An intravascular Doppler ultrasonic device (100) comprises a tip region (106) forming a fraction of a catheter body (102) at a distal end thereof and carrying an ultrasound probe (108). The tip region is bendable in a direction perpendicular to a longitudinal direction. An actuator (110) is provided in the tip region, which is configured to receive actuation drive power provided through the catheter body and to exert to the tip region a bending moment of a controllable amount. An actuation controller (134) is configured to control actuation drive power delivery to the actuator so as to control the amount of the bending moment. A Doppler spectrum analysis unit is configured to receive Doppler spectrum data and to determine from it a Doppler signal quality measure indicative of a signal quality of the Doppler spectrum. The actuation controller is configured to determine the actuation drive power in dependence on the determined Doppler signal quality measure.
