Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography

Induction of haemodynamic travelling waves by glial-related vasomotion in a rat model of neuroinflammation: implications for functional neuroimaging

BACKGROUND

Cerebral haemodynamics are crucial for brain homoeostasis and serve as a key proxy for brain activity. Although this process involves coordinated interaction between vessels, neurons, and glial cells, its dysregulation in neuroinflammation is not well understood.

METHODS

We used in vivo mesoscopic functional ultrasound imaging to monitor cerebral blood volume changes during neuroinflammation in male rats injected with lipopolysaccharide (LPS) in the visual cortex, under resting-state or visual stimulation, combined to advanced ex vivo techniques for glial cell reactivity analysis.

FINDINGS

Cortical neuroinflammation induced large oscillatory haemodynamic travelling waves in the frequency band of vasomotion (∼0.1 Hz) in both anaesthetized and awake rats. Vasomotor waves travelled through large distances between adjacent penetrating vessels, spanning the entire cortex thickness, and even extending to subcortical areas. Moreover, vasomotion amplitude correlated with microglial morphology changes and was significantly reduced by astrocytic toxins, suggesting that both microglia and astrocytes are involved in the enhancement of vasomotion during neuroinflammation. Notably, functional connectivity was increased under this oscillatory state and functional hyperaemia was exacerbated.

INTERPRETATION

These findings further reveal the spatiotemporal properties of cerebral vasomotion and suggest this is a major component of brain haemodynamics in pathological states. Moreover, reactive microglia and astrocytes are participating to increase vasomotion during neuroinflammation. For the field of functional neuroimaging, our results advocate for considering 0.1 Hz haemodynamic oscillations as an important complement to traditional measurements, particularly in neuroinflammatory conditions. Indeed, brain haemodynamics may provide insights not only into neuronal activity but also glial reactivity.

FUNDING

Supported by ANR ("LabCom-NI2D", "Labex Cortex") and Auvergne-Rhône-Alpes Region ("BI2D").

Preliminary application of robot-assisted teleultrasound-guided interventional system

BACKGROUND

Teleultrasound has gained significant traction in clinical practice in recent years. However, studies focusing on remote interventional ultrasound remain limited.

OBJECTIVES

To evaluate the feasibility and accuracy of percutaneous puncture using a robot-assisted teleultrasound-guided interventional system (RTIS).

MATERIALS AND METHODS

This study was approved by the institutional animal ethics committee and human research review board. Written informed consent was obtained from all patients. Two experienced interventional ultrasound physicians performed percutaneous punctures using both RTIS and conventional ultrasound guidance (CUG) in phantom and swine liver models, as well as in clinical settings. Puncture distance errors and operation durations were compared between the RTIS and CUG groups in the experimental models. For clinical applications, operation duration, success rates, and complications were recorded.

RESULTS

No significant differences were observed in puncture distance errors between the RTIS and CUG groups in the phantom study (2.85 ± 2.07 mm vs. 1.79 ± 1.93 mm; p = 0.158) or the swine liver study (3.28 ± 1.20 mm vs. 2.56 ± 0.98 mm; p = 0.148). However, puncture operation durations were significantly longer in the RTIS group compared to the CUG group across all scenarios: phantom study (50 ± 19 s vs. 19 ± 7 s; p < 0.001), swine liver study (106 ± 19 s vs. 61 ± 32 s; p = 0.001), and clinical application (200 ± 27.02 s vs. 104.8 ± 33.92 s; p < 0.001). All six patients in the RTIS group and ten patients in the CUG group successfully underwent percutaneous puncture without complications.

CONCLUSION

The RTIS demonstrated safety and feasibility for percutaneous puncture, providing comparable accuracy to conventional methods.

CLINICAL RELEVANCE STATEMENT

The RTIS offers a safe and effective solution for percutaneous puncture, with the potential to address the scarcity of medical resources in remote and underserved regions.

High-frequency contrast-enhanced ultrasound in discriminating benign and malignant superficial lymph nodes: a diagnostic comparison

BACKGROUND

Lymph nodes are critical immune system components, filtering harmful substances and acting as indicators in various disease states, including cancer. Accurate differentiation between benign and malignant superficial lymph nodes is essential for diagnosis and treatment planning. However, conventional diagnostic methods often lack the required precision. High-frequency contrast-enhanced ultrasound (H-CEUS) offers improved temporal resolution and visualization of microvascular structures, potentially providing better diagnostic accuracy than standard contrast-enhanced ultrasound (CEUS).

METHODS

This study included 77 patients with suspected abnormalities in superficial lymph nodes. Each patient underwent H-CEUS and CEUS examinations, with diagnoses confirmed through biopsy or surgical resection. The diagnostic performance of H-CEUS and CEUS was evaluated using sensitivity, specificity, positive predictive value, negative predictive value, and accuracy. Chi-square tests and ROC curve analysis were employed to compare the efficacy of H-CEUS and CEUS in differentiating benign from malignant lymph nodes.

RESULTS

H-CEUS demonstrated superior diagnostic performance over CEUS, with higher sensitivity (95.92% vs. 83.67%), specificity (92.86% vs. 57.14%), and accuracy (94.80% vs. 74.03%). H-CEUS enhanced microvascular morphology visualization, facilitating more accurate differentiation between benign and metastatic lymph nodes. The area under the ROC curve for H-CEUS (0.944) was significantly greater than that for CEUS (0.704), indicating improved diagnostic capability.

CONCLUSION

H-CEUS offers enhanced accuracy in diagnosing the nature of superficial lymph nodes, potentially improving clinical decision-making for patients with suspected lymph node malignancies. These findings support the integration of H-CEUS into routine clinical practice to achieve better diagnostic outcomes.

