Usefulness of an intravenous contrast medium in the characterization of high-grade internal carotid stenosis with color Doppler-assisted duplex imaging.

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Abstract
The remaining limitations of ultrasonographic imaging in accurately quantifying internal carotid stenosis or diagnosing internal carotid occlusion may be overcome by enhancing the echogenicity of flowing arterial blood with contrast agents. This study assessed the usefulness of the intravenous (transpulmonary) contrast medium SH U 508 A in improving the characterization and quantification of severe internal carotid stenosis. We examined 32 patients (30 had vessels with a stenosis of greater than 70% luminal narrowing and 2 had vessel occlusions) using a 7.5-MHz linear-array transducer for color Doppler-assisted duplex imaging before and after injection of the contrast medium. The SH U 508 A-induced increase in carotid blood echogenicity began 11 +/- 2 (mean +/- SD) seconds after the start of the bolus injection, peaked at 21 +/- 2 dB, and showed a half-life of 75 seconds. Quantitative vascular measurements (cross-sectional luminal area reduction and plaque length, respectively) obtained before and after contrast application were highly correlated (r > .90). Visualization of the entire length of the intrastenotic residual flow lumen, however, was significantly improved by contrast enhancement (52% versus 83%, P = .01). This pilot study on patients with extracranial carotid artery disease suggested that ultrasonic contrast media may be most useful in improving the ultrasonography-based diagnosis of internal carotid occlusion.