A catheter (12) has an image sensing system (S1-S5) for imaging the interior wall of a passageway in which the catheter is to be located. The catheter has a radial imaging system comprising a light source arrangement for generating a light output radially around the catheter and an image sensor for receiving the generally radial light after the light has been scattered back by the interior wall. The catheter is positioned within the passageway with a known position and orientation, for example a known angle with respect to the anterior-posterior plane along the length of the catheter, so that it is known where along the catheter length, and at which angular position around the catheter, it is close to the passageway wall. The light output has a different intensity at different radial directions and/or the catheter comprises a light transmission arrangement which gives rise to different transmission of the light output at different radial directions. These provide alternative measures to reduce the light received by the image sensor, thereby to prevent blooming in the captured image.
