Systems and methods for determining at least one correction parameter for a Positron Emission Tomography (PET) scanner including a plurality of detector units is provided. For each line of response (LOR) of a plurality of lines of response (LORs) associated with the plurality of detector units, the methods may include determining, based on scan data of one or more scans of a phantom at a plurality of positions, a first sum of coincidence events on the LOR, wherein the phantom is moved to the plurality of positions along an axis of a field of view of the PET scanner during the one or more scans, and a length of the phantom is less than a length of the field of view of the PET scanner along the axis; determining, based on the first sum of coincidence events, at least one correction parameter associated with the LOR.