In the scanner, coincidence events are observed and identified along their lines of response (LORs) between pairs of detector elements. To organize raw data as they are acquired, the LORs are stored in a in such a way that all the LORs passing through a single point in the patient trace a sinusoid curve in the raw data histogram, hence the term sinogram for the raw data format. The formation of sinograms is an important middle step in the PET data acquisition process, since necessary correlations are often applied at this level