Photomultiplier tube (Gamma camera)

The photomultiplier tube array of a Gamma camera detects the visible light produced by the scintillator, and converts it to a measurable electronic signal.

A series of photomultiplier tubes are mounted behind the scintillation crystal.

Each photomultiplier tube is composed of a tightly sealed, evacuated glass housing.

A photocathode exists at the end closest to the scintillator, which absorbs the light photons produced and emits photoelectrons in the process, via the photoelectric effect.

The photoelectrons are accelerated towards an anode at the end of the photomultiplier tube, colliding into a series of dynodes along the way, with each interaction producing further photoelectrons and therefore amplifying the electronic signal.

The amount of light detected by a photomultiplier tube is a function of its distance from the scintillation event. Tubes that are closer to the scintillation event will have a proportionally larger signal than those further away. Therefore, the location of the signal can be determined by the position of the photomultiplier tube that receives the greatest signal.