Which physical process enables PET imaging?

Which physical process enables PET imaging?

• A. X-ray attenuation
• B. Magnetic resonance
• C. Positron annihilation with photons
• D. Ultrasound scattering

Answer: (C)

Positron-emitting radiotracers set up events where a positron meets an electron and they annihilate, releasing two gamma photons of 511 keV that travel in nearly opposite directions. The PET detectors around the patient pick up these coincident photons, which defines a line of response along which the annihilation occurred. By collecting millions of such events, the scanner reconstructs an image of where the tracer—and thus metabolic activity—is concentrated. This annihilation with photons is the fundamental physical process behind PET imaging. X-ray attenuation relates to CT, magnetic resonance relies on nuclear magnetic resonance, and ultrasound uses mechanical wave scattering, so they don’t drive PET.

Positron-emitting radiotracers set up events where a positron meets an electron and they annihilate, releasing two gamma photons of 511 keV that travel in nearly opposite directions. The PET detectors around the patient pick up these coincident photons, which defines a line of response along which the annihilation occurred. By collecting millions of such events, the scanner reconstructs an image of where the tracer—and thus metabolic activity—is concentrated. This annihilation with photons is the fundamental physical process behind PET imaging. X-ray attenuation relates to CT, magnetic resonance relies on nuclear magnetic resonance, and ultrasound uses mechanical wave scattering, so they don’t drive PET.