An ultrasonic diagnostic imaging system produces contrast enhanced images which are processed differently during different stages of contrast agent wash-in. During an initial stage of contrast wash-in, imaging is done using pixels processed by maximum intensity detection, to better reflect the rapid change in contrast intensity. During a later stage of contrast wash-in, time averaged processing is used to diminish the effects of noise and motion on the pixel values. During an intermediate period of peak enhancement, a combination of both pixel values processed by both techniques is used. In another aspect, a wash-in period can be characterized by an appearance stage, a growth stage and a peak stage, in which contrast pixel data is adaptively processed in different ways during these periods.