Anti-scatter grid
Encyclopedia
An anti-scatter grid is a device for limiting the amount of radiation
scatter created in a radiographic
exposure reaching the detector.
The grid is constructed of a series of alternating parallel strips of lead
and a radiolucent substance such as a plastic
. The grid is placed between the patient
and the detector during the exposure. Primary beam radiation passes through the radiolucent strips as it travels roughly parallel to them, but scattered radiation which has, almost by definition, deviated from the parallel beam, cannot easily pass through the grid as it encounters the lead strips at an angle, and is attenuated, or lost, from the beam.
Grids are used particularly in examinations where a large quantity of scatter is created, ie, those involving a large volume of tissue being irradiated and those requiring high kV
. The scatter would otherwise degrade the image by reducing the contrast
and resolution
. Use of a grid, however, requires a greater radiation exposure to the patient as a good deal of primary beam is also attenuated by the lead slats, and for this reason grids are not used for all examinations.
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
scatter created in a radiographic
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
exposure reaching the detector.
The grid is constructed of a series of alternating parallel strips of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and a radiolucent substance such as a plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
. The grid is placed between the patient
Patient
A patient is any recipient of healthcare services. The patient is most often ill or injured and in need of treatment by a physician, advanced practice registered nurse, veterinarian, or other health care provider....
and the detector during the exposure. Primary beam radiation passes through the radiolucent strips as it travels roughly parallel to them, but scattered radiation which has, almost by definition, deviated from the parallel beam, cannot easily pass through the grid as it encounters the lead strips at an angle, and is attenuated, or lost, from the beam.
Grids are used particularly in examinations where a large quantity of scatter is created, ie, those involving a large volume of tissue being irradiated and those requiring high kV
KV
-In physics and chemistry:* Voltage-gated potassium channel,a large family of potassium channels* Kilovolts , 1000 volts* The rating of RPMs per volt as used in reference to the rotational speed of brushless motors...
. The scatter would otherwise degrade the image by reducing the contrast
Contrast
Contrast may refer to:* Contrast , the difference in color and light between parts of an image* Contrast , expressing distinctions between words...
and resolution
Optical resolution
Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged.An imaging system may have many individual components including a lens and recording and display components...
. Use of a grid, however, requires a greater radiation exposure to the patient as a good deal of primary beam is also attenuated by the lead slats, and for this reason grids are not used for all examinations.