A catheter based optical imaging system for imaging a patient comprising an optical pathway extending along a catheter in an axial direction from a proximal end to a distal end. An optical element 110 is disposed at the distal end of the catheter configured to direct optical radiation from an axial optical path to a radial optical path extending radially from the catheter’s longitudinal axis towards a vessel wall and to receive reflected radiation therefrom. Wherein the optical element is rotatable about the catheter’s longitudinal axis so as to vary the direction of the radial optical path and the optical element comprises a first transmissive interface 111, a second transmissive interface 113 and a first reflective interface 112. At least one of the first transmissive interface, the second transmissive interface and the first reflective surface comprises a focusing element. The focusing element may comprise a concave, convex or spherical surface 111a. The second transmissive interface may include a curved surface 113a for focusing a radially directed light beam.
