1. Pure beta minus emitter.

2. Medium/high energy (>1 meV).

3. Effective half-life = moderately long, e.g., days.

4. High target:nontarget ratio.

5. Minimal radiation dose to patient and Nuclear Medicine personnel

6. Patient Safety

7. Inexpensive, readily available radiopharmaceutical.

8. Simple preparation and quality control if manufactured in house.