26 February 2014 Laser speckle tracking for monitoring and analysis of retinal photocoagulation
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Laser coagulation of the retina is an established treatment for several retinal diseases. The absorbed laser energy and thus the induced thermal damage varies with the transmittance and scattering properties of the anterior eye media and with the pigmentation of the fundus. The temperature plays the most important role in the coagulation process. An established approach to measure a mean retinal temperature rise is optoacoustics, however it provides limited information on the coagulation. Phase sensitive OCT potentially offers a three dimensional temporally resolved temperature distribution but is very sensitive to slightest movements which are clinically hard to avoid. We develop an optical technique able to monitor and quantify thermally and coagulation induced tissue movements (expansions and contractions) and changes in the tissue structure by dynamic laser speckle analysis (LSA) offering a 2D map of the affected area. A frequency doubled Nd:YAG laser (532nm) is used for photocoagulation. Enucleated porcine eyes are used as targets. The spot is 100μm. A Helium Neon laser (HeNe) is used for illumination. The backscattered light of a HeNe is captured with a camera and the speckle pattern is analyzed. A Q-switched Nd:YLF laser is used for simultaneous temperature measurements with the optoacoustic approach. Radial tissue movements in the micrometer regime have been observed. The signals evaluation by optical flow algorithms and generalized differences tuned out to be able to distinguish between regions with and without immediate cell damage. Both approaches have shown a sensitivity of 93% and a specificity above 99% at their optimal threshold.
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Eric Seifert, Eric Seifert, Katharina Bliedtner, Katharina Bliedtner, Ralf Brinkmann, Ralf Brinkmann, "Laser speckle tracking for monitoring and analysis of retinal photocoagulation", Proc. SPIE 8946, Optical Elastography and Tissue Biomechanics, 89460F (26 February 2014); doi: 10.1117/12.2038860; https://doi.org/10.1117/12.2038860

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