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Title: Studies in the development of equipment for improving resolution in nuclear medicine imaging
Author: Mitchell, James G.
ISNI:       0000 0001 3411 758X
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1978
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A gamma camera system is described. This takes the following form. A conventional collimator-crystal system is set up to produce scintillation images corresponding to the pattern of radioactivity in a patient or phantom. Thereafter these faint points of light are imaged by a lens of high light-gathering power onto the photocathode of an image intensifier. This amplifies the light intensity by a factor of approximately 10. 6, \when they are photographed bya conventional camera. An important feature of the equipment is a system which switches the image intensifier on only when a wanted signal appears in the crystal: other spurious signals, e.g. background radiation, scattered gamma-rays from the patient, thermal electrons in the image Intensifier, are to a large extent rejected by this system. An important feature of it is the method of gathering spare light from the crystal by photomultiplier tubes placed round the periphery. Light guide designs to do this are described, with experimental results, and the appropriate calculations discussed. The design of the electronics equipment is examined, and its limitations, as these affect the sensitivity of the equipment, computed. In all of the above, the statistics of the process are discussed in detail and the effect on the basic sensitivity, quantum mottle, and degraded gamma-rays are computed. The effect of non-uniformity across the crystal on the pulse-height-analysis is measured, and its effect on the final design indicated. A very important loss of contrast was discovered in the form of scatter of light in the optics of the system, mainly in the crystal and its attendant light-guide/encapsulation. This was investigated thoroughly and possible cures discussed: it was felt that a gating system to differentiate between scattered light and wanted signal could be devised, using a G.C.T.V. system. This however imposed severe restrictions in that a greater fraction of the crystal's light was required to fall on the image intensifier cathode; calculations indicated that this was not possible with existing components - the main limitation being the image intensifier diameter. Calculations are carried out to indicate the specification of components necessary to overcome these limitations, and also to match the sensitivity of the Anger camera. The modulation transfer function of the crystal is calculated from the experimental results, using a programmable calculator. Simulated optical and X-ray experiments on moving the collimator (to eliminate possible structure) are described, and a proposed method of doing this requiring much less complicated equipment than was previously thought necessary, is described. Finally a detailed specification/design of a feasible clinical instrument is delineated, making use of the results of the experiments carried out with equipment actually built.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biophysics