Although the versatility of photodynamic therapy (PDT) is well established, the technical aspects of light delivery systems vary significantly depending on the targeted organ. This article describes the optical properties of a light and drug delivery system (catheter and light diffuser) suitable for intra-arterial PDT by using a planar imaging goniometer to measure the full radiance longitudinal and angular profiles at the surface of the diffuser at 652 nm. The results show that the system emits almost Lambertian and "top hat" profiles, an interesting feature to determine the light dosimetry in the many vascular applications of PDT.