Objective The carotid intima-media thickness (IMT) is one of the key parameters that can quantitatively evaluate cardiovascular diseases. This paper presents a semi-automatic and computer assisted method to measure the carotid IMT based on ultrasound images, with the introduction of Rician distribution in the segmentation algorithm. Methods The original Chan-Vese model is well suited for the extraction of carotid intima-media boundaries, yet it assumed a simple distribution for ultrasound speckle noises, which is not accurate for actual ultrasound images. This paper modifies the original Chan-Vese model based on Rician distribution which is more suitable for ultrasound speckle noises. The modified segmentation model is used twice to detect carotid intima-media boundaries. After the boundaries are detected, the IMT can be easily calculated. Results This method is used in actual ultrasound images and the results are optimal. Conclusions This method can quickly and accurately detect carotid intima-media boundaries without pre-processing steps.