Patients receiving rapid-acting or short-acting insulin can begin a PET scan after __________ hours following treatment.

The correct answer is based on the timing of insulin action and the safety protocols that are in place for patients undergoing a PET scan. Rapid-acting and short-acting insulins typically peak in effectiveness within a few hours after administration. This means that significant fluctuations in blood glucose levels can occur shortly after insulin is injected, which can be particularly important for ensuring patient safety.

After two hours, the peak action of rapid-acting insulin usually subsides, allowing a more stable blood glucose level. This timing is crucial because during a PET scan, the patient should be in a controlled and stable condition, reducing the risk of hypoglycemia or hyperglycemia during the procedure. Furthermore, if imaging requires fasting or monitoring of glucose levels, the two-hour mark provides a balance between minimizing insulin's immediate effects and ensuring that the patient is ready for the imaging process.

In other situations, such as immediately after insulin injection or waiting much longer, there could be either too high a risk of unstable glucose levels or unnecessary delays in imaging, which could affect patient care and outcomes.