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Aix-en-provence, France

Papadacci C.,Laue Langevin Institute | Papadacci C.,University Paris Diderot | Pernot M.,Laue Langevin Institute | Couade M.,SuperSonic Imagine | And 2 more authors.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Noninvasive ultrafast imaging of intrinsic waves such as electromechanical waves or remotely induced shear waves in elastography imaging techniques for human cardiac applications remains challenging. In this paper, we propose ultrafast imaging of the heart with adapted sector size by coherently compounding diverging waves emitted from a standard transthoracic cardiac phased-array probe. As in ultrafast imaging with plane wave coherent compounding, diverging waves can be summed coherently to obtain high-quality images of the entire heart at high frame rate in a full field of view. To image the propagation of shear waves with a large SNR, the field of view can be adapted by changing the angular aperture of the transmitted wave. Backscattered echoes from successive circular wave acquisitions are coherently summed at every location in the image to improve the image quality while maintaining very high frame rates. The transmitted diverging waves, angular apertures, and subaperture sizes were tested in simulation, and ultrafast coherent compounding was implemented in a commercial scanner. The improvement of the imaging quality was quantified in phantoms and in one human heart, in vivo. Imaging shear wave propagation at 2500 frames/s using 5 diverging waves provided a large increase of the SNR of the tissue velocity estimates while maintaining a high frame rate. Finally, ultrafast imaging with 1 to 5 diverging waves was used to image the human heart at a frame rate of 4500 to 900 frames/s over an entire cardiac cycle. Spatial coherent compounding provided a strong improvement of the imaging quality, even with a small number of transmitted diverging waves and a high frame rate, which allows imaging of the propagation of electromechanical and shear waves with good image quality. © 2014 IEEE. Source

Athanasiou A.,University Pierre and Marie Curie | Tardivon A.,University Pierre and Marie Curie | Tanter M.,French National Center for Scientific Research | Sigal-Zafrani B.,University Pierre and Marie Curie | And 5 more authors.

Purpose: To determine the appearance of breast lesions at quantitative ultrasonographic (US) elastography by using supersonic shear imaging (SSI) and to assess the correlation between quantitative values of lesion stiffness and pathologic results, which were used as the reference standard. Materials and Methods: This study was approved by the French National Committee for the Protection of Patients Participating in Biomedical Research Programs. All patients provided written informed consent. Conventional US and SSI quantitative elastography were performed in 46 women (mean age, 57.6 years;age range, 38-71 years) with 48 breast lesions (28 benign, 20 malignant;mean size, 14.7 mm);pathologic results were available in all cases. Quantitative lesion elasticity was measured in terms of the Young modulus (in kilopascals). Sensitivity, specifi city, and area under the curve were obtained by using a receiver operating characteristic curve analysis to assess diagnostic performance. Results: All breast lesions were detected at SSI. Malignant lesions exhibited a mean elasticity value of 146.6 kPa ± 40.05 (standard deviation), whereas benign ones had an elasticity value of 45.3 kPa ± 41.1 (P < .001). Complicated cysts were differentiated from solid lesions because they had elasticity values of 0 kPa (no signal was retrieved from liquid areas). Conclusion: SSI provides quantitative elasticity measurements, thus adding complementary information that potentially could help in breast lesion characterization with B-mode US. © RSNA, 2010. Source

Messas E.,Pole Cardiovasculaire | Pernot M.,ESPCI ParisTech | Couade M.,SuperSonic Imagine
Diagnostic and Interventional Imaging

Peripheral vascular disease is a frequently occurring disease and is most often caused by atherosclerosis and more rarely by anomalies of the collagen or other components of the arterial wall. Arterial stiffness problems form one of the precursor phenomena of peripheral vascular disease, and in the case of atherosclerosis represents an independent risk marker for the occurrence of cardiovascular disease. The first techniques, developed to evaluate arterial stiffness, use indirect measurements such as pulse wave velocity or the analysis of variations in pressure and volume to estimate arterial wall stiffness. Techniques based on the pulse wave lack precision because they assume that arterial stiffness is uniform throughout the path of the pulse wave, and that it is constant throughout the cardiac cycle. Moreover, measuring the velocity of the pulse wave may be less precise in certain pathological situations: metabolic syndrome, obesity, large chest, mega-dolico artery. Techniques based on the analysis of variations in pressure and in volume do not accurately measure blood pressure, which can only be taken externally. In addition, these techniques require dedicated equipment, which is not reimbursed by the French health care system, and which is cumbersome to use (especially for techniques based on variation in pressure) in clinical practice. This explains why these two techniques are not used in clinical practice. Ultrafast echography is a new ultrasound imaging method that can record up to 10,000 images per second. This high temporal resolution makes it possible tomeasure the velocity of the local pulse wave and arterial wall stiffness thanks to the remote palpation carried out by shear wave. The ease of use and the accuracy of these two techniques suggest that these diagnostic applications will play a significant role in vascular pathology in the future. It is possible in real time, using a traditional vascular ultrasound probe, to make an accurate assessment of local arterial stiffness and of its variation during the cardiac cycle. This technological breakthrough will probably improve phenotype evaluation of patients suffering from vascular diseases, to more effectively evaluate the cardiovascular risk for patients, at primary and secondary prevention level, and to carry out broad epidemiological studies on cardiovascular risks. © 2013 Published by Elsevier Masson SAS on behalf of the Éditions françaises de radiologie. Source

