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Proceedings Paper

Dependence of optoacoustic transients on exciting laser parameters for real-time monitoring of retinal photocoagulation
Author(s): J. Langejürgen; K. Schlott; M. Bever; K. Hausmann; S. Koinzer; L. Ptaszynski; J. Roider; R. Birngruber; R. Brinkmann
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Paper Abstract

The extent of retinal laser coagulations depends on the temperature increase at the fundus and the time of irradiation. Due to light scattering within the eye and variable fundus pigmentation the induced temperature increase and therefore the extent of the coagulations cannot be predicted solely from the laser parameters. We use optoacoustics to monitor the temperature rise in real-time in vivo (rabbit) and ex vivo (porcine eye) and to automatically control the coagulation strength. Continuous wave treatment laser radiation and pulsed probe laser light (1-1100 ns) are coupled into the same fibre and are imaged onto the retina by a laser slit lamp. The temperature dependent pressure waves are detected by an ultrasonic transducer embedded in a customary contact lens. Below the coagulation threshold the increase in acoustic amplitude due to thermal tissue expansion is up to 40 %. Best signal to noise ratios > 10 are achieved with probe pulse durations of 1 to 75 ns. Further a time critical algorithm is developed which automatically ceases laser treatment when a certain preset coagulation strength is achieved. Coagulations with similar extent are obtained with this method in vitro and in vivo even when varying the power of the treatment laser by 50 %. These preliminary results are very promising, thus this method might be suitable for an automatic feedback controlled photocoagulation with adjustable coagulation strength.

Paper Details

Date Published: 17 July 2009
PDF: 8 pages
Proc. SPIE 7373, Therapeutic Laser Applications and Laser-Tissue Interactions IV, 73730K (17 July 2009); doi: 10.1117/12.831913
Show Author Affiliations
J. Langejürgen, Univ. zu Lübeck (Germany)
K. Schlott, Medizinisches Laserzentrum Lübeck GmbH (Germany)
M. Bever, Medizinisches Laserzentrum Lübeck GmbH (Germany)
K. Hausmann, Medizinisches Laserzentrum Lübeck GmbH (Germany)
S. Koinzer, Clinic of Opthalmology, Univ. Hospital of Schleswig-Holstein (Germany)
L. Ptaszynski, Medizinisches Laserzentrum Lübeck GmbH (Germany)
J. Roider, Clinic of Opthalmology, Univ. Hospital of Schleswig-Holstein (Germany)
R. Birngruber, Medizinisches Laserzentrum Lübeck GmbH (Germany)
R. Brinkmann, Univ. zu Lübeck (Germany)
Medizinisches Laserzentrum Lübeck GmbH (Germany)

Published in SPIE Proceedings Vol. 7373:
Therapeutic Laser Applications and Laser-Tissue Interactions IV
Ronald Sroka; Lothar D. Lilge, Editor(s)

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