We have already demonstrated the potentiality of interferometry to perform timeresolved
measurements of the light scattered by a tissue: the fluctuations of the speckle
pattern, linked to a wavelength-modulation of the source, are registered, and the time-resolved
average intensity can be numerically obtained from these data[1]. The competitive results were
obtained with a simple photodiode as detector[2].
Such a method can be cheaper and more accessible for biomedical applications than
direct time-resolved methods, but it is not its unique advantage: this method allows to perform
Diffusing Wave Spectroscopy (DWS) with selected photon pathlengths[3,4]; for instance, we
have shown that we can improve the spatial resolution in transillumination imaging of a
dynamic heterogeneity through the selection of short photon transit times[4]. Therefore such a
method can offer interesting applications, for example in mammography.
A way to improve the signal to noise ratio of this method can consist in multiplying
the number of detectors. That's the reason why we decide to consider the use of a high speed
camera, that can reach a rate of 1000 frames per second. We will present the first results
obtained with this new system. The performance will be discussed, and compared to our
previous setup.
Diffusing Wave Spectroscopy (DWS) consists in the measurement of temporal correlation of the electromagnetic field in the diffusion regime, allowing a scan of dynamical properties deep inside a medium. DWS is of special interest in biomedical optics, as it is sensitive to blood circulation in capillaries inside the tissue.
However one main difficulty of this technique concerns data extraction which implies to perform an inverse problem taking into account the geometry and the optical coefficients of the medium. The use of time-resolved detection has been proved to be an efficient tool to discriminate the DWS information, but the photon path lengths were up to now limited to a few tens mean free paths.
In order to perform time-resolved DWS for much longer photon paths, we used a new method, based on the use of an interferometer and a wavelength modulated source. We have already demonstrated that this method, in addition to its lower cost, was very efficient to perform time-resolved measurements of the light scattered by a thick scattering medium. We will show in this poster some measurements performed by transillumination through a thick medium (4cm), opening the possibility of Time-Resolved DWS measurements in the human breast.
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