192 results found
Christensen-Jeffries K, Brown J, Harput S, et al., 2019, Poisson statistical model of ultrasound super-resolution imaging acquisition time, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 66, Pages: 1246-1254, ISSN: 0885-3010
A number of acoustic super-resolution techniques have recently been developed to visualize microvascular structure and flow beyond the diffraction limit. A crucial aspect of all ultrasound (US) super-resolution (SR) methods using single microbubble localization is time-efficient detection of individual bubble signals. Due to the need for bubbles to circulate through the vasculature during acquisition, slow flows associated with the microcirculation limit the minimum acquisition time needed to obtain adequate spatial information. Here, a model is developed to investigate the combined effects of imaging parameters, bubble signal density, and vascular flow on SR image acquisition time. We find that the estimated minimum time needed for SR increases for slower blood velocities and greater resolution improvement. To improve SR from a resolution of λ/10 to λ/20 while imaging the microvasculature structure modeled here, the estimated minimum acquisition time increases by a factor of 14. The maximum useful imaging frame rate to provide new spatial information in each image is set by the bubble velocity at low blood flows (<;150 mm/s for a depth of 5 cm) and by the acoustic wave velocity at higher bubble velocities. Furthermore, the image acquisition procedure, transmit frequency, localization precision, and desired super-resolved image contrast together determine the optimal acquisition time achievable for fixed flow velocity. Exploring the effects of both system parameters and details of the target vasculature can allow a better choice of acquisition settings and provide improved understanding of the completeness of SR information.
Zhou X, Zhou X, Leow CH, et al., Measurement of flow volume in the presence of reverse flow with ultrasound speckle decorrelation, Ultrasound in Medicine and Biology, ISSN: 0301-5629
Direct measurement of volumetric flow rate in the cardiovascular system withultrasound is valuable but has been a challenge because most current 2D flow imagingtechniques are only able to estimate the flow velocity in the scanning plane (in-plane). Ourrecent study demonstrated that high frame rate contrast ultrasound and speckle decorrelation(SDC) can be used to accurately measure the speed of flow going through the scanning plane(through-plane). The volumetric flow could then be calculated by integrating over the luminalarea, when the blood vessel wasscanned from the transverse view. However, a key disadvantageof this SDC method is that it cannot distinguish the direction of the through-plane flow, whichlimited its applications to blood vessels with unidirectional flow. Physiological flow in thecardiovascular system could be bidirectional due to its pulsatility, geometric features or underpathological situations. In this study, we proposed a method to distinguish the through-planeflow direction by inspecting the flow within the scanning plane from a tilted transverse view.This method was tested on computer simulations and experimental flow phantoms. It was foundthat the proposed method could detect flow direction and improved the estimation of the flowvolume, reducing the overestimation from over 100% to under 15% when there was flowreversal. This method showed significant improvement over the current SDC method in volumeflow estimation and can be applied to a wider range of clinical applications where bidirectionalflow exists.
Ahmadzadeh SMH, Chen X, Hagemann H, et al., 2019, Developing and using fast shear wave elastography to quantify physiologically-relevant tendon forces., Med Eng Phys, Vol: 69, Pages: 116-122
Direct quantification of physiologically-relevant tendon forces can be used in a wide range of clinical applications. However, tendon forces have usually been estimated either indirectly by computational models or invasively using force transducers, and direct non-invasive measurement of forces remains a big challenge. The aim of this study was to investigate the feasibility of using Shear Wave Elastography (SWE) for quantifying human tendon forces at physiological levels. An experimental protocol was developed to measure Shear Wave Speed (SWS) and tensile force in a human patellar tendon using SWE and conventional tensile testing to quantify the correlation between SWS and load. The SWE system was customised to allow imaging of fast shear waves expected in human tendons under physiological loading which is outside the normal range of the existing SWE systems. SWS increased from 10.8 m/s to 36.1 m/s with the increasing tensile load from 8 N to 935 N and a strong linear correlation between SWS and load (r = 0.99, p < 0.01) was observed. The findings in this study suggest that SWE can be used as a potential non-invasive method for direct quantification of physiologically-relevant tendon forces, as well as for validating the estimated forces from other methods such as computational models.
