Carotid duplex ultrasound: A review and update for clinicians

Abstract

The aim of this review is to provide clinicians with an update on the evolution and current status of the carotid duplex criteria, as well as clinical applications for the diagnosis and follow-up of carotid disease. The ‘duplex concept’ combined real-time B-mode imaging and pulsed Doppler flow detection in a single instrument, which enabled direct visualization of blood vessels and analysis of flow patterns. The first application of the prototype duplex scanner built in the 1970s was the evaluation of extracranial carotid artery disease, and the validation studies performed at the University of Washington established the first carotid duplex criteria, including the 125 cm/s peak systolic velocity (PSV) threshold for ⩾ 50% internal carotid stenosis. Over time, those criteria have been widely adopted and modified, resulting in significant variability among vascular laboratories. In the 1990s, the randomized clinical trials of medical versus surgical management of carotid disease prompted further refinement of the carotid criteria to include a PSV threshold of 230 cm/s for the clinically important internal carotid stenosis category of ⩾ 70%. The Society of Radiologists in Ultrasound (SRU) proposed a set of criteria in 2003 that included both of these PSV thresholds. However, concern regarding a lack of standardization prompted the Intersocietal Accreditation Commission (IAC) to conduct an independent validation study of the SRU criteria. The main recommendation from the IAC study, published in 2021, was to increase the PSV threshold for ⩾ 50% internal carotid stenosis to 180 cm/s. Although the carotid duplex criteria have been validated primarily for atherosclerotic lesions, they have also been applied to nonatherosclerotic carotid conditions such as dissection, aneurysms, and fibromuscular dysplasia. Duplex scanning plays a major role in follow-up after carotid interventions, although modified velocity criteria must be used to avoid overestimating the severity of restenosis. There is growing evidence that certain histologic plaque features are associated with ischemic cerebrovascular events, independent of the degree of stenosis, and some of these, such as intraplaque hemorrhage, may be identified on B-mode imaging. Although velocity parameters have been the primary components of the carotid duplex criteria, it is likely that assessment of plaque morphology will increase the overall clinical value of carotid duplex scanning in the future.