26 research outputs found
Non-invasive Evaluation of Aortic Stiffness Dependence with Aortic Blood Pressure and Internal Radius by Shear Wave Elastography and Ultrafast Imaging
Elastic properties of arteries have long been recognized as playing a major
role in the cardiovascular system. However, non-invasive in vivo assessment of
local arterial stiffness remains challenging and imprecise as current
techniques rely on indirect estimates such as wall deformation or pulse wave
velocity. Recently, Shear Wave Elastography (SWE) has been proposed to
non-invasively assess the intrinsic arterial stiffness. In this study, we
applied SWE in the abdominal aortas of rats while increasing blood pressure
(BP) to investigate the dependence of shear wave speed with invasive arterial
pressure and non-invasive arterial diameter measurements. A 15MHz linear array
connected to an ultrafast ultrasonic scanner, set non-invasively, on the
abdominal aorta of anesthetized rats (N=5) was used. The SWE acquisition
followed by an ultrafast (UF) acquisition was repeated at different moment of
the cardiac cycle to assess shear wave speed and arterial diameter variations
respectively. Invasive arterial BP catheter placed in the carotid, allowed the
accurate measurement of pressure responses to increasing does of phenylephrine
infused via a venous catheter. The SWE acquisition coupled to the UF
acquisition was repeated for different range of pressure. For normal range of
BP, the shear wave speed was found to follow the aortic BP variation during a
cardiac cycle. A minimum of (5.060.82) m/s during diastole and a maximum
of (5.970.90) m/s during systole was measured. After injection of
phenylephrine, a strong increase of shear wave speed (13.855.51) m/s was
observed for a peak systolic arterial pressure of (19010) mmHg. A
non-linear relationship between shear wave speed and arterial BP was found. A
complete non-invasive method was proposed to characterize the artery with shear
wave speed combined with arterial diameter variations. Finally, the results
were validated against two parameters the incremental elastic modulus and the
pressure elastic modulus derived from BP and arterial diameter variations
3D Quasi-Static Ultrasound Elastography With Plane Wave In Vivo
In biological tissue, an increase in elasticity is often a marker of
abnormalities. Techniques such as quasi-static ultrasound elastography have
been developed to assess the strain distribution in soft tissues in two
dimensions using a quasi-static compression. However, as abnormalities can
exhibit very heterogeneous shapes, a three dimensional approach would be
necessary to accurately measure their volume and remove operator dependency.
Acquisition of volumes at high rates is also critical to performing real-time
imaging with a simple freehand compression. In this study, we developed for the
first time a 3D quasi-static ultrasound elastography method with plane waves
that estimates axial strain distribution in vivo in entire volumes at high
volume rate. Acquisitions were performed with a 2D matrix array probe of 2.5MHz
frequency and 256 elements. Plane waves were emitted at a volume rate of 100
volumes/s during a continuous motorized and freehand compression. 3D B-mode
volumes and 3D cumulative axial strain volumes were successfully estimated in
inclusion phantoms and in ex vivo canine liver before and after a high
intensity focused ultrasound ablation. We also demonstrated the in vivo
feasibility of the method using freehand compression on the calf muscle of a
human volunteer and were able to retrieve 3D axial strain volume at a high
volume rate depicting the differences in stiffness of the two muscles which
compose the calf muscle. 3D ultrasound quasi-static elastography with plane
waves could become an important technique for the imaging of the elasticity in
human bodies in three dimensions using simple freehand scanning
Quantitative cardiac output assessment using 4D ultrafast Doppler imaging: an in vitro study
International audienceBackground, Motivation and Objective Echocardiography is routinely used in the clinic to evaluate the cardiac function. Anatomical indexes such as ventricular volume measurements or functional indexes such Cardiac Output are performed using standard echocardiography. However, 2D dimensional measurements induce inter-operator variability and standard 3D measurements do not have the sufficient volume rate to evaluate functional indexes. Moreover, the accuracy of flow velocity estimates is strongly reduced by the angular dependence of Doppler measurements. In this study, we propose to use 4D ultrafast Doppler to evaluate flow rates in a pipe to demonstrate the potentiality of performing Cardiac Output measurements without assumptions on the valve geometry and without angular dependence. Statement of Contribution/Methods An ultrasonic matrix array probe (central frequency 2.5MHz, 1024 elements, pitch 0.3 mm, bandwith 60%, Vermon, France) connected to a 1024 channels ultrasound scanner prototype was used to image the pipe output in three dimensions. 500 diverging waves (angular aperture 80°) were emitted at a volume rate of 2000 volumes/s during 250 ms. Color Doppler volumes (quantitative flow speed volumes) were computed by calculating the first moment of the Doppler spectrums in each voxel. The pipe flow rates (N=7) were calculated by integrating directly the flow speed over the cross section of the pipe. Results/Discussion The measured flow rates were found to be in a good agreement with the flowmeter values used as a gold standard (= 0.96). The four dimensional nature of the acquisition has the potential to enable the calculation of the Cardiac Output in vivo in patients without the need of making any assumption on the valve geometry or the direction of the ultrasonic beam usually responsible for errors
Imaging the dynamics of cardiac fiber orientation in vivo using 3D Ultrasound Backscatter Tensor Imaging
The assessment of myocardial fiber disarray is of major interest for the
study of the progression of myocardial disease. However, time-resolved imaging
of the myocardial structure remains unavailable in clinical practice. In this
study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel
ultrasound-based imaging technique that can map the myocardial fibers
orientation and its dynamics with a temporal resolution of 10 ms during a
single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is
based on ultrafast volumetric ultrasound acquisitions, which are used to
quantify the spatial coherence of backscattered echoes at each point of the
volume. The capability of 3D-BTI to map the fibers orientation was evaluated in
vitro in 5 myocardial samples. The helicoidal transmural variation of fiber
angles was in good agreement with the one obtained by histological analysis.
3D-BTI was then performed to map the fiber orientation dynamics in vivo in the
beating heart of an open-chest sheep at a volume rate of 90 volumes/s. Finally,
the clinical feasibility of 3D-BTI was shown on a healthy volunteer. These
initial results indicate that 3D-BTI could become a fully non-invasive
technique to assess myocardial disarray at the bedside of patients
Imaging the dynamics of cardiac fiber orientation in vivo using 3D Ultrasound Backscatter Tensor Imaging
ABSTRACT: The assessment of myocardial fiber disarray is of major interest for the study of the progression of myocardial disease. However, time-resolved imaging of the myocardial structure remains unavailable in clinical practice. In this study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel ultrasound-based imaging technique that can map the myocardial fibers orientation and its dynamics with a temporal resolution of 10 ms during a single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is based on ultrafast volumetric ultrasound acquisitions, which are used to quantify the spatial coherence of backscattered echoes at each point of the volume. The capability of 3D-BTI to map the fibers orientation was evaluated in vitro in 5 myocardial samples. The helicoidal transmural variation of fiber angles was in good agreement with the one obtained by histological analysis. 3D-BTI was then performed to map the fiber orientation dynamics in vivo in the beating heart of an open-chest sheep at a volume rate of 90 volumes/s. Finally, the clinical feasibility of 3D-BTI was shown on a healthy volunteer. These initial results indicate that 3D-BTI could become a fully non-invasive technique to assess myocardial disarray at the bedside of patients