Numerical investigation of optimal transmission-reception conditions for aliasing-free ultrasound localization microscopy

Ultrasound localization microscopy (ULM) can surpass the diffraction-limited resolution of conventional ultrasound by localizing individual microbubbles with sub-pixel precision. However, if the point-spread function (PSF) of the imaging system is insufficiently sampled, aliasing artifacts arise and degrade both microbubble localization and motion correction accuracy. In this study, we derive and validate a set of transmit-receive conditions that ensure artifact-free PSFs without unnecessary computational overhead. We demonstrate that by appropriately selecting the plane-wave steering angles, transmit pulse cycle count, and receive aperture (F-number) in relation to the pixel spacing, high spatial frequencies in the PSF remain within the Nyquist limit for all imaging depths. Through a series of simulations, wire phantom tests, and custom flow phantom experiments, we compare undersampled, oversampled, and balanced parameters. The balanced configurations, where the maximum frequency of the PSF matches the beamforming grid, consistently mitigate aliasing artifacts, eliminate grid-like patterns, and preserve microbubble trajectories under sub-pixel translations. In a flow phantom study, we further confirm that ULM images obtained with these optimized settings retain fine details without incurring the substantial computational costs of an overly fine sampling grid. Our findings highlight the importance of analysing PSF bandwidth in both lateral and axial dimensions and offer a straightforward method to align transmit pulse width, receive aperture, and grid spacing. Ultimately, this approach provides a pathway toward efficient, high-fidelity ULM, with significant implications for real-time super-resolution imaging in clinical and preclinical environments.

Carotid pulse wave velocity estimation based on incident waves using coherent plane wave compounding ultrasound

Objective. Local pulse wave velocity (PWV) plays a crucial role in assessing the regional arterial elasticity. Accurate estimation of local PWV is beneficial for the risk assessment and early diagnosis of cardiovascular diseases. In this study, a method involving incident waves based on coherent plane wave compounding ultrasound (IWCU) is proposed to suppress reflected waves in pulse waves (PW) and improve the performance of transit time (TT)-based local PWV estimation.Approach. The ultrasonic radio frequency echo signals are collected and coherently compounded, and the PWs and central blood flow velocities at 128 beam positions are calculated, from which the incident waves (IWs) are estimated based on the Kelvin-Voigt model. Then, the time delays (TDs) of the IWs propagating are calculated, and the local PWV is finally estimated. The mean and standard deviations (MSD) of the normalized root mean squared errors NRMSEs between the presupposed and estimated TDs and PWVs were calculated for quantitatively evaluating the performance of the proposed IWCU method, and compared with those of the PWs based on coherent plane wave compounding ultrasound and the regional upstroke tracking methods in simulation experiments. The relative errors, Bland-Altman analysis and coefficient of variation (CV) were measured to further assess the accuracy, reproducibility and variability of IWCU method inin vitroandin vivoexperiments.Main results. The IWCU method yields higher accuracy, reproducibility and lower variability for local PWV estimation. The MSD of the NRMSEs for TDs and local PWVs are 11.78 ± 0.52% and 4.10 ± 2.25%. Additionally, the mean relative error and CV are 6.10% and 12.56%, respectively.Significance. The IWCU method provides improved TT-based local PWV estimation, and has the potential to support future clinical diagnoses of arterial stiffness.

Twin Peak Method for Estimating Tissue Viscoelasticity Using Shear Wave Elastography

Tissue viscoelasticity is becoming an increasingly useful biomarker beyond elasticity and can theoretically be estimated using shear wave elastography by inverting the propagation and attenuation characteristics of shear waves. Estimating viscosity is often more difficult than elasticity because attenuation, the main effect of viscosity, leads to poor signal-to-noise ratio of the shear wave motion. In the present work, we provide an alternative to existing methods of viscoelasticity estimation, based on peaks in the frequency-wavenumber (f-k) domain, which are considered more robust against noise compared with other features in the f-k domain. Specifically, the method minimizes the difference between simulated and measured versions of two sets of peaks (twin peaks) in the f-k domain, obtained first by traversing through each frequency and then by traversing through each wavenumber. The slopes and deviation of the twin peaks are sensitive to elasticity and viscosity, respectively, leading to the effectiveness of the proposed inversion algorithm for characterizing mechanical properties. This expected effectiveness is confirmed through in silico verification, followed by ex vivo validation and in vivo application, indicating that the proposed approach can be used effectively in accurately estimating viscoelasticity, thus potentially contributing to the development of enhanced biomarkers.

Simultaneous measurement of tensile and shear elasticity and anisotropy in human skeletal muscle tissue using steered ultrasound shear waves

Load-bearing skeletal muscle tissues are reinforced by intricate networks of protein fibers aligned in preferential orientations, imparting direction-dependent mechanical properties (anisotropy). Characterizing this anisotropy in vivo is essential for understanding both normal and pathological muscle function, as well as structural integrity. However, current noninvasive techniques are limited in their ability to accurately measure the mechanical properties of anisotropic tissues such as skeletal muscle. Here, we used an innovative angle-resolved ultrasound elastography method, recently developed by our team, to simultaneously quantify tensile and shear elasticity and anisotropy, enabling comprehensive assessment of muscle biomechanics. We fully characterized the mechanical properties of the biceps brachii in fourteen healthy young adults under passive and active axial loadings, revealing distinct shear and tensile mechanical behaviors both along and across muscle fibers. Notably, tensile and shear moduli along the main fiber orientation were found to be uncoupled, while cross-muscle fiber measurements exhibited a consistent modulus ratio of 3.4 ± 0.2, regardless of axial loading conditions or intensities. These findings highlight the anisotropic nature of skeletal muscle and provide valuable insights into its in vivo mechanical behavior. Both shear and tensile anisotropy increased with muscle axial physiological loading, indicating that our method is sensitive to changes in anisotropic tissue mechanics. Lastly, we demonstrated that angle-resolved ultrasound shear wave elastography provides direct estimates of shear and tensile properties, offering significant promise for clinical applications, including neuromuscular disease diagnostics and monitoring, biomechanical modeling for predicting tissue responses to loading and therapies, and tissue engineering. STATEMENT OF SIGNIFICANCE: : Conventional ultrasound shear wave elastography techniques overlook the anisotropy of skeletal muscles, leading to incomplete tissue mechanical characterization. In this study, we leveraged an innovative angle-resolved elastography method to assess tensile and shear elasticity, along with their anisotropic factors, of human muscle in vivo. For the first time, we reveal the intricate relationships between tensile and shear elasticities during active and passive physiological loading. This technique enhances our understanding of muscle mechanics and has promising clinical implications for muscle health and neuromuscular disease management, where tissue structural and mechanical properties are often altered. Additionally, it could help in developing constitutive models for muscle tissue and contribute to the design of tissue-engineered materials.

Quantitative assessment of ultrasound microvessel imaging in Crohn's disease: correlation with pathological inflammation

OBJECTIVE

Ultrasound microvessel imaging (UMI) may offer noninvasive, highly sensitive microvessel imaging for assessing Crohn's disease (CD). However, a quantification metric that demonstrates a strong correlation with pathological inflammation is preferred. The objective was to determine if UMI can enhance IBD imaging interrogations.

