Qiong He

Ultrasound-Based Carotid Elastography for Detection of Vulnerable Atherosclerotic Plaques Validated by Magnetic Resonance Imaging

Ultrasound-based carotid elastography has been developed to estimate the mechanical properties of atherosclerotic plaques. The objective of this study was to evaluate the in vivo capability of carotid elastography in vulnerable plaque detection using high-resolution magnetic resonance imaging as reference. Ultrasound radiofrequency data of 46 carotid plaques from 29 patients (74 ± 5 y old) were acquired and inter-frame axial strain was estimated with an optical flow method. The maximum value of absolute strain rate for each plaque was derived as an indicator for plaque classification. Magnetic resonance imaging of carotid arteries was performed on the same patients to classify the plaques into stable and vulnerable groups for carotid elastography validation. The maximum value of absolute strain rate was found to be significantly higher in vulnerable plaques (2.15 ± 0.79 s(-1), n = 27) than in stable plaques (1.21 ± 0.37 s(-1), n = 19) (p < 0.0001). Receiver operating characteristic curve analysis was performed, and the area under the curve was 0.848. Therefore, the in vivo capability of carotid elastography to detect vulnerable plaques, validated by magnetic resonance imaging, was proven, revealing the potential of carotid elastography as an important tool in atherosclerosis assessment and stroke prevention.

An ultrasound elastography method to determine the local stiffness of arteries with guided circumferential waves

Arterial stiffness is highly correlated with the functions of the artery and may serve as an important diagnostic criterion for some cardiovascular diseases. To date, it remains a challenge to quantitatively assess local arterial stiffness in a non-invasive manner. To address this challenge, we investigated the possibility of determining arterial stiffness using the guided circumferential wave (GCW) induced in the arterial wall by a focused acoustic radiation force. The theoretical model for the dispersion analysis of the GCW is presented, and a finite element model has been established to calculate the dispersion curve. Our results show that under described conditions, the dispersion relations of the GCW are basically independent of the curvature of the arterial wall and can be well-described using the Lamb wave (LW) model. Based on this conclusion, an inverse method is proposed to characterize the elastic modulus of artery. Both numerical experiments and phantom experiments had been performed to validate the proposed method. We show that our method can be applied to the cases in which the artery has local stenosis and/or the geometry of the artery cross-section is irregular; therefore, this method holds great potential for clinical use.

Guided waves in pre-stressed hyperelastic plates and tubes: Application to the ultrasound elastography of thin-walled soft materials

We acknowledge support from the National Natural Science Foundation of China (Grant Nos. 11572179, 11172155, 11432008, and 81561168023) and from the Irish Research Council.

Tumor-homing, pH- and ultrasound-responsive polypeptide-doxorubicin nanoconjugates overcome doxorubicin resistance in cancer therapy

&NA; Nanomedicines hold promise in overcoming drug resistance in cancer therapy, but the in vivo therapeutic efficacy is limited by their inefficient tumor targeting, poor tumor penetration, low cellular uptake and insufficient drug release. Here we report tumor‐homing, pH‐ and ultrasound‐responsive polypeptide‐doxorubicin nanoconjugates for overcoming doxorubicin resistance. These nanoconjugates show accelerated cellular uptake and doxorubicin release and thus enhanced cytotoxicity to doxorubicin‐resistant cancer cells when exposed to ultrasound. In a doxorubicin‐resistant breast cancer mouse model, they exhibited improved tumor accumulation and penetration following exposure to ultrasound. More importantly, they displayed significantly improved in vivo anticancer efficacy without appreciable side effects post ultrasound irradiation. These findings suggest that these nanoconjugates are promising as a new class of intelligent nanomedicines for overcoming drug resistance in cancer therapy. Graphical abstract Ultrasound accelerates hydrolysis of the pH‐responsive hydrazone bond, promotes drug release and enhances tumor penetration of tumor‐homing, pH and ultrasound‐responsive polypeptide‐doxorubicin nanoconjugates for overcoming doxorubicin resistance. Figure. No caption available.

High frame rate and high line density ultrasound imaging for local pulse wave velocity estimation using motion matching: A feasibility study on vessel phantoms

