We extended the capabilities of functional ultrasound to whole-brain four-dimensional (4D) neuroimaging. Our multiplane-wave transmission scheme on matrix arrays at thousands of frames per second ...provides volumetric recordings of cerebral blood volume changes at high spatiotemporal resolution. We illustrated the approach in rats while providing multiple sensory stimuli, for 4D functional connectivity and during instantaneous tracking of epileptiform events.
High-contrast ultrafast imaging of the heart Papadacci, Clement; Pernot, Mathieu; Couade, Mathieu ...
IEEE transactions on ultrasonics, ferroelectrics and frequency control/IEEE transactions on ultrasonics, ferroelectrics, and frequency control,
02/2014, Letnik:
61, Številka:
2
Journal Article
Recenzirano
Odprti dostop
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.
Changes in cerebral blood flow are associated with stroke, aneurysms, vascular cognitive impairment, neurodegenerative diseases and other pathologies. Brain angiograms, typically performed via ...computed tomography or magnetic resonance imaging, are limited to millimetre-scale resolution and are insensitive to blood-flow dynamics. Here we show that ultrafast ultrasound localization microscopy of intravenously injected microbubbles enables transcranial imaging of deep vasculature in the adult human brain at microscopic resolution and the quantification of haemodynamic parameters. Adaptive speckle tracking to correct for micrometric brain-motion artefacts and ultrasonic-wave aberrations induced during transcranial propagation allowed us to map the vascular network of tangled arteries to functionally characterize blood-flow dynamics at a resolution of up to 25 μm and to detect blood vortices in a small deep-seated aneurysm in a patient. Ultrafast ultrasound localization microscopy may facilitate the understanding of brain haemodynamics and of how vascular abnormalities in the brain are related to neurological pathologies.
Ultrafast ultrasonic imaging is a rapidly developing field based on the unfocused transmission of plane or diverging ultrasound waves. This recent approach to ultrasound imaging leads to a large ...increase in raw ultrasound data available per acquisition. Bigger synchronous ultrasound imaging datasets can be exploited in order to strongly improve the discrimination between tissue and blood motion in the field of Doppler imaging. Here we propose a spatiotemporal singular value decomposition clutter rejection of ultrasonic data acquired at ultrafast frame rate. The singular value decomposition (SVD) takes benefits of the different features of tissue and blood motion in terms of spatiotemporal coherence and strongly outperforms conventional clutter rejection filters based on high pass temporal filtering. Whereas classical clutter filters operate on the temporal dimension only, SVD clutter filtering provides up to a four-dimensional approach (3D in space and 1D in time). We demonstrate the performance of SVD clutter filtering with a flow phantom study that showed an increased performance compared to other classical filters (better contrast to noise ratio with tissue motion between 1 and 10mm/s and axial blood flow as low as 2.6 mm/s). SVD clutter filtering revealed previously undetected blood flows such as microvascular networks or blood flows corrupted by significant tissue or probe motion artifacts. We report in vivo applications including small animal fUltrasound brain imaging (blood flow detection limit of 0.5 mm/s) and several clinical imaging cases, such as neonate brain imaging, liver or kidney Doppler imaging.
Objectives The goal of this study was to assess whether myocardial stiffness could be measured by shear wave imaging (SWI) and whether myocardial stiffness accurately quantified myocardial function. ...Background SWI is a novel ultrasound-based technique for quantitative, local, and noninvasive mapping of soft tissue elastic properties. Methods SWI was performed in Langendorff perfused isolated rat hearts (n = 6). Shear wave was generated and imaged in the left ventricular myocardium using a conventional ultrasonic probe connected to an ultrafast scanner (12,000 frames/s). The local myocardial stiffness was derived from shear wave velocity every 7.5 ms during 1 single cardiac cycle. Results The average myocardial stiffness was 8.6 ± 0.7 kPa in systole and 1.7 ± 0.8 kPa in diastole. Myocardial stiffness was compared with isovolumic systolic pressure at rest and during administration of isoproterenol (10−9 , 10−8 , and 10−7 mol/l, 5 min each). Systolic myocardial stiffness increased strongly up to 23.4 ± 3.4 kPa. Myocardial stiffness correlated strongly with isovolumic systolic pressure (r2 = 0.94; 0.98, p < 0.0001). Conclusions Myocardial stiffness can be measured in real time over the cardiac cycle using SWI, which allows quantification of stiffness variation between systole and diastole. Systolic myocardial stiffness provides a noninvasive index of myocardial contractility.
Functional neuroimaging modalities are crucial for understanding brain function, but their clinical use is challenging. Recently, the use of ultrasonic plane waves transmitted at ultrafast frame ...rates was shown to allow for the spatiotemporal identification of brain activation through neurovascular coupling in rodents. Using a customized flexible and noninvasive headmount, we demonstrate in human neonates that real-time functional ultrasound imaging (fUSI) is feasible by combining simultaneous continuous video-electroencephalography (EEG) recording and ultrafast Doppler (UfD) imaging of the brain microvasculature. fUSI detected very small cerebral blood volume variations in the brains of neonates that closely correlated with two different sleep states defined by EEG recordings. fUSI was also used to assess brain activity in two neonates with congenital abnormal cortical development enabling elucidation of the dynamics of neonatal seizures with high spatiotemporal resolution (200 μm for UfD and 1 ms for EEG). fUSI was then applied to track how waves of vascular changes were propagated during interictal periods and to determine the ictal foci of the seizures. Imaging the human brain with fUSI enables high-resolution identification of brain activation through neurovascular coupling and may provide new insights into seizure analysis and the monitoring of brain function.
