Principles behind gamma-camera detection
In a gamma-camera, every atom that disintegrates emits a gamma photon. Once the photon leaves a mark upon colliding with a scintillator, the signal is amplified by a photomultiplier. Le photon direction has to be gauged by tracing the path back to the source. This is achieved by the lead canal collimators, which distinguish between photons going in different directions. In the diagram above, only photon A reaches the scintillator (and will therefore also be detected by the photomultipliers) while photons B and C are absorbed by the lead. For gamma rays emitted by technetium atoms, 140 keV of energy will be deposited in the scintillators.
André Aurengo, Hôpital Pitié-Salpêtrière