What does two annihilation photons form between two crystals?

When a positron emitted from a radioisotope in a PET scan encounters an electron, they annihilate each other, producing two gamma photons. These photons are emitted in nearly opposite directions due to the conservation of momentum.

The term "Line of Response" (LOR) refers to the straight line connecting the point of annihilation (where the positron and electron met) to the points where the two annihilation photons are detected in the detector crystals. This LOR is crucial in the reconstruction of the image, as it aids in determining the origin of the annihilation event, allowing for the precise localization of radiotracer distribution within the scanned object.

The creation of a LOR is essential for the image processing in PET scanning, as the system relies on detecting pairs of photons that correlate to a particular path that the annihilation event has taken. The LOR helps in building a three-dimensional image from the two-dimensional data captured by the detectors.

In contrast, other terms such as "Signal Line," "Photon Pathway," or "Interaction Line" do not accurately describe the relationship between the annihilation photons and their detection within the context of PET imaging. The concept of a Line of Response is specifically tailored to the mechanics of how positions are