- As the radioisotope undergoes positron emission decay (also known as positive beta decay), it emits a positron (the antimatter counterpart of an electron).
- After travelling up to a few millimeters the positron encounters and annihilates with an electron, producing a pair of annihilation (gamma) photons moving in almost opposite directions.
- The most significant fraction of electron-positron decays result in two 511 keV gamma photons being emitted at almost 180 degrees to each other; hence it is possible to localize their source along
Application:
PET is both a medical and research tool. It is used heavily in:
-clinical oncology (medical imaging of tumors and the search for metastases),
- clinical diagnosis of certain diffuse brain diseases such as those causing various types of dementias.
-PET is also an important research tool to map normal human brain and heart function.
Gamma - decay
Radionuclides used in PET scanning are typically isotopes with short half lives such as:
-11C (~20 min),
-13N (~10 min),
-15O (~2 min),
-18F (~110 min).
-Due to their short half lives, the radionuclides must be produced in a cyclotron which is not too far away in delivery-time to the PET scanner. These radionuclides are incorporated into compounds normally used by the body such as glucose, water or ammonia and then injected into the body to trace where they become distributed. Such labelled compounds are known as radiotracers.
