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Collimation and equalization (wedge) filters

Two panels comparing beam-limiting collimation with intensity-shaping equalization filters. Left: collimator blades limit the field size (geometry), reducing exposed volume, scatter, DAP and excluding bright peripheral rays. Right: a wedge-shaped filter, thicker over thin peripheral anatomy, attenuates the less-attenuated edge rays so the detector receives an even fluence, reducing edge glare; it is partially attenuating, not a collimator and not radio-opaque.

Collimation versus equalization (wedge) filters Two panels comparing beam-limiting collimation with intensity-shaping equalization filters. Left: collimator blades limit the field size (geometry), reducing exposed volume, scatter, DAP and excluding bright peripheral rays. Right: a wedge-shaped filter, thicker over thin peripheral anatomy, attenuates the less-attenuated edge rays so the detector receives an even fluence, reducing edge glare; it is partially attenuating, not a collimator and not radio-opaque. Collimation — limits the field (geometry) x-ray tube collimator blades patient image receptor collimated field (teal) vs open field (dashed) Collimation reduces field size: • lower exposed volume, scatter and DAP (dose × area) • less scatter → higher image contrast • excludes bright unattenuated edge rays → less glare • auto-tracks the selected FOV (no larger than needed) Equalization (wedge) filter — evens out intensity x-ray tube wedge filter — lead-rubber / lead-acrylic (partially attenuating) patient (thicker centrally) image receptor detector fluence across field without filter: bright edges (glare) with filter: even exposure Thicker over the thin peripheral anatomy, it attenuates the less-attenuated edge rays → even exposure, less edge glare. Not a collimator (field size unchanged); not radio-opaque (some primary beam still reaches the detector).
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