Imperial College London

Professor MENGXING TANG

Faculty of EngineeringDepartment of Bioengineering

Professor of Biomedical Imaging
 
 
 
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Contact

 

+44 (0)20 7594 3664mengxing.tang Website

 
 
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Location

 

3.13Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

204 results found

Christensen-Jeffries K, Couture O, Dayton PA, Eldar YC, Hynynen K, Kiessling F, O'Reilly M, Pinton IGF, Schmitz G, Tang M-X, Tanter M, Van Sloun RJGet al., 2020, SUPER-RESOLUTION ULTRASOUND IMAGING, ULTRASOUND IN MEDICINE AND BIOLOGY, Vol: 46, Pages: 865-891, ISSN: 0301-5629

Journal article

Riemer K, Rowland EM, Leow CH, Tang MX, Weinberg PDet al., 2020, Determining Haemodynamic Wall Shear Stress in the Rabbit Aorta In Vivo Using Contrast-Enhanced Ultrasound Image Velocimetry., Ann Biomed Eng

Abnormal blood flow and wall shear stress (WSS) can cause and be caused by cardiovascular disease. To date, however, no standard method has been established for mapping WSS in vivo. Here we demonstrate wide-field assessment of WSS in the rabbit abdominal aorta using contrast-enhanced ultrasound image velocimetry (UIV). Flow and WSS measurements were made independent of beam angle, curvature or branching. Measurements were validated in an in silico model of the rabbit thoracic aorta with moving walls and pulsatile flow. Mean errors over a cardiac cycle for velocity and WSS were 0.34 and 1.69%, respectively. In vivo time average WSS in a straight segment of the suprarenal aorta correlated highly with simulations (PC = 0.99) with a mean deviation of 0.29 Pa or 5.16%. To assess fundamental plausibility of the measurement, UIV WSS was compared to an analytic approximation derived from the Poiseuille equation; the discrepancy was 17%. Mapping of WSS was also demonstrated in regions of arterial branching. High time average WSS (TAWSSxz = 3.4 Pa) and oscillatory flow (OSIxz = 0.3) were observed near the origin of conduit arteries. In conclusion, we have demonstrated that contrast-enhanced UIV is capable of measuring spatiotemporal variation in flow velocity, arterial wall location and hence WSS in vivo with high accuracy over a large field of view.

Journal article

Zhou X, Zhou X, Leow CH, Tang Met al., 2019, Measurement of flow volume in the presence of reverse flow with ultrasound speckle decorrelation, Ultrasound in Medicine and Biology, Vol: 45, Pages: 3056-3066, ISSN: 0301-5629

Direct measurement of volumetric flow rate in the cardiovascular system with ultrasound is valuable but has been a challenge because most current 2-D flow imaging techniques are only able to estimate the flow velocity in the scanning plane (in-plane). Our recent 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 luminal area, when the blood vessel was scanned from the transverse view. However, a key disadvantage of this SDC method is that it cannot distinguish the direction of the through-plane flow, which limited its applications to blood vessels with unidirectional flow. Physiologic flow in the cardiovascular system could be bidirectional due to its pulsatility, geometric features, or under pathologic situations. In this study, we proposed a method to distinguish the through-plane flow 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 found that the proposed method could detect flow direction and improved the estimation of the flow volume, reducing the overestimation from over 100% to less than 15% when there was flow reversal. This method showed significant improvement over the current SDC method in volume flow estimation and can be applied to a wider range of clinical applications where bidirectional flow exists.

Journal article

Zhou X, Vincent P, Zhou X, Leow CH, Tang M-Xet al., 2019, Optimization of 3-D Divergence-Free Flow Field Reconstruction Using 2-D Ultrasound Vector Flow Imaging, Ultrasound in Medicine and Biology, Vol: 45, Pages: 3042-3055, 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

Journal article

Zhu J, Lin S, Leow CH, Rowland E, Kai R, Harput S, Weinberg P, Tang Met al., 2019, High Frame Rate Contrast-Enhanced Ultrasound Imaging for Slow Lymphatic Flow: Influence of Ultrasound Pressure and Flow Rate on Bubble Disruption and Image Persistence, Ultrasound in Medicine and Biology, Vol: 45, Pages: 2456-2470, 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.

Journal article

Christensen-Jeffries K, Brown J, Harput S, Zhang G, Zhu J, Tang M-X, Dunsby C, Eckersley RJet 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.

