Coronary artery disease remains the leading cause of death and disability in the US. Intravascular ultrasound (IVUS) is one of the standard medical tests routinely performed in hospital to diagnose atherosclerosis by visualizing the structure of affected vessels and identifying the composition of plaques. Optical coherence tomography (OCT) possesses higher resolution to image vulnerable plaque near the lumen boundary, but with a shallow penetration depth. Thus, an integrated IVUS-OCT catheter would potentially capitalize the advantage of sufficient imaging depth of IVUS and the high resolution of OCT while offering improved diagnostic information. Different IVUS-OCT catheter designs have been reported previously by using either co-axial, co-planner or sequential configuration, which suffers from either the large size of catheter or suboptimal image co-registration. By placing the OCT probe and 45MHz single element IVUS transducer back-to-back at the same axial direction, this probe can provide automatically co-registered, co-axial IVUS-OCT imaging. To demonstrate its capability, IVUS-OCT imaging of major types of advanced plaques in human cadaver coronary segments was obtained using this catheter and system. Results were validated by histology analysis. © 2013 IEEE.