Functional ultrasound (fUS) is a novel neuroimaging technique, based on high-sensitivity ultrafas... more Functional ultrasound (fUS) is a novel neuroimaging technique, based on high-sensitivity ultrafast Doppler imaging of cerebral blood volume, capable of measuring brain activation and connectivity in rodents with high spatiotemporal resolution (100μm, 1ms). However, the skull attenuates acoustic waves, so fUS in rats currently requires craniotomy or a thinned-skull window. Here we propose a non-invasive approach by enhancing the fUS signal with a contrast agent, inert gas microbubbles. Plane-wave illumination of the brain at high frame rate (500Hz compounded sequence with three tilted plane waves, PRF=1500Hz with a 128 element 15MHz linear transducer), yields highly-resolved neurovascular maps. We compared fUS imaging performance through the intact skull bone (transcranial fUS) versus a thinned-skull window in the same animal. First, we show that the vascular network of the adult rat brain can be imaged transcranially only after a bolus intravenous injection of microbubbles, which le...
The aim of this study was to investigate the potential of coronary ultrafast Doppler angiography ... more The aim of this study was to investigate the potential of coronary ultrafast Doppler angiography (CUDA), a novel vascular imaging technique based on ultrafast ultrasound, to image noninvasively with high sensitivity the intramyocardial coronary vasculature and quantify the coronary blood flow dynamics. BACKGROUND Noninvasive coronary imaging techniques are currently limited to the observation of the epicardial coronary arteries. However, many studies have highlighted the importance of the coronary microcirculation and microvascular disease. METHODS CUDA was performed in vivo in open-chest procedures in 9 swine. Ultrafast plane-wave imaging at 2,000 frames/s was combined to an adaptive spatiotemporal filtering to achieve ultrahigh-sensitive imaging of the coronary blood flows. Quantification of the flow change was performed during hyperemia after a 30-s left anterior descending (LAD) artery occlusion followed by reperfusion and was compared to gold standard measurements provided by a flowmeter probe placed at a proximal location on the LAD (n ¼ 5). Coronary flow reserve was assessed during intravenous perfusion of adenosine. Vascular damages were evaluated during a second set of experiments in which the LAD was occluded for 90 min, followed by 150 min of reperfusion to induce myocardial infarction (n ¼ 3). Finally, the transthoracic feasibility of CUDA was assessed on 2 adult and 2 pediatric volunteers. RESULTS Ultrahigh-sensitive cine loops of venous and arterial intramyocardial blood flows were obtained within 1 cardiac cycle. Quantification of the coronary flow changes during hyperemia was in good agreement with gold standard measurements (r 2 ¼ 0.89), as well as the assessment of coronary flow reserve (2.35 AE 0.65 vs. 2.28 AE 0.84; p ¼ NS). On the infarcted animals, CUDA images revealed the presence of strong hyperemia and the appearance of abnormal coronary vessel structures in the reperfused LAD territory. Finally, the feasibility of transthoracic coronary vasculature imaging was shown on 4 human volunteers. CONCLUSIONS Ultrafast Doppler imaging can map the coronary vasculature with high sensitivity and quantify intramural coronary blood flow changes.
Supplementary Fig. 1 Flickering frequency optimisation repeatability. The protocol leading to Fig... more Supplementary Fig. 1 Flickering frequency optimisation repeatability. The protocol leading to Figure 3.D. has been repeated on 2 other rats: Rat #3 and Rat #4. For the sake of speed, only 4 trials instead of 5 where performed for each parameters and fewer frequencies were investigated. A. Influence of the flickering frequency on the response in the V1/V2 for the 3 rats. Error bars: Standard deviation. B. Influence of the flickering frequency on the response in the SC for the 3 rats. Error bars: Standard deviation. C. Averaged curves for the 3 rats in SC and V1/V2.
The assessment of myocardial fiber disarray is of major interest for the study of the progression... more The assessment of myocardial fiber disarray is of major interest for the study of the progression of myocardial disease. However, time-resolved imaging of the myocardial structure remains unavailable in clinical practice. In this study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel ultrasound-based imaging technique that can map the myocardial fibers orientation and its dynamics with a temporal resolution of 10 ms during a single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is based on ultrafast volumetric ultrasound acquisitions, which are used to quantify the spatial coherence of backscattered echoes at each point of the volume. The capability of 3D-BTI to map the fibers orientation was evaluated in vitro in 5 myocardial samples. The helicoidal transmural variation of fiber angles was in good agreement with the one obtained by histological analysis. 3D-BTI was then performed to map the fiber orientation dynamics in vivo in the beatin...