Zhou X, Peter V, Xiaowei Z, et al., Optimization of 3D Divergence Free Flow Field Reconstruction Using 2D Ultrasound Vector Flow Imaging, Ultrasound in Medicine and Biology, ISSN: 0301-5629
Abstract- 3D blood Vector Flow Imaging (VFI) is of great value for understanding and detecting cardiovascular diseases. Currently 3D Ultrasound (US) VFI requires 2D matrix probes which are expensive and suffer from sub-optimal image quality. Our recent study proposed an interpolation algorithm to obtain a divergence free reconstruction of the 3D flow field from 2D velocities obtained by High Frame Rate US Particle Imaging Velocimetry (HFR echo-PIV, also known as HFR UIV), using a 1D array transducer. This work aims to significantly improve the accuracy and reduce the time-to-solution of our previous approach thereby paving the way for clinical translation. More specifically, accuracy was improved by optimising the divergence free basis to reduce Runge-phenomena near domain boundaries, and time-to-solution was reduced by demonstrating that under certain conditions the resulting system could be solved using widely available and highly optimized Generalized Minimum Residual (GMRES) algorithms. To initially demonstrate the utility of the approach, coarse 2D sub-samplings of an analytical unsteady Womersely flow solution and a steady helical flow solution obtained using Computational Fluid Dynamics (CFD) were used to successfully reconstruct full flow solutions, with 0.82% and 4.8% average relative errors in the velocity field respectively. Subsequently, multi-plane 2D velocity fields were obtained through HFR UIV for a straight tube phantom and a carotid bifurcation phantom, from which full 3D flow fields were reconstructed. These were then compared with flow fields obtained via CFD in each of the two configurations, and average relative errors of 6.01% and 12.8% in the velocity field were obtained. These results reflect 15%-75% improvements in accuracy and 53~874 fold acceleration of reconstruction speeds for the four cases, when compared with the previous divergence free flow reconstruction method. In conclusion the proposed method provides an effective and fast metho
Zhu J, Lin S, Leow CH, et al., High frame rate contrast enhanced ultrasound imaging for slow flow: influence of ultrasound pressure and flow rate on bubble disruption and image persistence, Ultrasound in Medicine and Biology, ISSN: 0301-5629
Contrast enhanced ultrasound (CEUS) utilising microbubbles shows great potential for visualising lymphatic vessels and identifying sentinel lymph nodes (SLN) which is valuable for axillary staging in breast cancer patients. However, current CEUS imaging techniques have limitations that affect the accurate visualisation and tracking of lymphatic vessels and SLN. (1) Tissue artefacts and bubble disruption can reduce the image contrast. (2) Limited spatial and temporal resolution diminishes the amount of information that can be captured by CEUS. (3) The slow lymph flow makes Doppler based approaches less effective. This work evaluates on a lymphatic vessel phantom the use of high frame-rate (HFR) CEUS for the detection of lymphatic vessels where flow is slow. Specifically the work particularly investigates the impact of key factors in lymphatic imaging, including ultrasound pressure and flow velocity as well as probe motion during vessel tracking, on bubble disruption and image contrast. A trail was also conducted to apply HFR CEUS imaging on vasculature in a rabbit popliteal lymph node (LN). Our results show that (1) HFR imaging and SVD filtering can significantly reduce tissue artefacts in the phantom; (2) the slow flow rate within the phantom makes image contrast and signal persistence more susceptible to changes in ultrasound amplitude/MI, and an MI value can be chosen to reach a compromise between images contrast and bubble disruption under slow flow condition; (3) probe motion significantly decreases image contrast of the vessel, which can be improved by applying motion correction prior to SVD filtering; (4) the optical observation of the impact of ultrasound pressure in HFR CEUS further confirm the importance of optimising ultrasound amplitude MI; (5) Vessels inside rabbit LN with blood flow less than 3 mm/s are clearly visualised.
