CONSTRUCTION, QUALITY ASSURANCE AND CALIBRATION OF SPHERICAL ISOTROPIC FIBER OPTIC LIGHT DIFFUSERS

Spherical isotropic fibre optic light diffusers are used in photodynam ic therapy either as a light source or as a light detector. The constr uction of light diffusers using different materials is described, viz. an optical method involving local polymerization of a dental fissure sealant, which is referred to as the Henderson method, and a second me thod using plastic or ceramic prefabricated spheres. Quality tests nec essary for reliable clinical use are presented for the mechanical stre ngth, output power and isotropy. The maximum pull-off force and blow-o ff output power for the different kinds of diffusers were determined. The calibration procedures are given for measurement of the output pow er and wavelength of the light emitted by a diffuser and for measureme nt of the fluence rate by a light-detecting diffuser, using a compact integrating sphere device. With all types of diffusers described, an i sotropy can be obtained of better than +/-20% measured over a 320 degr ees angle for spheres as small as approximate to 1 mm. Larger ceramic diffusers are particularly suitable for delivering high output powers. A 3-mm-diameter ceramic diffuser mounted on a 600-mu m-core fibre can emit up to approximate to 5 W of continuous wave (CW) visible light i n air. Diffusers used for light detection can measure the light fluenc e rate in tissue with approximate to 15% accuracy or better if calibra tion factors are determined for each individual probe.