METHODS

UMI was performed on bowel wall segments from patients with CD requiring surgery (n = 55 patients). The vessel-length ratio (VLR) measured by UMI was compared with that obtained using color flow imaging (CFI) and with a histopathologic standard evaluated on all bowel layers. Correlations between VLR and pathological inflammation and receiver operating characteristic (ROC) curves between different groups were analyzed to demonstrate the advantages of VLR with UMI.

RESULTS

The correlation between VLR from UMI and pathological inflammation (R = 0.80) outperformed that of VLR from CFI (R = 0.59). UMI showed a significant difference (p < 0.01) between mild and non-mild inflammation cases, while CFI could not (p = 0.014). In the ROC analysis, VLR with UMI demonstrated an area under the curve (AUC) of 0.93, compared to the AUC of 0.80 for VLR with CFI, indicating better identification of pathological inflammation between mild and non-mild cases. For a sub-cohort of patients with stricture without penetrating complications (n = 19), VLR using UMI also showed better correlation (R = 0.93) with pathological inflammation scores and a higher AUC (0.96) than those of VLR using CFI (R = 0.66 and 0.88, respectively).

CONCLUSIONS

UMI enhances vessel detection sensitivity compared to CFI and more accurately reflects transmural inflammation in small bowel Crohn's disease. VLR using UMI strongly correlates with pathological inflammation, distinguishing between mild and non-mild cases, notably including patients with stricture without penetrating complications.

KEY POINTS

Question Bowel wall thickness and Limberg score from ultrasound are insufficient quantitative metrics for reliable diagnosis of inflammation severity for Crohn's disease. Findings Ultrasound microvessel imaging (UMI) with vessel-length ratio (VLR) is strongly correlated with pathological inflammation and had improved distinction between mild and non-mild inflammation cases. Clinical relevance UMI with VLR has the potential to enhance clinicians' ability to assess disease activity and evaluate therapeutic responses, thereby improving Crohn's disease patient outcomes.

Angle sub-sampling methods for enhanced ultrasound coherent plane wave compounding

Coherent plane wave compounding ultrasound imaging combines low-resolution frames acquired from multiple angles to generate a high-quality image. However, achieving an optimal balance between frame rate and image quality is challenging, as increasing the number of emission angles leads to a reduction in frame rate. In scenarios with sub-sampled angles, selecting an optimal subset of angles becomes crucial to minimizing data acquisition time while preserving image quality comparable to all-angle transmission. To address this challenge, we propose two methods: Coprime sub-sampled angle (CSA) and semi sub-sampled angle (SSA). These approaches strategically select two subsets of angles to effectively suppress grating lobes resulting from down-sampling in the transmission angle intervals. Unlike traditional methods like random or periodic subsampling, CSA and SSA offer controlled and robust suppression of grating lobes while maintaining image quality, making them ideal for sub-sampled angle configurations. Our validation with the Plane-wave Imaging Challenge in Medical Ultrasound dataset shows that CSA achieves comparable resolution with an 8.4% contrast ratio improvement using only 25.3% of all available angles. Meanwhile, SSA achieves similar resolution with a 7.7% contrast gain, using 36% of the angles, while effectively preserving speckle quality.

Plane wave compounding with adaptive joint coherence factor weighting

Coherent Plane Wave Compounding (CPWC) is widely used for ultrasound imaging. This technique involves transmitting plane waves into a sample at different transmit angles and recording the resultant backscattered echo at different receive positions. The time-delayed signals from the different combinations of transmit angles and receive positions are then coherently summed to produce a beamformed image. Various techniques have been developed to characterize the quality of CPWC beamforming based on the measured coherence across the transmit or receive apertures. Here, we propose a more granular approach where the signals from every transmit/receive combination are separately evaluated using a quality metric based on their joint spatio-angular coherence. The signals are then individually weighted according to their measured Joint Coherence Factor (JCF) prior to being coherently summed. To facilitate the comparison of JCF beamforming compared to alternative techniques, we further propose a method of image display standardization based on contrast matching. We show results from tissue-mimicking phantoms and human soft-tissue imaging. Fine-grained JCF weighting is found to improve CPWC image quality compared to alternative approaches.

Enhancing Liver Nodule Visibility and Diagnostic Classification Using Ultrasound Local Attenuation Coefficient Slope Imaging

OBJECTIVE

B-mode ultrasound (US) presents challenges in accurately detecting and distinguishing between benign and malignant liver nodules. This study utilized quantitative US local attenuation coefficient slope (LACS) imaging to address these limitations.

MATERIALS AND METHODS

This is a prospective, cross-sectional study in adult patients with definable solid liver nodules at US conducted from March 2021 to December 2023. The composite reference standard included histopathology when available or magnetic resonance imaging. LACS images were obtained using a phantom-free method. Nodule visibility was assessed by computing the contrast-to-noise ratio (CNR). Classification accuracy for differentiating benign and malignant lesions was assessed with the area under the receiver operating characteristic curve (AUC), along with sensitivity and specificity.

RESULTS

The study enrolled 97 patients (age: 62 y ± 13 [standard deviation]), with 57.0% malignant and 43.0% benign observations (size: 26.3 ± 18.9 mm). LACS images demonstrated higher CNR (12.3 dB) compared to B-mode (p < 0.0001). The AUC for differentiating nodules and liver parenchyma was 0.85 (95% confidence interval [CI]: 0.79-0.90), with higher values for malignant (0.93, CI: 0.88-0.97) than benign nodules (0.76, CI: 0.66-0.87). A LACS threshold of 0.94 dB/cm/MHz provided a sensitivity of 0.83 (CI: 0.74-0.89) and a specificity of 0.82 (CI: 0.73-0.88). LACS mean values were higher (p < 0.0001) in malignant (1.28 ± 0.27 dB/cm/MHz) than benign nodules (0.98 ± 0.19 dB/cm/MHz).

CONCLUSION

LACS imaging improves nodule visibility and provides better differentiation between benign and malignant liver nodules, showing promise as a diagnostic tool.

