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Biomedical subjects

R D Speller

Publications and source records attributed to R D Speller.

15 recordsLinked to original sources
PubMed1995

A CCD based focal spot camera.

Rapid, quantative assessment of x-radiation source intensity distributions would be useful in several areas of radiation physics. A simple x-ray sensitive CCD based camera for the measurement of focal spot and radiation beam intensity profiles has been constructed. Focal spot images recorded with the CCD camera and radiographic emulsion are compared and the advantage of the CCD camera in rapidly recording true radiation intensity distributions is demonstrated.

Photography↗
PubMed1992

Photon absorption measurements of bone density in the presence of scattered radiation.

Bone density measurements are frequently carried out using photon absorptiometry techniques. The analysis of data collected in this way depends upon scatter-free detector signals. In practice the detector and source collimation lead to high levels of scattered radiation being detected. An analysis of the problem using photon transport computer models has shown that the current systems are reasonably insensitive to the scatter contribution except where patient changes occur over a long series of measurements or where new results taken with DEXA are compared with those taken on older systems such as DPA. This is frequently the case since the major body of data related to serial bone density measurements has been achieved with DPA. Inclusion of scattered radiation in the bone density calculations can lead to a 0.5-3.5% reduction between system types. Patient size changes could lead to a reduction in bone density of 0.5% (femoral neck measurement) to 1% (lumbar spine measurement).

Absorptiometry, Photon↗
PubMed1990

Dual energy radiography using X-ray films and intensifying screens.

The aim of this study was to investigate dual energy (DE) systems using X-ray films and intensifying screens as detecting media. This has been studied using both experimental methods and numerical modelling. Numerical methods were used to calculate energy losses due to K-fluorescent escape originating from the phosphors of the intensifying screens. This enabled the calculation of absorbed energy in screens. The method for screen selection and prediction of performance used the fact that detector response depends upon impinging X-ray energy. By equating the detector's absorbing characteristics to the resultant optical density (OD), an absorbed energy constant was calculated. These constants were used to predict OD for a given X-ray spectrum and hence simulation of detector characteristics. Experimental techniques were used to investigate sensitivity to chemical composition changes. These results compared favourably with computed values. It was demonstrated that although limitations exist, detector simulations are valid and X-ray film intensifying screen combinations make adequate DE detectors.

Calibration↗
PubMed1983

A system for dual-energy radiography.

A system has been developed and theoretically analysed for the generation of chemical information from conventional radiography. A specially modified cassette has enabled dual-energy radiographs to be taken during a single exposure. A simple theoretical model has demonstrated that the concept of an optical density "standardised" to the local surroundings allows adequate quantification of the dual-energy radiographs. Using this method, data can be obtained relating to the effective atomic number of a radiographed material provided some estimate of its physical density is known. Simulated in vivo analysis of gall-stone composition has been demonstrated using these techniques.

Calibration↗
PubMed1982

Radiation dosimetry survey of computed tomography systems from ten manufacturers.

Profiles of the absorbed dose delivered throughout cylindrical and anthropomorphic phantoms during single scans by computed tomography systems from ten manufacturers were measured using LiF thermoluminescent dosemeters (TLD) and X-ray therapy verification film. The dose profiles demonstrate that a significant portion of the dose is delivered outside the imaged volume of a single scan. The doses measured in cylindrical Plexiglas phantoms were similar to those measured in anthropomorphic cross sections of tissue substitute materials except near the centre of the thorax section. The film results, obtained using a single calibration curve, agreed with the TLD results to within 25% for most systems.

Absorption↗
PubMed1981

Evaluating performance characteristics in computerized tomography.

The important radiographic and dosimetric performance parameters associated with computerized tomography (CT) are discussed together with the practical problems encountered when they are being evaluated. The parameters include alignment, slice thickness, noise, low-contrast detectability, spatial resolution, modulation transfer function and patient dose. A set of phantoms for determining these performance characteristics are described. The phantoms are of modular construction permitting measurement of the performance parameters at various sites within a number of 6 cm thick, regular-geometry, and realistic body sections. The regular-geometry sections include 20 cm diameter (skull size) and 33 cm diameter (abdomen size) sections. The realistic anthropomorphic sections include the skull, abdomen and thorax.

