Experimental validation of a novel technique for ultrasound imaging of cardiac fiber orientation

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A sparse reconstruction framework for Fourier-based plane wave imaging

International audienceUltrafast imaging based on plane-wave (PW) insonification is an active area of research due to its capability of reaching high frame rates. Among PW imaging methods, Fourier-based approaches have demonstrated to be competitive compared with traditional delay and sum methods. Motivated by the success of compressed sensing techniques in other Fourier imaging modalities, like magnetic resonance imaging, we propose a new sparse regularization framework to reconstruct high-quality ultrasound (US) images. The framework takes advantage of both the ability to formulate the imaging inverse problem in the Fourier domain and the sparsity of US images in a sparsifying domain. We show, by means of simulations, in vitro and in vivo data, that the proposed framework significantly reduces image artifacts, i.e., measurement noise and sidelobes, compared with classical methods, leading to an increase of the image quality

Adaptive minimum variance coupled with sign and phase coherence factors in IQ domain for plane wave beamforming

International audienceIn the framework of PICMUS challenge, the objective comparison between steered plane waves beamforming is proposed on an external platform. Our beamforming proposal consists in a weighted minimum variance approach which combines a phase coherence factor calculation and a minimum variance beamforming. The computation is made in the IQ domain in order to reduce the calculation effort. An adaptive scheme is used to optimize the number of elements that are considered for the MV beamforming, which depends on the depth and the lateral position of the reconstructed pixel. Moreover, the coherence maps are filtered in order to avoid strong discontinuities and speckle penalty on the platform. The obtained results on the MIDAS platform demonstrates higher CNR and resolution compare to classical DAS approach. The main limitation of our weighted MV lies on the final axial resolution which is not improved and limits the overall performance of the method

Cortical implication in lower voluntary muscle force production in non-hypoxemic COPD patients.

Recent studies have shown that muscle alterations cannot totally explain peripheral muscle weakness in COPD. Cerebral abnormalities in COPD are well documented but have never been implicated in muscle torque production. The purpose of this study was to assess the neural correlates of quadriceps torque control in COPD patients. Fifteen patients (FEV1 54.1±3.6% predicted) and 15 age- and sex-matched healthy controls performed maximal (MVCs) and submaximal (SVCs) voluntary contractions at 10, 30 and 50% of the maximal voluntary torque of the knee extensors. Neural activity was quantified with changes in functional near-infrared spectroscopy oxyhemoglobin (fNIRS-HbO) over the contralateral primary motor (M1), primary somatosensory (S1), premotor (PMC) and prefrontal (PFC) cortical areas. In parallel to the lower muscle torque, the COPD patients showed lower increase in HbO than healthy controls over the M1 (p<0.05), PMC (p<0.05) and PFC areas (p<0.01) during MVCs. In addition, they exhibited lower HbO changes over the M1 (p<0.01), S1 (p<0.05) and PMC (p<0.01) areas during SVCs at 50% of maximal torque and altered motor control characterized by higher torque fluctuations around the target. The results show that low muscle force production is found in a context of reduced motor cortex activity, which is consistent with central nervous system involvement in COPD muscle weakness

Optimization of resolution enhancement compression technique with plane wave imaging

International audienceHigh frame rate imaging became a world-wide use modality. It achieves by coherently coalescing the received radio frequency signal, as low-resolution image, after emitting plane waves. One common way to increase the image quality is to combine multiple low-resolution images, from different insonification angles, into a high-resolution image. However, this compounding technique significantly decrease the frame rate by a factor equal to the number of insonification. In this study, we proposed to increase the image quality in terms of resolution and contrast by using only one plane wave combine with a resolution enhancement compression technique. In comparison with conventional plane wave imaging, the results show a clear improvement of the axial resolution (31%), signal to noise ratio (13%) and contrast to noise ratio (101%). Moreover, an optimization, based on an experimental received signal from one scatterer as a deconvolution signal, is presented. This innovation allows increasing the contrast-to-noise ratio and signal-to-noise ratio of 159% and 29%, respectively in comparison with conventional plane wave imaging

Cortical motor output decreases after neuromuscular fatigue induced by electrical stimulation of the plantar flexor muscles.

