Towards a gold standard for quantitative coronary arteriography.

Densitometric quantification of coronary artery stenoses in angiographic images can be problematic for two reasons: (i) the x-rays are inadequately oriented with respect to the vessel segments of interest at image acquisition; (ii) non-linear effects due for instance to beam hardening, scattered radiation and veiling glare may reduce the accuracy. As a consequence, appreciable discrepancies between degrees of stenosis measured in two different projections can occur. To overcome these limitations, we have designed and tested a combined correction that compensates (at subsequent analysis) for the error contributions due to the cited sources. It implies 3D reconstruction of the vessel segments of interest and consequently requires an appropriate biplane coronary angiogram. In experiments performed with a dedicated phantom, application of the correction improved the correlation between measured and true area reduction percentages (without correction: y = 1.04x - 4%, r = 0.97, SEE = 6%, n = 35; with correction: y = 1.02x - 0%, r = 0.99, SEE = 3%, n = 35). Applied to ten area stenoses measured biplane in patients and exhibiting strong interplane discrepancies, the correction had a comparable effect (without correction: y = 0.83x - 11%, r = 0.86, SEE = 9%, n = 10; with correction: y = 0.83x + 2%, r = 0.98, SEE = 4%, n = 10). The new densitometric method could possibly be used as a gold standard in the objective evaluation of geometric methods in patients.