Where is the collimator placed in relation to the X-ray tube and cone?

• A. Between the X-ray tube and the cone
• B. Inside the cone
• C. Behind the patient
• D. Within the film holder

Answer: (A)

Collimation shapes and limits the primary X-ray beam, reducing exposure to the patient and improving image quality. Placing the collimator between the X-ray tube and the cone restricts the beam right at its source, before it travels through the cone toward the tooth. This early restriction keeps the field small and helps match it to the receptor, minimizing scatter and dose. If the collimator were inside the cone or behind the patient, the beam wouldn’t be properly restricted at the source, leading to more exposure and less control over the beam size. A collimator placed within the film holder wouldn’t affect the beam until after it has passed through the patient, which defeats its purpose.