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Hector Rabal
presents
Dynamic speckle in laser and ultrasound images
 
On 2017-06-20 11:00 at G205
 
When an optically rough surface is illuminated with coherent light it appears to
be covered with small bright points and dark regions. This phenomenon is called
speckle. It degrades the quality of the optical image and large efforts were
initially devoted to eliminate it or blur its texture appearance.

If  the optical path of the employed light changes along time the speckled
surface seems to boil.  It is called boiling speckle or dynamic speckle. This
can be due to movements of the scattering centers in the sample and/or changes
in the refractive index of the medium in what can be described as a generalized
Doppler effect.

The dynamics of the speckle are related to its physical causes and by measuring
the detected activity some information can be obtained on what is happening in
the illuminated sample.

The activity of the speckle is measured by applying several different
descriptors to their digital images. As speckle appears as a texture, the
descriptors usually used to characterize textures are sometimes used. 

This approach has been found to be useful in different fields: to measure blood
perfusion, seeds vigor and composition, plants roots growing, bruising in
fruits, bacterial chemotaxis, blood clotting time measurement, drying of
polymers, etc.

The choice of the adequate descriptors for the description of each phenomenon,
usually poorly known, is not easy to determine a priori. So, in practice, sets
of descriptors can be combined by using neural networks, both supervised and not
supervised.

Besides, optical singularities called vortices are present in the speckled
images. The spatial location of these singularities permits very precise
measurement of rigid motions in the sample as well as activity measurements.
Ultrasound images also show this speckle patterns and its dynamics. Usual
medical equipment filters out the dynamics to improve the images. 
We propose that the descriptors used for laser dynamic speckle can be used to
improve the diagnosis of pathologies in ultrasound images by using a similar
approach.

To intend such research, sets of ultrasound images of healthy and pathologic
cases with confirmed diagnosis should be provided and the results of their
processing evaluated by the corresponding experts.
We intend to join efforts between several speckle groups and interested US
experts to explore this possibility.
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