Practice question

Positron emission tomography images metabolic activity by injecting tracer molecules labeled with short-lived positron emitters such as fluorine-18, carbon-11 or oxygen-15. Inside tissue, emitted positron travels briefly then annihilates with an electron, producing two 511 keV gamma photons emitted in opposite directions. Ring detectors register coincident photon pairs, reconstructing tracer concentration. Fluordeoxyglucose PET highlights brain regions with high glucose utilization, reflecting synaptic activity. MRI visualizes anatomy via proton magnetic resonance, CT uses X-ray attenuation, SPECT detects single photons, only PET exploits positron annihilation for metabolic mapping.