A hospital compares four ways of obtaining the same diagnostic image. A score of at least 8 is needed for a usable image. For this comparison, dose is proportional to tracer activity multiplied by exposure time. Which method gives a usable image with the lowest dose?
| Method | Tracer activity in MBq | Exposure time in minutes | Image score |
|---|---|---|---|
| P | 40 | 3 | 7 |
| Q | 30 | 5 | 8 |
| R | 60 | 3 | 9 |
| S | 50 | 4 | 10 |
Method P
Method Q
Method R
Method S