Infographics / Fluoroscopy

Dual-energy / energy subtraction

Two near-simultaneous radiographs are acquired at low and high tube kV. At low kV the photoelectric effect dominates (proportional to Z cubed over E cubed) giving strong bone versus soft-tissue contrast; at high kV Compton scatter dominates, giving low bone contrast. A weighted, pixel-by-pixel subtraction produces two images: low kV minus high kV cancels soft tissue to give a bone-only image, while high kV minus low kV cancels bone to give a soft-tissue-only, bone-suppressed image revealing a lung nodule. Only two images are used and no pre-contrast mask is needed, unlike temporal digital subtraction angiography.

Dual-energy subtraction of low- and high-kVp images Two near-simultaneous radiographs are acquired at low and high tube kV. At low kV the photoelectric effect dominates (proportional to Z cubed over E cubed) giving strong bone versus soft-tissue contrast; at high kV Compton scatter dominates, giving low bone contrast. A weighted, pixel-by-pixel subtraction produces two images: low kV minus high kV cancels soft tissue to give a bone-only image, while high kV minus low kV cancels bone to give a soft-tissue-only, bone-suppressed image revealing a lung nodule. Only two images are used and no pre-contrast mask is needed, unlike temporal digital subtraction angiography. Dual-energy subtraction two images at different tube kV, weighted and subtracted to cancel one tissue type low kV photoelectric dominant (∝ Z³/E³) → high bone–soft-tissue contrast high kV Compton dominant, penetrating → low bone–soft-tissue contrast weighted subtraction scaled, pixel-by-pixel bone-only image low kV − high kV ribs soft tissue cancels → bony detail soft-tissue-only image high kV − low kV nodule bone suppressed → soft-tissue detail Unlike DSA (temporal subtraction — needs a pre-contrast mask to remove bone), dual-energy uses only two near-simultaneous kV images: no mask, little motion artefact.
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