10.6.3 Gamma camera

How a Gamma Camera Works

1. Photomultiplier Tube: The core component of a gamma camera is the photomultiplier tube (PMT), which is an evacuated tube containing several parts:

• A photocathode that releases electrons when gamma photons hit it.
• Dynodes, which are electrodes set at increasingly higher positive potentials. Each dynode release more electrons when hit by the initial electrons, causing an electron multiplication process called secondary emission. This significantly amplifies the electron signal, ensuring that a measurable output signal is produced. Once the electrons have multiplied sufficiently, they reach the anode, where they create an electrical signal that can be processed.

2. Lead Collimator: Gamma rays entering the camera first pass through a lead collimator. This component is designed to filter out scattered gamma photons by only allowing photons travelling parallel to the holes in the collimator to pass through. This helps to produce a sharper and more accurate image by reducing the background noise from scattered photons.

3. Scintillator: After passing through the collimator, the gamma photons reach the scintillator. The scintillator is a material that emits visible light photons when struck by gamma photons. This conversion from gamma radiation to visible light is crucial, as the photomultiplier tube can detect and amplify these light photons.

4. Image Creation: The light photons generated in the scintillator are captured by the photomultiplier tubes. The tubes then convert these light signals into electrical signals, which are processed by a computer. The computer reconstructs the spatial distribution of the gamma rays to form an image, which can be displayed on a monitor for diagnostic purposes.