The aim of this study was to investigate the potential of shear wave imaging (SWI), a novel ultra... more The aim of this study was to investigate the potential of shear wave imaging (SWI), a novel ultrasound-based technique, to noninvasively quantify passive diastolic myocardial stiffness in an ovine model of ischemic cardiomyopathy. BACKGROUND Evaluation of diastolic left ventricular function is critical for evaluation of heart failure and ischemic cardiomyopathy. Myocardial stiffness is known to be an important property for the evaluation of the diastolic myocardial function, but this parameter cannot be measured noninvasively by existing techniques. METHODS SWI was performed in vivo in open-chest procedures in 10 sheep. Ligation of a diagonal of the left anterior descending coronary artery was performed for 15 min (stunned group, n ¼ 5) and 2 h (infarcted group, n ¼ 5). Each procedure was followed by a 40-min reperfusion period. Diastolic myocardial stiffness was measured at rest, during ischemia, and after reperfusion by using noninvasive shear wave imaging. Simultaneously, end-diastolic left ventricular pressure and segmental strain were measured with a pressure catheter and sonomicrometers during transient vena caval occlusions to obtain gold standard evaluation of myocardial stiffness using end-diastolic strain-stress relationship (EDSSR). RESULTS In both groups, the end-systolic circumferential strain was drastically reduced during ischemia (from 14.2 AE 1.2% to 1.3 AE 1.6% in the infarcted group and from 13.5 AE 3.0% to 1.9 AE 1.8% in the stunned group; p <0.01). SWI diastolic stiffness increased after 2 h of ischemia from 1.7 AE 0.4 to 6.2 AE 2.2 kPa (p < 0.05) and even more after reperfusion (12.1 AE 4.2 kPa; p < 0.01). Diastolic myocardial stiffening was confirmed by the exponential constant coefficient of the EDSSR, which increased from 8.8 AE 2.3 to 25.7 AE 9.5 (p < 0.01). In contrast, SWI diastolic stiffness was unchanged in the stunned group (2.3 AE 0.4 kPa vs 1.8 AE 0.3 kPa, p ¼ NS) which was confirmed also by the exponential constant of EDSSR (9.7 AE 3.1 vs 10.2 AE 2.3, p ¼ NS). CONCLUSIONS Noninvasive SWI evaluation of diastolic myocardial stiffness can differentiate between stiff, noncompliant infarcted wall and softer wall containing stunned myocardium.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2015
Ultrafast Doppler imaging was introduced as a technique to quantify blood flow in an entire 2-D f... more Ultrafast Doppler imaging was introduced as a technique to quantify blood flow in an entire 2-D field of view, expanding the field of application of ultrasound imaging to the highly sensitive anatomical and functional mapping of blood vessels. We have recently developed 3-D ultrafast ultrasound imaging, a technique that can produce thousands of ultrasound volumes per second, based on a 3-D plane and diverging wave emissions, and demonstrated its clinical feasibility in human subjects in vivo. In this study, we show that noninvasive 3-D ultrafast power Doppler, pulsed Doppler, and color Doppler imaging can be used to perform imaging of blood vessels in humans when using coherent compounding of 3-D tilted plane waves. A customized, programmable, 1024-channel ultrasound system was designed to perform 3-D ultrafast imaging. Using a 32 × 32, 3-MHz matrix phased array (Vermon, Tours, France), volumes were beamformed by coherently compounding successive tilted plane wave emissions. Doppler processing was then applied in a voxel-wise fashion. The proof of principle of 3-D ultrafast power Doppler imaging was first performed by imaging Tygon tubes of various diameters, and in vivo feasibility was demonstrated by imaging small vessels in the human thyroid. Simultaneous 3-D color and pulsed Doppler imaging using compounded emissions were also applied in the carotid artery and the jugular vein in one healthy volunteer.
