Simultaneous photoacoustic and laser-ultrasound imaging
Gerhild Wurzinger
University of Graz, Institute of Physics, KFU
http://physik.uni-graz.at/exp/magnetometrie/magnetometrie.php
17:00 - 17:40 Thursday 24 October 2013 AT02002J The photoacoustic (PA) effect describes the excitation of an ultrasonic (US) wave after irradiating an object with a short laser pulse. Absorption of the diffusely propagating light in tissue leads to a localized temperature rise followed by thermoelastic expansion and the launch of an US pulse. The propagating pressure waves are detected outside and after reconstruction an image depicting the distribution of the absorbed energy is obtained. PA imaging therefore mainly depicts the optical properties of an object, with absorption as the main source of contrast.
The laser ultrasound (LUS) method uses the PA effect for the generation of incoming US waves at optically absorbing targets in front of the sample. These waves are back scattered at interfaces of different acoustic impedances. Thus, by detecting the back scattered US waves an image depicting the mechanical/elastic properties of the object can be obtained after reconstruction.
Speed-of-sound (SOS) maps, on the other hand, can be obtained upon the detection of US pulses that have traversed the sample. Due to a special arrangement of the absorbing targets for LUS generation a single laser pulse yields information for a projection of the SOS distribution within the sample.
In the presented setup a free laser beam, which is part of a Mach-Zehnder interferometer, is used for the detection of the US signals coming from and passing through the sample.
As PA and US imaging use the same instrumentation for the detection of acoustic waves they can be combined easily. By combining these two imaging modalities the information content can be drastically increased as they are based on different physical principles.
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