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At least 1,333 records · Page 74Linked to original sources
PubMed1976

Evaluation of perfusion with the 81Rb-81mKr generator.

The development of the 81Rb-81mKr generator-delivery system has made available an ultrashort (13-sec) half-life radionuclide for continuous, constant-rate delivery as a gas, or as an isotonic, nonionic solution in 5% dextrose and water. This system has been evaluated and applied to the scintigraphic imaging of various organs and anatomic regions by intravenous and intraarterial infusion and by inhalation and deglutition. This diffusible, noble gas is inert chemically and biologically. When the gas is administered intraarterially, the volume of tissue being perfused may be defined with the scintillation camera. The 13-sec half-life is of a similar magnitude to the rate of capillary exchange, producing a heterogeneous image with steady-state administration in which the intensity of detectable radioactivity is proprotional to the time of diffusion into the tissue. This system appears capable of defining the rate of capillary exchange and the moment-to-moment changes brought about by vasoactive stimuli in specific organs.

Animals↗
PubMed1976

Concepts and clinical utility of the measurement of cerebral blood flow.

Within the past several decades, techniques that accurately measure regional cerebral blood flow have been developed. At the present time, the inert gas washout technique using an intraarterial injection of 133Xe with the Anger scintillation camera or multiple probes as the external detector is the most established of these methods. While quantitative measures of cerebral blood flow have been important in elucidating the physiology of cerebral hemodynamics, the techniques are too invasive for routinely screening patients with cerebrovascular disease. As a result, less invasive methods have been sought for diagnostic screening. Because it requires only an intravenous injection of 99mTc-pertechnetate, the radionuclide cerebral angiogram has achieved some popularity as a semiquantitative measure of cerebral hemodynamics, particularly when coupled with static brain scintigraphy. This review examines our current understanding of cerebral hemodynamics and the advantages and limitations of techniques used to measure cerebral blood flow.

Brain Diseases↗
PubMed1979

Cardiovascular nuclear medicine: an overview.

Some of the available cardiovascular nuclear medicine methods are incompletely validated, and others are incompletely developed. They are, however, of very great potential in diagnostic cardiology, and in patient management. A new era of clinical research and acute care monitoring has been opened by serial, noninvasive, hemodynamic measurements of right ventricular as well as left ventricular function. Stress testing has become more specific, and should, with future developments, become more specific, and should, with future developments, become more sensitive, using radionuclide procedures. Serious quality control and validation questions concerning thallium stress testing must be addressed. Intracoronary injection of radiogases has great potential, although minimal present application. Emission computerized tomography will be an important research tool. Compartmental analysis modeling of first pass tracer injections has much to offer, but is not yet validated. Present growth rate of these procedures is very rapid. Fully developed, cardiovascular nuclear medicine may become the largest component of clinical nuclear medicine practice.

Adult↗
PubMed1980

Scintigraphic evaluation of regional pulmonary ventilation.

Radioactive gases are useful for evaluating pulmonary ventilation because they allow assessment of regional lung function in a physiologic, noninvasive manner. The most widely used radioactive gases are Xe-133, Xe-127, and Kr-81m. These gases provide visual and/or quantitative assessments of regional ventilation or ventilation-perfusion matching in obstructive airways disease, and aid the scintigraphic diagnosis of pulmonary embolism. The precision of ventilation scintigraphy is limited by detector resolution, signal distortion at depth, poor counting statistics, and respiratory motion.

Airway Obstruction↗
PubMed2003

The measurement of liver blood flow: a review of experimental and clinical methods.

Changes in hepatic blood flow reflect adaptive responses of the liver to injury, regeneration, and the development of disease states. The measurement of hepatic blood flow is, however, technically challenging and although theoretically useful has not become routine in clinical work. The different techniques that have been developed for quantitative measurement of hepatic blood flow require careful interpretation of the results obtained but are frequently applied without careful considerations of their technical limitations. In particular, many noninvasive techniques depend on good hepatocellular function and are thus irrelevant under most clinical conditions. Many other potentially useful techniques are poorly validated and standardized and there is a need for further research into smethodology. This review summarizes the salient technical features of the different techniques for quantitative measurement of hepatic blood flow. The techniques are divided into invasive, minimally invasive, and noninvasive categories and the relevance of each technique to both routine clinical application or research is discussed.

Animals↗
PubMed2001

Influence of thickness on the properties of hydroxyapatite coatings deposited by KrF laser ablation.

The growth of hydroxyapatite coatings obtained by KrF excimer laser ablation and their adhesion to a titanium alloy substrate were studied by producing coatings with thicknesses ranging from 170 nm up to 1.5 microm, as a result of different deposition times. The morphology of the coatings consists of grain-like particles and also droplets. During growth the grain-like particles grow in size, partially masking the droplets, and a columnar structure is developed. The thinnest film is mainly composed of amorphous calcium phosphate. The coating 350nm thick already contains hydroxyapatite, whereas thicker coatings present some alpha tricalcium phosphate in addition to hydroxyapatite. The resulting coating to substrate adhesion was evaluated through the scratch test technique. Coatings fail under the scratch test by spallating laterally from the diamond tip and the failure load increases as thickness decreases, until not adhesive but cohesive failure for the thinnest coating is observed.

Alloys↗
PubMed1997

Atomic force microscopic study of the surface morphology of apatite films deposited by pulsed laser ablation.

Atomic force microscopy (AFM) has been used to study the surface morphology of apatite films deposited on metallic and polyethylene substrates by laser ablation using KrF and transversely excited atmospheric CO2 lasers. The films are found to consist of a smooth apatite coating with macroparticles scattered on the surface. A wide variety of macroparticles, differing in size, shape and roughness, were found and analysed employing the high spatial resolution of AFM (< 1 nm). We have investigated the correlation between the apatite film morphology and the deposition conditions. Of particular importance are laser fluence, gas pressure, the nature of the target and the substrate temperature. We have explained these dependencies on the basis of a theoretical model which includes evaporation and a cluster-type laser ablation mechanism.

Apatites↗
PubMed1985

Treatment of proliferative diabetic retinopathy. Long-term results of argon laser photocoagulation.

Panretinal photocoagulation (PRP) is the treatment of choice for proliferative diabetic retinopathy. Indications for treatment are the presence of disc new vessels or the presence of new vessels elsewhere with hemorrhage. Rubeosis iridis and retinal neovascularization undergo involution following panretinal photocoagulation. The long-term visual results are excellent excepting for eyes with diffuse diabetic retinal ischemia. Long-term follow-up and repeat photocoagulation as needed are advised.

Adult↗