Positron Emission Tomography with Three-Dimensional Reconstruction

Sammanfattning: In this thesis, the developments of two different low-cost scanners for positron emission tomography (PET) based on 3D acquisition, are presented. 3D reconstruction methods for these systems are also presented. The first scanner consists of two rotating scintillation cameras, and produces quantitative images, which have shown to be clinically useful . The second one is a system with two opposed sets of detectors, based on the limited angle tomography principle, dedicated for mammographic studies. The development of low-cost PET scanners can increase the clinical impact of PET, which is an expensive modality, only available at a few centres world-wide and mainly used as a research tool. The conventional way to image a 3D volume in PET, by acquisition of data in a set of parallel slices, which are reconstructed as independent planes, makes an inefficient use of the available photon fluence. With 3D acquisition, also photons which traverse more than one transaxial slice are detected. In this case, fully 3D reconstruction is needed. The main problems in 3D reconstruction for PET are the size of the data sets, the computation time and how to theoretically incorporate all the data. A 3D reconstruction method was developed that utilizes all the available data. The size of the data- sets is considerably reduced, using the single-slice rebinning approximation. The 3D reconstruction is divided into 1D axial deconvolution and 2D transaxial reconstruction, which makes it relatively fast. This method was developed for the rotating scanner, but was also implemented for multi-ring scanners with and without inter-plane septa. An iterative 3D reconstruction method was developed for the limited angle scanner, based on the new concept of "mobile pixels", which reduces the finite pixel errors and leads to an improved signal to noise ratio.