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Fig. 1: Recommended method of measuring carotid stenosis. The residual lumen diameter (N) is measured at the point of greatest narrowing on the angiographic projection that shows the stenosis at its maximum. This diameter is compared with the lumen diameter of the distal internal carotid artery at a point where the arterial walls become parallel (D), not at a point of poststenotic dilatation distal to the obstruction (d). The percentage stenosis is calculated as (1-N/D) × 100. cca = common carotid artery, eca = external carotid artery, ica = internal carotid artery.
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