What does the Y-axis in a sinogram represent?

The Y-axis in a sinogram represents the angle of projection. In the context of PET imaging, a sinogram is a visual representation of the projections collected at various angles around the object being scanned. Each pixel of the sinogram corresponds to the intensity of the detected signals (from positron emissions) at a specific projection angle, which is plotted along the Y-axis. The X-axis typically represents the radial distance from the center of the detector configuration. By analyzing the sinogram, clinicians and technologists can reconstruct the image of the distribution of radioactivity in the patient, ultimately providing valuable diagnostic information.