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. Author manuscript; available in PMC: 2010 Oct 21.
Published in final edited form as: Nucl Instrum Methods Phys Res A. 2009 Oct 21;610(1):11–15. doi: 10.1016/j.nima.2009.05.032

Figure 3.

Figure 3

Origin of ragial elongation. Gamma rays can penetrate a significant distance into the scintillator crystal ring before they interact (solid circles). Most PET detector modules only identify which crystal the interaction took place in, and so locate the event position at the front face of the crystals (solid squares). The positron annihilation is incorrectly assumed to lie on the line connecting the interaction positions (the dashed line), which leads to a distorted image. By measuring the depth of interaction within the scintillator crystals, the positron annihilation is correctly assumed to lie on the line connecting the solid circles, which eliminates this distortion.