PET

Biomedical Engineering System

Dedicated to:Sir Fahad Akbar Ali.

From:Muhammad Ovais Ur Rehman2011/BM/20

Fb: www.facebook.com/muhammad.ovais.56

What is PET

• PET stands for positron emission tomography.

• PET is a noninvasive, diagnostic imaging technique for measuring the metabolic activity of cells in the human body.

• It was developed in the mid 1970s and it was the first scanning method to give functional information about the brain.

PET

How does it work?

• In this technique a chemical compound with desired biological activity is labeled with radioactive isotope that decays and emit positron.

• The emitted positron immediately combines with an electron and these two are mutually annihilated with gamma rays.

• The gamma rays photons travelling in opposite directions penetrate the surrounding tissues and recorded outside the subject by circular array of detectors.

Annihilation of a positron and electron• The positron will encounter an electron and completely annihilate

each other resulting in converting all their masses into energy. This is the result of two photons, or gamma rays.

• Because of conservation of energy and momentum, each photon has energy of 511keV and head in an almost 180 degrees from each other.

• 511keV is the ideal rest state annihilation value.

Coincidence detection• Types of coincidence–True–Scatter–random

– True conincidence– It’s a simulataneous detection of the two emission resulting from

a single decay– Scattered coincidence– When both photons from a single decay event are scattered and

both are detected– Random coincidence– The simultaneous detection of emission from more than one

decay events.

Schematic diagram

What are some of the uses for PET

• Patients with conditions affecting the brain.• Heart.• Certain types of Cancer.• Alzheimer’s disease.• Some neurological disorders .

Thank you