Extraction 3D du réseau vasculaire cérébral chez le rat à partir d'images Doppler ultrasensible

International audienceL'imagerie Doppler ultrasensible est une nouvelle technique d'imagerie médicale permettant d'observer des flux sanguins très rapides et de détecter des formes vasculaires très fines. Elle réalise, par reconstruction tomographique, l'acquisition de véritables cartes vasculaires 3D du cerveau de rat, à haute résolution spatiale de l'ordre de 100 micrometer. Ces réseaux vasculaires contiennent une information de localisation cruciale pour pouvoir se repérer dans le cerveau et ainsi tirer profit des avantages pratiques de l'imagerie ultrasonore. Nous proposons dans cette étude une méthode numérique permettant l'extraction en 3D de chemins décrivant l'ensemble du réseau vasculaire cérébral du rat, et une estimation du diamètre apparent en chaque point. La méthode est basée sur l'algorithme du Fast Marching permettant l'extraction de chemins minimaux selon une métrique particulière

Ultrafast Doppler for neonatal brain imaging

The emergence of functional neuroimaging has dramatically accelerated our understanding of the human mind. The advent of functional Magnetic Resonance Imaging paved the way for the next decades' major discoveries in neuroscience and today remains the "gold standard" for deep brain imaging. Recent improvements in imaging technology have been somewhat limited to incremental innovations of mature techniques instead of breakthroughs. Recently, the use of ultrasonic plane waves transmitted at ultrafast frame rates was shown to highly increase Doppler ultrasound sensitivity to blood flows in small vessels in rodents. By identifying regions of brain activation through neurovascular coupling, Ultrafast Doppler was entering into the world of preclinical neuroimaging. The combination of many advantages, including high spatio-temporal resolution, deep penetration, high sensitivity and portability provided unique information about brain function. Recently, Ultrafast Doppler imaging was found able to non-invasively image the spatial and temporal dynamics of microvascular changes during seizures and interictal periods with an unprecedented resolution at bedside. This review summarizes the technical basis, the added value and the clinical perspectives provided by this new brain imaging modality that could create a breakthrough in the knowledge of brain hemodynamics, brain insult, and neuroprotection

Extraction 3D du réseau vasculaire cérébral chez le rat à partir d'images Doppler ultrasensible

International audienceL'imagerie Doppler ultrasensible est une nouvelle technique d'imagerie médicale permettant d'observer des flux sanguins très rapides et de détecter des formes vasculaires très fines. Elle réalise, par reconstruction tomographique, l'acquisition de véritables cartes vasculaires 3D du cerveau de rat, à haute résolution spatiale de l'ordre de 100 micrometer. Ces réseaux vasculaires contiennent une information de localisation cruciale pour pouvoir se repérer dans le cerveau et ainsi tirer profit des avantages pratiques de l'imagerie ultrasonore. Nous proposons dans cette étude une méthode numérique permettant l'extraction en 3D de chemins décrivant l'ensemble du réseau vasculaire cérébral du rat, et une estimation du diamètre apparent en chaque point. La méthode est basée sur l'algorithme du Fast Marching permettant l'extraction de chemins minimaux selon une métrique particulière

Adaptive Spatiotemporal SVD Clutter Filtering for Ultrafast Doppler Imaging Using Similarity of Spatial Singular Vectors

Singular value decomposition of ultrafast imaging ultrasonic data sets has recently been shown to build a vector basis far more adapted to the discrimination of tissue and blood flow than the classical Fourier basis, improving by large factor clutter filtering and blood flow estimation. However, the question of optimally estimating the boundary between the tissue subspace and the blood flow subspace remained unanswered. Here, we introduce an efficient estimator for automatic thresholding of subspaces and compare it to an exhaustive list of thirteen estimators that could achieve this task based on the main characteristics of the singular components, namely the singular values, the temporal singular vectors, and the spatial singular vectors. The performance of those fourteen estimators was tested in vitro in a large set of controlled experimental conditions with different tissue motion and flow speeds on a phantom. The estimator based on the degree of resemblance of spatial singular vectors outperformed all others. Apart from solving the thresholding problem, the additional benefit with this estimator was its denoising capabilities, strongly increasing the contrast to noise ratio and lowering the noise floor by at least 5 dB. This confirms that, contrary to conventional clutter filtering techniques that are almost exclusively based on temporal characteristics, efficient clutter filtering of ultrafast Doppler imaging cannot overlook space. Finally, this estimator was applied in vivo on various organs (human brain, kidney, carotid, and thyroid) and showed efficient clutter filtering and noise suppression, improving largely the dynamic range of the obtained ultrafast power Doppler images

