1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to calculate a constant delay value throughout depths based on a sample volume by using a mid-point algorithm, transmit ultrasound signals to a living body, receive ultrasound echo signals from the living body and form digital signals based on the ultrasound echo signals, the ultrasound data acquisition unit being further configured to apply the constant delay value to the digital signals to acquire ultrasound data corresponding to a high pulse rate frequency Doppler image of the sample volume.