Zhang G, Lin S, Leow CH, et al., 2019, Quantification of vaporized targeted nanodroplets using high-frame-rate ultrasound and optics, Ultrasound in Medicine and Biology, Vol: 45, Pages: 1131-1142, ISSN: 0301-5629
Owing to their ability to efficiently deliver biological cargo and sense the intracellular milieu, vertical arrays of high aspect ratio nanostructures, known as nanoneedles,are being developed as minimally invasive tools for cell manipulation. However, little is known of the mechanisms of cargo transfer across the cell membrane-nanoneedle interface. Particularly,the contributions of membrane piercing, modulation of membrane permeability and endocytosis to cargo transfer remain largelyunexplored. Here, combining state-of-the-art electron and scanning ion conductance microscopy with molecular biology techniques, we show that porous silicon nanoneedle arrays concurrently stimulate independent endocytic pathways which contribute to enhanced biomolecule delivery into human mesenchymal stem cells. Electron microscopy of the cell membrane at nanoneedle sites shows an intact lipid bilayer, accompanied by an accumulation of clathrin-coated pits and caveolae. Nanoneedles enhance the internalisation of biomolecular markers of endocytosis, highlighting the concurrent activation of caveolae-and clathrin-mediated endocytosis, alongside macropinocytosis. These events contribute to the nanoneedle-mediated delivery (nanoinjection) of nucleic acids into human stem cells, which distribute across the cytosol and the endolysosomal system. This data extends the understanding of how nanoneedles modulate biological processes to mediate interaction with the intracellular space, providing indications for the rational design of improved cell-manipulation technologies.
Brown J, Christensen-Jeffries K, Harput S, et al., 2019, Investigation of microbubble detection methods for super-resolution imaging of microvasculature, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 66, Pages: 676-691, ISSN: 0885-3010
Ultrasound super-resolution techniques use the response of microbubble contrast agents (MBs) to visualize the microvasculature. Techniques that localize isolated bubble signals first require detection algorithms to separate the MB and tissue responses. This work explores the three main MB detection techniques for super-resolution of microvasculature. Pulse inversion (PI), differential imaging (DI) and singular value decomposition (SVD) filtering were compared in terms of the localization accuracy, precision and contrast to tissue ratio (CTR). MB responses were simulated based on the properties of Sonovue™ and using the Marmottant model. Non-linear propagation through tissue was modelled using the k-Wave software package. For the parameters studied, the results show that PI is most appropriate for low frequency applications, but also most dependent on transducer bandwidth. SVD is preferable for high frequency acquisition where localization precision on the order of a few microns is possible. PI is largely independent of flow direction and speed compared to SVD and DI, so is appropriate for visualizing the slowest flows and tortuous vasculature. SVD is unsuitable for stationary MBs and can introduce a localization error on the order of hundreds of microns over the speed range 0- 2 mm/s and flow directions from lateral (parallel to probe) to axial (perpendicular to probe). DI is only suitable for flow rates > 0.5 mm/s or as flow becomes more axial. Overall, this study develops a MB and tissue non-linear simulation platform to improve understanding of how different MB detection techniques can impact the super-resolution process and explores some of the factors influencing the suitability of each.
