Tracers

Question 1

Explain why the effective half-life of a radionuclide in a biological system is always less than the physical half-life

Answer 1

The physical half-life depends only on the properties of the radioactive nuclide
biological removal of the nuclide also occurs (thus removing the nuclide more quickly overall)

Question 2

How is Technetium-99m made?

Answer 2

In Molybdenum-Technetium generator, Molybdenum is combined with aluminium oxide, it decays, producing Technetium-99m which does not bond as strongly with the aluminium oxide. A saline solution, placed into the generator, washes out any Technetium-99m.

Question 3

How do Gamma cameras detect gamma radiation emitted by radiotracer?

Answer 3

Gamma rays hit sodium iodide crystals, emitting a flash of light. A photomultiplier tube turns the flashes of light into electricity. Each tube contains a photocathode that releases an electron when hit by a photon (electric effect), each electron is multiplied into a cascade of electrons. An electronic circuit collects the signals.

Question 4

Purpose of a lead collimator

Answer 4

Vertical holes only allow gamma rays parallel to the holes to pass through.

Question 5

Treating cancer with radiation

Answer 5

Firing focused beams of high energy X-rays at mutated cells or beta-emitter implants can be placed next to tumor limiting the amount of damage to healthy tissue as beta has a short range.