2013 IEEE International Ultrasonics Symposium (IUS), 2013
In this study shear wave dispersion was measured in vivo in four Achilles tendons by applying the... more In this study shear wave dispersion was measured in vivo in four Achilles tendons by applying the Supersonic Shear Imaging technique and the concept of Shear Wave Spectroscopy parallel and perpendicular to the tendon fiber orientation. In tissues shear wave dispersion is related to two main physical causes: the geometry of the investigated medium which can lead to guided waves and/or the viscosity of the medium (if Voigt model is assumed). By modeling the Achilles tendon as a transverse isotropic plate it was possible to estimate the tendon elastic properties described by the five independent elastic constants (C 11 , C 33 , C 13 , C 55 and C 66) of the Christoffel's tensor. We show that parallel to fibers the geometrical effect leading to guided wave propagation is prominent, while perpendicularly to fibers viscosity must be also taken into account to fully describe the experimental data. The obtained results agree with those reported in the literature. In this study we have demonstrated that the use of a dispersion model must be taken into account in order to properly estimate the tendon viscoelastic properties.
Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, Jan 11, 2014
Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. ... more Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue's mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue's elastic modulus through the measurement of shear wave speed. The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc. An in vitro approach was chosen to test the hypothesis that shear wave speed can be used to evaluate intervertebral disc mechanical properties and to assess measurement repeatability. In total, 11 oxtail intervertebral discs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to ...
Ultrasonography has been widely used for diagnosis since it was first introduced in clinical prac... more Ultrasonography has been widely used for diagnosis since it was first introduced in clinical practice in the 1970's. Since then, new ultrasound modalities have been developed, such as Doppler imaging, which provides new information for diagnosis. Elastography was developed in the 1990's to map tissue stiffness, and reproduces/replaces the palpation performed by clinicians. In this paper, we introduce the principles of elastography and give a technical summary for the main elastography techniques: from quasi-static methods that require a static compression of the tissue to dynamic methods that uses the propagation of mechanical waves in the body. Several dynamic methods are discussed: vibro-acoustography, Acoustic Radiation Force Impulsion (ARFI), transient elastography, shear wave imaging, etc. This paper aims to help the reader at understanding the differences between the different methods of this promising imaging modality that may become a significant tool in medical imag...
The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue ... more The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. Thi...
The disappearance of ultrasound contrast agents after disruption can provide useful information o... more The disappearance of ultrasound contrast agents after disruption can provide useful information on their environment. However, in vivo acoustical imaging of this transient phenomenon, which has a duration on the order of milliseconds, requires high frame rates that are unattainable by conventional ultrasound scanners. In this article, ultrafast imaging is applied to microbubble tracking using a 128-element linear array and an elastography scanner. Contrast agents flowing in a wall-less tissue phantom are insonified with a high-intensity disruption pulse followed by a series of plane waves emitted at a 5kHz PRF. A collection of compounded images depicting the evolution of microbubbles is obtained after the echoes are beamformed in silico. The backscattering of the microbubbles appears to increase in the first image after disruption (4 ms) and decrease following an exponential decay in the next hundred milliseconds. This microbubble dynamic depends on the length and amplitude of the h...
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2014
Heart diseases can affect intraventricular blood flow patterns. Real-time imaging of blood flow p... more Heart diseases can affect intraventricular blood flow patterns. Real-time imaging of blood flow patterns is challenging because it requires both a high frame rate and a large field of view. To date, standard Doppler techniques can only perform blood flow estimation with high temporal resolution within small regions of interest. In this work, we used ultrafast imaging to map in 2-D human left ventricular blood flow patterns during the whole cardiac cycle. Cylindrical waves were transmitted at 4800 Hz with a transthoracic phased-array probe to achieve ultrafast Doppler imaging of the left ventricle. The high spatio-temporal sampling of ultrafast imaging permits reliance on a much more effective wall filtering and increased sensitivity when mapping blood flow patterns during the pre-ejection, ejection, early diastole, diastasis, and late diastole phases of the heart cycle. The superior sensitivity and temporal resolution of ultrafast Doppler imaging makes it a promising tool for the noninvasive study of intraventricular hemodynamic function.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
2010 7th Ieee International Symposium on Biomedical Imaging: from Nano to Macro, 2010
Supersonic Shear Imaging (SSI) is a quantitative stiffness imaging technique based on the combina... more Supersonic Shear Imaging (SSI) is a quantitative stiffness imaging technique based on the combination of a radiation force induced in tissue by an ultrasonic beam and ultrafast ultrasound imaging sequence (up to more than 10000 frames per second) catching in real time the propagation of the resulting shear waves. Local shear wave speed is estimated and enables the two dimensional mapping of shear elasticity. This imaging modality is implemented on conventional probes driven by dedicated ultrafast echographic devices and can be performed during a standard ultrasound exam. The clinical potential of SSI is today extensively investigated for many potential applications such as breast cancer diagnosis, liver fibrosis staging, cardiovascular applications, ophthalmology. This invited lecture presents a short overview of the current investigated applications of SSI.
Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2014
The assessment of fiber architecture is of major interest in the progression of myocardial diseas... more The assessment of fiber architecture is of major interest in the progression of myocardial disease. Recent techniques such as Magnetic Resonance (MR) Diffusion Tensor Imaging or Ultrasound Elastic Tensor Imaging (ETI) can derive the fiber directions by measuring the anisotropy of water diffusion or tissue elasticity, but these techniques present severe limitations in clinical setting. In this study, we propose a new technique, the Backscatter Tensor Imaging (BTI) which enables determining the fibers directions in skeletal muscles and myocardial tissues, by measuring the spatial coherence of ultrasonic speckle. We compare the results to ultrasound ETI. Acquisitions were performed using a linear transducer array connected to an ultrasonic scanner mounted on a motorized rotation device with angles from 0° to 355° by 5° increments to image ex vivo bovine skeletal muscle and porcine left ventricular myocardial samples. At each angle, multiple plane waves were transmitted and the backscattered echoes recorded. The coherence factor was measured as the ratio of coherent intensity over incoherent intensity of backscattered echoes. In skeletal muscle, maximal/minimal coherence factor was found for the probe parallel/perpendicular to the fibers. In myocardium, the coherence was assessed across the entire myocardial thickness, and the position of maxima and minima varied transmurally due to the complex fibers distribution. In ETI, the shear wave speed variation with the probe angle was found to follow the coherence variation. Spatial coherence can thus reveal the anisotropy of the ultrasonic speckle in skeletal muscle and myocardium. BTI could be used on any type of ultrasonic scanner with rotative phased-array probes or 2-D matrix probes for non-invasive evaluation of myocardial fibers.
Functional ultrasound (fUS) is a novel neuroimaging technique, based on high-sensitivity ultrafas... more Functional ultrasound (fUS) is a novel neuroimaging technique, based on high-sensitivity ultrafast Doppler imaging of cerebral blood volume, capable of measuring brain activation and connectivity in rodents with high spatiotemporal resolution (100μm, 1ms). However, the skull attenuates acoustic waves, so fUS in rats currently requires craniotomy or a thinned-skull window. Here we propose a non-invasive approach by enhancing the fUS signal with a contrast agent, inert gas microbubbles. Plane-wave illumination of the brain at high frame rate (500Hz compounded sequence with three tilted plane waves, PRF=1500Hz with a 128 element 15MHz linear transducer), yields highly-resolved neurovascular maps. We compared fUS imaging performance through the intact skull bone (transcranial fUS) versus a thinned-skull window in the same animal. First, we show that the vascular network of the adult rat brain can be imaged transcranially only after a bolus intravenous injection of microbubbles, which le...
The aim of this study was to investigate the potential of coronary ultrafast Doppler angiography ... more The aim of this study was to investigate the potential of coronary ultrafast Doppler angiography (CUDA), a novel vascular imaging technique based on ultrafast ultrasound, to image noninvasively with high sensitivity the intramyocardial coronary vasculature and quantify the coronary blood flow dynamics. BACKGROUND Noninvasive coronary imaging techniques are currently limited to the observation of the epicardial coronary arteries. However, many studies have highlighted the importance of the coronary microcirculation and microvascular disease. METHODS CUDA was performed in vivo in open-chest procedures in 9 swine. Ultrafast plane-wave imaging at 2,000 frames/s was combined to an adaptive spatiotemporal filtering to achieve ultrahigh-sensitive imaging of the coronary blood flows. Quantification of the flow change was performed during hyperemia after a 30-s left anterior descending (LAD) artery occlusion followed by reperfusion and was compared to gold standard measurements provided by a flowmeter probe placed at a proximal location on the LAD (n ¼ 5). Coronary flow reserve was assessed during intravenous perfusion of adenosine. Vascular damages were evaluated during a second set of experiments in which the LAD was occluded for 90 min, followed by 150 min of reperfusion to induce myocardial infarction (n ¼ 3). Finally, the transthoracic feasibility of CUDA was assessed on 2 adult and 2 pediatric volunteers. RESULTS Ultrahigh-sensitive cine loops of venous and arterial intramyocardial blood flows were obtained within 1 cardiac cycle. Quantification of the coronary flow changes during hyperemia was in good agreement with gold standard measurements (r 2 ¼ 0.89), as well as the assessment of coronary flow reserve (2.35 AE 0.65 vs. 2.28 AE 0.84; p ¼ NS). On the infarcted animals, CUDA images revealed the presence of strong hyperemia and the appearance of abnormal coronary vessel structures in the reperfused LAD territory. Finally, the feasibility of transthoracic coronary vasculature imaging was shown on 4 human volunteers. CONCLUSIONS Ultrafast Doppler imaging can map the coronary vasculature with high sensitivity and quantify intramural coronary blood flow changes.
