Final answer:
The prescan delay in an N-13 PET scan refers to the time between the radioisotope administration and the scan start, which is short due to N-13's short half-life of about 10 minutes. A detailed calculation of photon arrival times based on distance to the detector requires the speed of light, which is not given. Extremely high time resolution is required to achieve 1.00 mm position resolution in PET scans.
Step-by-step explanation:
The question pertains to a specific detail regarding N-13 PET scans, which are a type of positron emission tomography (PET) used for medical imaging. Positron emission tomography relies on the detection of annihilation photons produced when positrons emitted by a radioisotope (like N-13) encounter electrons in the body. However, the question about the prescan delay in N-13 PET does not seem to provide enough context to give a precise answer. Typically, the prescan delay would refer to the time between the administration of the radiopharmaceutical and the start of the scan. This can vary based on the biological half-life of the radioisotope and the type of tissue being imaged. For N-13, which has a half-life of approximately 10 minutes, this prescan delay is generally short to capture the peak activity before significant decay occurs.
In regard to the difference in arrival times of annihilation photons when one photon is closer by 9.00 cm to the detector, we use the speed of light to calculate this time difference. However, without the speed of light in the given information, a numerical answer cannot be provided. To achieve a position resolution of 1.00 mm using time difference, extremely high time resolution is required due to the speed of light, on the order of picoseconds (10-12 seconds).