What does the presence of non-collinearity of annihilation photons and finite positron range affect in PET?

The presence of non-collinearity of annihilation photons and the finite positron range significantly impacts positional accuracy in Positron Emission Tomography (PET).

In a perfect scenario, when a positron from a radiopharmaceutical decays, it annihilates with an electron, resulting in the emission of two 511 keV gamma photons. These photons should ideally travel in opposite directions along the same line (collinear). However, due to slight deviations from this perfect alignment (non-collinearity) and the fact that positrons do not travel an infinite distance before annihilation (finite positron range), the detected photons may not accurately reflect the true origin of the annihilation event.

When these factors come into play, the system's ability to pinpoint where the annihilation occurred in the body becomes compromised. This leads to inaccuracies in the image, as the detected signals are not aligned with the actual source of the radiation. Consequently, the reconstruction of images reflects these inaccuracies, resulting in potential blurring or misrepresentation of structures in the imaging outputs, thereby impacting overall diagnostic quality.

Thus, positional accuracy is notably affected by these phenomena, reinforcing the importance of understanding how the physical attributes of annihilation photons and positron interactions influence PET imaging.