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Biomedical subjects

G H Simmons

Publications and source records attributed to G H Simmons.

16 recordsLinked to original sources
PubMed1990

ACR survey results: diagnostic imaging scientists and engineers.

The American College of Radiology's Committee on Physics Resources of the Commission on Human Resources conducted a survey of diagnostic imaging scientists and engineers to assess who is providing radiologic physics and related services in diagnostic imaging departments. The survey forms were distributed through the members of the American Healthcare Radiology Administrators. Survey results showed a predominance of M.S. and Ph.D. degrees in physics and medical/radiological physics. Nearly all respondents had their time split between numerous categories of work, such as clinical and research, and between different modalities such as diagnostic x-ray, nuclear medicine and radiation oncology. To enhance physics services in important areas such as CT, which currently receive little time, support is needed for work prioritization, for training, and for positions for physics and physics-support personnel.

Certification↗
PubMed1986

111In-chloride thorax scintigraphic study for demonstration of pulmonary edema: canine model.

Pulmonary edema induced by injections of oleic acid was demonstrated using 111In-chloride lung/heart image in five anesthetized dogs. The anesthetized dogs were positioned under a gamma camera interfaced to a computer. After 111In-chloride IV injections, dynamic data were recorded at 1 frame/min before and after induced pulmonary edema. The computer generated the curve of the lung-to-heart activity ratio; the ratio rose from 0.5-0.6 at baseline to 0.85-1.5 at the end of the study in the dogs. At the end of each study, the removed lungs demonstrated edematous fluid, and a few red blood cells were seen in the alveoli. The results indicating pulmonary edema exhibited in the 111In-chloride lung-to-heart ratio obtained from a computerized gamma camera were compatible with the pathological result. Since 111In-chloride instantly binds to plasma transferrin, an excellent intravascular imaging agent, leakage of this tracer into alveoli indicates loss of membranous wall competence. Pulmonary edema, as in the adult respiratory distress syndrome, is sometimes difficult to diagnose; and this 111In-chloride lung-to-heart imaging technique may be potentially useful.

Animals↗
PubMed1981

Acute hemodynamic effects and blood pool kinetics of polystyrene microspheres following intravenous administration.

The acute hemodynamic effect of intravenous administration of polystyrene microspheres was investigated and correlated with their distribution pattern and kinetics. Microspheres of three diameters (3.4, 7.4, and 11.6 micrometer) were administered. The 7.4- and 11.6-micrometer diameter microspheres were filtered by the pulmonary capillary network following intravenous administration, the majority during the first pass. There was no significant hemodynamic effect following administrations of the 7.4- and 11.6-micrometer diameter microspheres in doses as high as 3.0 X 10(9) and 6.1 X 10(8) respectively (total cross-sectional area of 1.3 X 10(11) and 6.4 X 10(10) micrometer2, respectively). Intravenous administration of 3.4-micrometer diameter microspheres produced significant dose-dependent systemic hypotension and depression of myocardial performance at dosages as slow as 1.0 X 10(10) (cross-sectional area of 9.1 X 10(10) micrometer2). These differences in acute hemodynamic effect from the 7.4- and 11.6-micrometer diameter microspheres may be due to the differences in distribution kinetics and fate of the 3.4-micrometer diameter microspheres, which readily pass through the lungs to the spleen. Although elimination of the smaller spheres from the blood during the first 6-8 min was rapid, i.e., t 1/2 = 1.62 and 1.72 min from the venous and arterial blood circulation, respectively, levels of 10(3) spheres/g of blood were present in the circulation for greater than 1 hr. These findings must be considered in the planning of intravenous administration of microspheres as a drug delivery system to target organs.

Animals↗
PubMed1981

Acute toxicity of latex microspheres.

The distribution and acute lethality of i.v. administered 3 micrometers latex spheres were determined in rats. The results extend previous studies demonstrating the similarity between dog and rat in the dynamics of microspheres in these species and the inverse relationship between sphere diameter and hemodynamic toxicity. The results suggest that 3 micrometers spheres may be safe imaging agents or drug delivery systems for spleen and liver when administered slowly. Acute hemodynamic toxicity appears to be a function of the total volume of the spheres injected.

Animals↗
PubMed1975

A non-linear programming method for optimizing parallel-hole collimator design.

A new method for optimizing the design of multi-aperture parallel-hole collimators for the gamma scintillation camera is presented. The method takes into account the frequency spectrum of a plane source object distribution as well as the energy of the radiation. A frequency dependent statistical figure of merit is calculated and combined with a weighted object distribution frequency spectrum to obtain an objective function which, when maximized, yields the optimum collimator design according to the chosen criteria. The optimization is performed by means of a sequential pattern search technique. The results show a positive correlation between te objective function and an experimental performance index evaluated for existing collimators. The optimal designs obtained by maximizing the objective function, under the assumption of no scatter within the source, exhibit somewhat higher sensitivity and lower resolution than the commercial low energy collimators tested. It is concluded that much of the resolution capability of very high resolution collimators is unused because of the limitation imposed by the intrinsic resolution of the detector assembly.

Computers↗