Mickael Tanter

Acousto-optic imaging using plane waves (Conference Presentation)

Acousto-optic imaging is a multi-modal imaging technique where coherent light diffusing in a complex medium is ‘tagged’ over time by a ballistic ultrasound pulse of frequency ωus. The photons which paths cross with the ultrasound pulse undergo the acousto-optic effect, resulting in the frequency shift of ωus that can be selectively detected using heterodyne interferometry. Since the ultrasounds propagate at a known velocity, a time-to-space map of the tagged photons results in an image I(x, z), where x is the lateral direction and z the depth direction of the diffuse medium. Images at propagation depths much greater than the average mean free path, typically ~1mm in biological tissue, can be obtained. In most images obtained so far, the ultrasounds are focused line after line to recover an image, and therefore limited by the probe emission rate which is ~1-10 KHz depending on the probe size and the acoustic pulse power. Therefore, in order to acquire acoustic images at frame rates greater than 1 Hz for ‘direct visualization’ of the system under study, it is crucial to minimize the number of individual acquisitions necessary to reconstruct an image. Here, we present an alternative probe configuration where plane waves emitted at various angles are used rather than focused waves to tag the diffuse light. This approach, first proposed by P.Kuchment and L.Kunyansky (2010), is similar to X-ray tomography since the image information is contained in the various angular scans performed for one acquisition. Because the piezo-elements on the acoustic probe are non-isotropic emitters, the angular scan is typically limited to +/20 degrees, which is sufficient to recover information and can be improved using more than one probe. An inversion algorithm based on inverse Radon-transform is than used to reconstruct the image

Pulsed Cavitational Ultrasound Softening: a new non-invasive therapeutic approach of calcified bioprosthetic valve stenosis 2 Brief Title: Non-invasive ultrasound therapy of calcified bioprosthesis 3 4

Visual Abstract

Expanding the treatment envelope for brain therapy: simulation models and head phantoms

Thermal therapy is currently limited to central areas of the brain in order to maximize the antenna gain between the outer cortex and the target. So far, clinical applications have been limited to thalamotomies for neuropathic pain, essential tremor and Parkinsonian tremor. We developed numerical simulations and head phantoms in order to investigate the possibility to target more eccentric targets in the brain in silico and in vitro.

Ultrasonic Time Reversal Mirrors

For more than ten years, time reversal techniques have been developed in many different fields of applications including detection of defects in solids, underwater acoustics, room acoustics and also ultrasound medical imaging and therapy. The essential property that makes time reversed acoustics possible is that the underlying physical process of wave propagation would be unchanged if time were reversed. In a non dissipative medium, the equations governing the waves guarantee that for every burst of sound that diverges from a source there exists in theory a set of waves that would precisely retrace the path of the sound back to the source. If the source is pointlike, this allows focusing back on the source whatever the medium complexity. For this reason, time reversal represents a very powerful adaptive focusing technique for complex media. The generation of this reconverging wave can be achieved by using Time Reversal Mirrors (TRM). It is made of arrays of ultrasonic reversible piezoelectric transducers ...