Supplementary Fig. 1 Flickering frequency optimisation repeatability. The protocol leading to Fig... more Supplementary Fig. 1 Flickering frequency optimisation repeatability. The protocol leading to Figure 3.D. has been repeated on 2 other rats: Rat #3 and Rat #4. For the sake of speed, only 4 trials instead of 5 where performed for each parameters and fewer frequencies were investigated. A. Influence of the flickering frequency on the response in the V1/V2 for the 3 rats. Error bars: Standard deviation. B. Influence of the flickering frequency on the response in the SC for the 3 rats. Error bars: Standard deviation. C. Averaged curves for the 3 rats in SC and V1/V2.
The assessment of myocardial fiber disarray is of major interest for the study of the progression... more The assessment of myocardial fiber disarray is of major interest for the study of the progression of myocardial disease. However, time-resolved imaging of the myocardial structure remains unavailable in clinical practice. In this study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel ultrasound-based imaging technique that can map the myocardial fibers orientation and its dynamics with a temporal resolution of 10 ms during a single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is based on ultrafast volumetric ultrasound acquisitions, which are used to quantify the spatial coherence of backscattered echoes at each point of the volume. The capability of 3D-BTI to map the fibers orientation was evaluated in vitro in 5 myocardial samples. The helicoidal transmural variation of fiber angles was in good agreement with the one obtained by histological analysis. 3D-BTI was then performed to map the fiber orientation dynamics in vivo in the beatin...
The aim of this study was to investigate the potential of shear wave imaging (SWI), a novel ultra... more The aim of this study was to investigate the potential of shear wave imaging (SWI), a novel ultrasound-based technique, to noninvasively quantify passive diastolic myocardial stiffness in an ovine model of ischemic cardiomyopathy. BACKGROUND Evaluation of diastolic left ventricular function is critical for evaluation of heart failure and ischemic cardiomyopathy. Myocardial stiffness is known to be an important property for the evaluation of the diastolic myocardial function, but this parameter cannot be measured noninvasively by existing techniques. METHODS SWI was performed in vivo in open-chest procedures in 10 sheep. Ligation of a diagonal of the left anterior descending coronary artery was performed for 15 min (stunned group, n ¼ 5) and 2 h (infarcted group, n ¼ 5). Each procedure was followed by a 40-min reperfusion period. Diastolic myocardial stiffness was measured at rest, during ischemia, and after reperfusion by using noninvasive shear wave imaging. Simultaneously, end-diastolic left ventricular pressure and segmental strain were measured with a pressure catheter and sonomicrometers during transient vena caval occlusions to obtain gold standard evaluation of myocardial stiffness using end-diastolic strain-stress relationship (EDSSR). RESULTS In both groups, the end-systolic circumferential strain was drastically reduced during ischemia (from 14.2 AE 1.2% to 1.3 AE 1.6% in the infarcted group and from 13.5 AE 3.0% to 1.9 AE 1.8% in the stunned group; p <0.01). SWI diastolic stiffness increased after 2 h of ischemia from 1.7 AE 0.4 to 6.2 AE 2.2 kPa (p < 0.05) and even more after reperfusion (12.1 AE 4.2 kPa; p < 0.01). Diastolic myocardial stiffening was confirmed by the exponential constant coefficient of the EDSSR, which increased from 8.8 AE 2.3 to 25.7 AE 9.5 (p < 0.01). In contrast, SWI diastolic stiffness was unchanged in the stunned group (2.3 AE 0.4 kPa vs 1.8 AE 0.3 kPa, p ¼ NS) which was confirmed also by the exponential constant of EDSSR (9.7 AE 3.1 vs 10.2 AE 2.3, p ¼ NS). CONCLUSIONS Noninvasive SWI evaluation of diastolic myocardial stiffness can differentiate between stiff, noncompliant infarcted wall and softer wall containing stunned myocardium.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2015
