the potential to shorten scan time and simplify the acquisition and processing of scan and blood data.
Abstract: Positron emission tomography studies with the opiate antagonist [18F]cyclofoxy ([18F]CF) were performed in baboons. Bolus injection studies demonstrated initial uptake dependent on blood flow. The late uptake showed highest binding in caudate nuclei, amygdala, thalamus, and brainstem and the least accumulation in cerebellum. By 60 min postinjection, regional brain radioactivity cleared at the same rate as metabolite-corrected plasma, i.e., transient equilibrium was achieved. Compartmental modeling methods were applied to time-activity curves from brain and metabolite-corrected plasma. Individual rate constants were estimated with poor precision. The model estimate of the total volume of distribution (VT), representing the ratio of tissue radioactivity to metabolite-corrected plasma at equilibrium, was reliably determined. The apparent volume of distribution (Va), the concentration ratio of tissue to metabolite-corrected plasma during transient equilibrium, was compared with the fitted VT values to determine if single-scan methods could provide accurate receptor measurements. Va significantly overestimated VT and produced artificially high image contrast. These differences were predicted by compartment model theory and were caused by a plasma clearance rate that was close to the slowest tissue clearance rate. To develop a simple method to measure VT, an infusion protocol consisting of bolus plus continuous infusion (B/I) of CF was designed and applied in a separate set of studies. The Va values from the B/I studies agreed with the VT values from both B/I and bolus studies. This infusion approach can produce accurate receptor measurements and has the potential to shorten scan time and simplify the acquisition and processing of scan and blood data.
375 citations
TL;DR: Two positron emission tomography measurements were performed in each of six healthy men, the first with rapid bolus injection and the second with continuous infusion of [11C]raclopride, representing cross-validation of these methods.
Abstract: Several approaches have been applied for quantification of D2 dopamine receptors in positron emission tomography studies using [11C]raclopride. Initial approaches were based on analyses of data obtained after rapid bolus injection of [11C]raclopride. A continuous infusion paradigm has more recently been applied. The current study compares these approaches in healthy men. Two positron emission tomography measurements were performed in each of six healthy men, the first with rapid bolus injection and the second with continuous infusion of [11C]raclopride. In rapid bolus injection, the binding potential was calculated by the following methods. One approach is the kinetic analysis using the standard three-compartment model. Another is to define a transient equilibrium at the moment when the specific binding reaches its maximum. In continuous infusion, binding potential was calculated by using time-activity data at equilibrium condition. All methods gave almost identical binding potential, representing cross-v...
169 citations
TL;DR: The influence function is used to introduce the concept of a practical equilibrium, which requires conditions which are not fulfilled for high-energy photon beams, but a transient equilibrium can be considered.
Abstract: The concept of electronic equilibrium is presented in its general aspects. Absolute equilibrium requires conditions which are not fulfilled for high-energy photon beams, but a transient equilibrium can be considered. The influence function is used to introduce the concept of a practical equilibrium. Transition stages at a plane interface perpendicular to the beam direction are dealt with by a simplified form of the influence function, reduced to one parameter. Some particular conditions are considered for which experimental data are available, e.g. interface between vacuum and medium, interface between low-density and high-density media, and the interface between media of different atomic composition.
47 citations
Journal Article•
TL;DR: It is shown that terms describing equilibrium are not used in the same way by various authors, and specific definitions are proposed that suggest that secular equilibrium is a subset of transient equilibrium.
Abstract: Equations describing serial radioactive decay are reviewed along with published descriptions of transient and secular equilibrium. It is shown that terms describing equilibrium are not used in the same way by various authors. Specific definitions are proposed; they suggest that secular equilibrium is a subset of transient equilibrium.
18 citations
TL;DR: The physical decay patterns of 95Zr–95Nb accumulated by rat tissues are determined to determine whether some tissues show preference for zirconium- 95, while others concentrate niobium-95 in four days after intraperitoneal administration of 95 Zr– 95Nb in transient equilibrium.
Abstract: ZIRCONIUM-95, one of the γ-ray emitting isotopes in fall-out, has a physical half-life of 65 days. It decays to niobium-95 which emits γ-rays and has a physical half-life of 35 days. Therefore, both these isotopes contribute to the total radiation hazard of fall-out. During the first year, these two isotopes share no less than 20 per cent of the total activity of fission products aged from a few days to one year1. A knowledge of the metabolism of the parent isotope (zirconium-95) in relation to that of the daughter (niobium-95) is essential in order to estimate the total internal radiation hazard due to 95Zr–95Nb because the parent and the daughter decay at different rates. Further, the photopeak energies of zirconium-95 (0.72 MeV) and niobium-95 (0.764 MeV) are so close to one another that it is not possible to resolve and identify the individual photopeaks of the parent and daughter isotopes by γ-scintillation spectrometry1. Therefore, we have determined the physical decay patterns of 95Zr–95Nb accumulated by rat tissues to determine whether some tissues show preference for zirconium-95, while others concentrate niobium-95 in four days after intraperitoneal administration of 95Zr–95Nb in transient equilibrium (Fig. 1).
16 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2017 | 1 |
| 2014 | 1 |
| 2012 | 1 |
| 2008 | 3 |
| 2006 | 1 |
| 1998 | 1 |