3. Presentation Outline
What is PET?
The Basic PET Process
Basic Principle of PET
1) Positron Emission
2) Emission Detection
A positron emission tomography (PET) scan is
done to
Clinical Applications of PET
Advantages and Disadvantages of PET
4. What is PET?
PET stands for Positron Emission
Tomography and is an imaging technique
which uses small amounts of radiolabeled
biologically active compounds (tracers) to
help in the diagnosis of disease. The
tracers are introduced into the body, by
either injection or inhalation of a gas, and
a PET scanner is used to produce an image
showing the distribution of the tracer in
the body.
7. Basic Principle of PET (Positron
Emission)
Positron Emission occurs when the Proton
rich isotope (Unstable Parent Nucleus)
decays and a Proton decays to a Neutron,
a Positron and a Neutrino. After traveling a
short distance (3-5mm), the positron
emitted encounters an electron from the
surrounding environment. The two
particles combine and "annihilate" each
other, resulting in the emission of two
gamma rays in opposite directions of
0.511 MeV each.
13. Positron Emission
The image acquisition is based on the external
detection in coincidence of the emitted Gammarays, and a valid annihilation event requires a
coincidence within 12 nanoseconds between two
detectors on opposite sides of the scanner. For
accepted coincidences, lines of response
connecting the coincidence detectors are drawn
through the object and used in the image
reconstruction. Any scanner requires that the
radioisotope, in the field of view, does not
redistribute during the scan.
15. Basic Principle of PET (Emission
Detection)
As positron annihilation occurs, the tomograph
detects the isotope's location and concentration.
16. Emission Detection
Shown here in schematic form, the light photons are
converted to electrical signals that are registered by the
tomograph's electronics almost instantly.
17. Emission Detection
The ring of squares schematically represents one ring of
detectors in a PET scanner, which may, for example, have
fifteen such rings for simultaneous tomography of many
transaxial slices
18. Emission Detection
The tomograph's reconstruction software then takes the
coincidence events measured at all angular and linear
positions to reconstruct an image that depicts the
localization and concentration of the radioisotope within a
plane of the organ that was scanned.
19. A positron emission tomography
(PET) scan is done to
Study the brain's blood flow and metabolic activity. A
PET scan can help a doctor find nervous system
problems, such as Alzheimer's disease, Parkinson's
disease, multiple sclerosis, transient ischemic attack
(TIA), amyotrophic lateral sclerosis (ALS),
Huntington's disease, stroke, and schizophrenia.
Find changes in the brain that may cause epilepsy.
Find some cancers, especially lymphoma or cancers
of the breast, brain, lung, colon, or prostate. In its
early stages cancer may show up more clearly on a
PET scan than on a CT scan or an MRI.
See how advanced a cancer is and whether it has
spread to another area of the body (metastasized). It
is often necessary to do both CT and PET scans to
evaluate cancer.
20. A positron emission tomography
(PET) scan is done to
Help a doctor choose the best treatment for cancer.
PET scans may also be done to see whether surgery
can be done to remove a tumor.
Find poor blood flow to the heart, which may mean
coronary artery disease.
Find damaged heart tissue, especially after a heart
attack.
Help choose the best treatment, such as coronary
artery bypass graft surgery, for a person with heart
disease.
21.
22. Advantages and Disadvantages of PET
Advantages:
PET imaging is unique in that it shows the
chemical functioning of organs and tissues in
vivo, while other imaging techniques – such as
X-ray, CT and MRI – show structure.
increased sensitivity and accurate attenuation
correction provided by the PET imaging
modality.
23. Imaging
Advantages
Disadvantages
PET
-Shows organ functionality
-Gives nervous system detail
-Uses ionizing radiation
-Expensive and uncommon
-Poor resolution
-Requires care with radionuclides
MRI
-Shows 3D images with high
resolution
-Can ‘remove’ unwanted
layers
-Excellent soft tissue contrast
-Can show functionality of
nervous system in details
-Safe for patients, painless,
non-invasive
-Very expensive
-Scanning takes a long time
-Hazards with implants
-Claustrophobia
-High skill in using it is
needed
-Cannot be used with
patients with metallic devices
X-Ray
-Cheap
-Simple to use
-Readily available
-Rapid imaging
-Good bone resolution
-Uses ionizing radiation
-Radiation dose is cumulative
-Does not show soft tissue
well
-Does not show functioning
