Lecture PET

7 important questions on Lecture PET

When is a positron created?

When an unstable nuclear isotope decays.

Which three types of events are there in PET?

  1. true coincidence: both gamma rays escape without scatter and interact in detectors.
  2. scatter coincidence: one or both gamma rays scatter in tissue.
  3. random coincidence: two gamma rays from seperate emissions strike the detecotrs at the same time.

Wherefore is pre-processing required in PET?

  • to correct for random coincidences
  • estimation and substraction of scattered photons.
  • detector dead-time correction
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Which factors determine the spatial resolution in PET?

  1. The rms distance (root mean square distance) travelled by the positrons after being emitted by a isotope and before annihilation (sending out gamma rays).
  2. The residual energy of the electron-positron pair.

What is time of flight PET?

Advances in electronis and detection crystals make it possible to measure the time difference between the arrival of two photons, This limits the location of the annihilation event.

What is a cyclotron?

This is used to generate a nucleus.
Electrons are "stripped" of protons, proton shoots out of the circle and is trapped into a molecule.

This process has to happen shorter than half life

When would you consider PET over MRI?

  • ROI is inferior temporal lobe
  • When you're interested in something with a low concentration; with PET you can measure strong signals from substances with low concentrations.

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