Disclosed is a high resolution intravascular ultrasound imaging system including a catheter with a rotatable imaging assembly and an image processor. The image processor in turn features a pulser configured to energize the ultrasound transducer of the rotatable imaging assembly with a multi-frequency ultrasound waveform signal. The image processor further contains a receiver configured to decompose received ultrasound energy as reflected by the target vessel into a plurality of individual subband signals, individually process these signals and reconstitute these signals into a high resolution image of the blood vessel. The IVUS system of the invention may be useful in characterizing cap thickness of vulnerable plaques or other detailed studies of blood vessels.