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Biomedical subjects

M A Flower

Publications and source records attributed to M A Flower.

63 records · Page 4Linked to original sources
PubMed1983

The spatial resolution of a rotating gamma camera tomographic facility.

An important feature determining the spatial resolution in transverse sections reconstructed by convolution and back-projection is the frequency filter corresponding to the convolution kernel. Equations have been derived giving the theoretical spatial resolution, for a perfect detector and noise-free data, using four filter functions. Experiments have shown that physical constraints will always limit the resolution that can be achieved with a given system. The experiments indicate that the region of the frequency spectrum between KN/2 and KN where KN is the Nyquist frequency does not contribute significantly to resolution. In order to investigate the physical effect of these filter functions, the spatial resolution of reconstructed images obtained with a GE 400T rotating gamma camera has been measured. The results obtained serve as an aid to choosing appropriate reconstruction filters for use with a rotating gamma camera system.

Air↗
PubMed1981

A comparison of three systems for performing single-photon emission tomography.

A comparison is made between the performance of three transverse axial single-photon emission tomographic machines, namely a rotating gamma-camera and two different scanning systems. Each system has been evaluation in terms of the spatial resolution, sensitivity and efficiency. The functional dependence of the volume sensitivity on the size of the emitting object has been derived using a theoretical model of the photon emission, attenuation and detection. The model is shown to predict this size dependence well and is consistent with the experimental observations.

Tomography, Emission-Computed↗
PubMed1980

An instrument for checking the radioactivity in shielded syringes.

A description is given of an instrument that can be used for checking, to within ten percent, the radioactivity in shielded syringes. The unit is simple in design and construction and easy to use. The lead shield of the syringe does not have to be removed, since only radiation emitted along the direction of the barrel is detected. A range of syringe sizes can be accommodated and, whilst the instrument is calibrated for 99Tcm with activities in the range 1-10 mCi, both higher and lower activities and other radionuclides can be used. Each measurement takes only a few seconds and the activity of radiopharmaceuticals can be routinely checked immediately before injection.

Radiometry↗
PubMed1980

Quantitative imaging using the Cleon emission tomography system: recent developments.

A revised method of correcting for attenuation has been investigated through experiments using discrete sources within a radioactive background. The effects of changing the source size, the source position relative to the central axis, and the ratio of the concentrations in the source and background have been studied. A comparison of the results obtained using old and new attenuation corrections show marked improvement. The measurement of radioactive concentration on the central axis had a typical systematic error of -14%, compared to -60% previously, but is generally dependent on source size, source position, and source and background concentrations. An allowance can be made for this error using experimental data.

Brain↗
PubMed1979

Feasibility of absolute activity measurements using the Cleon emission tomography system.

Large volume and small discrete sources of Tc-99m were used to study the spatial resolution, sensitivity, linearity and reproducibility of the radionuclide brain images. The spatial resolution is constant both within and perpendicular to the section. For uniform distributions of activity the response is uniform over the field of view, and the mean pixel count rate is a linear function of the radioactive concentration and is independent of the diameter of the source. However, for discrete sources, the sensitivity was found to vary with the position of the source, and the potential of the system for quantitative assessment of the uptake of radioactivity in organs and tumors was limited initially. Later studies, with modified software, show that this undesirable effect has been reduced.

Brain↗
PubMed1978

Toward hospital library standards in Canada.

A report is given on Canadian hospital library standards as recently developed and incorporated in a new Guide to Hospital Accreditation, 1977. The new Canadian standards are compared with MLA recommendations to the Joint Commission on Accreditation of Hospitals. Their development is sketched and the contribution from Quebec of a model of hospital classification is examined. This model provides differential minimal library standards based on the function of the hospital rather than on its size alone. Use of these minimal standards as a practical means of developing hospital libraries is discussed and their implications for accreditation visits are underlined.

Accreditation↗
PubMedDate not supplied

Constrained deconvolution of SPECT liver tomograms by direct digital image restoration.

Several techniques for performing digital image restoration are reviewed and the problems associated with evaluating image processing are discussed. An application of constrained deconvulution to images of the liver produced by single-photon emission computed tomography is presented. Specific evaluation criteria are suggested and based on these, the choice of conditions best suited for processing liver images is proposed. Typically cold tumor contrast can be improved by a factor of greater than 2 whilst image mottle increases negligibly.

Filtration↗
PubMedDate not supplied

Improved quantification of radionuclide uptake using deconvolution and windowed subtraction techniques for scatter compensation in single photon emission computed tomography.

A comparison of two methods of scatter compensation in single photon emission computed tomography (SPECT) imaging is made on the basis of improvements in quantification. The methods, scatter-window subtraction and constrained deconvolution of an average point source response function (PSRF), are described; the theoretical basis of each method is also briefly assessed. Improvements in relative quantification offered by each method are measured by examining ratios of counts in hot cylinders to counts in a slightly radioactive background. The cylinder/background concentration ratio was varied by a factor of five; the sizes of the cylinders remained constant. Keeping the diameter of the cylinders constant allowed for an assessment of the effect of concentration differences, without the conflicting effect of variation in the size of the hot source. Results showed that while both scatter-window subtraction and constrained deconvolution offer quantification improvements in the final image, the method of prereconstruction deconvolution of a planar PSRF from each planar projection is substantially more successful than either scatter-window subtraction or other methods of implementing the deconvolution procedure.

Biophysical Phenomena↗