Journal article

Ahmadzadeh SMH, Chen X, Hagemann H, Tang M-X, Bull AMJet al., 2019, Developing and using fast shear wave elastography to quantify physiologically-relevant tendon forces, Medical Engineering and Physics, Vol: 69, Pages: 116-122, ISSN: 1350-4533

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.

Journal article

Zhu J, Rowland E, Harput S, Riemer K, Leow CH, Clark B, Cox K, Lim A, Christensen-Jeffries K, Zhang G, Brown J, Dunsby C, Eckersley R, Weinberg P, Tang Met al., 2019, 3D super-resolution ultrasound imaging of rabbit lymph node vasculature in vivo using microbubbles, Radiology, Vol: 291, Pages: 642-650, 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.

Journal article

Zhang G, Harput S, Hu H, Christensen-Jeffries K, Zhu J, Brown J, Leow CH, Eckersley R, Dunsby C, Tang M-Xet 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, Vol: 66, Pages: 1039-1046, 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.

Journal article

Leow CH, Bush N, Stanziola A, Braga M, Shah A, Hernández-Gil J, Long NJ, Aboagye E, Bamber J, Tang Met al., 2019, 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, Vol: 66, Pages: 939-948, 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

Journal article

Hernandez-Gil J, Braga M, Harriss B, Carroll LS, Leow CH, Tang M-X, Aboagye EO, Long NJet al., 2019, Development of Ga-68-labelled ultrasound microbubbles for whole-body PET imaging, Chemical Science, Vol: 10, Pages: 5603-5615, ISSN: 2041-6520

Microbubble (MB) contrast agents have revolutionalised the way ultrasound (US) imaging can be used clinically and pre-clinically. Contrast-enhanced US offers improvements in soft-tissue contrast, as well as the ability to visualise disease processes at the molecular level. However, its inability to provide in vivo whole-body imaging can hamper the development of new MB formulations. Herein, we describe a fast and efficient method for achieving 68Ga-labelling of MBs after a direct comparison of two different strategies. The optimised approach produces 68Ga-labelled MBs in good yields through the bioorthogonal inverse-electron-demand Diel–Alder reaction between a trans-cyclooctene-modified phospholipid and a new tetrazine-bearing HBED-CC chelator. The ability to noninvasively study the whole-body distribution of 68Ga-labelled MBs was demonstrated in vivo using positron emission tomography (PET). This method could be broadly applicable to other phospholipid-based formulations, providing accessible solutions for in vivo tracking of MBs.

Journal article

Zhang G, Lin S, Leow CH, Pang KT, Hernandez Gil J, Long N, Eckersley R, Matsunaga T, Tang Met 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.

Journal article

Brown J, Christensen-Jeffries K, Harput S, Zhang G, Zhu J, Dunsby C, Tang M-X, Eckersley RJet 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.

Journal article

Zhou X, Papadopoulou V, Leow CH, Vincent P, Tang M-Xet 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.

Journal article

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

Journal article

Hau Leow C, Bush NL, Stanziola A, Braga M, Shah A, Hemández-Gil J, Long NJ, Aboagye EO, Bamber JC, Tang MXet 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.

Conference paper

Leow CH, Braga M, Bush NL, Stanziola A, Shah A, Hernández-Gil J, Long NJ, Aboagye EO, Bamber JC, Tang MXet 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.

Conference paper

Toulemonde M, Zhang G, Eckersley RJ, Tang MXet 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.

Conference paper

Harput S, Christensen-Jeffries K, Ramalli A, Brown J, Zhu J, Zhang G, Leow CH, Toulemonde M, Boni E, Tortoli P, Eckersley RJ, Dunsby C, Tang M-Xet al., 2019, 3-D super-resolution ultrasound (SR-US) imaging with a 2-D sparse array

