Noninvasive Vascular Elastography Based On Ultrafast Imaging

In recent years, cerebrovascular disease has become the leading cause of death and disability for Chinese population. Carotid atherosclerosis is a major cause of ischemic stroke. Carotid atherosclerotic plaque can be divided into stable and unstable plaques. Unstable plaques can lead to acute ischemic events, especially the vulnerable plaque. Ultrasonography is regarded as one of the most effective means for the assessment of atherosclerotic plaque in clinic. However, conventional ultrasound is difficult to measure the mechanical properties of the internal plaque accurately, therefore cannot differentiate the vulnerable plaques from the stable ones. Studies have shown that the mechanical properties of different components of plaque are significantly different. As an imaging method, ultrasound elastography can provide the mechanical information of atherosclerotic plaque for clinicians.Currently, researchers have developed quasi-static elastography and intra-vascular ultrasound strain imaging techniques for imaging the mechanical properties of atherosclerotic plaque. The intra-vascular ones are invasive, therefore, our focus is on the noninvasive quasistatic technique. The basic principle is to image the blood vessel wall motion during the change of intraluminal blood pressure. With the frame rate at around 40 frames/s, the tissue motion between two adjacent frames may be too large to lead signal decorrelation. Hence, the main purpose of this study is to develop a new quasi-static elastography method combining with high frame rate ultrasound imaging technique for carotid atherosclerotic plaque quantification.With the open research platform Verasonics Vantage 256 system, we developed a novel noninvasive vascular strain imaging methods using coherent plane-wave compounding algorithm. In our method, the frame rate of B-mode imaging is nearly 1000 frames per second. We have implemented two beamforming algorithms to obtain the ultrafast imaging to acquire the motion of the carotid. Both phantom and patient experiments show that our method can differentiate focal atherosclerosis with high sensitivity.