Glass waveguides with artificially laser placed scattering centers improve the applicability for medical applications

Objective: Currently applied medical wave guides in medical therapy, e.g. laser induced interstitial thermotherapy (LITT) use a so-called diffuser attached at the distal end. These manually fabricated diffusers are filled with scattering particles embedded in a polymer matrix and are expensive and not very reproducible. The objective is to induce scattering centers directly by utilizing ultra-short laser pulse excitation and selective material reaction inside a quartz waveguide. The laser based processing method allows an integrated diffuser production saving costs and increasing reliability. Furthermore, it is expected that the direction and intensity of the deflected laser light can be strongly influenced by the design and distribution of the scattering centers, creating more selective therapeutic approaches.

Material and methods: Ultra-short laser pulses are focused inside a rotating quartz waveguide to induce and distribute several 100,000 micro modifications, each acting as an individual optical scattering center. The scattering centers were distributed along a predefined length at varying designs. Light extraction profiles as well as thermal images and temperature profiles had been determined and compared.

Results: An exponential decrease in the intensity of the extracted light along the modified area can be detected because only a defined percentage of the laser light is extracted by the induced scattering centers. Implementation of strategies enforcing a non-uniform distribution of scattering centers along the modification length result in constant light extraction over the entire area. The laser modified quartz waveguides for medical applications demonstrate an improved single path light extraction efficiency as well as a higher thermal and mechanical stability compared to the conventional flexible diffusers.

Conclusion: The implementation of diffusers in quartz waveguides by ultra-short laser pulses allows cost effective, high reproducible in process production of medical quartz wave guides. Highly efficient and adjustable light extraction along the modified area as well as a high thermal and mechanical stability promise a much better usability for medical applications as laser induced interstitial thermotherapy (LITT) or interstitial photodynamic therapy (IPDT), compared with the currently used diffuser applications. Focusing very precisely on the treatable tumor area may open new opportunities for highly effective tumor therapy with low side effects.

Acknowledgement: Recent support of this project by BMWi KF ZIM; Reference Number KF 2821701KJ1