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Biomedical subjects

J G Stears

Publications and source records attributed to J G Stears.

18 recordsLinked to original sources
PubMed1992

Beam-shaping device for long-film angiography.

Uniform radiologic exposure from the pelvis to the ankles is often difficult to achieve when long films (51-inch) are used for femoral angiography. A unique device developed to shape the x-ray beam accomplishes this task by using a movable shutter to obscure a portion of the x-ray beam. A microprocessor-controlled stepper motor modulates the amount of beam cutoff by regulating the movement of the shutter from the foot end of the film. The goal is to match exposure factors to the patient's body shape. This beam-shaping device has been evaluated and tested in examinations of 500 patients over the past year. A substantial improvement in image quality over that achieved with earlier systems of graduated screens and multiple wedge filters was seen in all cases. The system is esy to use, flexible, and especially valuable in imaging obese patients or those who have legs disproportionately smaller than their pelvis or abdomen.

Abdomen↗
PubMed1992

Acceptance testing of radiologic systems: experience in testing 129 imaging systems at two major medical facilities.

The problems encountered in acceptance testing of newly installed imaging equipment at two major medical institutions over a 10-year period are presented. Acceptance tests were conducted in 129 newly installed imaging systems with conventional acceptance testing methods. A total of 1,132 problems were documented. Problems were classified as major or minor; there were 772 major problems and 360 minor problems. An average of six major and three minor problems were documented in each new equipment installation tested. In some instances, final payment was withheld for several months or more to ensure correction of the problems identified. This experience confirms the need of thorough acceptance testing of new imaging equipment before final payment is made to the vendor.

Alabama↗
PubMed1986

Half-value-layer increase owing to tungsten buildup in the x-ray tube: fact or fiction.

The half-value layer (HVL) of an x-ray beam is generally believed to increase with x-ray tube use. This increase in HVL has previously been attributed to the hardening of the x-ray beam as a result of a buildup of tungsten on the x-ray tube glass window. Radiographs and HVL measurements were obtained to determine the effect of tungsten deposited on the x-ray tube windows. This work, along with the HVL data from approximately 200 functioning x-ray tubes used for all applications that were monitored for more than 8 years, indicated there is no significant increase in HVL with diagnostic x-ray tube use.

Glass↗
PubMed1984

Fluoroscopic imaging: quantitation of image lag or smearing.

Image lag (smearing or persistence of the image) is a characteristic of video imaging systems that is exhibited when rapidly moving objects are blurred due to motion. Video pick-up tubes can exhibit differing amounts of image lag depending on the age of the tube, the amount of light reaching the tube, the set-up parameters used (e.g., beam current and target voltages, etc.), and the tube type. We describe a new quantitative method for measuring image lag that requires only a storage oscilloscope and an inexpensive shutter. Examples of lag measurements on different systems under varying clinical conditions are given. Suggested limits for clinically acceptable amounts of image lag range from 10% to 50% depending on the particular application.

Data Display↗
PubMed1983

Shaped, lead-loaded acrylic filters for patient exposure reduction and image-quality improvement.

Shaped filters that are constructed of lead-loaded acrylic material for use in patient radiography are discussed. Use of the filters will result in improved overall image quality with significant exposure reduction to the patient (approximately a 2X reduction in breast exposure and a 3X reduction in thyroid gland exposure). Detailed drawings of the shaped filters for scoliosis radiography, cervical spine radiography, and for long film changers in special procedures are provided. The use of the scoliosis filters is detailed and includes phantom and patient radiographs and dose reduction information.

Acrylic Resins↗
PubMedDate not supplied

Scatter radiation.

Explore the source record for details and available documents.

Absorption↗
PubMedDate not supplied

X-ray tube warm-ups.

Explore the source record for details and available documents.

Technology, Radiologic↗
PubMedDate not supplied

Evaluation of pH monitoring as a method of processor control.

Sensitometry and pH values of the developer solution were compared in controlled over-replenishment, developer depletion, fixer contamination experiments, and on a daily quality control basis. The purpose of these comparisons was to evaluate the potential of pH monitoring as a method of processor control, or a supplement to sensitometry as a method of quality control. Reasonable correlation was found between pH values and film density in two of the three experiments but little or no correlation was found in the third experiment and on a day-to-day basis. The conclusion drawn from these comparisons is that pH monitoring has several limitations which render it unsuitable as a method of daily processor quality control as either a primary or supplementary technique. Sensitometry takes into account all the variables encountered in film processing and is the clear method of choice for processor quality control.

Chemical Phenomena↗
PubMedDate not supplied

X-ray waveform monitoring for radiographic quality control.

Noninvasive monitoring of x-ray output waveforms during acceptance testing, quality of control, and troubleshooting is beneficial in an ongoing radiographic quality assurance program. The intent of waveform monitoring is to watch for abnormalities that provide additional information about the condition of the x-ray system. Because waveform monitoring is performed generally in conjunction with other quality control procedures, few, if any, additional exposures are needed and length of the testing time is affected minimally. In six years of experience with acceptance testing, quality control, and troubleshooting on more than 160 radiographic and fluoroscopic units, noninvasive waveform monitoring has detected numerous abnormalities that would have affected image quality, generator calibration, and equipment life.

Quality Control↗
PubMedDate not supplied

Use of the posteroanterior projection: a method of reducing x-ray exposure to specific radiosensitive organs.

The posteroanterior projection was studied to determine if it could be a substitute for the commonly used anteroposterior projection as a method of reducing x-ray exposure to specific radiosensitive organs during intracranial tomography and scoliosis radiography. The use of the posteroanterior projection resulted in a reduction of 95% in exposure to the lens of the eye during intracranial tomography and of more than 90% to the thyroid, sternum, and breasts during scoliosis radiography. In addition to the major reduction in radiation exposure, the diagnostic capability of the examination was not reduced and comfort in most patients was not affected.

Brain Diseases↗