A method for bringing an IVUS and an OCT image into register. In one embodiment, the method includes obtaining an IVUS image of an area of a lumen； obtaining an OCT image of the same area of the lumen； determining the same asymmetry in each of the IVUS and OCT images； and overlaying the IVUS and OCT images and rotating them with respect to one another until the asymmetry in each of the IVUS and OCT images are in register, and determining the angle of rotation that resulted in the registration. In another aspect, the invention relates to a probe for OCT and IVUS imaging. In one embodiment, the probe includes a sheath having a first end and a second end defining a lumen； a marker that is opaque to light and ultrasound located between the first end and second end； and an IVUS/OCT probe head positioned within the sheath.