Adaptive Doppler blood flow estimation in ultrasound with enhanced spectral resolution and contrast using limited observation windows

Measuring blood velocities during the acceleration and deceleration phases of the systolic period can be challenging due to the trade-off between spectral and temporal resolution. This can significantly affect the accuracy of spectrogram reproduction. When temporal samples are reduced, the spectral width may broaden over time, especially during systole. Additionally, shorter observation windows negatively impact factors such as frequency resolution and contrast. This study hypothesizes that a more accurate ultrasound spectrogram can be generated using a new blood velocity estimator with a minimal observation window length of N=2. The spectrogram's accuracy is assessed using various criteria, including spectral resolution, contrast, and spectral broadening over time. The proposed adaptive method integrates a new coherence-based post-filter with the Eigenspace-based Forward-Backward Amplitude Spectrum Capon (ESB-FBASC) technique. The method's performance was evaluated in different conditions, including simulations of the femoral artery, stationary and complex flow, and in vivo data. Under rapid flow conditions simulated over three heartbeats in 0.2 s, the proposed method demonstrated better temporal resolution compared to the Welch-Ref estimator, effectively capturing rapid velocity changes and reducing spectral broadening, despite using only N=2 slow-time samples. For clinical data on the hepatic vein, the proposed estimator improved spectral resolution by 24 %, 44 %, and 67 %, and increased contrast by 79.8 dB, 120.8 dB, and 155.5 dB compared to MASC, Pr.Capon, and Capon, respectively, for N=2. Furthermore, the narrowest power spectrum width at 40 dB was achieved with the proposed method, showing an improvement of 38 % and 75 % compared to MASC and Pr.Capon, respectively. As a result, the proposed method effectively reduces power spectrum width and enhances spectrogram accuracy by improving spectral resolution and contrast, all while using the limited observation window length of N=2.

Dual-frequency excitation in high-frame-rate ultrasonic backscatter coefficient analysis of hemorheological properties

Hemorheological properties, such as erythrocyte aggregation can be assessed by ultrasonic backscatter coefficient analysis. In this study, a data-acquisition sequence with dual-frequency (dual-f) excitation was proposed to expand the ultrasonic frequency bandwidth with high-frame-rate imaging. The approach was experimentally validated using ex vivo porcine blood measurements and in vivo human imaging. The center frequency of the excitation wave was alternated between 7.8 (f1) and 12.5 (f2) MHz in the frequency spectral analysis using the reference phantom method. The frequency spectra revealed that the dual-f sequence achieved a bandwidth of 4.5-15 MHz at -20 dB, almost equivalent to those achieved with conventional single-frequency excitation (5.0-15 MHz) with a short-duration wave at 10 MHz (mono-f) in reference media with the sufficient condition of signal-to-noise ratio. The aggregation and disaggregation states of porcine blood suspended in high-molecular-weight dextran were determined by the isotropic diameter and packing factor using the structure factor size estimator. The discrimination performance of the dual-f approach increased, owing to the broadband frequency responses, in contrast with the limited performance of mono-f due to a low signal-to-noise ratio. This approach incorporating dual-f sequence is beneficial for obtaining robustly frequency spectra of hemorheological properties from in vivo scenarios.

Null subtraction imaging combined with modified delay multiply-and-sum beamforming for coherent plane-wave compounding

Coherent plane-wave compounding, while efficient for ultrafast ultrasound imaging, yields lower image quality due to unfocused waves. Delay multiply-and-sum (DMAS) beamformer is one of the representative coherence-based methods which can improve images quality, but suffers from poor speckle quality brought by oversuppression. Current DMAS-based methods involve trade-offs between contrast, resolution, and speckle preservation. To overcome this limitation, a new beamformer method combining the null subtraction imaging (NSI) and DMAS is investigated. The proposed method explores the DMAS on different beamformers which employs NSI and delay and sum (DAS) at receive and do multiply-and-sum on different beamformers across transmitting dimension, thereby simultaneously possessing the speckle quality of DAS and the high resolution of NSI. The effectiveness of the proposed method is evaluated through simulation, phantom, and in vivo datasets. From the experimental study, in comparison with NSI, the proposed method has improved contrast ratio by 10.02%, speckle signal-to-noise ratio by 45.19%, and generalized contrast-to-noise ratio by 12.37%. The method has also improved the full width at half maximum by up to 0.24 mm. The results indicate that the proposed method achieves better resolution and contrast, while also alleviating the issue of excessive compression.

Towards quantitative assessment of cerebrovascular autoregulation in human neonates using ultrafast ultrasound imaging

Newborns with congenital heart diseases requiring cardiopulmonary bypass (CPB) are at risk of neurodevelopmental impairment. The impact of deep hypothermia cardiopulmonary bypass (DH-CPB) on cerebrovascular autoregulation (CAR) that controls brain perfusion in the presence of blood pressure variation is not well understood. Recently, ultrafast power Doppler (UPD) showed potential to study CAR in neonates based on cerebral blood volume (CBV). However, since CAR relies mainly on arterial vasoconstriction/vasodilation, monitoring of brain perfusion variation based on CBV requires the discrimination of arterial from venous CBV. This study aims to use UPD combined with an algorithm for the discrimination of arteries and veins to monitor CAR during DH-CPB in neonates. Transfontanellar ultrafast power Doppler was performed in two groups of newborns: those undergoing deep hypothermic cardiopulmonary bypass with circulatory arrest (18-20 °C, n = 6, "DH group") and those undergoing full-flow CPB at mild hypothermia (32-34 °C, n = 6, "non-DH group"). Blood flow directionality was used to differentiate arterial compartments of CBV from venous CBV in specific brain regions where arterial and venous flows exhibit opposite directions. To study CAR, a linear mixed effect model was used to find the association between arterial CBV and mean arterial blood pressure (MAP). In the "non-DH group", we found a negative association between arterial CBV and MAP, indicating that an increase in MAP is associated with a decrease in arterial CBV (slope = -0.020 [Formula: see text], p = 0.047). Conversely, in the "DH group" no significant association was found such that arterial CBV remained stable as MAP increased (p = 0.314). We interpret the reduction in arterial CBV with increasing MAP in the "non-DH group" as an active arterial vasoconstriction triggered by CAR, whereas the lack of variation of arterial CBV in the DH group suggests impaired CAR response. Our findings highlight the potential of ultrafast ultrasound imaging for intra-operative CAR monitoring, paving the way for a better understanding of the impact of different types of CPB on cerebral perfusion.

