48. NUCLEAR MEDICINE: RADIOPHARMACEUTICALS

Question 1

1. What happens with the Pharmaceuticals when they are given to a patient?

Answer 1

• they are ingested by the patient
• they can be injected into the patient
• the radiation source is inside the patient

Question 2

2. What can be obtained when we combine tomographic imaging with radiopharmaceuticals?

Answer 2

• functional information can be obtained

Question 3

3. What does the Radioactive Compound act as?

Answer 3

• it acts as a Radiation Source

Question 4

4. What do we use Tomographic Techniques for?

Answer 4

• we use them to reconstruct the concentration of the
  Radiopharmaceutical

Question 5

5. What are the 2 different types of Radio labels that are used?

Answer 5

1. GAMMA EMITTERS
   - for Single Photon Emission Computed Tomography
   - SPECT
2. POSITRON EMITTERS
   - for Positron Emission Tomography
   - PET

Question 6

6. List 2 examples of Gamma Emitters?

Answer 6

1. Krypton
   - 81 m Ke
2. Technetium
   - 99 m Tc

Question 7

7. List 5 examples of Positron Emitters?

Answer 7

1. Fluoride
   - 18 F
2. Oxygen
   - 15 O
3. Nitrogen
   - 13 N
4. Carbon
   - 11 C
5. Rubidium
   - 82 Rb

Question 8

8. Can Radioactive Substances be used directly?

Answer 8

• yes
• in some cases

Question 9

9. How can a patient absorb Krypton (81 m Kr)?

Answer 9

• it can be inhaled
• for immediate lung ventilation studies

Question 10

10. How do we often label specifically physiologically relevant compounds?

Answer 10

• we label them with a Radioactive Atom

Question 11

11. What is Fluorodeoxglucose (FDG) an example of?

Answer 11

IT IS AN EXAMPLE OF:
- a physiologically relevant compound that is labelled
with a Radioactive atom

Question 12

12. What is Fluorodeoxyglucose (FDG)?

Answer 12

• it is a substance that is metabolised at sites of high
  glucose demand

EG:
- demands from the brain
- demands from some tumours

Question 13

13. What does the Spatial Distribution of FDG accurately reflect?

Answer 13

• it reflects the Glucose uptake in the body

Question 14

14. What do we need to do in order for the local concentrations of glucose to be imaged with PET?

Answer 14

WE SUBSTITUTE:
- the stable 9 F
- for the Positron-Emitter 18 F

Question 15

15. What kind of decay is desirable for Radiopharmaceuticals?

Answer 15

• fast radioactive decay
• they need to have a low half life

Question 16

16. Why do Radiopharmaceuticals need a fast decay rate?

Answer 16

• this reduces the patient dose
• this reduces the total patient exposure
• the Radiopharmaceuticals are often excreted through
  the urine

Question 17

17. What is the half-life of 18 F ?

Answer 17

• 2 hours
• this means that only 1.6% of the initially administered
  18 F is left in the body after 12 hours

Question 18

18. List the 6 requirements for an ideal Radiopharmaceutical?

Answer 18

1. HAVING A SHORT PHYSICAL HALF-LIFE
2. BEING ELIMINATED FROM THE BODY
   - with an effective half-life
   - that is approximately equal to the examination time
3. EMIT PURE GAMMA RAYS
   - with no subsequent change in the nucleus
4. EMIT MONO-ENERGETIC GAMMA RAYS
5. HAVE A HIGH ACTIVITY PER UNIT MASS
   - this is with regards to the Specific Activity
6. BE ABLE TO LOCALISE LARGELY
   - and quickly at the target site

Question 19

19. List the 3 more requirements for an ideal Radiopharmaceutical?

Answer 19

1. DECAY INTO A MORE STABLE DAUGHTER NUCLEUS
2. EASILY AND EFFECTIVELY BE ATTACHED
   - to the chemical compound
   - at room temperature
3. BE EASILY PRODUCED
   - or found a the hospital site