pet scan

1. PET
Positron Emission Tomography:
is an imaging technique which uses small amounts of radiolabeled biologically active compounds to help in the
diagnosis of disease and that can help in reveal the metabolic or biochemical function of tissues and organs .
The PET scan uses a radioactive drug (tracer) to show both normal and abnormal metabolic activity.
A PET scan can often detect the abnormal metabolism of the tracer in diseases before the disease shows up on other
imaging tests, such as CT and MRI.
The tracers are introduced into the body, by either injection or inhalation of a gas.
The PET scanner is used to produce an image showing the distribution of the tracer in the body.
Main System Components
1-Scanner Gantry
a- Detector b- Septa c- Coincidence Circuit
2-Table
3- Computer
4- Cyclotron
The most frequently used radioisotopes in PET are:
18FDG (Fluorodeoxyglucose) is the most widely used PET tracer.
Andothersare
1 Carbon-11
2- Nitrogen-13
3- Oxygen-15
4- Fluorine-18
Principle of PET Positron Emission
Positron Emission occurs when the isotope 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
Emission Detection
As positron annihilation occurs, the detector detects the isotope's location and concentration

2. The resultant light photons are converted to electrical signals that are registered by the system electronics almost
instantly
The reconstruction software then takes the coincidence events measured at all angular and linear positions to
reconstruct an image
Image Acquisition
Synthesize radiotracer
Inject radiotracer
Measure gamma ray emission from isotopes
Reconstruct image from radiotracer distribution
Clinical Applications of PET
1- Oncology
Cancer cells show up as bright spots on PET scans because they have a higher metabolic rate than do normal cells.
PET scans may be useful in:
Detecting cancer
Revealing whether your cancer has spread (staging of malignant lesions)
Checking whether a cancer treatment is working
Finding a cancer recurrence
18FDG-PET may be of benefit in patients with cervical nodal metastases from an unknown primary
PET scans must be interpreted carefully because noncancerous conditions can look like cancer, and some cancers
do not appear on PET scans.
2- Heart disease
Heart PET can help find damaged heart tissue especially after a heart attack and can help choose the best treatment
such as coronary bypass heart surgery for a person with heart disease.
3- Brain disorders
Brain PET Study the brain's blood flow and metabolic activity. It aid in discovery of nervous system problems,
such as Alzheimer's disease, Parkinson's disease tumors, and seizures. etc.
Disadvantages
1- Ionizing radiation ( can expose to unborn baby if pregnant and child if breastfeeding)
2- Radioactive compound is short lived.

3. 3- Radioisotope must be produced in a laboratory near the PET scanner.