Principles behind gamma-camera detection
In a gamma-camera, every decaying technetium radionuclei emits a gamma photon. After measuring the position of the gamma impact on the detector, one needs to know its direction to go back to its origin. A collimation is necessary. This collimation is obtained by lead channels selecting the photons travelling through. In the figure above, only the photon A which reaches the scintillator will be detected by the photomultipliers, the photons B and C being absorbed by the lead.
André Aurengo, Hôpital Pitié-Salpêtrière