Undergoing a PET scan is generally a painless procedure. The tracer is injected intravenously, and patients may experience a mild sensation or temporary discomfort at the injection site. The actual scanning process is non-invasive and does not cause any pain. However, some individuals may feel claustrophobic during the scan due to the requirement of lying still in a confined space. So, if you have concerns, it is best to talk to your healthcare provider.