Vector Concentration used for Stenosis Assessment in the Carotid Artery before and after Carotid Stenting

Angiography of carotid stenosis is the preferred method for stenosis assessment, but the method is invasive and ionizing. The ultrasound technique Vector Flow Imaging (VFI) is proposed as a noninvasive and nonionizing alternative for stenosis assessment. Vessel stenosis and flow complexity are associated, and VFI can measure flow complexity with Vector Concentration (VC). VC goes towards 1 for laminar flow and 0 for complex flow. In this preliminary study, 5 patients treated with carotid stent for carotid artery stenosis were examined with VFI to evaluate if VC estimations were comparable with the corresponding digital substraction angiography (DSA) calculated stenosis degree percentage. VFI was obtained with a bk5000 ultrasound scanner and an 8L2 linear transducer with a frequency range from 2-8 MHz (BK Medical, Herlev, Denmark), while angiography data were obtained with Siemens Artis Q (Siemens, Erlangen, Germany). The flow in the stenosis was evaluated with VC as a mean over 100 frames with a frame rate of 30 Hz. VC of the stenotic carotid artery was low for all patients before stenting with a mean of 0.59 (SD:0.07), while mean VC increased to 0.97 (SD:0.02) after stenting (p=0.016). Mean DSA stenosis degree percentage was 82% (SD:9%) before stenting and was reduced to 11% (SD:6%) after stenting (p=0.001). Correlation coefficient between VC and DSA stenosis degree was strong 0.97. This is the first preliminary study that shows VFI can be used to evaluate stent treatment of carotid stenosis. The results indicate that VC is a useful parameter for flow complexity assessment, and that VC and stenosis degree are comparable for patients with carotid stenosis.