Abstract
Speckle tracking is capable of searching the complete vector velocity butis susceptible to the frame-to-frame image de-correlation. With plane-waveexcitation (PWE), the high frame-rate reduces the scatterer displacement andthus increases the signal correlation. Nevertheless, the lower image qualitywith PWE may suffer from spatial velocity gradient outside the sample volume andreduce the achievable accuracy of speckle tracking. In this study, we propose arecursive PWE compounding technique to improve the image quality for accuracyof vector velocity estimation while the high-frame-rate nature of PWE for vectorvelocity estimation is retained. In the proposed compounding, several PWEimages from different steering angles are combined coherently to suppress thebeam sidelobes at the cost of longer acquisition time. The coherent PWEcompounding is further combined with a recursive technique to generatehigh-resolution images with different features at a frame rate of pulserepetition frequency; thus retaining the high frame-rate nature. The neighboringhigh-resolution image pairs with the same image feature are utilized forvelocity detection with speckle tracking. Extensive simulations were performedto test the recursive PWE compounding method for its performance inspeckle-tracking based vector velocity estimation. Results indicate that, thelateral estimation is more susceptible to the spatial flow velocity gradientthan the axial estimation is. When the Doppler angle is 0, it is shown that themean axial velocity remains close to the ideal parabolic profile while thedetection of lateral velocity is markedly interfered by the flow gradient. Inthe case of large Doppler angle, it is also evident that an accurate lateralestimation is achieved with the coherent PWE compounding method. Note that thestandard deviation with the PWE compounding is generally smaller as compared tothe conventional PWE image, indicating the improved robustness in both lateraland axial estimation. Nevertheless, the error of lateral estimation is stilllarger than that of axial estimation. It is demonstrated that the recursive PWEcompounding with speckle tracking is capable of improving estimation of vectorvelocity with high frame rate. In addition to vector velocity estimation, theproposed method can also be potentially applied to elastography. © 2010IEEE.