Lecture 3 Flashcards
What is molecular imaging and what is it good for?
Visualisation, description and measurement of biological processes on the molecular and cellular level. It can aid in early diagnosis and identification of functional changes in tissue. Enable changes in individual patient management in real time. Facilitate drug development
What is internal conversion? What is the equation?
Energy of transition –> BE + KE of electron
The excited daughter emits gamma ray but energy transferred to an orbital electron. This escapes atom with discrete energy and cascade with xray emission occurs.
What does the probability of internal conversion increase with?
higher Z
Lower energy of transition
The longer the lifetime of the excited state
What is an isomeric transition and why is it useful?
Occurs when an excited nucleus has a long lived metastable state- considered as a separate decay. It can separate out the particulate emission stage ( parent to daughter) from the pure photon emission stage ( daughter de-excitation). This results in a lower dose to the patient.
What is the physical half life equation?
At= A0e^-λt.
If A=A0/2 i.e. half the atoms are left then ln2=λ x t1/2
What is the equation for effective half life?
Combines biological and physics half life.
1/t 1/2 eff= 1/t1/2 phys + 1/t1/2 biol
Describe the features of a cyclotron
Evacuated system with 2 dees and a B field
1 dee is slightly +ve compared to the other so that particles are accelerated across the gap, moves faster and in a slightly larger circle
Alternating power supply causes it to accelerate across the gap in a spiral
High speed, high energy particles can be deflected towards the target.
Comprised of: dees, ion source, vacuum system, target system, beam extraction system, magnet
Name a cyclotron produced radionuclide (PET)
F18
Name a non-PET cyclotron product
Thallium 201- myocardial perfusion
Gallium 67- infection or inflammation imaging
What is a generator used for?
A container of long lived parents is delivered to the end user. This generates a source of shorter-lived daughter nuclides which can easily be extracted. They provide hospitals with an on-site supply of short half life pharmaceuticals
What are the characteristics of an ideal generator?
- Convenient, easy to use
- High yield of clinically useful daughters
Adequate shielding - Sterile and pyrogen free
- Daughter decays to stable nuclide.
What is transient equilibrium?
When the parent half life is 50-100 times longer than the daughter half life. The activity of the daughter builds up to become more than aren’t but decays with an apparent half life= parent
What is secular equilibrium?
The half life of the parent is so long that there is negligible decrease in parent activity.
What 6 things should you check for in radionuclide quality control?
- Physics characteristics
- pH and ionic strength
- Radiochemical purity
- Radionuclide purity
- Chemical purity
- Biological tests
What is radiochemical purity? What causes it and what are the impacts?
The fraction of a specific radionuclide present in the desired chemical form and in the specified molecular position. Radiochemical impurities may arrive from incomplete reactions, side reactions etc. Impurities increase radiation dose to the patient, create image artefacts and may cause waste disposal problems.
