Basics for nuclear medicine image reconstruction

Introduction and evolution of digital imaging proved to be a great tool for clinical and experimental medicine, changing the pathway in which patients are diagnosed and progress of therapy is monitored. The demand for diagnostic imaging procedures is constantly increasing, and sophisticated procedures, like Nuclear medicine (NM) and positron emission tomography (PET)-computed tomography (CT), are now state of the art in most of the developed countries. Nuclear medicine professionals benefitted in their practices, together with the evolutions of scanners and development of radiotracers, with the improvement of computational ability of systems devoted to image reconstruction. In this chapter, we will explore the basic of NM image reconstruction in an effort to describe the processes that arise from the detection of radiation emitted to the creation of clinically effective pictorial representation. The first part will analyze the physical and technological principles of image formation in planar NM imaging, including dynamic and whole body. It will describe image quality parameters, matrix size, interpolation and impact of computational processing capability evolution on image reconstruction. The second part will consider tomographic image reconstruction, discussing the role of sinograms and the most common processing algorithms, discussing also the impact of enhanced computational ability of modern systems on data analysis. It will start explaining analytical reconstruction and its role in single photon emission computed tomography (SPECT) systems and early PET detectors. It will then cover different logarithmic filters used to improve image quality. The chapter will also consider the evolution from filtered back-projection to the modern algorithms for iterative reconstruction including also specific PET-CT reconstruction. The chapter will offer to nuclear medicine professional the basics of the topic and instrument to facilitate the understanding of more specific NM and PET-CT techniques and reconstructions, described in other part of the book.