Abstract: An image segmentation algorithm based on region growing combined with time domain information is proposed for delineating the arterial boundaries in ultrasound contrast images and improving the measurement accuracy of the velocimetry.Firstly,window frame difference is constructed by the intensity difference of two consecutive frames according to the flow characteristics of ultrasound contrast microbubbles in blood.Region growing is proceeded by the growing condition combined with window frame difference and neighborhood intensity.Then the close operator of morphology is used to fill the holes generated in region growing and a customized method is developed to smooth the irregular boundaries.Finally,the experimental results verify the efficiency and feasibility of the proposed algorithm in segmenting ultrasound contrast images of rat carotid arteries.The proposed algorithm is able to extract the obscure arterial boundaries and has low time complexity.