Collimator

Collimator

Write short note on collimator.
Answer. Radiation beam emitted by X-ray tube is shaped using special diaphragm known as collimator. Collimation is the method by which one can control size and shape of the X-ray beam.

• Collimator decreases the risk of radiation, minimizes scattered radiation and decreases the fog with sharp image and better contrast.
• Collimators used in intra-oral machines are fixed while in extra-oral machines collimators used are adjustable.

Types of Collimators

Following are the type of collimators:

Diaphragm collimator

• It consists of a thick plate of radiopaque material with opening in it.
• Collimator should lie over the port in X-ray head by which X-ray beam emerges.
• Aperture should be of different size and shape depending on requirement.

Tubular collimator

• It is a tube which is manufactured by radiopaque material.
• Combination of diaphragm type and tubular type is used.
• The combination helps in reducing the penumbra at periphery of image.
• Longer the tube small is penumbra.

Rectangular collimator

• They limit the size and they are larger than size of an X-ray film.
• It can be incorporated in a film-holding device.

Slit collimator

It is used in OPG machines.

In CT machines, collimators are of two types i.e:

• Source collimator: It lies in front of X-ray tube and reduces the beam of radiation to form maximum required fan beam and determines the emitted dose.
• Detector collimator: It is positioned directly in front of detector and is used to shield detector against scattered radiation and prevents the artifacts.