Search PubMed⌕ Search

Biomedical subjects

Mickael Tanter

Publications and source records attributed to Mickael Tanter.

5 recordsLinked to original sources
PubMed2005

Viscoelastic shear properties of in vivo breast lesions measured by MR elastography.

Elastography is a technique to assess the viscoelastic properties of tissue by measuring an acoustic wave propagating though the object. Here, the technique is applied in the course of standard MR mammography to 15 patients with different pathologies (six breast cancer cases, six fibroadenoma cases and three mastopathy cases). Low-frequency mechanical waves are coupled longitudinally into the tissue in order to obtain sufficient wave amplitude throughout the entire breast. This leads to the presence of a substantial fraction of compressional waves, which contribute to the total displacement field. It is shown theoretically that the correct evaluation of these contributions from the compressional wave is rather difficult due to the almost incompressible nature of tissue. To overcome this problem, it is proposed to apply the curl-operator to the measured displacement field in order to completely remove contributions from the compressional wave. Results from simulations and a breast phantom demonstrate the feasibility of the technique. The in vivo results show a good separation between breast cancer and benign fibroadenoma utilizing the shear modulus. Breast cancer appears on average 2.2 (P<.001) times stiffer. All breast cancer cases showed a good delineation to the surrounding breast tissue with an average elevation of a factor of 3.3 (P< 1.4 x 10(-6)). The results as obtained for the shear viscosity do not indicate to be useful for separating benign from malignant lesions.

Acoustics↗
PubMed2004

Temperature estimation using ultrasonic spatial compound imaging.

The feasibility of temperature estimation during high-intensity focused ultrasound therapy using pulse-echo diagnostic ultrasound data has been demonstrated. This method is based upon the measurement of thermally-induced modifications in backscattered RF echoes due to thermal expansion and local changes in the speed of sound. It has been shown that strong ripple artifacts due to the thermo-acoustic lens effect severely corrupt the temperature estimates behind the heated region. We propose here a new imaging technique that improves the temperature estimation behind the heated region and reduces the variance of the temperature estimates in the entire image. We replaced the conventional beamforming on transmit with multiple steered plane wave insonifications using several subapertures. A two-dimensional temperature map is estimated from axial displacement maps between consecutive RF images of identically steered plane wave insonifications. Temperature estimation is then improved by averaging the two-dimensional maps from the multiple steered plane wave insonifications. Experiments were conducted in a tissue-mimicking gelatin-based phantom and in fresh bovine liver.

Animals↗
PubMed2003

Sound focusing in rooms: the time-reversal approach.

New perspectives in audible range acoustics, such as virtual sound space creation and active noise control, rely on the ability of the rendering system to recreate precisely a desired sound field. This ability to control sound in a given volume of a room is directly linked to the capacity to focus acoustical energy both in space and time. However, sound focusing in rooms remains a complicated problem, essentially because of the multiple reflections on obstacles and walls occurring during propagation. In this paper, the technique of time-reversal focusing, well known in ultrasound, is experimentally applied to audible range acoustics. Compared to classical focusing techniques such as delay law focusing, time reversal appears to considerably improve quality of both temporal and spatial focusing. This so-called super-resolution phenomenon is due to the ability of time reversal to take into account all of the different sound paths between the emitting antenna and the focal point, thus creating an adaptive spatial and temporal matched filter for the considered propagation medium. Experiments emphasize the strong robustness of time-reversal focusing towards small modifications in the medium, such as people in motion or temperature variations. Sound focusing through walls using the time-reversal approach is also experimentally demonstrated.

Acoustics↗
PubMed2003

Time-reversal acoustics in biomedical engineering.

Time reversal is a very powerful method for focusing through complex and heterogeneous media and shows very promising results in biomedical applications. In this paper, we review some of the main applications investigated during the past decade. An iterative implementation of the time-reversal process allows tracking gallstones in real time during lithotripsy treatments. In this application domain, a smart exploitation of the reverberations in solid waveguides permits the focusing of high-amplitude ultrasonic shock waves with a small number of transducers. Finally, because time reversal is able to correct the strong distortions induced by the skull bone on ultrasonic propagation, this adaptive focusing technique is very promising for ultrasonic hyperthermia brain therapy.

Acoustics↗