Final answer:
The Point of Equal Time (PET) or Critical Point (CP) is the point at which two annihilation gamma rays in a PET scan originate at the same point and travel to detectors on either side of the patient. To find the difference in arrival times of the photons, subtract the time it takes for one photon to reach one detector from the time it takes for the other photon to reach the other detector.
Step-by-step explanation:
The Point of Equal Time (PET) or Critical Point (CP) is the point at which two annihilation gamma rays in a PET scan originate at the same point and travel to detectors on either side of the patient. To find the difference in arrival times of the photons, we can subtract the time it takes for one photon to reach one detector from the time it takes for the other photon to reach the other detector.
For example, if the point of origin is 9.00 cm closer to one of the detectors, the difference in arrival times would be the time it takes for the photons to travel 9.00 cm longer distance to the other detector.
To measure arrival time differences accurately and achieve a position resolution of 1.00 mm, we would need to be able to measure the time with a high precision, such as milliseconds or microseconds.