1. PET Imaging Positron Emission Tomography

2. Positron is an Anti-particle
When a particle and an antiparticle interact they annihilate
Both particles are destroyed
Two photons(Gamma-rays) are created
Photons are emitted along a straight line (180 degrees angled)

3. Photon Energy
Each photon has the energy of the particle that is destroyed
For positron-electron annihilation
511 keV (for each gamma-ray)

4. Where do positrons come from?
Cosmic rays
High energy photon interactions (pair production)
Radioactive decay
Radioactive material can be incorporated into radiopharmaceuticals

5. Annihilation Detection
In coincidence counting an event is ONLY registered
if a signal is received from two detectors within a
window. The smaller the window the more accurate
the coincidence measurement. A few nanoseconds
is usually used.
Annihilation Detection
Coincidence

6. PET scanner
They do have septal rings to reduce cross walk from ring to ring
With septal rings in 2D
Without septal rings 3D
3D works best in head

7. PET camera components Ring of crystals. Photomultiplier tubes.
Pulse height analyzers.
Timing discriminators.
Coincidence circuits.
Septal rings.

8. Main problems in PET Attenuation correction.
Photon emission occurring at other than 180 degrees
Reconstruction of the image.

9. Image Reconstruction Methods
Filtered back projection - like CT
Iterative reconstruction

10. Advantages of PET Imaging
Higher sensitivity because no collimator used.
Higher resolution because of coincidence detection.
Less image errors because of using time of flight calculations

11. PET CT Replace rod source with CT scanner Better attenuation maps
Image fusion

12. Advantages of PET-CT
1- Faster scan 2- Better image quality 3- More information in the image 4- Improve lesion localisation

13. Exposure Causes Main sources of radiation exposure:
Handling doses and injecting patients
Radiation from patients
Radiation from sources
Contamination

14. Patients
Patients usually rest about 30 min before scanning to enable radiopharmaceutical to spread within the body
Scan takes about 40 min
Exposure is about 1.5 mR/hr per 10 mCi

15. Individuals of Concern
Technologists
Pregnant Technologists
Other Workers
Visitors
Companions

16. PET: The use of the positron annihilation products in imaging of internal body organs.
True coincidence events: Events from a single positron annihilation that was produced by emission of a positron.
Single events: Events produced from unpaired photon.
Line Of Response (LOR): an imaginary line drawn between two detectors registering a signal.