Antiscatter

Antiscatter refers to methods and devices used to reduce scattered radiation in X-ray imaging, thereby improving image contrast and reducing patient dose. Scatter is produced when primary X-ray photons interact with matter, especially within the patient, and is deflected in many directions. The resulting scattered photons reach the detector and degrade image quality by reducing contrast and blurring details.

The most common antiscatter device is the radiographic grid, or anti-scatter grid. A grid consists of alternating lead strips and radiolucent interspaces. Grids are characterized by grid ratio (height of the lead strips to the interspace distance), linear or crossed designs, and whether they are focused to a particular beam geometry. Higher grid ratios reject more scatter but also attenuate more of the primary beam, which typically necessitates higher exposure to maintain image brightness. Grid movement (the Potter-Bucky diaphragm) helps blur grid lines on the final image and reduces artifacts.

Other approaches to antiscatter include the air-gap technique, which increases the distance between the patient and the detector to allow scattered photons to miss the detector, and beam restriction through collimation. Digital methods also contribute, with post-processing algorithms and scatter correction models that estimate and subtract scattered contributions from the image. Material choices and detector design can influence scatter sensitivity as well, particularly in specialized imaging modalities.

In practice, antiscatter measures are standard in many X-ray examinations, especially chest and abdominal radiography, where high-contrast information is needed. Modern systems combine adjacent strategies to balance scatter reduction, image quality, and patient dose.