Matthieu Toulemonde

Ultrasound Imaging with Microbubbles [Life Sciences]

Medical ultrasound (US) imaging, also known as echography, is one of the most frequently used front-line clinical imaging modalities and is characterized by its safety, affordability, accessibility, and real-time image display. Sound pulses, typically in the megahertz range, are sent into the body and the backscattered echoes are used to create a tomographic image. The contrast of an US image arises from local variations in the physical properties of the tissues, primarily density and elasticity, revealing tissue structures at depth.

Cardiac imaging with high frame rate contrast enhanced ultrasound: In-vivo demonstration

This work presents the first in-vivo High-frame rate Contrast Enhanced Ultrasound (HFR CEUS) for cardiac application. The in-vivo acquisition has been made on a sheep. A coherent compounding of diverging waves combined with Pulse Inversion (PI) transmission allow a frame rate of 250 frame per seconds which is 8 times faster than standard CEUS acquisition in cardiac application. The proposed method improves the image contrast compared to the CEUS and allows a better tracking of fast movement of the heart.

Cardiac flow mapping using high frame rate diverging wave contrast enhanced ultrasound and image tracking

Contrast echocardiography (CE) ultrasound with microbubble contrast agents have significantly advanced our capability in assessing cardiac function. However in conventional CE techniques with line by line scanning, the frame rate is limited to tens of frames per second, making it difficult to track the fast flow within cardiac chamber. Recent research in high frame-rate (HFR) ultrasound have shown significant improvement of the frame rate in non-contrast cardiac imaging. In this work we show the feasibility of microbubbles flow tracking in HFR CE acquisition in vivo with a high temporal resolution and low MI as well as the detection of vortex near the valves during filling phases agreeing with previous study.

Fully Automatic Myocardial Segmentation of Contrast Echocardiography Sequence Using Random Forests Guided by Shape Model

Myocardial contrast echocardiography (MCE) is an imaging technique that assesses left ventricle function and myocardial perfusion for the detection of coronary artery diseases. Automatic MCE perfusion quantification is challenging and requires accurate segmentation of the myocardium from noisy and time-varying images. Random forests (RF) have been successfully applied to many medical image segmentation tasks. However, the pixel-wise RF classifier ignores contextual relationships between label outputs of individual pixels. RF which only utilizes local appearance features is also susceptible to data suffering from large intensity variations. In this paper, we demonstrate how to overcome the above limitations of classic RF by presenting a fully automatic segmentation pipeline for myocardial segmentation in full-cycle 2-D MCE data. Specifically, a statistical shape model is used to provide shape prior information that guide the RF segmentation in two ways. First, a novel shape model (SM) feature is incorporated into the RF framework to generate a more accurate RF probability map. Second, the shape model is fitted to the RF probability map to refine and constrain the final segmentation to plausible myocardial shapes. We further improve the performance by introducing a bounding box detection algorithm as a preprocessing step in the segmentation pipeline. Our approach on 2-D image is further extended to 2-D+t sequences which ensures temporal consistency in the final sequence segmentations. When evaluated on clinical MCE data sets, our proposed method achieves notable improvement in segmentation accuracy and outperforms other state-of-the-art methods, including the classic RF and its variants, active shape model and image registration.

3D flow velocity reconstruction in a human radial artery from measured 2D high-frame-rate plane wave contrast enhanced ultrasound in two scanning directions — A feasibility study

Hemodynamics play an important role in the development of cardiovascular disease, with atherosclerosis and intimal hyperplasia arising at sites with low wall shear stress and disturbed endoluminal mixing. Computational fluid dynamics (CFD) can study blood rheology, however performance relies on precise 3D anatomy and accurate blood flow measurements to seed the initial and boundary conditions. Recently, ultrasound (US) 2D high frame-rate (HFR) acquisitions using plane-wave (PW) imaging combined with contrast agent tracking have been used for US image velocimetry (UIV) to measure blood flow profiles (Leow CH, UMB 2015). Here we investigate the experimental feasibility of combining multiple 2D UIV acquired in two nonparallel scanning directions along a human brachial artery for estimating the 3D blood flow velocity profile.

