Anti-scatter grid

In medical imaging, an anti-scatter grid (also known as a Bucky-Potter grid) is a device for limiting the amount of scattered radiation reaching the detector, thereby improving the quality of diagnostic medical x-ray images. The grid is positioned on the opposite side of the patient from the x-ray source, and between the patient and the X-ray detector or film. Reducing the amount of scattered x-rays increases the image's contrast resolution, and consequently the visibility of soft tissues. The device was first invented by German radiologist Gustav Peter Bucky, 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. 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 and a radiolucent substance such as a plastic, carbon fibre, aluminium, even paper. The grid is placed between the patient 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.