Theoretical & experimental study of the positron emission tomograph-analysis of the spherical positron emission tomogtaph

Abstract

In this dissertation, three topics are studied which are relevant to achieving high resolution in positron emission tomography (PET). First, sampling scheme for a circular ring system is discussed and a new scheme is proposed which is termed as dichotomic sampling. Computer simulation is performed and compared with wobbling scheme widely accepted so far. The results show that unlike wobbling scheme the proposed dichotomic scheme offers uniform sampling interval therefore better reconstructed images. In addition, it is quite more flexible in adjusting the sampling interval or number of scan stops. Even more important is the fact that it can be easily applicable to a multilayer spherical system since its mechanical motion is one dimensional while wobbling is two dimensional. The dichotomic sampling scheme has been realized in DICHOTOM-I through the modification of CRTAPC system. This modification and the results of experiments done with the DICHOTOM-I are also presented. Second, since the sensitivity improvement is a crucial factor to support high resolution, S-PET (Spherical Positron Emission Tomography) system proposed to achieve the resolution of 2-3mm ultimate in PET imaging adopts spherical shape and focused annular collimators to improve sensitivity. To see the sensitivity of the S-PET system, it is quantitatively analysed through mathematical formulation together with the calculation of the image degradation factors, i.e., scatter and random coincidences. By calculating the same things for the system of cylindrical shape on the same condition and comparing them with those of the proposed spherical system, the efficacy of spherical shape and focused annular collimators for the improvement of sensitivity and suppression of scatter and random coincidences is demonstrated. Third, the coincidence circuit to be used for the multilayer system such as S-PET which is designed to exploit oblique rays is required to have the capabilities of handling millions of co...