In terms of sinogram representation, what does the X-axis represent?

In sinogram representation, the X-axis typically represents the shift on the Line of Response (LOR). The sinogram is a two-dimensional array used in reconstructing images in techniques such as computed tomography (CT) and, in this case, positron emission tomography (PET).

Every sinogram is generated from multiple projections taken at different angles. Each element in the sinogram corresponds to a specific shift along the LOR, which connects the source of the emitted radiation (such as a radioactive tracer) to the detector. By measuring the intensity of the detected signals at various angles and shifts, the PET system gathers the necessary data for image reconstruction.

Thus, the X-axis effectively indicates how far along the LOR the data was acquired, allowing for a spatial representation that is crucial for reconstructing the final image. Understanding this aspect of sinograms is vital in grasping how PET imaging works, especially in the context of data collection and image generation.