15 March 2016 Estimation of the skull insertion loss using an optoacoustic point source
Author Affiliations +
Abstract
The acoustically-mismatched skull bone poses significant challenges for the application of ultrasonic and optical techniques in neuroimaging, still typically requiring invasive approaches using craniotomy or skull thinning. Optoacoustic imaging partially circumvents the acoustic distortions due to the skull because the induced wave is transmitted only once as opposed to the round trip in pulse-echo ultrasonography. To this end, the mouse brain has been successfully imaged transcranially by optoacoustic scanning microscopy. Yet, the skull may adversely affect the lateral and axial resolution of transcranial brain images. In order to accurately characterize the complex behavior of the optoacoustic signal as it traverses through the skull, one needs to consider the ultrawideband nature of the optoacoustic signals.

Here the insertion loss of murine skull has been measured by means of a hybrid optoacoustic-ultrasound scanning microscope having a spherically focused PVDF transducer and pulsed laser excitation at 532 nm of a 20 μm diameter absorbing microsphere acting as an optoacoustic point source. Accurate modeling of the acoustic transmission through the skull is further performed using a Fourier-domain expansion of a solid-plate model, based on the simultaneously acquired pulse-echo ultrasound image providing precise information about the skull's position and its orientation relative to the optoacoustic source. Good qualitative agreement has been found between the a solid-plate model and experimental measurements.

The presented strategy might pave the way for modeling skull effects and deriving efficient correction schemes to account for acoustic distortions introduced by an adult murine skull, thus improving the spatial resolution, effective penetration depth and overall image quality of transcranial optoacoustic brain microscopy.
Conference Presentation
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Héctor Estrada, Johannes Rebling, Jake Turner, Moritz Kneipp, Shy Shoham, Daniel Razansky, "Estimation of the skull insertion loss using an optoacoustic point source", Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97080M (15 March 2016); doi: 10.1117/12.2211183; https://doi.org/10.1117/12.2211183
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