Purpose:
Measured values of ultrasound attenuation in bone represent a combination of different loss mechanisms. As a wave is transmitted from a fluid into bone, reflections occur at the interface. ...In the bone, mode conversion occurs between longitudinal and shear modes and the mechanical wave is scattered by its complex internal microstructure. Finally, part of the wave energy is absorbed by the bone and converted into heat. Due to the complexity of the wave propagation and the difficulty in performing measurements that are capable of separating the various loss mechanisms, there are currently no estimates of the absorption in bone. The aim of this paper is, thus, to quantify the attenuation, scattering, and thermal absorption in bone.
Methods:
An attenuating model of wave propagation in bone is established and used to develop a three-dimensional finite difference time domain numerical algorithm. Hydrophone and optical heterodyne interferometer measurements of the acoustic field as well as a x-ray microtomography of the bone sample are used to drive the simulations and to measure the attenuation. The acoustic measurements are performed concurrently with an infrared camera that can measure the temperature elevation during insonication. A link between the temperature and the absorption via a three-dimensional thermal simulation is then used to quantify the absorption coefficients for longitudinal and shear waves in cortical bone.
Results:
We demonstrate that only a small part of the attenuation is due to absorption in bone and that the majority of the attenuation is due to reflection, scattering, and mode conversion. In the nine samples of a human used for the study, the absorption time constant for cortical bone was determined to be 1.04 μs ± 28%. This corresponds to a longitudinal absorption of 2.7 dB/cm and a shear absorption of 5.4 dB/cm. The experimentally measured attenuation across the approximately 8 mm thick samples was 13.3 ± 0.97 dB/cm.
Conclusions:
This first measurement of ultrasound absorption in bone can be used to estimate the amount of heat deposition based on knowledge of the acoustic field.
A new ultrasound-based technique is proposed to assess the arterial stiffness: the radiation force of an ultrasonic beam focused on the arterial wall induces a transient shear wave (∼10 ms) whose ...propagation is tracked by ultrafast imaging. The large and high-frequency content (100 to 1500 Hz) of the induced wave enables studying the wave dispersion, which is shown experimentally in vitro and numerically to be linked to arterial wall stiffness and geometry. The proposed method is applied in vivo. By repeating the acquisition up to 10 times per second (theoretical maximal frame rate is ∼100 Hz), it is possible to assess in vivo the arterial wall elasticity dynamics: shear modulus of a healthy volunteer carotid wall is shown to vary strongly during the cardiac cycle and measured to be 130 ± 15 kPa in systole and 80 ± 10 kPa in diastole.
Transthoracic shear-wave elastography (SWE) of the myocardium remains very challenging due to the poor quality of transthoracic ultrafast imaging and the presence of clutter noise, jitter, phase ...aberration, and ultrasound reverberation. Several approaches, such as diverging-wave coherent compounding or focused harmonic imaging, have been proposed to improve the imaging quality. In this study, we introduce ultrafast harmonic coherent compounding (UHCC), in which pulse-inverted diverging waves are emitted and coherently compounded, and show that such an approach can be used to enhance both SWE and high frame rate (FR) B-mode Imaging. UHCC SWE was first tested in phantoms containing an aberrating layer and was compared against pulse-inversion harmonic imaging and against ultrafast coherent compounding (UCC) imaging at the fundamental frequency. In vivo feasibility of the technique was then evaluated in six healthy volunteers by measuring myocardial stiffness during diastole in transthoracic imaging. We also demonstrated that improvements in imaging quality could be achieved using UHCC B-mode imaging in healthy volunteers. The quality of transthoracic images of the heart was found to be improved with the number of pulse-inverted diverging waves with a reduction of the imaging mean clutter level up to 13.8 dB when compared against UCC at the fundamental frequency. These results demonstrated that UHCC B-mode imaging is promising for imaging deep tissues exposed to aberration sources with a high FR.
Shear wave imaging was evaluated for the in vivo assessment of myocardial biomechanical properties on ten open chest sheep. The use of dedicated ultrasonic sequences implemented on a very high frame ...rate ultrasonic scanner (>; 5000 frames per second) enables the estimation of the quantitative shear modulus of myocardium several times during one cardiac cycle. A 128 element probe remotely generates a shear wave thanks to the radiation force induced by a focused ultrasonic burst. The resulting shear wave propagation is tracked using the same probe by cross-correlating successive ultrasonic images acquired at a very high frame rate. The shear wave speed estimated at each location in the ultrasonic image gives access to the local myocardial stiffness (shear modulus μ). The technique was found to be reproducible (standard deviation <; 3%) and able to estimate both systolic and diastolic stiffness on each sheep (respectively μ dias ≈ 2 kPa and μ syst ≈ 30 kPa). Moreover, the ability of the proposed method to polarize the shear wave generation and propagation along a chosen axis permits the study the local elastic anisotropy of myocardial muscle. As expected, myocardial elastic anisotropy is found to vary with muscle depth. The real time capabilities and potential of Shear Wave Imaging using ultrafast scanners for cardiac applications is finally illustrated by studying the dynamics of this fractional anisotropy during the cardiac cycle.
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