A 40-nm 169mW Ultrasound Imaging Processor Supporting Advanced Modes for Hand-Held Devices

Hand-held ultrasound devices have been widely used in the field of healthcare and power-efficient, real-time imaging is essential. This work presents the world's first ultrasound imaging processor supporting advanced modes, including vector flow imaging and elastography imaging. Plane-wave beamforming is utilized to ensure that the pulse repetition frequency (PRF) is sufficiently high for the advanced mode. The storage size and power consumption are minimized through algorithm-architecture co-optimization. The proposed plane-wave beamforming reduces the storage size of the required delay values by 43.7%. By exchanging the processing order, the storage size is reduced by 78.1% for elastography imaging. Parallel beamforming and interleaved firing are employed to achieve real-time imaging for all the supported modes. Fabricated in 40-nm CMOS technology, the proposed processor integrates 4.7M logic gates in core area of 3.24mm. This work achieves a 20.3 higher beamforming rate with 5.3-to-29.1 lower power consumption than the state-of-the-art design. It also has 60% lower hardware complexity (in terms of gate count), in addition to the capability for supporting the advanced mode.

Three-dimensional complementary breast ultrasound (3D CBUS): Improving 3D spatial resolution uniformity with orthogonal images

BACKGROUND

With increasing evidence supporting three-dimensional (3D) automated breast (AB) ultrasound (US) for supplemental screening of breast cancer in increased-risk populations, including those with dense breasts and in limited-resource settings, there is an interest in developing more robust, cost-effective, and high-resolution 3DUS imaging techniques. Compared with specialized ABUS systems, our previously developed point-of-care 3D ABUS system addresses these needs and is compatible with any conventional US transducer, which offers a cost-effective solution and improved availability in clinical practice. While conventional US transducers have high in-plane resolution (axial and lateral), their out-of-plane resolution is constrained by the poor intrinsic elevational US resolution. Consequently, any oblique view plane in an acquired 3DUS image will contain high in-plane and poor out-of-plane resolution components, diminishing spatial resolution uniformity and overall diagnostic utility.

PURPOSE

To develop and validate a novel 3D complementary breast ultrasound (CBUS) approach to improve 3DUS spatial resolution uniformity using a conventional US transducer by acquiring and generating orthogonal 3DUS images.

METHODS

We previously developed a cost-effective, portable, dedicated 3D ABUS system consisting of a wearable base, a compression assembly, and a mechanically driven scanner for automated 3DUS image acquisition, compatible with any commercial linear US transducer. For this system, we have proposed 3D CBUS approach which involves acquiring and registering orthogonal 3DUS images (V A ${V}_A$ andV B ${V}_B$ ) with an aim of overcoming the poor resolution uniformity in the scanning direction in 3D US images. The voxel intensity values in the 3D CBUS image are computed with a spherical-weighted algorithm from the original orthogonal 3DUS images. Experimental validation was performed with 2DUS frame densities of 2, 4, 6 frames mm-1 using an agar-based phantom with a speed of sound of 1540 ms-1 and an embedded nylon bead. Lateral and axial full-width at half-maximum (FWHMLAT and FWHMAX) values were calculated from cross-sections taken at polar view planes ranging from 0° to 90° for 3DUS and 3D CBUS images of a bead phantom in focal zone and far field regions. Kendall's Tau-b correlation coefficients were calculated between FWHM measurements and cross-section angle for all frame density settings at a significance level ofα = 0.05 $\alpha = 0.05$ . Volumetric 3D segmentations were performed for 3DUS and 3D CBUS images of an inclusion phantom to confirm volumetric reconstruction accuracy. For statistical analysis, a repeated measures ANOVA with the Greenhouse-Geisser correction was performed at a significance level ofα = 0.05 $\alpha = 0.05$ .

RESULTS

Experimental validation of the orthogonal 3DUS images show complementary trends of increasing and decreasing FWHMLAT from in-plane to out-of-plane (0° and 90° and vice versa) views. This is exemplified with the scan taken at 4 frames mm-1 in the focal zone, where FWHMLAT ranges from 3.51 to 1.10 mm forV A ${V}_A$ and 1.02-3.02 mm forV B ${V}_B$ , spanning 0°-90°, respectively. When combined in the 3D CBUS image, the FWHMLAT exhibits greater uniformity across view angles by mitigating poor out-of-plane resolution using its complementary in-plane component, with corresponding FWHMLAT values of 1.27 and 1.46 mm. While visual enhancements were seen in the 3D CBUS image, no statistically significant differences were found in volumetric measurements of the spherical inclusions in the 3DUS and 3D CBUS images.

CONCLUSION

The out-of-plane resolution in the orthogonal 3DUS images is improved upon their combination into a single 3D CBUS image. These results demonstrate that the proposed 3D CBUS generation approach can improve 3D spatial resolution uniformity, while employing a commercial US transducer. The proposed 3D CBUS method shows potential utility for improving image resolution uniformity in 3D ABUS images, with the goal of improving point-of-care breast cancer supplemental screening and diagnostic applications, particularly in women with dense breasts and limited resource settings.

Ultrafast Coherence-Based Power Doppler Estimation Using Nonlinear Compounding With Complementary Subset Transmit

OBJECTIVE

Conventional coherent plane wave compounding (CPWC) and sum-of-square power Doppler (PD) estimation lead to low contrast and high noise level in ultrafast PD imaging when the number of plane-wave angle and the ensemble length is limited. The coherence-based PD estimation using temporal-multiply-and-sum (TMAS) of high-lag autocorrelation can effectively suppress the uncorrelated noises but at the cost of signal power due to the blood flow decorrelation.

METHODS

In this study, the TMAS PD estimation is incorporated with complementary subset transmit in nonlinear compounding (DMAS-CST) to leverage the signal coherence in both angular and temporal dimensions for improvement of PD image quality. The CST correlation can be performed not only within the same Doppler ensemble (i.e., intra-correlation) but also across the adjacent Doppler ensembles (i.e., inter-correlation) to increase the number of correlation pairs in TMAS PD estimation.

RESULTS

In both simulations and experiments, DMAS-CST is capable of improving the contrast of TMAS PD image by over 10 dB compared to the nonlinear compounding alone by enhanced noise suppression and lower flow decorrelation. When the CST correlations are performed both intra and inter Doppler ensembles, the noise level further reduces in DMAS-CST.

