Nuclear Medicine - Radiopharmacy Flashcards
Which method of radionuclide production happens in a cyclotron?
Charged particle bombardment
What methods of radionuclide production happen in a reactor?
Neutron bombardment.
Fission products.
Explain how a cyclotron produces radionuclides by charged particle bombardment
Pair of hollow Ds separated by a gap are placed in a magnetic field.
Charged particle introduced in the centre - accelerated towards a D by applied voltage.
No electric field inside D so particle takes curved path because of the magnetic field.
Particle continually accelerates across gap and spirals out through Ds.
Fired with high energy at target.
By what process do cyclotron products decay?
Electron capture or positron emission - as they are proton-rich.
How is Tc99m eluated from a Mo Generator?
Mo in form of [MoO4]2- is absorbed onto Al2O3 column.
[MoO4]2- decays to pertechnetate ([TcO4]-). The single charge means that it is more loosely bound to the column.
As saline is pulled through the column, the chloride ions are replaced by [TcO4]- ions.
Eluate contains Na+[TcO4]-.
Explain the function of the tubing, filter, and lead shielding in a Mo/Tc generator
Tubing - allows the column to be washed, elating the Tc99m.
Filter - keeps any Aluminium Oxide particles in the column and out of the tube.
Lead Shielding - operator safety. Stops gamma photons from leaving the generator from both parent and daughter nuclides.
How does a radionuclide calibrator measure the activity of a sample?
Radionuclide calibrator contains ion chamber, high voltage supply, and electrometer.
The ion chamber contains a pressurised gas surrounded by high voltage plates.
When radiation is emitted it causes an ionisation in the gas, the ions travel to the oppositely charged plate, and a current is measured.
The current is proportional to the activity but depends on several other factors.
What will the current in a radionuclide calibrator depend on?
Activity of the radiation source Source-container geometry (vial or syringe) Measurement position Composition of gas Energy of radiation Applied voltage
What region of the current/voltage graph does a dose calibrator operate?
Ion saturation region - not dependent on voltage fluctuations
How are different radionuclides differentiated in a radionuclide calibrator?
Each calibrator will have a button for the specific nuclide being tested that apples a specific conversion factor for the nuclide.
What QC is performed on a radionuclide calibrator?
Relative response (Daily):
- Longlived source (Cs-137) measured and response checked against baseline values for different calibration setting.
- Also, it can be used to detect leaks in the chamber or faulty electronics.
Accuracy (NPL Traceable - Annually):
- Source activity measured on departmental secondary standard - traceable to NPL, then measured on the calibrator.
Linearity (Annually):
The measured response over ~10 half-lives compared to expected activity. Tolerance of 0.1% for decay constant value calculated.
Define radionuclide purity
The ratio of the radioactivity of the radionuclide concerned to the total radioactivity of the source
What are the three sources of radionuclide impurity?
Manufacturing process - fission by-products
Daughter radionuclides
Parent radionuclides
What problems are associated with radionuclide impurity?
Radionuclide impurity could increase the patient dose, and affect the image quality
Describe how a Molybdenum breakthrough test assesses the radiopurity of a sample
- Mo breakthrough test should be performed on the first elation of a new generator, or if the generator is moved.
- It calculates the fraction of activity on Mo99/Tc99m.
- The calibrator cannot distinguish between the two nuclides, so the first elation is placed in a lead pot.
- The 141keV gammas from the Tc99m will be attenuated by the pot, but Mo99 has higher energy decays which can penetrate the pot.
- The limit of activity is 1MBq/GBq.
