A method of obtaining a Doppler image of tissue, which is captured using an ultrasonic wave, the method including: transmitting an ultrasonic signal to a target object such that a plurality of ensembles are formed receiving a ultrasonic response signal from the target object filtering the received ultrasonic response signal by using a variable filter estimating a frequency of the received ultrasonic response signal based on the filtered data and generating the Doppler image of the tissue based on the estimated frequency.
