Nuclear medicine relies on two imaging modalities to assess internal function and diagnose disease. Positron emission tomography (PET) typically uses fluorine-18, a radiotracer that releases positrons, and a special scanner to detect the resulting gamma rays. Single-photon emission computed tomography (SPECT) is similar, but usually depends on injecting the technetium-99m radioisotope and a gamma camera to detect where it goes in the body.
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https://www.medgadget.com/2019/08/worlds-first-pet-spect-scanner-developed-using-compton-camera.html
Source: Medgadget