GCSE Questions: Medical Physics
- scanning and therapy
Doctors sometimes need to know how much blood a patient has.
They can find out by using a radioactive solution.
Radiation from radioactive substances can harm your body cells.
The doctors use a radioactive substance called Technicium 99-m which loses half of its radioactivity every six hours.
After measuring how radioactive a small syringe-full of the solution is they inject it into the patient's blood.
They then wait for 30 minutes so that the solution has time to become completely mixed into the blood.
Finally, they take a syringe-full of blood and measure how radioactive it is.
Example: If the doctor injects 10 cm3 of the radioactive solution into the patient and this is found to have been diluted 500 times by the blood there must be 10 × 500 = 5000 cm3 of blood
(Total 9 marks)