1. Radioisotopes
P3 describe the production and
detection of radiopharmaceuticals

2. Radionuclides can be produced artificially.
This is usually by the bombardment of stable nuclei by
high-energy particles.
Radionuclides can be chemically incorporated into another
compound and injected into the body for diagnostic
purposes - this is then known as a radiopharmaceutical

3. Radionuclides for radiopharmaceuticals must have
certain properties:
•Emit only gamma radiation
•Emit gamma with the right energy (140 keV) to allow
detection by a gamma camera
•Have a short half-life
•Be cheap
•Be readily available
•Be easily attached to transport compounds

4. Technetium-99m
99m
Tc is the most commonly used
radionuclide.
It is formed from the decay of
molybdenum:
99
42 Mo -> 99m43 Tc + 0 -1e (T1/2 = 67 hours)
99m
43 Tc -> 9943Tc + γ (T1/2= 6 hours)

5. The technetium generator
As T1/2 = 6 hours 99mTc needs to be generated in the
hospital

6. 131
I
131
I an important radionuclide in the detection
of thyroid problems. However, it also emits
beta radiation and at 364 keV the gamma is
of too high an energy for a good image. Its
T1/2 = 8 days is also too long. Te is produced
by bombarding tellurium with neutrons in a
nuclear reactor:
52Te + 0n -> 52Te + γ
130 1 131
131
Te -> 13153I + 0-1e
52

7. 123
I
This is a better choice than 131I, as it
only emits gamma, has T1/2 = 13 hours,
emits gamma of 159 keV.
However, it is more expensive.

8. M2 compare the desirable biological properties and radiological properties
of radionuclides used for imaging
emit only γ-radiation, since α- and β-radiations are readily
absorbed in the body, causing damage through ionisation and
difficulty with detection
have a conveniently short half-life, short enough to avoid excessive
radiation damage, yet long enough to allow detection
emit γ- radiation of an energy suitable for easy detection by a
gamma camera
be readily and cheaply available, at high concentrations
be easily attached to convenient compounds to transport it to the
targeted destination

9. D2 evaluate the choice of radiopharmaceuticals for
a range of clinical imaging requirement
Why is 99m Tc used in most cases?
Why is 123 I preferred to 131 I in most cases?