Nguyen T.-M.,ESPCI ParisTech | Aubry J.-F.,ESPCI ParisTech | Touboul D.,University of Bordeaux 1 | Fink M.,ESPCI ParisTech | And 3 more authors.
Investigative Ophthalmology and Visual Science

Purpose. Keratoconus disease or post-LASIK corneal ectasia are increasingly treated using UV-A/riboflavin-induced corneal collagen cross-linking (CXL). However, this treatment suffers from a lack of techniques to provide an assessment in real-time of the CXL effects. Here, we investigated the potential interest of corneal elasticity as a biomarker of the efficacy of this treatment. Methods. For this purpose, supersonic shear wave imaging (SSI) was performed both ex vivo and in vivo on porcine eyes before and after CXL. Based on ultrasonic scanners providing ultrafast frame rates (~30 kHz), the SSI technique generates and tracks the propagation of shear waves in tissues. It provides two- and three-dimensional (2-D and 3-D) quantitative maps of the corneal elasticity. Results. After CXL, quantitative maps of corneal stiffness clearly depicted the cross-linked area with a typical 200-μm lateral resolution. The CXL resulted in a 56% ± 15% increase of the shear wave speed for corneas treated in vivo (n = 4). Conclusions. The in vivo CXL experiments performed on pigs demonstrated that the quantitative estimation of local stiffness and the 2-D elastic maps of the corneal surface provide an efficient way to monitor the local efficacy of corneal cross-linking. © 2012 The Association for Research in Vision and Ophthalmology, Inc. Source

Marsac L.,University Paris Diderot | Chauvet D.,University Paris Diderot | Larrat B.,University Paris Diderot | Pernot M.,SuperSonic Imagine | And 5 more authors.
Medical Physics

Purpose: This study aims to demonstrate, using human cadavers the feasibility of energy-based adaptive focusing of ultrasonic waves using magnetic resonance acoustic radiation force imaging (MR-ARFI) in the framework of non-invasive transcranial high intensity focused ultrasound (HIFU) therapy. Methods: Energy-based adaptive focusing techniques were recently proposed in order to achieve aberration correction. The authors evaluate this method on a clinical brain HIFU system composed of 512 ultrasonic elements positioned inside a full body 1.5 T clinical magnetic resonance (MR) imaging system. Cadaver heads were mounted onto a clinical Leksell stereotactic frame. The ultrasonic wave intensity at the chosen location was indirectly estimated by the MR system measuring the local tissue displacement induced by the acoustic radiation force of the ultrasound (US) beams. For aberration correction, a set of spatially encoded ultrasonic waves was transmitted from the ultrasonic array and the resulting local displacements were estimated with the MR-ARFI sequence for each emitted beam. A noniterative inversion process was then performed in order to estimate the spatial phase aberrations induced by the cadaver skull. The procedure was first evaluated and optimized in a calf brain using a numerical aberrator mimicking human skull aberrations. The full method was then demonstrated using a fresh human cadaver head. Results: The corrected beam resulting from the direct inversion process was found to focus at the targeted location with an acoustic intensity 2.2 times higher than the conventional non corrected beam. In addition, this corrected beam was found to give an acoustic intensity 1.5 times higher than the focusing pattern obtained with an aberration correction using transcranial acoustic simulation-based on X-ray computed tomography (CT) scans. Conclusions: The proposed technique achieved near optimal focusing in an intact human head for the first time. These findings confirm the strong potential of energy-based adaptive focusing of transcranial ultrasonic beams for clinical applications. © 2012 American Association of Physicists in Medicine. Source

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