The Diameter Symmetry of a Stenosis is a parameter determining the symmetry in arterial plaque distribution.

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The Symmetry Index is defined by:
*
a
*
/
*
b
*
where
*
a
*
is smaller or equal to than
*
b
*
.
*
a
*
and
*
b
*
are measured in the reconstructed artery at the position of the minimal luminal diameter.

Possible values of symmetry range from 0 to 1, where 0 indicates complete asymmetry and 1 indicates complete symmetry.

Reference: Quantitative coronary arteriography; physiological aspects, page 102-103 in: Reiber and Serruys, Quantitative coronary arteriography, 1991