What is the function of the collimator?

What is the function of the collimator?

• A. Separates gamma rays and keeps scattered rays from entering scintillation crystal
• B. Focusing gamma rays onto the scintillation crystal
• C. Amplifies photon energy
• D. Speeds up photon travel to PMTs

Answer: (A)

In gamma imaging, the collimator provides directionality to the photons that reach the detector. Gamma rays are emitted in all directions, so without a collimator you’d collect photons from many angles, resulting in a blurry image. The collimator is a dense material with many small holes. Photons that travel nearly straight along a hole’s axis pass through and reach the scintillation crystal, while photons coming in at oblique angles strike the walls and are absorbed. This filtering effect means only photons traveling in known directions contribute to the image, which sharpens spatial localization of the radioactive source and reduces background from scattered photons. It does not focus photons, amplify energy, or accelerate them—the collimator’s job is to block undesired angles and preserve directional information.

In gamma imaging, the collimator provides directionality to the photons that reach the detector. Gamma rays are emitted in all directions, so without a collimator you’d collect photons from many angles, resulting in a blurry image. The collimator is a dense material with many small holes. Photons that travel nearly straight along a hole’s axis pass through and reach the scintillation crystal, while photons coming in at oblique angles strike the walls and are absorbed. This filtering effect means only photons traveling in known directions contribute to the image, which sharpens spatial localization of the radioactive source and reduces background from scattered photons. It does not focus photons, amplify energy, or accelerate them—the collimator’s job is to block undesired angles and preserve directional information.