Zhang G, Harput S, Hu H, et al., 2019, Fast acoustic wave sparsely activated localization microscopy (fast-AWSALM): ultrasound super-resolution using plane-wave activation of nanodroplets, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN: 0885-3010
Localization-based ultrasound super-resolution imaging using microbubble contrast agents and phase-change nano-droplets has been developed to visualize microvascular structures beyond the diffraction limit. However, the long data acquisition time makes the clinical translation more challenging. In this study, fast acoustic wave sparsely activated localization microscopy (fast-AWSALM) was developed to achieve super-resolved frames with sub-second temporal resolution, by using low-boiling-point octafluoropropane nanodroplets and high frame rate plane waves for activation, destruction, as well as imaging. Fast-AWSALM was demonstrated on an in vitro microvascular phantom to super-resolve structures that could not be resolved by conventional B-mode imaging. The effects of the temperature and mechanical index on fast-AWSALM was investigated. Experimental results show that sub-wavelength micro-structures as small as 190 lm were resolvable in 200 ms with plane-wave transmission at a center frequency of 3.5 MHz and a pulse repetition frequency of 5000 Hz. This is about a 3.5 fold reduction in point spread function full-width-half-maximum compared to that measured in conventional B-mode, and two orders of magnitude faster than the recently reported AWSALM under a non-flow/very slow flow situations and other localization based methods. Just as in AWSALM, fast-AWSALM does not require flow, as is required by current microbubble based ultrasound super resolution techniques. In conclusion, this study shows the promise of fast-AWSALM, a super-resolution ultrasound technique using nanodroplets, which can generate super-resolution images in milli-seconds and does not require flow.
Cox K, Tang M-X, Zhu J, 2019, Diagnosing and Managing the Malignant Axilla in Breast Cancer, CURRENT BREAST CANCER REPORTS, Vol: 11, Pages: 1-8, ISSN: 1943-4588
Zhou X, Papadopoulou V, Leow CH, et al., 2019, 3-D flow reconstruction using divergence-free interpolation of multiple 2-D contrast-enhanced ultrasound particle imaging velocimetry measurements, Ultrasound in Medicine and Biology, Vol: 45, Pages: 795-810, ISSN: 0301-5629
Quantification of 3-D intravascular flow is valuable for studying arterial wall diseases but currently there is a lack of effective clinical tools for this purpose. Divergence-free interpolation (DFI) using radial basis function (RBF) is an emerging approach for full-field flow reconstruction using experimental sparse flow field samples. Previous DFI reconstructs full-field flow from scattered 3-D velocity input obtained using phase-contrast magnetic resonance imaging with low temporal resolution. In this study, a new DFI algorithm is proposed to reconstruct full-field flow from scattered 2-D in-plane velocity vectors obtained using ultrafast contrast-enhanced ultrasound (>1000 fps) and particle imaging velocimetry. The full 3-D flow field is represented by a sum of weighted divergence-free RBFs in space. Because the acquired velocity vectors are only in 2-D and hence the problem is ill-conditioned, a regularized solution of the RBF weighting is achieved through singular value decomposition (SVD) and the L-curve method. The effectiveness of the algorithm is determined via numerical experiments for Poiseuille flow and helical flow with added noise, and it is found that an accuracy as high as 95.6% can be achieved for Poiseuille flow (with 5% input noise). Experimental feasibility is also determined by reconstructing full-field 3-D flow from experimental 2-D ultrasound image velocimetry measurements in a carotid bifurcation phantom. The method is typically faster for a range of problems compared with computational fluid dynamics, and has been found to be effective for the three flow cases.