Exploring mild bubble disruption and high frame rate contrast enhanced ultrasound for specific imaging of lymphatic vessel

Contrast enhanced ultrasound imaging shows great potential for visualising lymphatic vessels and identifying sentinel lymph nodes. However current approaches still have artefacts reducing the lymphatic vessel contrast against background tissue [A. Sever, Clinical Radiology, 2012]. Pulse inversion (PI) detects nonlinear echoes from microbubbles but also from tissue due to nonlinear propagation of ultrasound [M.X. Tang, UMB, 2010]. Doppler acquisition has difficulties due to slow lymph flow rate. In this study, we propose mild bubble disruption imaging (MIDI) that utilises high frame-rate (HFR) plane wave transmission at modest MI to reduce nonlinear tissue artefact for lymphatic imaging with slow flow.

High frame rate contrast enhanced ultrasound imaging of lymphatic vessel phantom

Contrast enhanced ultrasound (CEUS) shows great potentials for visualising lymphatic vessels and identifying sentinel lymph nodes (SLN) which aid the diagnosis of breast cancer. However, current CEUS imaging techniques have some limitations: 1) Nonlinear tissue artefacts result in false bubble signals and reduce the image contrast; 2) Low spatial and temporal resolution limits the amount of information that can be captured by CEUS; 3) The slow lymph flow makes Doppler based approaches less effective. These limitations have prevented the accurate visualisation of lymphatic vessels and SLN. This work demonstrates the potential of high frame-rate (HFR) CEUS in detecting lymphatic vessels, and investigates the effects of flow velocity and ultrasound pressure on HFR CEUS imaging of lymph vessels in terms of image contrast and bubble signal persistence over time. It is shown that under slow flow, ultrasound amplitude has significant impacts on both image contrast and signal persistence.

Effects of motion on high frame rate contrast enhanced echocardiography and its correction

Contrast echocardiography (CE) ultrasound with microbubble contrast agents have significantly advanced our capability in assessing cardiac function, including myocardium perfusion imaging and quantification. However in conventional CE techniques with line by line scanning, the frame rate is limited to tens of frames per second and image quality is low. Recent research works in high frame-rate (HFR) ultrasound have shown significant improvement of the frame rate in non-contrast cardiac imaging. But with a higher frame rate, the coherent compounding of HFR CE images shows some artifacts due to the motion of the microbubbles. In this work we demonstrate the impact of this motion on compounded HFR CE in simulation and then apply a motion correction algorithm on in-vivo data acquired from the left ventricle (LV) chamber of a sheep. It shows that even if with the fast flow found inside the LV, the contrast is improved at least 100%.

High frame rate contrast enhanced echocardiography: Microbubbles stability and contrast evaluation

Contrast Echocardiography (CE) with microbubble contrast agents have significantly advanced our capability in assessing cardiac function, including myocardium perfusion imaging and quantification. However in conventional CE techniques with line by line scanning, the frame rate is limited to tens of frames per second and image quality is low. Recent works in high frame-rate (HFR) ultrasound have shown significant improvement of the frame rate. The aim of this work is to investigate the MBs stability and the contrast improvement using HFR CE compared to CE transmission at an echocardiography relevant frequency for different mechanical indices (MIs). Our results show that the contrast and bubble destruction of HFR CE and standard CEUS varies differently as a function of space and MIs. At low MIs, HFR CE shows a similar behavior as focused CE with little MB destruction, and generates better CTR (up to 3 folds). As MI increases, the MB destruction is more significant for HFR CE with a reduction of the CTR.

High Frame-Rate Contrast Echocardiography: In-Human Demonstration

Contrast Echocardiography (CE) using microbubble contrast agents enables sensitive imaging of chamber flow dynamics and myocardial perfusion [(1)][1]. However, the clinical value of CE is affected by the image qualityxa0achievable by the existing systems. Recent advances in ultrasound engineering, by