The invention relates to photoacoustic imaging and ultrasound echo imaging In combination, and applies in particular to the field of imaging a lumen of an organ or vessel of a subject, wherein the Images are acquired from within a lumen of the organ or vessel, especially a lumen of a blood vessel to diagnose and treat vascular disease An exemplary embodiment of the invention is a catheter having an ultrasound transducer, the transducer comprising a probe suitable for generating and detecting photoacoustic signals and ultrasound echo signals, wherein the photoacoustic signals and the ultrasound echo signals are convertible to images which are integrated into an enriched image. The photoacoustic signals are generated by a multiplicity of energy sources suitable for inducing the walls of the blood vessel to generate acoustic waves, wherein the energy sources are arrayed in an annulus around the flexible tubular member.