CONCLUSION

Since the TMAS PD estimation is often limited by the loss of signal power due to temporal decorrelation, the design of complementary subsets in DMAS-CST should be carefully examined to preserve the blood flow signal. Future work of this study will focus on how to combine the conventional PD and the TMAS PD for better signal preservation and effective noise suppression.

Estimation of the phase velocity dispersion curves for viscoelastic materials using Point Limited Shear Wave Elastography

Ultrasound shear wave elastography (SWE) is widely used in clinical applications for non-invasive measurements of soft tissue viscoelasticity. The study of tissue viscoelasticity often involves the analysis of shear wave phase velocity dispersion curves, which show how the phase velocity varies with frequency or wavelength. In this study, we propose an alternative method to the two-dimensional Fourier transform (2D-FT) and Phase Gradient (PG) methods for shear wave phase velocity estimation. We introduce a new method called Point Limited Shear Wave Elastography (PL-SWE), which aims to reconstruct phase velocity dispersion curves using a minimal number of measurement points in the spatial domain (as few as two signals can be utilized). We investigated how the positioning of the first signal and the distance between selected signals affect the shear wave velocity dispersion estimation in PL-SWE. The effectiveness of this novel approach was evaluated through the analysis of analytical phantom data in viscoelastic media, along with experimental data from custom-made tissue-mimicking elastic and viscoelastic phantoms, and in vivo renal transplant data. A comparative analysis with the 2D-FT technique revealed that PL-SWE provided phase velocity dispersion curve estimates with root mean squared percentage error (RMSPE) values of less than 1.61% for analytical phantom data, 1.58% for elastic phantoms, 4.29% for viscoelastic phantoms and 7.68% for in vivo data, while utilizing significantly fewer signals compared to 2D-FT. The results demonstrate that the PL-SWE method also outperforms the PG method. For the viscoelastic phantoms, the mean RMSPE values using PL-SWE ranged from 2.61% to 4.29%, while the PG method produced RMSPE values between 3.56% and 15%. In the case of in vivo data, PL-SWE yielded RMSPE values between 7.01% and 7.68%, while PG results ranged from 17% to 418%. These findings highlight the superior accuracy and reliability of the PL-SWE method, particularly when compared to the PG approach. Our tests demonstrate that PL-SWE can effectively measure the phase velocity of both elastic and viscoelastic materials and tissues using a limited number of signals. Utilizing a minimal number of spatial measurement points could enable accurate assessments even in cases with restricted field of view, thereby expanding the applicability of SWE across various patient populations.

A molecular mechanism mediating clozapine-enhanced sensorimotor gating

The atypical antipsychotic clozapine targets multiple receptor systems beyond the dopaminergic pathway and influences prepulse inhibition (PPI), a critical translational measure of sensorimotor gating. Since PPI is modulated by atypical antipsychotics such as risperidone and clozapine, we hypothesized that p11-an adaptor protein associated with anxiety- and depressive-like behaviors and G-protein-coupled receptor function-might modulate these effects. In this study, we assessed the role of p11 in clozapine's PPI-enhancing effect by testing wild-type and global p11 knockout (KO) mice in response to haloperidol, risperidone, and clozapine. We also performed structural and functional brain imaging. Contrary to our expectation that anxiety-like p11-KO mice would exhibit an augmented startle response and heightened sensitivity to clozapine, PPI tests showed that p11-KO mice were unresponsive to the PPI-enhancing effects of risperidone and clozapine. Imaging revealed distinct regional brain volume differences and reduced hippocampal connectivity in p11-KO mice, with significantly blunted clozapine-induced connectivity changes in the CA1 region. Our findings highlight a novel role for p11 in modulating clozapine's effects on sensorimotor gating and hippocampal connectivity, offering new insight into its functional pathways.

Mitigating high frame rate demands in shear wave elastography using radial basis function-based reconstruction: An experimental phantom study

BACKGROUND

Shear wave elastography (SWE) is a technique that quantifies tissue stiffness by assessing the speed of shear waves propagating after being excited by acoustic radiation force. SWE allows the quantification of elastic tissue properties and serves as an adjunct to conventional ultrasound techniques, aiding in tissue characterization. To capture this transient propagation of the shear wave, the ultrasound device must be able to reach very high frame rates.

METHODOLOGY

In this paper, our aim is to relax the high frame rate requirement for SWE imaging. To this end, we propose lower frame rate SWE imaging followed by employing a 2-dimensional (2D) radial basis functions (RBF)-based interpolation. More specifically, the process involves obtaining low frame rate data and then temporal upsampling to reach a synthetic high frame rate data by inserting the 'UpS-1' image frames with missing values between two successive image frames (UpS: Upsampling rate). Finally, we apply the proposed interpolation technique to reconstruct the missing values within the incomplete high frame rate data.

RESULTS AND CONCLUSION

The results obtained from employing the proposed model on two experimental datasets indicate that we can relax the frame rate requirement of SWE imaging by a factor of 4 while maintaining shear wave speed (SWS), group velocity, and phase velocity estimates closely align with the high frame rate SWE model so that the error is less than 3%. Furthermore, analysis of the structural similarity index (SSIM) and root mean squared error (RMSE) on the 2D-SWS maps highlights the efficacy of the suggested technique in enhancing local SWS estimates, even at a downsampling (DS) factor of 4. For DS≤4, the SSIM values between the 2D-SWS maps produced by the proposed technique and those generated by the original high frame rate data consistently remain above 0.94. Additionally, the RMSE values is below 0.37 m/s, indicating promising performance of the proposed technique in reconstruction of SWS values.

Monitoring microvascular changes over time with a repositionable 3D ultrasonic capacitive micromachined row-column sensor

eHealth devices, including smartwatches and smart scales, have the potential to transform health care by enabling continuous, real-time monitoring of vital signs over extended periods. Existing technologies, however, lack comprehensive monitoring of the microvascular network, which is linked to conditions such as diabetes, hypertension, and small vessel diseases. This study introduces an ultrasound approach using a capacitive micromachined ultrasound transducer row-column array for continuous, ultrasensitive three-dimensional (3D) Doppler imaging of microvascular changes such as hemodynamic variations or vascular remodeling. In vitro tests and in vivo studies with healthy volunteers demonstrated the sensor's ability to image the 3D microvascular network at high resolution over different timescales with automatic registration and to detect microvascular changes with high sensitivity. Integrating this technology into wearable devices could, one day, enhance understanding, monitoring, and possibly early detection of microvascular-related health conditions.

