Design optimization of a continuous detector for PEM imaging with high resolution and DOI capability

Abstract

The objective of this thesis is to improve the resolution of a continuous detector by using an algorithm other than Anger algorithm. Our aim is to obtain a reasonable resolution necessary for Positron Emission Mammography (PEM) imaging. Many research groups have been involved in developing different types of high resolution Positron emission tomography (PET) systems. Among those, most designs have consisted of detectors assembled using tiny discrete crystal elements identified by position sensitive or multichannel photomultiplier tubes. However using narrow, pixellated crystals for higher resolution causes several problems including inter crystal scatter, light collection difficulty, practical difficulties of crystal size, and high cost. In this work, the feasibility of using a continuous crystal detector for PEM imaging with high resolution has been investigated through simulations. We aim to reduce the system cost and to improve system performance. Simulations confirmed that Anger algorithm is not a feasible algorithm to use in a small size detector since it needs further processing to correct the linearity distortion problem and it does not provide any information about the depth of interaction. Simulations also showed that, when calculating the location of interaction with Anger algorithm, there can be a shift about 1 mm depending on the depth of interaction in a 10 mm thick NaI crystal. The nearest neighbor algorithm by using a lookup table gave better results than Anger algorithm and also provided information about depth of interaction. We adapted a second threshold, called Proximity value, to the algorithm to eliminate possible Compton scatterings. This improves the resolution while trading off the number of interactions used. An optimum proximity value has been suggested depending on the simulation results.|Keywords: Positron emission tomography (PET), continuous scintillator, depth of interaction (DOI), Anger logic.