Ultrafast Doppler imaging was introduced as a technique to quantify blood flow in an entire 2-D f... more Ultrafast Doppler imaging was introduced as a technique to quantify blood flow in an entire 2-D field of view, expanding the field of application of ultrasound imaging to the highly sensitive anatomical and functional mapping of blood vessels. We have recently developed 3-D ultrafast ultrasound imaging, a technique that can produce thousands of ultrasound volumes per second, based on a 3-D plane and diverging wave emissions, and demonstrated its clinical feasibility in human subjects in vivo. In this study, we show that noninvasive 3-D ultrafast power Doppler, pulsed Doppler, and color Doppler imaging can be used to perform imaging of blood vessels in humans when using coherent compounding of 3-D tilted plane waves. A customized, programmable, 1024-channel ultrasound system was designed to perform 3-D ultrafast imaging. Using a 32 × 32, 3-MHz matrix phased array (Vermon, Tours, France), volumes were beamformed by coherently compounding successive tilted plane wave emissions. Doppler processing was then applied in a voxel-wise fashion. The proof of principle of 3-D ultrafast power Doppler imaging was first performed by imaging Tygon tubes of various diameters, and in vivo feasibility was demonstrated by imaging small vessels in the human thyroid. Simultaneous 3-D color and pulsed Doppler imaging using compounded emissions were also applied in the carotid artery and the jugular vein in one healthy volunteer.
2013 IEEE International Ultrasonics Symposium (IUS), 2013
In this study shear wave dispersion was measured in vivo in four Achilles tendons by applying the... more In this study shear wave dispersion was measured in vivo in four Achilles tendons by applying the Supersonic Shear Imaging technique and the concept of Shear Wave Spectroscopy parallel and perpendicular to the tendon fiber orientation. In tissues shear wave dispersion is related to two main physical causes: the geometry of the investigated medium which can lead to guided waves and/or the viscosity of the medium (if Voigt model is assumed). By modeling the Achilles tendon as a transverse isotropic plate it was possible to estimate the tendon elastic properties described by the five independent elastic constants (C 11 , C 33 , C 13 , C 55 and C 66) of the Christoffel's tensor. We show that parallel to fibers the geometrical effect leading to guided wave propagation is prominent, while perpendicularly to fibers viscosity must be also taken into account to fully describe the experimental data. The obtained results agree with those reported in the literature. In this study we have demonstrated that the use of a dispersion model must be taken into account in order to properly estimate the tendon viscoelastic properties.
Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, Jan 11, 2014
Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. ... more Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue's mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue's elastic modulus through the measurement of shear wave speed. The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc. An in vitro approach was chosen to test the hypothesis that shear wave speed can be used to evaluate intervertebral disc mechanical properties and to assess measurement repeatability. In total, 11 oxtail intervertebral discs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to ...
Ultrasonography has been widely used for diagnosis since it was first introduced in clinical prac... more Ultrasonography has been widely used for diagnosis since it was first introduced in clinical practice in the 1970's. Since then, new ultrasound modalities have been developed, such as Doppler imaging, which provides new information for diagnosis. Elastography was developed in the 1990's to map tissue stiffness, and reproduces/replaces the palpation performed by clinicians. In this paper, we introduce the principles of elastography and give a technical summary for the main elastography techniques: from quasi-static methods that require a static compression of the tissue to dynamic methods that uses the propagation of mechanical waves in the body. Several dynamic methods are discussed: vibro-acoustography, Acoustic Radiation Force Impulsion (ARFI), transient elastography, shear wave imaging, etc. This paper aims to help the reader at understanding the differences between the different methods of this promising imaging modality that may become a significant tool in medical imag...
The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue ... more The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. Thi...
