PET Flashcards
(55 cards)
What is nuclear medicine?
- applies unsealed radioactive substances, administered in the form of radiopharmaceuticals
Used for the diagnosis and treatment of disease
Non-invasive imaging aimed at capturing functional and metabolic images of the target body tissue.
What is the process of Nuclear Medicine
A small dose of a radioisotope is administered to the
patient in the form of a radiopharmaceutical or tracer,
which is designed to enter the cells of the target organ.
The radioisotope decays to emit energy in the form of
gamma radiation that can be detected by the gamma
camera or PET/CT Scanner.
Scanned data represents the distribution and uptake of the tracer in the body
What is radioactive decay?
◦ decay is spontaneous process aimed at achieving stability in the atom
◦ Decay can result in the emission of energy in the form of
electromagnetic radiation or the emission of particles.
Unit of radioactive decay
The unit of radioactivity is the Becquerel (Bq)
One Bq. corresponds to 1 decay per second
What is the half-life
Half-life is the length of time that it takes for an element to decay to half its activity.
When a nucleon is transitioning from excited state back to ground state, energy is released in the form of…
electromagnetic radiation - Υ ray (gamma ray)
When an electron transitions from the excited state back to the ground state, energy is released in the form of…
electromagnetic radiation - X rays
What is SPECT Imaging
Camera rotates around the patient recording multiple images that are then reconstructed into a 3-D data set
Cross sectional imaging
Disadvantages of sole SPECT imaging
◦ Low resolution leads to decreased reporting confidence
◦ Acquisition times long, motion a problem
◦ Lack of anatomical landmarks
What is the benefit of SPECT CT
Combines the low resolution of SPECT with High Resolution of CT
Provides specificity to the image interpretation
Allows for image attenuation correction, localisation and registration
How is SPECT CT beneficial to RT
CT images for SPECT are typically LDCT’s and their purpose is for attenuation
correction, image co-registration for the purpose of pathology localisation
Once the CT is imported and registered to the RT planning data the nuclear
medicine metabolic data can then be accurately used to assist with
treatment planning
How is SPECT CT beneficial to RT
CT images for SPECT are typically LDCT and their purpose is for attenuation
correction, image co-registration for the purpose of pathology localisation
How to maintain radiation safety
Time - reduce time spent surrounding the patient
Distance - maintain distance between the patient and yourself (distance greater than 1.0m shown to be effective when communicating)
attempt to schedule around other procedures especially ultrasound which does require close contact
PET overview
◦ provides metabolic and functional imaging
◦ Uses short lived positron emitting isotopes
◦ uses annihilation coincidence detection
How are short-lived positron emitting radiopharmaceuticals created?
Cyclotron - stores isotropes used to make radiopharmaceuticals
A cyclotron is a type of particle accelerator which repeatedly propels a beam of charged particles (protons) in a circular path
What is positron decay
Positron decay is a way for an atom with too many protons to achieve a more relaxed state
P + -> n + e + + neutrino + energy
A proton in a nucleus is transformed into a neutron and a
positively charged electron – or a positron.
The positively charged electron and a neutrino are ejected
from the nucleus
What is a positron?
A positron is the antiparticle of an ordinary electron
What happens to a positron once ejected from a nucleus?
After ejection from nucleus it loses kinetic energy in collisions with atoms in surrounding matter and comes to rest within millimetres of the site of origin (10 -9sec)
The positron then combines with an ordinary electron in an annihilation reaction
In which its mass and that of the ordinary electron are converted into energy
This energy appears in the form of two 0.511MeV annihilation photons
PET/CT relation to annihilation photons
PET uses annihilation coincidence detection to create the image
This is based on two 511kev photons are emitted in opposite directions following the annihilation of a positron and an ordinary electron
Why is attenuation correction important in PET/CT
Photons from deep in the tissue are absorbed –> therefore need to correct for depth
Where can the attenuation coefficient be applied in PET/CT
Where the tissue structure is relatively uniform’ e.g. the head, a standard attenuation value can be used uniformly across the structure
What was the motivation for PET/CT
The motivation for the development of PET/CT was the need to be able to identify areas of increased
radiopharmaceutical (metabolic information) with patient-specific anatomy under identical “conditions”.
How can malignant tumours be visualised on a PET/CT
Increased glycolysis is a distinct marker of malignant tumours compared to normal tissue
Typical biodistribution of FDG throughout the body
The Brain
High Uptake - Cortical and cerebellar grey matter, nuclei, and thalamus
Low/No Uptake - White matter and ventricular system
Body
Liver > Spleen
Mediastinum (blood vessels)
Kidneys, Ureters and Bladder
Muscles and Bone Marrow