Leow CH, Bush N, Stanziola A, et al., 3D microvascular imaging using high frame rate ultrasound and ASAP without contrast agents: development and initial in vivo evaluation on non-tumour and tumour models, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN: 0885-3010
Three-dimensional imaging is valuable to non-invasively assess angiogenesis given the complex 3D architecture of vascular networks. The emergence of high frame rate (HFR) ultrasound, which can produce thousands of images per second, has inspired novel signal processing techniques and their applications in structural and functionalimaging of blood vessels. Although highly sensitive vascular mapping has been demonstrated using ultrafast Doppler, the detectability of microvasculature from the background noise may be hindered by the low signal to noise ratio (SNR) particularly in deeper region and without the use of contrast agents. We have recently demonstrated a coherence based technique, acoustic sub-aperture imaging (ASAP), for super-contrast vascular imaging and illustrated the contrast improvement using HFR contrast-enhanced ultrasound. In this work, we provide a feasibility study for microvascular imaging using ASAP without contrast agents, and extend its capability from 2D to volumetric vascular mapping. Using an ultrasound research system and a pre-clinical probe, we demonstrated the improved visibility of microvascular mapping using ASAP in comparison to ultrafast Power Doppler (PD) on a mouse kidney, liver and tumour without contrast agent injection. The SNR of ASAP images improves in average by 10dB when compared to PD. Besides, directional velocity mappings were also demonstrated by combining ASAP with the phase information extracted from lag-1 autocorrelation. Three-dimensional vascular and velocity mapping of the mouse kidney, liver and tumour were demonstrated by stackingthe ASAP images acquired using 2D ultrasound imaging and a trigger-controlled linear translation stage. The 3D results depicted clear micro-vasculature morphologies and function
Zhu J, Rowland E, Harput S, et al., 3D super-resolution ultrasound imaging of rabbit lymph node vasculature in vivo using microbubbles, Radiology, ISSN: 0033-8419
Background: Variations in lymph node (LN) microcirculation can be indicative of metastasis. Identifying and quantifying metastatic LNs remains essential for prognosis and treatment planning but a reliable non-invasive imaging technique is lacking. 3D super-resolution (SR) ultrasound has shown potential to noninvasively visualize microvascular networks in vivo.Purpose: To study the feasibility of 3D SR ultrasound imaging of rabbit lymph node (LN) microvascular structure and blood flow using microbubbles.Materials and Methods: In vivo studies were carried out to image popliteal LNs of two healthy male New Zealand White rabbits aged 6-8 weeks. 3D high frame rate contrast enhanced ultrasound was achieved by mechanically scanning a linear imaging probe. Individual microbubbles were identified, localized, and tracked to form 3D SR images and super-resolved velocity maps. Acoustic sub-aperture processing (ASAP)was used to improve image contrast and generateenhanced power Doppler (PD) and color Doppler (CD) images. Vessel size and blood flow velocity distributions were evaluated and assessed by Student’s paired t-test. Results:SR images revealed micro-vessels in the rabbitLN, with branches clearly resolved when separated by 30 μm, which is less than half of the acoustic wavelength and not resolvable by power or color Doppler. The apparent size distribution of most vessels in the SR images was below 80 μm and agrees with micro-CT data whereas most of those detected by Doppler techniques were larger than 80 μm. The blood flow velocity distribution indicated that most of the blood flow in the rabbit popliteal LN was at velocities lower than 5mm/s. Conclusion: 3D super-resolution ultrasound imaging using microbubbles allows non-invasive and non-ionizing visualization and quantification of rabbit lymph node microvascular structures and blood flow dynamics with resolution below the wave diffraction limit.
Leow CH, Braga M, Bush NL, et al., 2019, Contrast vs non-contrast enhanced microvascular imaging using acoustic sub-aperture processing (ASAP): in vivo demonstration, IEEE International Ultrasonics Symposium, IUS. 2018, Publisher: IEEE, ISSN: 1948-5719
Angiogenesis plays a vital role in the progression of cancer. Non-invasive imaging techniques capable of assessing the microenvironment are therefore of clinical interest. Although highly sensitive vascular mapping has been demonstrated using ultrafast Power Doppler (PD), the detectability of microvasculature from the background noise may be hindered by the low signal-to-noise ratio (SNR) in deeper region and without the use of contrast agents. We recently developed acoustic sub-aperture processing (ASAP) processing for super-contrast vasculature imaging. This technique relies on the spatial coherence of the backscattered echoes over different acquisitions to substantially reduce the noise floor compared to the power Doppler (PD) technique. In this study, we demonstrate the feasibility of applying ASAP processing for non-contrast enhanced microvascular imaging in preclinical condition, and compare it with contrast enhanced ASAP as well as ultrafast PD. Comparing to PD, ASAP exhibit SNR improvement up to 12 dB. Higher SNR and extra visibility of smaller vessel are also demonstrated in contrast enhanced images in comparison to the non-contrast images. In conclusion, we have demonstrated the feasibility of using ASAP in vivo for non-contrast microvascular imaging, and the added benefit of using contrast agents in microvascular imaging.