The disappearance of ultrasound contrast agents after disruption can provide useful information o... more The disappearance of ultrasound contrast agents after disruption can provide useful information on their environment. However, in vivo acoustical imaging of this transient phenomenon, which has a duration on the order of milliseconds, requires high frame rates that are unattainable by conventional ultrasound scanners. In this article, ultrafast imaging is applied to microbubble tracking using a 128-element linear array and an elastography scanner. Contrast agents flowing in a wall-less tissue phantom are insonified with a high-intensity disruption pulse followed by a series of plane waves emitted at a 5kHz PRF. A collection of compounded images depicting the evolution of microbubbles is obtained after the echoes are beamformed in silico. The backscattering of the microbubbles appears to increase in the first image after disruption (4 ms) and decrease following an exponential decay in the next hundred milliseconds. This microbubble dynamic depends on the length and amplitude of the h...
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2014
Heart diseases can affect intraventricular blood flow patterns. Real-time imaging of blood flow p... more Heart diseases can affect intraventricular blood flow patterns. Real-time imaging of blood flow patterns is challenging because it requires both a high frame rate and a large field of view. To date, standard Doppler techniques can only perform blood flow estimation with high temporal resolution within small regions of interest. In this work, we used ultrafast imaging to map in 2-D human left ventricular blood flow patterns during the whole cardiac cycle. Cylindrical waves were transmitted at 4800 Hz with a transthoracic phased-array probe to achieve ultrafast Doppler imaging of the left ventricle. The high spatio-temporal sampling of ultrafast imaging permits reliance on a much more effective wall filtering and increased sensitivity when mapping blood flow patterns during the pre-ejection, ejection, early diastole, diastasis, and late diastole phases of the heart cycle. The superior sensitivity and temporal resolution of ultrafast Doppler imaging makes it a promising tool for the noninvasive study of intraventricular hemodynamic function.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
2010 7th Ieee International Symposium on Biomedical Imaging: from Nano to Macro, 2010
Supersonic Shear Imaging (SSI) is a quantitative stiffness imaging technique based on the combina... more Supersonic Shear Imaging (SSI) is a quantitative stiffness imaging technique based on the combination of a radiation force induced in tissue by an ultrasonic beam and ultrafast ultrasound imaging sequence (up to more than 10000 frames per second) catching in real time the propagation of the resulting shear waves. Local shear wave speed is estimated and enables the two dimensional mapping of shear elasticity. This imaging modality is implemented on conventional probes driven by dedicated ultrafast echographic devices and can be performed during a standard ultrasound exam. The clinical potential of SSI is today extensively investigated for many potential applications such as breast cancer diagnosis, liver fibrosis staging, cardiovascular applications, ophthalmology. This invited lecture presents a short overview of the current investigated applications of SSI.
Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2014
The assessment of fiber architecture is of major interest in the progression of myocardial diseas... more The assessment of fiber architecture is of major interest in the progression of myocardial disease. Recent techniques such as Magnetic Resonance (MR) Diffusion Tensor Imaging or Ultrasound Elastic Tensor Imaging (ETI) can derive the fiber directions by measuring the anisotropy of water diffusion or tissue elasticity, but these techniques present severe limitations in clinical setting. In this study, we propose a new technique, the Backscatter Tensor Imaging (BTI) which enables determining the fibers directions in skeletal muscles and myocardial tissues, by measuring the spatial coherence of ultrasonic speckle. We compare the results to ultrasound ETI. Acquisitions were performed using a linear transducer array connected to an ultrasonic scanner mounted on a motorized rotation device with angles from 0° to 355° by 5° increments to image ex vivo bovine skeletal muscle and porcine left ventricular myocardial samples. At each angle, multiple plane waves were transmitted and the backscattered echoes recorded. The coherence factor was measured as the ratio of coherent intensity over incoherent intensity of backscattered echoes. In skeletal muscle, maximal/minimal coherence factor was found for the probe parallel/perpendicular to the fibers. In myocardium, the coherence was assessed across the entire myocardial thickness, and the position of maxima and minima varied transmurally due to the complex fibers distribution. In ETI, the shear wave speed variation with the probe angle was found to follow the coherence variation. Spatial coherence can thus reveal the anisotropy of the ultrasonic speckle in skeletal muscle and myocardium. BTI could be used on any type of ultrasonic scanner with rotative phased-array probes or 2-D matrix probes for non-invasive evaluation of myocardial fibers.
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