Question

How can doctors best detect medical problems?

by using a radioactive isotope to kill unwanted cells and target diseased tissue
by measuring the half-life of an isotope found in the skin with high-energy gamma radiation from outside the body
by injecting a radioactive isotope that travels to the target tissue and measures the amount of radioactive decay
by administering a drug that targets replicating cells

Answer 1

"By injecting a radioactive isotope that travels to the target tissue and measures the amount of radioactive decay."

Explanation: this describes nuclear medicine imaging (e.g., PET and SPECT) in which a radiotracer (like FDG for PET) is given, accumulates in tissues of interest, and emitted gamma photons from radioactive decay are detected to reveal physiological or metabolic abnormalities. This is a diagnostic technique.

Why the others are incorrect:
- Using a radioactive isotope to kill unwanted cells = radiation therapy (treatment, not detection).
- Measuring the half-life of an isotope in the skin with external high‑energy gamma radiation is not a practical or safe diagnostic method.
- Administering a drug that targets replicating cells is chemotherapy (treatment), not primarily a detection method.