Hau Leow C, Bush NL, Stanziola A, et al., 2019, High-contrast 3D in vivo microvascular imaging using scanning 2D ultrasound and acoutic sub-aperture processing (ASAP), IEEE International Ultrasonics Symposium, IUS. 2018, Publisher: IEEE, ISSN: 1948-5719
Non-invasive techniques for microvascular environment assessment are invaluable for clinical diagnosis and treatment monitoring. We recently developed a super contrast processing to suppress noise background in ultrafast Power Doppler, known an acoustic sub-aperture processing (ASAP), and demonstrate using 2D contrast enhance ultrasound. However, 2D imaging is insufficient to represent the 3D complex vascular environment. We therefore extend our study to demonstrate the feasibility of our technique for volumetric imaging. A pseudo-3D imaging technique was developed and demonstrated using a research system and preclinical transducer. A mouse liver was scanned using 2D ultrafast ultrasound and a mechanical translation stage. Initial results not only demonstrated a substantial noise reduction in 2D vascular images using ASAP, but also a high contrast volumetric rendering of a mouse liver. Our technique is ready for clinical use to provide better evaluation of angiogenesis.
Toulemonde M, Zhang G, Eckersley RJ, et al., 2019, Flow Visualization Through Locally Activated Nanodroplets and High Frame Rate Imaging, IEEE International Ultrasonics Symposium, IUS. 2018, ISSN: 1948-5719
© 2018 IEEE. Blood flow visualization and quantification with ultrasound contrast agents using High-Frame-Rate (HFR) imaging has been investigated but the real-time feedback is limited because of the high computational cost. Nanodroplets have been investigated as an alternative to microbubble contrast agents, due to their smaller size, longer in vivo half-life, and spatial and temporal control on activation. In this work, a non-invasive flow visualization method is proposed through non-invasively "injecting" contrast agents by using locally activatinged decafluorobutane nanodroplets and HFR diverging imaging. Vortexes, residual flows or global flow patterns can be visualized thanks to the high temporal resolution and low computational complexity image processing.
Stanziola A, Toulemonde M, Li Y, et al., 2019, Motion artifacts and correction in multipulse high-frame rate contrast-enhanced ultrasound, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 66, Pages: 417-420, ISSN: 0885-3010
High-frame-rate (HFR) ultrasound (US) imaging and contrast-enhanced US (CEUS) are often implemented using multipulse transmissions, to enhance image quality. Multipulse approaches, however, suffer from degradation in the presence of motion, especially when coherent compounding and CEUS are combined. In this paper, we investigate this effect on the intensity of HFR CEUS in deep tissue imaging using simulations and in vivo contrast echocardiography (CE). The simulation results show that the motion artifact is much higher when the flow is in an axial direction than a lateral direction. Using a pulse repetition frequency suitable for cardiac imaging, a motion of 35 cm/s can cause as much as 28.5 dB decrease in image intensity, where compounding can contribute up to 18.7 dB of intensity decrease (11 angles). These motion effects are also demonstrated for in vivo cardiac HFR CE, where the large velocities of both the myocardium and the blood are present. Intensity reductions of 10.4 dB are readily visible in the chamber. Finally, we demonstrate how performing motion–correction before pulse inversion compounding greatly reduces such motion artifact and improve image signal-to-noise ratio and contrast.
