The half-life of technetium-99m is 6 hours. This means that after 6 hours, half of the technetium-99m will remain, and after another 6 hours (for a total of 12 hours), half of that remaining amount will still be present.
Let's break it down:
- After the first 6 hours, 50% of the original dose remains.
- After another 6 hours (which totals 12 hours), half of the remaining 50% will be left:
- 50% / 2 = 25%
Therefore, after 12 hours, 25.0% of the technetium-99m will remain within the patient's body.
The correct answer is 25.0%.