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DSA misregistration and motion artefact

Two panels. Top: digital subtraction angiography subtracts a pre-contrast mask frame from a contrast frame; if anatomy moves between frames, subtraction leaves residual ghost edges (misregistration), caused by breathing, cardiac motion, peristalsis or patient movement, and reduced by remasking or pixel-shift for rigid motion only. Bottom: in radiography a moving object smears its edge over a blur width proportional to velocity times exposure time; a sharp stationary edge versus a blurred moving edge is shown, with mitigations of shorter exposure, immobilisation, faster detector and small magnification, and a trade-off toward geometric unsharpness.

Motion artefact: DSA misregistration and radiographic movement unsharpness Two panels. Top: digital subtraction angiography subtracts a pre-contrast mask frame from a contrast frame; if anatomy moves between frames, subtraction leaves residual ghost edges (misregistration), caused by breathing, cardiac motion, peristalsis or patient movement, and reduced by remasking or pixel-shift for rigid motion only. Bottom: in radiography a moving object smears its edge over a blur width proportional to velocity times exposure time; a sharp stationary edge versus a blurred moving edge is shown, with mitigations of shorter exposure, immobilisation, faster detector and small magnification, and a trade-off toward geometric unsharpness. Digital subtraction angiography — misregistration mask (pre-contrast) − contrast (live) = subtraction Ghost edges Residual outlines remain where anatomy shifted between frames. Fix: remask / pixel-shift the mask — rigid shift only, not non-rigid motion (peristalsis). Cause: anatomy moves between the mask and contrast frames, so pixels no longer cancel on subtraction. Sources — breathing, cardiac motion, peristalsis, patient movement. Radiographic movement unsharpness stationary — sharp edge moving — blurred edge signal blur Δ ≈ v × t position on detector Reduce movement unsharpness · shorter exposure time t (raise mA) · immobilise / breath-hold (lower v) · faster detector or screen · keep object close to detector — blur scales with magnification M = SID/SOD Trade-off: a very short exposure may need a larger focal spot → increased geometric unsharpness (penumbra).
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