Imaging of Distal Internal Carotid Artery by Ultrasonography With a 3.5-MHz Convex Probe

Background and Purpose— Conventionally, carotid ultrasonography has been performed with a 7.5-MHz linear probe to evaluate the extracranial internal carotid artery (ICA). However, usually only the carotid bulb or proximal portion of the ICA can be evaluated. We attempted to evaluate the distal extracranial ICA with a 3.5-MHz convex probe. Methods— The subjects were 17 consecutive patients with ICAs free of occlusive disease and 3 other patients with distal extracranial ICA stenosis. Using a 7.5-MHz linear probe and a 3.5-MHz convex probe, we performed long-axis B-mode imaging of the ICAs to evaluate the distance between the distal limit of visualized ICA and the bifurcation of the common carotid artery. Results— The distal limit of the ICA, visualized with a 7.5- or a 3.5-MHz probe, was 31±11 or 57±8 mm distal to the common carotid artery bifurcation, respectively. In the 3 patients with distal extracranial ICA stenosis, the lesion could be successfully diagnosed with only the 3.5-MHz probe. Conclusions— This form of carotid imaging is feasible and may be potentially useful in the evaluation of carotid disease.