Neuromuscular electrical stimulation (NMES) causes early onset of neuromuscular fatigue. Peripheral electrophysiological explorations suggest that supra-spinal alterations are involved through sensitive afferent pathways. As sensory input is projected over the primary somatosensory cortex (S1), S1 area involvement in inhibiting the central motor drive can be hypothesized. This study assessed cortical activity under a fatiguing NMES protocol at low frequency. Twenty healthy males performed five NMES sequences of 17 trains over the plantar flexors (30 Hz, 4 s on/6 s off). Before and after each sequence, neuromuscular tests composed of maximal voluntary contractions (MVCs) were carried out. Cortical activity was assessed during MVCs with functional near-infrared spectroscopy over S1 and primary motor (M1) areas, through oxy- [HbO] and deoxy-haemoglobin [HbR] variation. Electrophysiological data (H-reflex during MVC, EMG activity and level of voluntary activation) were also recorded. MVC torque significantly decreased after the first 17 NMES trains (P < 0.001). The electrophysiological data were consistent with supra-spinal alterations. In addition, [HbO] declined significantly during the protocol over the S1 and M1 areas from the first 17 NMES trains (P < 0.01 and P < 0.001 respectively), while [HbR] increased (P < 0.05 and P < 0.01 respectively), indicating early decline in cortical activity over both primary cortical areas. The declining cortical activity over the M1 area is highly consistent with the electrophysiological findings and supports motor cortex involvement in the loss of force after a fatiguing NMES protocol. In addition, the declining cortical activity over the S1 area indicates that the decreased motor output from M1 is not due to increased S1 inhibitory activity

Fast Nonlinear Ultrasound Propagation Simulation Using a Slowly Varying Envelope Approximation

International audienceMedical systems usually consider linear propagation of ultrasound, an approximation of reality. However, numerous studies have attempted to accurately simulate the nonlinear pressure wave distortion and to evaluate the contribution of harmonic frequencies. In such simulations, the computation time is very large, except for the method based on the angular spectrum scheme where the derivative order is reduced using the Fourier transform. However, the harmonic computation is usually limited to the second harmonic because of quasi-linear approximation. In this paper, a slowly varying envelope approximation (SVEA) is used in the Fourier domain to compute the entire nonlinear distortion induced, including high harmonics and nonlinear mixing frequencies. The simulation by SVEA is evaluated by comparison with other simulation tools. The obtained deviation and difference remain low enough to fully validate such an approximation. Moreover, the simulator is implemented on a GPU to obtain a very fast tool, where the full nonlinear distorted 3-D + t field is computed in less than 10 s

SPECTROSCOPIE OPTIQUE ET IMAGERIE PHOTOACOUSTIQUE : ETUDE COMPARATIVE

International audienceL’imagerie photoacoustique (PA) repose sur l’illumination d’une zone d’intérêt par des impulsions laser qui permettent une expansion thermoélastique des tissus. De celle-ci résulte la création d’ondes ultrasonores spécifiques à chaque milieu en fonction de l’absorption optique. Ces ondes sont détectées à la surface par une sonde échographique et permettent la reconstruction d’images PA de la zone d’intérêt. L’absorption optique est fonction de la longueur d’onde, la réponse PA l’est donc également. L’acquisition d’images PA à différentes longueurs d’ondes permet la caractérisation de tissus par leurs réponses multispectrales PA [1]. Cette étude vise à comparer la réponse multispectrale PA, mesurée expérimentalement, et l’absorption optique mesurée par spectroscopie pour le développement de fantômes multi-modaux complexes et la validation de méthodes de classifications multispectrales. Les milieux imagés sont des fantômes en agar colorés par six encres