Zhang G, Harput S, Hu H, et al., 2018, Fast Acoustic Wave Sparsely Activated Localization Microscopy (fast-AWSALM) using Octafluoropropane Nanodroplets, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Stanziola A, Robins T, Riemer K, et al., 2018, A Deep Learning Approach to Synthetic Aperture Vector Flow Imaging, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Zhang G, Pang KT, Ghim M, et al., 2018, Investigation of Nanodroplet Adhesion to Endothelial Cells under Atheroprone Flow Conditions, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Harput S, Christensen-Jeffries K, Brown J, et al., 2018, 3-D super-resolution ultrasound (SR-US) imaging using a 2-D sparse array with high volumetric imaging rate, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE
Super-resolution ultrasound imaging has been sofar achieved in 3-D by mechanically scanning a volume witha linear probe, by co-aligning multiple linear probes, by usingmultiplexed 3-D clinical ultrasound systems, or by using 3-D ultrasound research systems. In this study, a 2-D sparsearray was designed with 512 elements according to a density-tapered 2-D spiral layout and optimized to reduce the sidelobesof the transmitted beam profile. High frame rate volumetricimaging with compounded plane waves was performed usingtwo synchronized ULA-OP256 systems. Localization-based 3-Dsuper-resolution images of two touching sub-wavelength tubeswere generated from a 120 second acquisition.
Harput S, Christensen-Jeffries K, Brown J, et al., 2018, 3-D motion correction for volumetric super-resolution ultrasound (SR-US) imaging, IEEE International Ultrasonics Symposium (IUS) 2018, Publisher: IEEE
Motion during image acquisition can cause imagedegradation in all medical imaging modalities. This is particularlyrelevant in 2-D ultrasound imaging, since out-of-plane motioncan only be compensated for movements smaller than elevationalbeamwidth of the transducer. Localization based super-resolutionimaging creates even a more challenging motion correction taskdue to the requirement of a high number of acquisitions to forma single super-resolved frame.In this study, an extension of two-stage motion correctionmethod is proposed for 3-D motion correction. Motion estimationwas performed on high volumetric rate ultrasound acquisitionswith a handheld probe. The capability of the proposed methodwas demonstrated with a 3-D microvascular flow simulation tocompensate for handheld probe motion. Results showed that two-stage motion correction method reduced the average localizationerror from 136 to 18μm.
Zhou X, Zhou X, Leow CH, et al., 2018, 3D Flow Reconstruction and Wall Shear Stress Evaluation with 2D Ultrafast Ultrasound Particle Imaging Velocimetry, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Brown J, Kolas S, Christensen-Jeffries K, et al., 2018, Development of Simultaneous Optical Imaging and Super-Resolution Ultrasound to Improve Microbubble Localization Accuracy, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Christensen-Jeffries K, Harput S, Brown J, et al., 2018, 3D In Vitro Ultrasound Super-Resolution Imaging using a Clinical System, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Stanziola A, Toulemonde M, Corbett R, et al., 2018, Benefits of adaptive beamforming methods for contrast enhanced high frame-rate ultrasound, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Zhou X, Leow CH, Rowland E, et al., 2018, 3D velocity and volume flow measurement in vivo using speckle decorrelation and 2D high frame rate contrast-enhanced ultrasound, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 65, Pages: 2233-2244, ISSN: 0885-3010
Being able to measure 3D flow velocity and volumetric flow rate effectively in the cardiovascular system is valuable but remains a significant challenge in both clinical practice and research. Currently there has not been an effective and practical solution to the measurement of volume flow using ultrasound imaging systems due to challenges in existing 3D imaging techniques and high system cost. In this study, a new technique for quantifying volumetric flow rate from the cross-sectional imaging plane of the blood vessel was developed by using speckle decorrelation, 2D high frame rate imaging with a standard 1D array transducer, microbubble contrast agents, and ultrasound imaging velocimetry (UIV). Through speckle decorrelation analysis of microbubble signals acquired with a very high frame rate and by using UIV to estimate the two in-plane flow velocity components, the third and out-of-plane velocity component can be obtained over time and integrated to estimate volume flow. The