What is represented by the variable 'D' in the TOF calculation formula?

In the Time-of-Flight (TOF) calculation in PET imaging, the variable 'D' represents the Distance from Center. This is crucial in understanding how PET scans determine the location of the annihilation events. By measuring the time difference between photons detected at different locations, the system can compute not only the timing but also the spatial relationship of the detected events relative to a reference point, which is often the center of the detector array.

The Distance from Center is a key factor in localizing the positron emission events in three-dimensional space. This spatial aspect enhances image quality and resolution, allowing for more accurate representation of metabolic activity within the body.

Understanding this variable in the context of TOF helps clarify how modern PET systems improve upon standard techniques by incorporating timing information, leading to more precise imaging outcomes.