Gillen, Gerard J.
Single photon emission computed tomography: performance assessment, development and clinical applications.
PhD thesis, University of Glasgow.
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This is a general investigation of the SPECT imaging process. The primary aim is to determine the manner in which the SPECT studies should be performed in order to maximise the relevant clinical information given the characteristics and limitations of the particular gamma camera imaging system used. Thus the first part of this thesis is concerned with an assessment of the performance characteristics of the SPECT system itself. This involves the measurement of the fundamental planar imaging properties of the camera, their stability with rotation, the ability of the camera to rotate in a perfect circle and the accuracy of the transfer of the information from the camera to the computing system. Following this the performance of the SPECT system as a whole is optimised. This is achieved by examining the fundamental aspects of the SPECT imaging process and by optimising the selection of the parameters chosen for the acquisition and reconstruction of the data. As an aid to this a novel mathematical construct is introduced. By taking the logarithm of the power spectrum of the normalised projection profile data the relationship between the signal power and the noise power in the detected data can be visualised. From a theoretical consideration of the available options the Butterworth filter is chosen for use because it provides the best combination of spatial frequency transfer characteristics and flexibility. The flexibility of the Butterworth filter is an important feature because it means that the form of the actual function used in the reconstruction of a transaxial section can be chosen with regard to the relationship between the signal and the noise in the data. A novel method is developed to match the filter to the projection data. This consists of the construction of a mean angular power spectrum from the set of projection profiles required for the reconstruction of the particular transaxial section in question. From this the spatial frequency at which the the signal becomes dominated by the noise is identified. The value which the Butterworth filter should take at this point can then be determined with regard to the requirements of the particular clinical investigation to be performed. The filter matching procedure can be extended to two dimensions in a practical manner by operating on the projection data after it has been filtered in the y direction. The efficacy of several methods to correct for the effects of scatter, attenuation and camera non-uniformity are also investigated. Having developed the optimised methodology for the acquisition and reconstruction of the SPECT data the results which are obtained are applied in the investigation of some specific clinical problems. The assessment of intractable epilepsy using 99mTc-HMPAO is performed followed by the investigation of ischaemic heart disease using 99mTc-MIBI and finally, the diagnosis of avascular necrosis of the femoral head using 99mTc-MDP is studied. The SPECT studies described in this thesis make a significant contribution to patient management.
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