Answer: Radioactively-labeled materials
Step-by-step explanation: nuclear medicine is a medical specialty that uses radioactive tracers to diagnose and treat different diseases. Radioactive tracers are materials that can vary according to the purpose of the method. For most diagnostic, the radioactive tracer is administered by intravenous injection. However it may also be administered by inhalation, by oral ingestion, or by direct injection into an organ.
SPECT scans are primarily used to diagnose and track the progression of heart disease, and the major purpose of PET scans is to detect cancer and monitor its progression, response to treatment, and to detect metastases. This two methods are the most used in nuclear medicine.