Fig. 7.

Schematic drawing of the basic principle of time-of-flight (TOF) PET. Annihilation events are marked as stars and the line of response as double-headed arrows. In conventional PET (non-TOF, yellow), the location of the annihilation event cannot be further located on the line of response and can only be deducted by reconstruction. In TOF PET (TOF, red), the time difference between the detection of both γ-rays is recorded, allowing for an estimation of the location of the annihilation event and resulting in a higher signal-to-noise ratio