Pulse wave imaging (PWI) is an ultrasound-based method to visualize the propagation of pulse wave and to quantitatively estimate regional pulse wave velocity (PWV) of the arteries within the imaging field of view (FOV). To guarantee the reliability of PWV measurement, high frame rate imaging is required, which can be achieved by reducing the line density of ultrasound imaging or transmitting plane wave at the expense of spatial resolution and/or signal-to-noise ratio (SNR). In this study, a composite, full-view imaging method using motion matching was proposed with both high temporal and spatial resolution. Ultrasound radiofrequency (RF) data of 4 sub-sectors, each with 34 beams, including a common beam, were acquired successively to achieve a frame rate of ∼507 Hz at an imaging depth of 35 mm. The acceleration profiles of the vessel wall estimated from the common beam were used to reconstruct the full-view (38-mm width, 128-beam) image sequence. The feasibility of mapping local PWV variation along the artery using PWI technique was preliminarily validated on both homogeneous and inhomogeneous polyvinyl alcohol (PVA) cryogel vessel phantoms. Regional PWVs for the three homogeneous phantoms measured by the proposed method were in accordance with the sparse imaging method (38-mm width, 32-beam) and plane wave imaging method. Local PWV was estimated using the above-mentioned three methods on 3 inhomogeneous phantoms, and good agreement was obtained in both the softer (1.91±0.24 m/s, 1.97±0.27 m/s and 1.78±0.28 m/s) and the stiffer region (4.17±0.46 m/s, 3.99±0.53 m/s and 4.27±0.49 m/s) of the phantoms. In addition to the improved spatial resolution, higher precision of local PWV estimation in low SNR circumstances was also obtained by the proposed method as compared with the sparse imaging method. The proposed method might be helpful in disease detections through mapping the local PWV of the vascular wall.

Evaluating the Significance of Viscoelasticity in Diagnosing Early-Stage Liver Fibrosis with Transient Elastography

Transient elastography quantifies the propagation of a mechanically generated shear wave within a soft tissue, which can be used to characterize the elasticity and viscosity parameters of the tissue. The aim of our study was to combine numerical simulation and clinical assessment to define a viscoelastic index of liver tissue to improve the quality of early diagnosis of liver fibrosis. This is clinically relevant, as early fibrosis is reversible. We developed an idealized two-dimensional axisymmetric finite element model of the liver to evaluate the effects of different viscoelastic values on the propagation characteristics of the shear wave. The diagnostic value of the identified viscoelastic index was verified against the clinical data of 99 patients who had undergone biopsy and routine blood tests for staging of liver disease resulting from chronic hepatitis B infection. Liver stiffness measurement (LSM) and the shear wave attenuation fitting coefficient (AFC) were calculated from the ultrasound data obtained by performing transient elastography. Receiver operating curve analysis was used to evaluate the reliability and diagnostic accuracy of LSM and AFC. Compared to LSM, the AFC provided a higher diagnostic accuracy to differentiate early stages of liver fibrosis, namely F1 and F2 stages, with an overall specificity of 81.48%, sensitivity of 83.33% and diagnostic accuracy of 81.82%. AFC was influenced by the level of LSM, ALT. However, there are no correlation between AFC and Age, BMI, TBIL or DBIL. Quantification of the viscoelasticity of liver tissue provides reliable measurement to identify and differentiate early stages of liver fibrosis.

Coded excitation for diverging wave cardiac imaging: a feasibility study

Diverging wave (DW) based cardiac imaging has gained increasing interest in recent years given its capacity to achieve ultrahigh frame rate. However, the signal-to-noise ratio (SNR), contrast, and penetration depth of the resulting B-mode images are typically low as DWs spread energy over a large region. Coded excitation is known to be capable of increasing the SNR and penetration for ultrasound imaging. The aim of this study was therefore to test the feasibility of applying coded excitation in DW imaging to improve the corresponding SNR, contrast and penetration depth. To this end, two types of codes, i.e. a linear frequency modulated chirp code and a set of complementary Golay codes were tested in three different DW imaging schemes, i.e. 1 angle DW transmit without compounding, 3 and 5 angles DW transmits with coherent compounding. The performances (SNR, contrast ratio (CR), contrast-to-noise ratio (CNR), and penetration) of different imaging schemes were investigated by means of simulations and in vitro experiments. As for benchmark, corresponding DW imaging schemes with regular pulsed excitation as well as the conventional focused imaging scheme were also included. The results showed that the SNR was improved by about 10 dB using coded excitation while the penetration depth was increased by 2.5 cm and 1.8 cm using chirp code and Golay codes, respectively. The CNR and CR gains varied with the depth for different DW schemes using coded excitations. Specifically, for non-compounded DW imaging schemes, the gain in the CR was about 5 dB and 3 dB while the gain in the CNR was about 4.5 dB and 3.5 dB at larger depths using chirp code and Golay codes, respectively. For compounded imaging schemes, using coded excitation, the gain in the penetration and contrast were relatively smaller compared to non-compounded ones. Overall, these findings indicated the feasibility of coded excitation in improving the image quality of DW imaging. Preliminary in vivo cardiac images of a healthy volunteer were presented finally, and higher SNR and deeper penetration depth can be achieved by coded schemes.

Compressed sensing for high frame rate, high resolution and high contrast ultrasound imaging.

