Infographics / CT Physics

Causes of streak artefacts

A schematic CT slice shows thin high- and low-density streaks radiating from a central dense object, illustrating that streak artefacts arise when projection data are inconsistent between view angles and filtered back-projection spreads the error. Six labelled cards give the named causes and how each streak looks: beam hardening (dark bands between two dense objects, plus central cupping), photon starvation (streaks along the most-attenuating path, noise proportional to one over root N), motion (windmill streaks and blurred double edges), cone beam effect (shading and streaks at the periphery, off-isocentre), inadequate field of view or truncation (streaks radiating from anatomy cut off at the field-of-view edge), and partial volume effect (streaks beside a high-contrast interface).

CT streak artefacts: causes and their characteristic appearance A schematic CT slice shows thin high- and low-density streaks radiating from a central dense object, illustrating that streak artefacts arise when projection data are inconsistent between view angles and filtered back-projection spreads the error. Six labelled cards give the named causes and how each streak looks: beam hardening (dark bands between two dense objects, plus central cupping), photon starvation (streaks along the most-attenuating path, noise proportional to one over root N), motion (windmill streaks and blurred double edges), cone beam effect (shading and streaks at the periphery, off-isocentre), inadequate field of view or truncation (streaks radiating from anatomy cut off at the field-of-view edge), and partial volume effect (streaks beside a high-contrast interface). Streak artefact Thin bright / dark lines that radiate across the slice from a dense object. Shared mechanism: projection data are inconsistent between view angles, so filtered back-projection spreads the error. Named causes and their look, below. Beam hardening Dark bands between two dense objects (petrous bones, metal); plus central cupping. Photon starvation Streaks along the most- attenuating path; few photons so noise rises as 1 / √N. Motion Windmill streaks and blurred double edges from a moving structure. Cone beam effect Shading / streaks at the edge, off-isocentre; worse with wide z-collimation. Inadequate field of view Streaks radiating from anatomy truncated at the field-of-view edge. Partial volume effect Streaks / shading beside a high-contrast interface; worse with thick slices.
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