Abstract
Recent studies demonstrate therapeutic benefits in retinal laser therapy even for non-visible effects of the irradiation. However, in practice, ophthalmologists often rely on the visual inspection of irradiation sites to manually set the laser power for subsequent ones. Since absorption properties vary strongly between sites, this procedure can lead to under- or over-treatment. To achieve safe automatic retinal laser therapy, this article proposes a robust control scheme based on photoacoustic feedback of the retinal temperature increase. The control scheme is further extended to adapt to real-time parameter estimates and associated bounds on the uncertainty of each irradiation site. Both approaches are successfully validated in ex vivo experiments on pigs’ eyes, achieving consistent irradiation durations of 55 ms despite the uncertainty in absorption properties.
Zusammenfassung
Aktuelle Studien haben therapeutisch relevante Effekte bei der retinalen Lasertherapie auch im Falle nicht-sichtbarer Effekte der Energieeinträge belegen können. In der Praxis ist es jedoch üblich, dass Ophthalmologen die Laserleistung anhand sichtbarer Läsionen an vorangegangenen Bestrahlungensorten für die jeweils nachfolgenden einstellen. Da jedoch die Absorptionseigenschaften stark variieren, kann dies zu Unter- oder Überbehandlung führen. Zur Gewährleistung sicherer, automatisierter retinaler Laserbehandlungen diskutiert dieser Beitrag ein robustes Regelkonzept basierend auf der Echtzeit-Rückkopplung der photoakustisch gemessenen Temperaturerhöhung auf der Retina. Das Regelkonzept wird zudem erweitert, um während der Behandlung geschätzte Modellparameter und die damit assoziierte Unsicherheit zur Adaption zu verwenden. Beide Regelansätze sind erfolgreich in ex-vivo Experimenten an Schweineaugen validiert worden und gewährleisten kurze Bestrahlungszeiten von 55 ms trotz der großen Unsicherheiten in den Absorptionseigenschaften.
Funding source: Bundesministerium für Bildung und Forschung
Award Identifier / Grant number: 13GW0043B
Funding statement: This work was funded by the German Ministry of Education and Research (BMBF) in the consortium “Innovative imaging and intervention for retinal laser therapies (I-cube)” Fkz: 13GW0043B.
About the authors
Christian Herzog, né Hoffmann, studied mechatronics at Hamburg University of Technology (TUHH) from 2008–2011 and received his Ph. D. in 2015 studying nonlinear and distributed control with the Institute of Control Systems, TUHH. Since 2015 he is a tenured researcher at the Institute for Electrical Engineering in Medicine at the University of Lübeck and active in probabilistic algorithms in systems and control. He is also strongly interested in engineering ethics.
Ole Thomsen was born in 1994 in Kiel and studies Medical Engineering Science at the University of Lübeck since 2014. Having received his B. Sc. degree in 2017 he is currently pursuing his M. Sc. He received the second prize for the best paper award at the AUTOMED 2018 for his preliminary work on the temperature-controlled laser therapy of the retina via robust adaptive
Benedikt Schmarbeck was born in 1988 in Kiel. He studied medical engineering science in Lübeck and graduated in 2016 with a master’s degree. Afterwards he joined the Medical Laser Center in Lübeck and worked in the field of automated retinal photocoagulation until the beginning of 2018. In 2018 he joined ZF TRW as optical engineer in automated driver’s assistance systems.
Marlin Siebert was born in 1995 in Wolfenbüttel and is studying medical engineering at the University to Lübeck since 2013. He received his B. Sc. degree in 2017 and is currently pursuing his M. Sc. His bachelor’s thesis contributed to the active power regulation of treatment lasers for the temperature-controlled photocoagulation of the retina.
Ralf Brinkmann studied physics at the University of Hannover, Germany, with a focus on quantum optics and lasers. After a 5-year industrial interim period, he joined the Medical Laser Center in Lübeck, Germany, in 1993, and received his Ph. D. from the University of Lübeck. Since 2005 he has been holding a permanent position as a faculty member at the University’s Institute of Biomedical Optics, focusing on biophotonics and laser applications in medicine. As also strongly interested in technology transfer of basic research results to industry, he is also leading the Medical Laser Center Lübeck, a non-profit R & D company on the BioMedTec Science campus Lübeck, as CEO.
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Article note
A brief version of this paper was presented during the proceedings of AUTOMED 2018 – Automatisierungstechnische Verfahren für die Medizin, on March 15th, 2018 in Villingen-Schwenningen.
© 2018 Walter de Gruyter GmbH, Berlin/Boston