Positron Emission Tomography (PET) is a powerful clinical tool for imaging cancerous tumors. PET data is collected in sinogram format that is then reconstructed with Filtered Backprojection or other reconstruction methods. In order to create the sinogram, the PET scanner must know where high-energy photons entered the PET detectors. The PET detector modules output a voltage pattern that is then analyzed to determine the point of interaction of the photon and thus determine which line of response (sinogram bin element) to populate. In this talk, I will briefly describe the mechanisms of two types of PET detectors used in clinical practice. I will then discuss the inverse problem: given an output voltage pattern from a PET detector, how can the line of response be determined?