Apparatuses, systems, and methods for intravascular ultrasound (IVUS) imaging and blood flow velocity measurement within a vessel using a rotational IVUS catheter are disclosed. The rotational IVUS catheter includes a transducer that is mounted to the catheter at an angle relative to the longitudinal axis of the catheter shaft, such that the imaging surface is substantially nonperpendicular to the angle of the blood flow. The IVUS imaging system includes the rotational IVUS catheter with the tilted transducer, sequencing hardware to generate a series of uniformly spaces transmit pulses and acquisitions per encoder pulse, and signal processing hardware to extract the phase from the ultrasound echo signals for velocity estimation at every pixel of the IVUS image. The system is configured to generate a hybrid IVUS image showing both structural and velocity characteristics of the vessel and the blood therein.
