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23 February 2012 Frequency analysis of optoacoustic signals in laser heated tissues
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Laser thermal therapy involves heating tissue using light to temperatures between 55 °C and 95 °C for several minutes resulting in coagulation and cell death. This treatment method has been under investigation for use as a minimally invasive method for treating solid tumors and cancer cells. Heating tissues results in highly variable outcomes and challenges; for example, ensuring complete coagulation of the target tissue while avoiding damage to surrounding healthy tissues. Overcoming such challenges requires precise and real-time monitoring. Optoacoustic imaging has been proposed as a real-time, noninvasive method for monitoring laser thermal. Ex-vivo porcine tenderloin samples were heated using a 1000 μm core optical fiber coupled to an 810 nm diode laser at a constant power of 7 W for 10 minutes. Lesions (6-7 mm diameter) were scanned using a prototype reverse-mode optoacoustic system consisting of a pulsed laser which operates at 1064 nm coupled to a bifurcated fibre bundle, and an 8 element annular array wideband ultrasound transducer with a central frequency ~5 MHz. Scanning was done across native and coagulated tissue with an energy of 6.5 mJ at a 1064 nm wavelength. Three lesions of similar size, shape and coagulation state were chosen for analysis. Thermal coagulation effects were analyzed using optoacoustic signal amplitude and spectral analysis of the optoacoustic RF data. Results show that the signal amplitude and the intercept and midband fit of the power spectrum exhibit interesting differences between native and coagulated tissue states.
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Annie Ladéroute, Michelle P. Patterson, Michael C. Kolios, and William M. Whelan "Frequency analysis of optoacoustic signals in laser heated tissues", Proc. SPIE 8223, Photons Plus Ultrasound: Imaging and Sensing 2012, 822341 (23 February 2012);

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