Developed by electronic engineer Hal O. Anger, the Anger camera is really a series of evolving implementations to form images from gamma rays. Anger's first approach used lead pinholes to direct gammas directly onto photographic film, but this was extremely slow and unsafe in the clinical applications involved. His major advance came when he placed an array of lead collimators in front of large single scintillating crystal -- a material, such as sodium iodide, that emitted light when struck by gammas -- and put an array of photomultiplier tubes on the back of the crystal.
The intensity of the light was proportional to the energy of the gamma photons striking the crystal. In generating the image from the scintillation patterns, the photomultiplier pulses were integrated and formed into a false-color image; the collimator and filters could exclude light from photons of energy levels not of interest.
Anger cameras are the basic image-forming devices in a wide range of instruments in nuclear medicine, especially the Single-Photon Emission-Computed Tomography (SPECT) and Positron-Emission Computed Tomography (PET).
Evolving versions use multiple scintillating crystals, which may be integrated into a solid-state light amplifier.