Humans↗
PubMed1981

A survey of 29 EMI CT machines in Britain.

During 1978/79 a survey was made of the performance characteristics of 29 EMI brain and body CT scanners in Britain. Comparative data on such performance parameters as noise, uniformity of CT numbers, low-contrast detectability, resolution, modulation transfer function (MTF) and effective photon energy were measured using a set of regular-geometry and anthropomorphic phantoms. In addition, dose profiles were obtained for a single slice using TLD and film. The results of the survey are presented; the dependence of the performance characteristics on the types of machines surveyed and the operating modes employed is discussed.

Brain↗
PubMed1981

An evaluation of CT systems from ten manufactures.

During the past three years, 23 computerized tomography (CT) machines from ten different manufacturers located in Europe and the USA have been evaluated. Using the same set of phantoms and measurement techniques, performance data have been derived including noise, uniformity of CT numbers, low contrast detectability, spatial resolution, modulation transfer function, effective photon energy and linearity of CT numbers. Thermoluminescent and film dosimetry were used to determine single-slice dose profiles at the periphery and centre of specialized anthropomorphic phantoms. The results of this study are presented in tabular and graphical form together with some general conclusions on their implications.

Brain↗
PubMed1980

The measurement of effective photon energy and "linearity" in computerized tomography.

Two liquid systems have been developed for the measurement of effective photon energy (Eeff) and "linearity" in computerized tomography (CT). A group of sixteen "keV liquids" enables an Eeff to be rapidly determined, by comparing the CT numbers of the specially formulated organic liquid mixtures with similar data for water. The "linearity" of the CT scanner, relating CT nubers to linear attenuation coefficients, may be investigated using 14 selected organic "linearity liquids". Details of these systems, together with some typical results, are presented.

Elementary Particles↗
PubMed1979

Size measurements on isolated rat heart cells using Coulter analysis and light scatter flow cytometry.

Isolated ventricular muscle cells from the adult rat heart have been examined by both Coulter analysis and light scatter flow cytometry. The dispersed cell preparations contain two main cell types: viable, rod-shaped cells and damaged, round cells. Coulter analytical techniques provided statistical data on cell volume for both cell types. The contribution of each population to the Coulter pulse height distributions were separated by a subtraction method using data obtained from digitonin-treated preparations that contain only round cells. A shape factor for cells aligned with the flow direction was computed from light microscope measurements and the effects of cell orientation within the Coulter aperture were approximately assessed. The estimated volumes for intact myocytes compare favourably with those reported in the literature. No significant size difference was observed between fresh and fixed cells. Narrow angle, forward light scatter measurements were made on individual cells flowing across a focused laser beam. Both scatter pulse height and pulse width (pulse duration) distributions were collected. Values for myocyte length calculated from pulse width information agree well with published data and confirm that the hydrodynamic forces in the flow system produced alignment of the cells with the flow direction. Scatter pulse width distributions reveal two distinct peaks assignable to either rod or round cells. Preliminary electronic gating experiments, using pulse height signals, suggest that signals derived from round cells could be eliminated entirely using a gating regime based on pulse width. This would enable flow cytometric measurements to be made on only the intact myocytes present in heterogeneous preparations.

Animals↗
PubMedDate not supplied

A Monte Carlo study of multiple scatter effects in Compton scatter densitometry.

The contribution of multiple scatter to the measured signal in x- and gamma-ray Compton scatter densitometry has been investigated theoretically by the use of Monte Carlo techniques to follow individual photon life histories. A three component phantom was employed in the computer model to simulate the patient at three examination sites; the radius/ulna, the femoral neck, and the lumbar spine. Monoenergetic radiation beams of 60- and 100-keV photons and polyenergetic x-ray spectra of 100 and 140 kVp were used. Scattered events were detected over 360 degrees and classified according to their origin and frequency of scatter. The single scatter in bone to multiple scatter ratio was studied as an indication of the signal-to-noise ratio and this was found to vary with phantom size but was independent of photon energy. Correction factors to be used in a clinical densitometer to account for the inclusion of multiple scatter events were computed. These were found to be 0.65-0.58 at the optimum scattering angles for the phantoms considered.

Absorptiometry, Photon↗