Fig. 3.

Demonstrates the principle of the J-PET scanner based on two plastic strips. Analog signals measured at four PMTs are also shown. For a scintillator of length L and considering the effective velocity of the light photons inside the scintillator (${\text{Veff}}_{\text{Light}}$), the formula for calculating the hit position and hit time is shown in the figure. The annihilation point can be reconstructed from the measured TOF information between two hit positions (in different/opposite stripes)