In medical imaging, an anti-scatter grid (also known as a Bucky-Potter grid) is a device for limiting the amount of scattered

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, vi ...

reaching the detector, thereby improving the quantity of diagnostic medical x-ray images. The grid is positioned on the opposite side of the patient from the

x-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

source, and between the patient and the

X-ray detector X-ray detectors are devices used to measure the flux, spatial distribution, spectrum, and/or other properties of X-rays. Detectors can be divided into two major categories: imaging detectors (such as photographic plates and X-ray film ( photograp ...

or film. Reducing the amount of scattered x-rays increases the image's contrast resolution, and consequently the visibility of

soft tissues Soft tissue is all the tissue in the body that is not hardened by the processes of ossification or calcification such as bones and teeth. Soft tissue connects, surrounds or supports internal organs and bones, and includes muscle, tendons, ...

History

The device was first invented by German

radiologist Radiology ( ) is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiati ...

Gustav Peter Bucky Gustav Peter Bucky (September 3, 1880Several sources list an 1899 birthdate, but this would mean that Bucky was in his early teens when he introduced the Bucky diaphragm. - February 19, 1963) was a German-American radiologist who made early contri ...

, who showed in 1913 that a grid can be used to 'reject' scattered x-rays before they reach the detector. It was later improved by American radiologist Hollis E. Potter by introducing moving grid. The Bucky-Potter grid facilitated the transition from small glass photographic plates to film in a variety of sizes.

Operation

Scattered x-rays do not travel in parallel to rays that pass directly through the patient. The quantity of scattering depends on several factors including: x-ray beam area, x-ray photon energies (determined by tube voltage setting), thickness of the tissue, and the composition of the tissue. By 'rejecting' scattered x-rays before they reach the detector, the Bucky-Potter grid improves recorded contrast. The grid is constructed of a series of alternating parallel strips of

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

and a radiolucent substance such as a

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English The use of the English language in current and former member countries of the Commonwealth of Nations was largely inherited fro ...

aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...

, even paper. The grid is placed between the

patient A patient is any recipient of health care services that are performed by healthcare professionals. The patient is most often ill or injured and in need of treatment by a physician, nurse, optometrist, dentist, veterinarian, or other health ...

and the detector during the exposure. Radiation which has travelled straight through the patient from the x-ray source moves directly through the radiolucent potions of the grid and strikes the detector. Radiation which has been scattered while travelling through the patient strikes the lead strips at an angle, and is either attenuated or further scattered. As a result, only radiation which has travelled directly through the patient is imaged on the detector, increasing contrast. The single most important parameter that influences the performance of an anti-scatter grid is the grid ratio. The grid ratio is the ratio of the height to the width of the interspaces (not the grid bars) in the grid. Grid ratios of 8:1, 10:1, and 12:1 are most. A 5:1 grid is most common for

mammography Mammography (also called mastography) is the process of using low-energy X-rays (usually around 30 kVp) to examine the human breast for diagnosis and screening. The goal of mammography is the early detection of breast cancer, typically through d ...

. The grid is essentially a one-dimensional

Collimator A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spat ...

and increasing the grid ratio increases the degree of collimation. Higher grid ratios provide better scatter cleanup, but they also result in greater radiation doses to the patient. In addition, though higher ratios are possible, they require greater radiation intensity increases when used, require more precise positioning, and are more expensive to produce.

Drawbacks

Grids are used particularly in examinations where a large quantity of scatter is created, i.e., those involving a large volume of tissue being irradiated and those requiring low energy i.e.

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

. 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, particularly in pediatric practice. One drawback of a fixed radiographic grid is that it creates grid lines on the image. Hollis Potter (1880-1964) showed in 1920 that these grid lines could be eliminated by moving the grid at right angles to the grid lines during the exposure. If the range and speed of motion is sufficient, the grid lines will be blurred out. The motion may be oscillating, vibrating, or reciprocating and must be continuous and smooth. The motion must also begin before exposure and continue until after exposure.

References

{{reflist Radiology X-ray instrumentation