Nonlinearity parameter estimation method from fundamental band signal depletion in pulse-echo using a dual-energy model

The estimation of the nonlinearity parameter (B/A) has the potential to be used in the clinical diagnosis of conditions such as liver steatosis. Recently, a pulse-echo method to estimate B/A based on the theory of the fundamental band amplitude depletion of weak waves, namely, the depletion method, was proposed. In the present work, the depletion method is presented with more technical detail. Then, the robustness of the depletion method is assessed by using simulations that diverge from the model requirements: (1) monochromatic plane wave propagation and (2) quadratic power-law frequency dependence attenuation. Regarding requirement (1), the results led to a critical finding that when using wideband pulses (37%-113% bandwidth), the bias of the B/A estimates is larger than the bias obtained using narrowband pulses (11%-28% bandwidth), even if requirement (2) holds. Regarding requirement (2), power-law frequency dependence closer to those of soft tissues, i.e., 1.1 or 1.2, using narrowband pulses presented bias of less than 10%. The use of narrowband pulses also was shown to be robust when the reference phantom and sample had attenuation mismatches of around 60%. Finally, the experimental feasibility of the depletion method was evaluated, showing results with good accuracy (bias <17%), which are consistent with the observations in the simulations.

Ultrafast 3D synthetic aperture imaging with Hadamard-encoded aperiodic interval codes and aperiodic sparse arrays with separate transmitters and receivers

3D synthetic aperture (SA) imaging of volumes can be obtained using sparse 2D ultrasound arrays. However, even with just 256 elements, the volumetric imaging rate can be relatively slow due to having to transmit on each element in succession. Hadamard Aperiodic Interval (HAPI) codes can be used to image the full SA dataset in one extended transmit to speed up the synthetic aperture imaging, but their long nature produces large deadzones if the same elements are used as both transmitters and receivers. In this simulation study, we use a 2D Costas sparse array with separate transmitters and receivers to remedy the deadzone problem, and use it with the HAPI-coded imaging scheme to obtain fully transmit-receive focused, wide field-of-view 3D volumes with high-resolution and high SNR at ultrafast volumetric imaging rates of more than 500 volumes per second, almost nine times faster than non-coded SA imaging with the same imaging parameters. We show similar PSF performance compared to non-coded SA, and a 26 dB improvement in SNR with order-256 HAPI codes. We also present cyst simulations showing similar contrast for the HAPI-coded SA method compared to non-coded SA in the context of no noise, and improved contrast in the context of noise.

Frequency-Domain Decoding of Cascaded Dual- Polarity Waves for Ultrafast Ultrasound Imaging

Ultrafast plane-wave (PW) ultrasound imaging is a versatile tool that has become increasingly relevant for blood flow imaging using speckle tracking but suffers from a low signal-to-noise ratio (SNR). Cascaded dual-polarity wave (CDW) imaging can improve the SNR by transmitting pulse trains, which are subsequently decoded to recover the imaging resolution. However, the current decoding method (in the time domain) requires a set of two acquisitions, which introduces motion artifacts that result in incorrect speckle tracking at high flow velocities. Here, we evaluate an inverse filtering approach that uses frequency-domain decoding to decode acquisitions independently. Experiments using a disk phantom show that frequency-domain decoding of a four-pulse train achieves an SNR gain of up to 4.2 dB, versus 5.9 dB for conventional decoding. The benefit of frequency-domain decoding for flow quantification is assessed through experiments performed with a rotating disk phantom and a parabolic flow, and through matching linear simulations. Both CDW methods improve the tracking accuracy compared to single PW imaging. Time-domain decoding outperforms frequency-domain decoding in low SNR conditions and low velocities ( m/s), as a result of the higher SNR gain. In contrast, frequency-domain decoding outperforms time-domain decoding for high peak velocities in imaging of the rotating disk (1 m/s) and of the parabolic flow (2 m/s), when significant scatterer motion between acquisitions causes imperfect time-domain decoding. Its ability to decode individual acquisitions makes the used frequency-domain decoding of CDW (F-CDW) a promising approach to improve the SNR and thereby the accuracy of flow quantification at high velocities.

Adaptive multilevel thresholding for SVD-based clutter filtering in ultrafast transthoracic coronary flow imaging

BACKGROUND AND OBJECTIVE

The integration of ultrafast Doppler imaging with singular value decomposition clutter filtering has demonstrated notable enhancements in flow measurement and Doppler sensitivity, surpassing conventional Doppler techniques. However, in the context of transthoracic coronary flow imaging, additional challenges arise due to factors such as the utilization of unfocused diverging waves, constraints in spatial and temporal resolution for achieving deep penetration, and rapid tissue motion. These challenges pose difficulties for ultrafast Doppler imaging and singular value decomposition in determining optimal tissue-blood (TB) and blood-noise (BN) thresholds, thereby limiting their ability to deliver high-contrast Doppler images.

METHODS

This study introduces a novel local blood subspace detection method that utilizes multilevel thresholding by the valley-emphasized Otsu's method to estimate the TB and BN thresholds on a pixel-based level, operating under the assumption that the magnitude of the spatial singular vector curve of each pixel resembles the shape of a trimodal Gaussian. Upon obtaining the local TB and BN thresholds, a weighted mask (WM) is generated to assess the blood content in each pixel. To enhance the computational efficiency of this pixel-based algorithm, a dedicated tree-structure k-means clustering approach, further enhanced by noise rejection (NR) at each singular vector order, is proposed to group pixels with similar spatial singular vector curves, subsequently applying local thresholding (LT) on a cluster-based (CB) level.

RESULTS

The effectiveness of the proposed method was evaluated using an ex-vivo setup featuring a Langendorff swine heart. Comparative analysis with power Doppler images filtered using the conventional global thresholding method, which uniformly applies TB and BN thresholds to all pixels, revealed noteworthy enhancements. Specifically, our proposed CBLT+NR+WM approach demonstrated an average 10.8-dB and 11.2-dB increase in Contrast-to-Noise ratio and Contrast in suppressing the tissue signal, paralleled by an average 5-dB (Contrast-to-Noise ratio) and 9-dB (Contrast) increase in suppressing the noise signal.

CONCLUSIONS

These results clearly indicate the capability of our method to attenuate residual tissue and noise signals compared to the global thresholding method, suggesting its promising utility in challenging transthoracic settings for coronary flow measurement.

