A system to monitor for fibre breakage during photodynamic therapy with diffuser fibres

There is concern that the delicate fibres and cylindrical diffuser tips used for intraluminal PDT of blood vessels might break during the treatment. We have developed and tested a simple system to monitor for fibre breakage during PDT. Light from the laser is passed through a beam expander, then a beam splitter, and then is again contracted into the inlet of a diffuser fibre. Light reflected from the distal diffuser is also partially reflected by the beam splitter into a photodiode, which monitors changes in the intensity of the reflected light. The system was tested by simulating catastrophic failures in four fibres. In each case the output fell very significantly (DV=0.44-1.68 V, SD=0.01 V). Despite the small statistical sample, the average change in the reflected light intensity is still significant (p < 0.025, paired Student's t-test). Our conclusion was that this device can monitor the integrity of diffuser fibres during PDT.