MORPHOLOGICAL AND HEMODYNAMIC ASSESSMENTS OF CAROTID STENOSIS USING QUANTITATIVE DIGITAL SUBTRACTION ANGIOGRAPHY

Background and Purpose Digital angiography is the best established too l for assessing atheromatous disease of extracranial blood vessels. Ad vances in computer technology have now made it possible and practicabl e to extract quantitative information (length, width, cross-sectional area, and flow velocity) from good-quality clinical angiograms, allowi ng calculation of volume flow and pressure gradient. The technique of quantitative angiography (QA) is used for assessing coronary artery di sease, but to date there has been no clinical application in patients with cerebrovascular disease. Summary of Report We have developed a co mputer program for off-line analysis of routine digital subtraction an giographic images. From biplanar images, the program reconstructs the angiogram in three dimensions and performs quantitative analysis of ea ch vessel. From this data, the pressure drop from the aortic arch to t he circle of Willis is then calculated. We assessed the clinical appli cability of QA in five patients investigated for transient ischemic at tack. The carotid artery ipsilateral to the symptomatic hemisphere was occluded in one patient and had minor plaque in another. In the remai ning three patients, ipsilateral internal carotid artery stenosis was measured by QA as producing area reductions of 55%, 72%, and 88% (equi valent to diameter reductions of 33%, 48%, and 65%, respectively). In these patients, the quantitative stenosis pressure gradients were calc ulated as 1.2, 3.0, and 3.5 mm Hg, respectively. Further calculation s howed that each stenosis contributed to 18%, 24%, and 60%, respectivel y, of the total carotid pressure gradient from the aortic arch to the circle of Willis. These carotid arteries carried 47%, 42%, and 26%, re spectively, of the total cerebral flow. The results of quantitative an alysis were validated by comparing, within each patient, the differenc es in pressure gradients between right and left carotid systems or bet ween right and left vertebral arteries (overall mean difference in pre ssure gradient, 0.6+/-0.5 mm Hg; P=NS). Finally, comparison was made o f pressure gradients across the circle of Willis between the carotid a nd vertebrobasilar circulations (mean difference in pressure gradient, 4.1+/-5.3 mm Hg; P=NS). Conclusions Quantitative angiography allows d etermination of the hemodynamic parameters of a vessel or stenosis. It has significant potential, both as a research tool and in routine cli nical practice, for the investigation of cerebrovascular disease.