Compressed sensing (CS) or compressive sampling allows much lower sampling frequency than the Nyquist sampling frequency. In this paper, we propose a novel technique, named compressed sensing based synthetic transmit aperture (CS-STA), to speed up the acquisition of ultrasound imaging. Ultrasound transducer transmits plane wave with random apodizations for several times and receives the corresponding echoes. The full dataset of STA is then recovered from the recorded echoes using a CS reconstruction algorithm. Finally, a standard STA beamforming is performed on the dataset to form a B-mode image. When the number of CS-STA firings is smaller than the number of STA firings, higher frame rate is achieved. In addition, CS-STA maintains the high resolution of STA because of the CS recovered full dataset of STA, and improves the contrast due to plane wave firings. Computer simulations and phantom experiments are carried out to investigate the feasibility and performance of the proposed CS-STA method. The CS-STA method is proven to be capable of obtaining simultaneously high frame rate, high solution and high contrast ultrasound imaging.Compressed sensing (CS) or compressive sampling allows much lower sampling frequency than the Nyquist sampling frequency. In this paper, we propose a novel technique, named compressed sensing based synthetic transmit aperture (CS-STA), to speed up the acquisition of ultrasound imaging. Ultrasound transducer transmits plane wave with random apodizations for several times and receives the corresponding echoes. The full dataset of STA is then recovered from the recorded echoes using a CS reconstruction algorithm. Finally, a standard STA beamforming is performed on the dataset to form a B-mode image. When the number of CS-STA firings is smaller than the number of STA firings, higher frame rate is achieved. In addition, CS-STA maintains the high resolution of STA because of the CS recovered full dataset of STA, and improves the contrast due to plane wave firings. Computer simulations and phantom experiments are carried out to investigate the feasibility and performance of the proposed CS-STA method. The CS-STA method is proven to be capable of obtaining simultaneously high frame rate, high solution and high contrast ultrasound imaging.

Performance optimization of lateral displacement estimation with spatial angular compounding

HIGHLIGHTSThe performance optimization of spatial angular compounding was investigated.The effects of key factors were investigated through simulations and experiments.It is necessary to filter the GLN for better displacement estimation.Better estimation performance is associated with a larger NSA and bigger MSA.The results are in agreement with theoretical analysis. ABSTRACT Elastography provides tissue mechanical information to differentiate normal and disease states. Nowadays, axial displacement and strain are usually estimated in clinical practice whereas lateral estimation is rarely used given that its accuracy is typically one order of magnitude worse than that of axial estimation. To improve the performance of lateral estimation, spatial angular compounding of multiple axial displacements along ultrasound beams transmitting in different steering angles was previously proposed. However, few studies have been conducted to evaluate the influence of key factors such as grating lobe noise (GLN), the number of steering angles (NSA) and maximum steering angle (MSA) in terms of performance optimization. The aim of this study was thus to investigate the effects of these factors through both computer simulations and phantom experiments. Only lateral rigid motion was considered in this study to separate its effects from those of axial and lateral strains on lateral displacement estimation. The performance as indicated by the root mean square error (RMSE) and standard deviation (SD) of the estimated lateral displacements validates the capability of spatial angular compounding in improving the performance of lateral estimation. It is necessary to filter the GLN for better estimation, and better performance is associated with a larger NSA and bigger MSA in both simulations and experiments, which is in agreement with the theoretical analysis. As indicated by the RMSE and SD, two steering angles with a larger steering angle are recommended. These results could provide insights into the performance optimization of lateral displacement estimation with spatial angular compounding.

A Compressed Sensing Strategy for Synthetic Transmit Aperture Ultrasound Imaging

A novel beamforming technique, named compressed sensing based synthetic transmit aperture (CS-STA) is proposed to speed up the acquisition of ultrasound imaging. This technique consists of three steps. First, the ultrasound transducer transmits randomly apodized plane waves for a number of times and receives the backscattered echoes. Second, the recorded backscattered echoes are used to recover the full channel dataset of synthetic transmit aperture (STA) with a compressed sensing (CS) reconstruction algorithm. Finally, an STA image is beamformed from the recovered full STA dataset. As CS allows recovering a signal from its few linear measurements with high probability, CS-STA is capable of recovering the STA image with fewer firings (i.e., higher frame rate) and retaining the high resolution of STA. In addition, the contrast of the STA image can be improved at the same time owing to the higher energy of plane wave firing in CS-STA. Simulations demonstrate that CS-STA is capable of recovering the STA channel dataset with a smaller number of firings. The performance of CS-STA is evaluated in phantom experiments through comparisons with STA, multi-element STA, conventional focused mode and coherent plane wave imaging. The results demonstrate that, implemented with the same frame rate, CS-STA achieves higher or comparable resolution and contrast. Moreover, comparisons are conducted on the biceps brachii muscle and thyroid of a human subject, and the results demonstrate the feasibility and competitiveness of CS-STA in the in vivo conditions.