PERFORMANCE EVALUATION OF INTERPOLATED AVERAGE CT FOR CARDIAC AND LUNG PET ATTENUATION CORRECTION by Ho Yuen Ting Thesis Supervisor: Prof. Greta, Seng Peng Mok Department of Electrical and Computer Engineering Integrated Positron emission tomography (PET) and computed tomography (CT) system, which combines two tomographic modalities, allows both scans to be performed in a single session without moving the patient. It allows the physicians to fuse both functional and anatomical images and thus providing more accurate lesion localization and characterization than separate PET and CT images. However, as the data acquisition time is different for these two modalities, when using the CT data for attenuation correction in PET reconstruction, respiratory misalignment artifacts are frequently seen in the lower thoracic region which may further lead to medical mis-diagnosis or affect the later oncology treatment planning. In this study, we propose to evaluate a new CT protocol, i.e., interpolated average CT (IACT), for reducing respiratory misalignment artifacts between PET and CT for both cardiac and oncology applications.as compared to the conventional helical CT (HCT) and cine average CT (CACT) which is a 4D CT acquisition Our results showed that the performance of IACT was similar to that of CACT but with a lower radiation dose. Fewer artifacts were observed in reconstructed images when using IACT or CACT for attenuation correction in PET as compared to HCT. IACT can improve PET/CT matching as well as thoracic lesion localization and quantitation for a wide range of lesion characteristics. The first chapter of this thesis introduces the basic principle of PET/CT instrumentation, its role in detecting thoracic tumors and cardiac study. Attenuation correction and respiratory misalignments in PET/CT are also introduced. In the second chapter, several current existing methods for the reduction of misalignments are reviewed. The third chapter describes our proposed IACT method, including theory and implementation. Computer simulation and clinical study for evaluation of our method are discussed in chapter 4 and 5 respectively. The conclusion and future work are demonstrated in the end of this thesis.