Iona and David, my parents, for your love, support, dedication and understanding over so many years. My wife Marta and son Rafael, for your constant love, encouragement, understanding that you have shown, as well as your faith in my abilities. You have patiently shared our living space with so many books and computers during these past years. To my brother-in-law, Marco Antonio Silva, for your encouragement and support when I decided to venture down the academic road after many years away from Universities. My supervisor, Dr. Marco Antonio Gutierrez, and staff at the Informatics Division at the Heart Institute (InCor), São Paulo, Brazil, for your help and encouragement during my studies. Dr. Sergio Furuie for deepening my understanding of image processing in the post-grad courses I took with you. In your kind and patient manner you made your wide knowledge and experience available, which has guided me through this project. Dr. André Kohn for your help, support and openness throughout these years studying, besides the wonderful instruction you gave me in your neuroscience course. The patient teachers who helped to develop my understanding in their courses at the Escola Politécnica, University of São Paulo, particularly Dra. Idágene Cestari in Biomedical Engineering, Dr. Luis Baccalá and Dr. Magno Silva in Signal Processing. I feel privileged to have studied with you, as few have had this great opportunity. Marco Oliveira for your great efforts and involvement in my doctoral project. You have always been happy to share your extensive knowledge of Nuclear Medicine with me, and have dedicated many hours in selecting and sending images over the hospital PACS; it was really great fun to work with you. Thanks also to Luis Tonello for your descriptions about radiopharmaceuticals and help with producing PET/CT fusion images.