Examples for filtering clutter signals from receive signals obtained in a Doppler mode in an ultrasound system are disclosed. The signal processing unit processes received echoes to provide 2-dimensional image data of the target object, the 2-dimensional image data being representative of a 2-dimensional image. A region of interest (ROI) is set on the 2-dimensional image of the target object, The signal processing unit obtains a Doppler mode image pixel data corresponding to the ROI. The signal processing unit sets filter cutoff frequencies based on characteristics of the Doppler mode image pixel data and filter the Doppler mode image pixel data with the set filter cutoff frequencies to output filtered pixel data with clutter signals filtered.
