arXiv subjects

Justine Robin

Publications and source records attributed to Justine Robin.

6 recordsLinked to original sources

arXiv2023

Three-Dimensional Ultrasound Matrix Imaging

Matrix imaging paves the way towards a next revolution in wave physics. Based on the response matrix recorded between a set of sensors, it enables an optimized compensation of aberration phenomena and multiple scattering events that usually drastically hinder the focusing process in heterogeneous media. Although it gave rise to spectacular results in optical microscopy or seismic imaging, the success of matrix imaging has been so far relatively limited with ultrasonic waves because wave control is generally only performed with a linear array of transducers. In this paper, we extend ultrasound matrix imaging to a 3D geometry. Switching from a 1D to a 2D probe enables a much sharper estimation of the transmission matrix that links each transducer and each medium voxel. Here, we first present an experimental proof of concept on a tissue-mimicking phantom through ex-vivo tissues and then, show the potential of 3D matrix imaging for transcranial applications.

eess.IV↗

arXiv2022

In vivo Adaptive Focusing for Clinical Contrast-Enhanced Transcranial Ultrasound Imaging in Human

Imaging the human brain vasculature with high spatial and temporal resolution remains challenging in the clinic today. Transcranial ultrasound is scarcely used for cerebrovascular imaging, due to low sensitivity and strong phase aberrations induced by the skull bone that only enable major brain vessel imaging, even with ultrasound contrast agent injection (microbubbles). Here, we propose an adaptive aberration correction technique for skull bone aberrations based on the backscattered signals coming from intravenously injected microbubbles. Our aberration correction technique was implemented to image brain vasculature in adult humans through temporal and occipital bone windows. For each patient, an effective speed of sound, as well as a phase aberration profile, were determined in several isoplanatic patches spread across the image. This information was then used in the beamforming process. It improved image quality both for ultrafast Doppler imaging and Ultrasound Localization Microscopy (ULM), especially in cases of thick bone windows. For ultrafast Doppler images, the contrast was increased by 4dB on average, and for ULM, the number of detected microbubble tracks was increased by 38%. This technique is thus promising for better diagnosis and follow-up of brain pathologies such as aneurysms or stroke and could make transcranial ultrasound imaging possible even in particularly difficult-to-image patients.

physics.med-ph↗

arXiv2021

Ultrasound Matrix Imaging-Part II: The distortion matrix for aberration correction over multiple isoplanatic patches

This is the second article in a series of two which report on a matrix approach for ultrasound imaging in heterogeneous media. This article describes the quantification and correction of aberration, i.e. the distortion of an image caused by spatial variations in the medium speed-of-sound. Adaptive focusing can compensate for aberration, but is only effective over a restricted area called the isoplanatic patch. Here, we use an experimentally-recorded matrix of reflected acoustic signals tosynthesize a set of virtual transducers. We then examine wave propagation between these virtual transducers and an arbitrary correction plane. Such wave-fronts consist of two components: (i) An ideal geometric wave-front linked to diffraction and the input focusing point, and; (ii) Phase distortions induced by the speed-of-sound variations. These distortions are stored in a so-called distortion matrix, the singular value decomposition of which gives access to an optimized focusing law at any point. We show that, by decoupling the aberrations undergone by the outgoing and incoming waves and applying an iterative strategy, compensation for even high-order and spatially-distributed aberrations can be achieved. After a numerical validation of the process, ultrasound matrix imaging (UMI) is applied to the in-vivo imaging of a gallbladder. A map of isoplanatic modes is retrieved and is shown to be strongly correlated with the arrangement of tissues constituting the medium. The corresponding focusing laws yield an ultrasound image with drastically improved contrast and transverse resolution. UMI thus provides a flexible and powerful route towards computational ultrasound.

eess.IV↗

arXiv2021

Ultrasound Matrix Imaging-Part I: The focused reflection matrix, the F-factor and the role of multiple scattering

This is the first article in a series of two dealing with a matrix approach for aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a confocal ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A fitting process enables the quantification of the single scattering, multiple scattering and noise components in the image. From the single scattering contribution, a focusing criterion is defined, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the state-of-the-art coherence factor, this new indicator is robust to multiple scattering and electronic noise, thereby providing a contrasted map of the focusing quality at a much better transverse resolution. After a validation of the proof-of-concept based on time-domain simulations, UMI is applied to the in-vivo study of a human calf. Beyond this specific example, UMI opens a new route for speed-of-sound and scattering quantification in ultrasound imaging.

physics.app-ph↗

arXiv2021

Dual-Mode Volumetric Optoacoustic and Contrast Enhanced Ultrasound Imaging with Spherical Matrix Arrays

Spherical matrix arrays arguably represent an advantageous tomographic detection geometry for non-invasive deep tissue mapping of vascular networks and oxygenation with volumetric optoacoustic tomography (VOT). Hybridization of VOT with ultrasound (US) imaging remains difficult with this configuration due to the relatively large inter-element pitch of spherical arrays. We suggest a new approach for combining VOT and US contrast-enhanced imaging employing injection of clinically-approved microbubbles. Power Doppler (PD) and US localization imaging were enabled with a sparse US acquisition sequence and model-based inversion based on infimal convolution of total variation (ICTV) regularization. Experiments in tissue-mimicking phantoms and in vivo in mice demonstrate the powerful capabilities of the new dual-mode imaging system for blood velocity mapping and anatomical imaging with enhanced resolution and contrast.

physics.med-ph↗

arXiv2020

Noninvasive three-dimensional optoacoustic localization microangiography of deep tissues

Structural microvascular alterations and dysfunction serve as key disease indicators of cancer, diabetes, ischemic stroke, neurodegenerative disorders and many other conditions. In vivo visualization of the microvasculature has traditionally been restricted to millimeter scale depths accessible with optical microscopy. Optoacoustic imaging has enabled breaking through the barrier imposed by light diffusion to map functional hemodynamic parameters in deep-seated vessels, but diffraction and dispersion of ultrasound waves in heterogeneous living tissues prevents reaching capillary resolution. Herein, we demonstrate three-dimensional microangiography of deep mouse brain beyond the acoustic diffraction limit (<20$\mu$m resolution) through the intact scalp and skull via optoacoustic localization of sparsely-distributed highly absorbing microparticles. This was enabled by devising 5$\mu$m sized extremely absorbing dichloromethane microdroplets exhibiting four orders of magnitude higher optical absorption than red blood cells at near-infrared wavelengths, thus facilitating in vivo compatibility and single particle sensitivity in the presence of highly absorbing blood background. Accurate mapping of the blood flow velocity within microvascular structures was also facilitated by the high 3D frame rate of the optoacoustic tomography system. We further show that the detected optoacoustic signal intensities from the localized particles may serve for estimating the light fluence distribution within optically heterogeneous tissues, a long-standing quantification challenge in biomedical optics. Given the intrinsic sensitivity of optoacoustics to various functional, metabolic and molecular events in living tissues, this new approach paves the way for non-invasive deep-tissue microscopic observations with unrivaled resolution, contrast and speed.

physics.bio-ph↗