Image quality with non-standard nuclides in PET.

Non-standard positron emission tomography (PET) nuclides bring with them the prospect of new chemistry leading the way to novel approaches for targeted imaging and therapy. In particular, the kinetic energy of the positron of some of these nuclides is high (as much as 4 MeV) and, thus, a highly specific PET probe can be very lethal to cancerous cells. However, the high positron energy will degrade the spatial resolution, and this degradation will be more important in high-resolution, small animal PET imaging, where most of the novel tracers are developed. This paper discusses the image quality in small animal PET imaging obtained with such nuclides. The nuclides of (60)Cu, (61)Cu and (64)Cu, (76)Br, (94)mTc, and (89)Zr will be particularly analyzed. The spatial resolution will be seen to degrade with nuclides with higher positron end-point energy, going from 1.7 mm for (18)F to 2.2 mm for (76)Br, for example. Many of these novel PET nuclides decay by the emission of cascades gamma rays that are detected in coincidence with the positron annihilation photons which create additional noise on the images. However, the use of an image reconstruction algorithm, which includes a model of the statistical nature of nuclear decay and the modeling of the tomograph response, contributes to both improve the spatial resolution and at the same time reduce the image noise.