Applications of catheter-based optical coherence tomography (OCT) - originally developed for cardiovascular imaging - have expanded to other organ systems. However, currently available algorithms to co-register 3D OCT data to a second imaging modality were developed for cardiovascular applications and with it, are tailored to small tubular tissue structures. The available algorithms can often not be applied outside the cardiovascular system, e.g. when an OCT probe is introduced into the kidney, lungs, or wrist. Here, we develop a generic co-registration algorithm with potentially numerous applications. This algorithm only requires that the OCT probe is visible on the second imaging modality and ...