3-D ultrafast doppler imaging applied to the noninvasive mapping of blood vessels in vivo

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 three-dimensional plane and diverging wave emissions, and demonstrated its clinical feasibility in human subjects in vivo. In this study, we show that non-invasive 3-D Ultrafast Power Doppler, Pulsed Doppler, and Color Doppler Imaging can be used to perform quantitative imaging of blood vessels in humans when using coherent compounding of three-dimensional tilted plane waves. A customized, programmable, 1024-channel ultrasound system was designed to perform 3-D Ultrafast Imaging. Using a 32X32, 3-MHz matrix phased array (Vermon, France), volumes were beamformed by coherently compounding successive tilted plane wave emissions. Doppler processing was then applied in a voxel-wise fashion. 3-D Ultrafast Power Doppler Imaging was first validated by imaging Tygon tubes of varying diameter and its 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

4D point cloud registration for tumor vascular networks monitoring from ultrasensitive Doppler images

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4D microvascular imaging based on ultrafast Doppler tomography

International audience4D ultrasound microvascular imaging was demonstrated by applying ultrafast Doppler tomography (UFD-T) to the imaging of brain hemodynamics in rodents. In vivo real-time imaging of the rat brain was performed using ultrasonic plane wave transmissions at very high frame rates (18,000 frames per second). Such ultrafast frame rates allow for highly sensitive and wide-field-of-view 2D Doppler imaging of blood vessels far beyond conventional ultrasonography. Voxel anisotropy (100 mu m x 100 mu m x 500 mu m) was corrected for by using a tomographic approach, which consisted of ultrafast acquisitions repeated for different imaging plane orientations over multiple cardiac cycles. UFT-D allows for 4D dynamic microvascular imaging of deep-seated vasculature (up to 20 mm) with a very high 4D resolution (respectively 100 mu m x 100 mu m x 100 mu m and 10 ms) and high sensitivity to flow in small vessels (>1 mm/s) for a whole-brain imaging technique without requiring any contrast agent. 4D ultrasound microvascular imaging in vivo could become a valuable tool for the study of brain hemodynamics, such as cerebral flow autoregulation or vascular remodeling after ischemic stroke recovery, and, more generally, tumor vasculature response to therapeutic treatment

Bedside functional monitoring of the dynamic brain connectivity in human neonates

Clinicians have long been interested in functional brain monitoring, as reversible functional losses often precedes observable irreversible structural insults. By characterizing neonatal functional cerebral networks, resting-state functional connectivity is envisioned to provide early markers of cognitive impairments. Here we present a pioneering bedside deep brain resting-state functional connectivity imaging at 250-μm resolution on human neonates using functional ultrasound. Signal correlations between cerebral regions unveil interhemispheric connectivity in very preterm newborns. Furthermore, fine-grain correlations between homologous pixels are consistent with white/grey matter organization. Finally, dynamic resting-state connectivity reveals a significant occurrence decrease of thalamo-cortical networks for very preterm neonates as compared to control term newborns. The same method also shows abnormal patterns in a congenital seizure disorder case compared with the control group. These results pave the way to infants' brain continuous monitoring and may enable the identification of abnormal brain development at the bedside

Functional ultrasound imaging of brain activity in human newborns

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

Spatiotemporal Clutter Filtering of Ultrafast Ultrasound Data Highly Increases Doppler and fUltrasound Sensitivity

International audienceUltrafast 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