The Velocity Vector Imaging Evaluation Neck Radiation Effects On Common Carotid Artery

Radiotherapy of head and neck cancer (such as nasopharyngeal carcinoma) is commonly used in clinical treatment. However, carotid injury after irradiation is a major concern which contributes to the quality of life in head and neck patients, especially in long term survivors. Precaution and management of carotid artery damage after irradiation have significant clinical value to long term survivors. Color Doppler ultrasound is commonly used in detecting the change of carotid artery after irradiation in the clinic.Recently, velocity vector imaging(VVI)technology has gained great attention in the access to a variety of mechanical parameters of the vessel wall. It is based on two-dimensional gray-scale image, no angle dependence, can be applied on axial, longitudinal and rotational movement, and allows multi-parameter vascular study. With VVI, the vascular wall can be tracked accurately and automatically. Dynamic vector map indicating wall motion direction and speed of the blood vessels may be created. A large number of detailed biomechanical data reflecting the properties of vascular may be obtained. Therefore, VVI technique shows broad prospects in the noninvasive assessment of mechanical properties of arterial injury. Objective:The movements of common carotid artery (CCA) were quantitative analyzed by using VVI technique to assess the influence of radiotherapy on cervical vascular wall.Methods:Twenty-eight patients of nasopharyngeal carcinoma after cervical radiotherapy (radiotherapy group) and thirty-three cases of healthy subjects without cardiovascular disease (control group) were examined using VVI technique.Images were acquired using Siemens Sequoia 512 Ultrasound scanner, subjects were taken supine, resting state with electrocardiogram connected. Scanning was performed on the bilateral carotid artery. In VVI mode, short axis images 2.0cm away from the bifurcation was stored. Each loop contained three consecutive two-dimensional cardiac cycle gray-scale images. Analysis was performed with Syngo VVI Workplace 2.0.Intima-media layer was manually outlined in images which intima-media layer was well defined. The software automatically identified and tracked the intima-media layer with the origin settled at the vessel center, then automatically calculated out data such as the velocity, strain and strain rate of each point, and drew velocity curve, strain curve, strain rate curve and 3D simulation diagram.One specific point was marked respectively in each wall of bilateral carotid artery such as anterior wall, posterior wall, inner wall and outer wall, and the Smax of each marked point were measured and recorded.Statistical software SPSS 14.0 was used for data processing and analysis.Results:In normal group, axis motion of carotid intima-media layer was synchronous with accordant changes of the direction of velocity vector line.In normal group, the curves of velocity, strain, strain rate of various points of carotid wall changed consistently with good synchronization.In radiotherapy group, curves of velocity, strain, strain rate were irregular, compared with curves of the control group. The curves of various points showed erratic changes with poor synchronization in systolic and diastolic phases.The Smax of the each marked point in radiotherapy group were significantly lower than those in normal group(P<0.05).Conclusion:VVI is a new method to assess the function of carotid wall, which is valuable in detecting carotid injury early in patients received cervical radiotherapy.