High frame rate 3-D ultrasound imaging technology combined withsuper-resolution processing method can visualize 3-D microvascular structuresby overcoming the diffraction limited resolution in every spatial direction.However, 3-D super-resolution ultrasound imaging using a full 2-D arrayrequires a system with large number of independent channels, the design ofwhich might be impractical due to the high cost, complexity, and volume of dataproduced. In this study, a 2-D sparse array was designed and fabricated with 512elements chosen from a density-tapered 2-D spiral layout. High frame ratevolumetric imaging was performed using two synchronized ULA-OP 256 researchscanners. Volumetric images were constructed by coherently compounding 9-angleplane waves acquired in 3 milliseconds at a pulse repetition frequency of 3000Hz. To allow microbubbles sufficient time to move between consequent compoundedvolumetric frames, a 7-millisecond delay was introduced after each volumeacquisition. This reduced the effective volume acquisition speed to 100 Hz andthe total acquired data size by 3.3-fold. Localization-based 3-Dsuper-resolution images of two touching sub-wavelength tubes were generatedfrom 6000 volumes acquired in 60 seconds. In conclusion, this work demonstratesthe feasibility of 3D super-resolution imaging and super-resolved velocitymapping using a customized 2D sparse array transducer.

Working paper

Stanziola A, Toulemonde M, Li Y, Papadopoulou V, Corbett R, Duncan N, Eckersley R, Tang Met 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.

Journal article

Zhang G, Wang B, Stanziola A, Shah A, Bamber J, Tang M-Xet al., 2019, High Signal-to-Noise Ratio Contrast-Enhanced Photoacoustic Imaging using Acoustic Sub-Aperture Processing and Spatiotemporal Filtering, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 494-497, ISSN: 1948-5719

Conference paper

Stanziola A, Toulemonde M, Papadopoulou V, Corbett R, Duncan N, Grisan E, Tang Met al., 2019, Sparse Image Reconstruction for Contrast Enhanced Cardiac Ultrasound using Diverging Waves, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 908-911, ISSN: 1948-5719

Conference paper

Zhang G, Harput S, Zhu J, Christensen-Jeffries K, Brown J, Leow CH, Dunsby C, Eckersley RJ, Tang M-Xet al., 2019, Minimization of Nanodroplet Activation Time using Focused-Pulses for Droplet-Based Ultrasound Super-Resolution Imaging, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 372-375, ISSN: 1948-5719

Conference paper

Zhang G, Harput S, Shah A, Hernandez-Gil J, Zhu J, Christensen-Jeffries K, Brown J, Long NJ, Eckersley RJ, Dunsby C, Bamber J, Tang M-Xet al., 2019, Photoacoustic Super-Resolution Imaging using Laser Activation of Low-Boiling-Point Dye-Coated Nanodroplets in vitro and in vivo, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 944-947, ISSN: 1948-5719

Conference paper

Harput S, Zhang G, Toulemonde M, Zhu J, Christensen-Jeffries K, Brown J, Eckersley RJ, Dunsby C, Tang M-Xet al., 2019, Activation and 3D Imaging of Phase-change Nanodroplet Contrast Agents with a 2D Ultrasound Probe, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 2275-2278, ISSN: 1948-5719

Conference paper

Zhang G, Harput S, Toulemonde M, Broughton-Venner J, Zhu J, Riemer K, Christensen-Jeffries K, Brown J, Eckersley RJ, Weinberg P, Dunsby C, Tang M-Xet al., 2019, Acoustic Wave Sparsely-Activated Localization Microscopy (AWSALM): In Vivo Fast Ultrasound Super-Resolution Imaging using Nanodroplets, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 1930-1933, ISSN: 1948-5719

Conference paper

Zhang G, Wang B, Shah A, Bamber J, Tang M-Xet al., 2019, Contrast-Enhanced Photoacoustic Imaging of Low-boiling-point Phase-Change Nanodroplets, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 2271-2274, ISSN: 1948-5719

Conference paper

Harput S, Fong LH, Stanziola A, Zhang G, Toulemonde M, Zhu J, Christensen-Jeffries K, Brown J, Eckersley RJ, Grisan E, Dunsby C, Tang M-Xet al., 2019, Super-Resolution Ultrasound Image Filtering with Machine-Learning to Reduce the Localization Error, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 2118-2121, ISSN: 1948-5719

Conference paper

Zhang G, Harput S, Hu H, Christensen-Jeffries K, Zhu J, Brown J, Leow CH, Dunsby C, Eckersley RJ, Tang M-Xet al., 2018, Fast Acoustic Wave Sparsely Activated Localization Microscopy (fast-AWSALM) using Octafluoropropane Nanodroplets, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719

Conference paper

Stanziola A, Robins T, Riemer K, Tang M-Xet al., 2018, A Deep Learning Approach to Synthetic Aperture Vector Flow Imaging, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719

Conference paper

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