proposed technique was evaluated on a wall-less flow phantom in both steady and pulsatile flow. UIV in the longitudinal direction was conducted as a reference. The influences of frame rate, mechanical index, orientation of imaging plane, and compounding on velocity estimation were also studied. In addition, an in vivo trial on the abdominal aorta of a rabbit was conducted. The results show that the new system can estimate volume flow with an averaged error of 3.65±2.37% at a flow rate of 360 ml/min and a peak velocity of 0.45 m/s, and an error of 5.03±2.73% at a flow rate of 723 ml/min and a peak velocity of 0.8 m/s. The accuracy of the flow velocity and volumetric flow rate estimation directly depend on the imaging frame rate. With a frame rate of 6000 Hz, a velocity up to 0.8 m/s can be correctly estimated. A higher mechanical index (MI=0.42) is shown to produce greater errors (up to 21.78±0.49%, compared to 3.65±2.37% at MI=0.19). An in vivo trial, where velo
Tang M-X, Tortoli P, 2018, Introduction to the Special Issue on High Frame Rate/Ultrafast Contrast-Enhanced Ultrasound Imaging, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Vol: 65, Pages: 2210-2211, ISSN: 0885-3010
Toulemonde MEG, Li Y, Lin S, et al., 2018, High-frame-rate contrast echocardiography using diverging waves: initial in-vitro and in-vivo evaluation, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 65, Pages: 2212-2221, ISSN: 0885-3010
Contrast Echocardiography (CE) ultrasound with microbubble contrast agents (UCA) has significantly advanced our capability for assessment of cardiac function, including myocardium perfusion quantification. However in standard CE techniques obtained with line by line scanning, the frame rate and image quality are limited. Recent research has shown significant frame rate improvement in non-contrast cardiac imaging. In this work we present and initially evaluate, both in-vitro and in-vivo, a high frame rate (HFR) CE imaging system using diverging waves and pulse inversion sequence. An imaging frame rate of 5500 frames per second before and 250 frames per second after compounding is achieved. A destruction-replenishment sequence has also been developed. The developed HFR CE is compared with standard CE in-vitro on a phantom and then in-vivo on a sheep heart. The image signal to noise ratio, contrast between the myocardium and the chamber are evaluated. Results show up to 13.4 dB improvement in contrast for HFR CE over standard CE when compared at the same display frame-rate even when the average spatial acoustic pressure in HFR CE is 36% lower than the standard CE. It is also found that when coherent compounding is used the HFR CE image intensity can be significantly modulated by the flow motion in the chamber.
Stanziola A, Leow CH, Bazigou E, et al., 2018, ASAP: super-contrast vasculature imaging using coherence analysis and high frame- rate contrast enhanced ultrasound, IEEE Transactions on Medical Imaging, Vol: 37, Pages: 1847-1856, ISSN: 0278-0062
The very high frame rate afforded by ultrafast ultrasound, combined with microbubble contrast agents, opens new opportunities for imaging tissue microvasculature. However, new imaging paradigms are required to obtain superior image quality from the large amount of acquired data while allowing real-time implementation. In this paper, we report a technique - acoustic sub-aperture processing (ASAP) - capable of generating very high contrast/SNR images of macro- and microvessels, with similar computational complexity to classical Power Doppler (PD) imaging. In ASAP, the received data are split into sub- groups. The reconstructed data from each sub-group are temporally correlated over frames to generate the final image. As signals in sub-groups are correlated but the noise is not, this substantially reduces the noise floor compared to PD. Using a clinical imaging probe, the method is shown to visualize vessels down to 200μm with a SNR 10dB higher than PD, and to resolve microvascular flow/perfusion information in rabbit kidneys non-invasively in vivo at multiple centimeter depth. With careful filter design, the technique also allows estimation of flow direction and separation of fast flow from tissue perfusion. ASAP can readily be implemented into hardware/firmware for real-timing imaging, and can be applied to contrast enhanced and potentially non-contrast imaging and 3D imaging.
Toulemonde M, Zhang G, Riemer K, et al., Locally activated nanodroplets and high frame rate imaging for real-time flow visualization – preliminary in-vivo demonstration, BioMedEng18
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