Data acquisition in PET imaging.

Data acquisition is substantially different in PET than it is in planar nuclear medicine and SPECT. There is an entirely different set of definitions and considerations. The objective of this paper is to provide the reader with the terminology and understanding of how PET data are acquired and organized as well as the issues involved in choosing one approach over another. Sinograms and projection views will be presented as methods of storing and viewing raw PET data. Different approaches to increase axial sampling while maintaining a sufficient number of counts for each reconstructed slice are discussed, as well as the use of sinogram compression or "mashing" to reduce the storage requirements of raw PET data. The differences between 2-dimensional (2D) and 3-dimensional (3D) PET and how storage of raw 3D data may differ from that of 2D data are described. The concept of "Michelograms" as a means of displaying the nature of the axial sampling in both 2D and 3D PET is discussed. After reading this paper, the reader will be able to describe 2 methods used to store and display raw PET data and compare them with methods used in SPECT. The reader will be able to define the terms "span" and "maximum ring difference" and describe how they relate to the axial sampling in 2D and 3D PET. The reader will also be able to list 3 ways in which 3D PET differs from 2D PET.