In vivo assessment of shear modulus along the fibers of pennate muscle during passive lengthening and contraction using steered ultrasound push beams

Ultrasound shear wave elastography (SWE) has emerged as a promising non-invasive method for muscle evaluation by assessing the propagation velocity of an induced shear wavefront. In skeletal muscles, the propagation of shear waves is complex, depending not only on the mechanical and acoustic properties of the tissue but also upon its geometry. This study aimed to comprehensively investigate the influence of muscle pennation angle on the shear wave propagation, which is directly related to the shear modulus. A novel elastography method based on steered pushing beams (SPB) was used to assess the shear modulus along the fibers of the gastrocnemius medialis (pennate) muscle in twenty healthy volunteers. Ultrasound scans were performed during passive muscle lengthening (n = 10) and submaximal isometric contractions (n = 10). The shear modulus along the fibers was compared to the apparent shear modulus, as commonly assessed along the muscle shortening direction using conventional SWE sequences. The shear modulus along the muscle fibers was significantly greater than the apparent shear modulus for passive dorsiflexion angles, while not significantly different throughout the range of plantar flexion angles (i.e., under any or very low tensile loads). The concomitant decrease in pennation angle along with the gradual increase in the shear modulus difference between the two methods as the muscle lengthens, strongly indicates that non-linear elasticity exerts a greater influence on wave propagation than muscle geometry. In addition, significant differences between methods were found across all submaximal contractions, with both shear modulus along the fibers and the pennation angle increasing with the contraction intensity. Specifically, incremental contraction intensity led to a greater bias than passive lengthening, which could be partly explained by distinct changes in pennation angle. Overall, the new SPB sequence provides a rapid and integrated geometrical correction of shear modulus quantification in pennate muscles, thereby eliminating the necessity for specialized systems to align the ultrasound transducer array with the fiber's orientation. We believe that this will contribute for improving the accuracy of SWE in biomechanical and clinical settings.

Improving Ultrasound B-Mode Image Quality with Coherent Plane-Wave Compounding Using Adaptive Beamformers Based on Minimum Variance

Medical ultrasound imaging using coherent plane-wave compounding (CPWC) for higher frame-rate applications has generated considerable interest in the research community. The adaptive Eigenspace Beamformer technique combined with a Generalized Sidelobe Canceler (GSC) provides noise and interference reduction in images, improving resolution and contrast compared to basic methods: Delay and Sum (DAS) and Minimum Variance (MV). Different filtering approaches are applied in ultrasound image processing to reduce speckle signals. This work introduces the combination of beamformer Eigenspace Based on Minimum Variance (ESBMV) associated with GSC (EGSC) and the Kuan (EGSCK), Lee (EGSCL), and Wiener (EGSCW) filters and their enhanced versions to obtain better quality of plane-wave ultrasound images. The EGSCK technique did not present significant improvements compared to other methods. However, the EGSC with enhanced Kuan (EGSCKe) showed a remarkable reduction in geometric distortion, i.e., 0.13 mm (35%) and 0.49 mm (67%) compared to the EGSC and DAS techniques, respectively. The EGSC with Enhanced Wiener (EGSCWe) showed the best improvements in contrast radio (CR) aspects, i.e., 74% compared to the DAS technique and 60% to the EGSC technique. Furthermore, our proposed method reduces geometric distortion, making it a good option for plane-wave ultrasound imaging.

Bedside cerebral microvascular imaging of patients with disorders of consciousness: a feasibility study

Background

Efficient bedside neurofunctional monitoring is crucial for managing disorders of consciousness (DoC). Ultrafast Power Doppler Imaging (uPDI) outperforms traditional Ultrasound in bedside for assessing the microcirculatory system. However, intracranial blood flow imaging traditionally faces limitations due to the skull's impedance. This constraint is circumvented in common post-craniectomy DoC patients, who present a unique observational window for uPDI.

Methods

We conducted uPDI scans on five DoC patients of different ages and consciousness levels who had undergone decompressive craniectomy. We compared the imaging results from uPDI with traditional PDI and identified the physiological and pathological conditions with uPDI.

Results

Detailed microvascular images of both cortical and subcortical areas were obtained using uPDI through the craniectomy window. Notably, uPDI demonstrates high sensitivity and imaging depth, revealing microvessels as small as 320 μm in diameter at 4 cm depth, and detecting blood flow signals up to 6 cm beneath the scalp.

Conclusion

Through the decompressive cranial windows of DoC patients, we obtained cerebral microvascular images with significantly higher sensitivity without the need for contrast agents.

Significance

Our research provides a novel bedside cerebral microcirculation imaging method for patients with DoC, offering convenient neurofunctional assessment to improve the clinical management of DoC patients.

Relationship between contrast-enhanced ultrasound combined with ultrasound resolution microscopy imaging and histological features of hepatocellular carcinoma

OBJECTIVES

Using contrast-enhanced ultrasound (CEUS) and ultrasound resolution microscopy (URM) imaging, this study aimed to evaluate the relationship between microvascular parameters of small hepatocellular carcinoma (sHCC) (≤ 3 cm) and microscopic histological features, which include vessels encapsulating tumour clusters (VETC), microvascular invasion (MVI), and histological grade.

METHODS

Sixteen patients with solitary resected sHCC were prospectively enrolled. CEUS and URM were performed one week before resection. All "ratio" refers to comparisons between the active area (where CEUS microbubble show visible motion track by URM) and the entire lesion. Blood vessel complexity (ratio), blood vessel density (ratio), area (ratio), flow velocity, blood vessel diameter, and perfusion index ("flow velocity" × "vessel ratio") were analysed using URM. The relationships between URM parameters and microscopic histological features (MVI, VETC, and histological grade) were analysed.

RESULTS

There were 5 (31.3%), 8 (50%), and 7 (43.7%) cases of poorly differentiated, MVI-positive, and VETC-positive HCC, respectively. The mean velocity of the entire lesion was higher in the poorly differentiated group than that in the moderately differentiated group (p = 0.026). The complexity ratio (MVI-positive: 1.07 ± 0.03, MVI-negative: 1.03 ± 0.02, p = 0.012), area ratio (MVI-positive: 0.63 ± 0.18, MVI-negative: 0.39 ± 0.16, p = 0.017), and perfusion index (MVI-positive: 8.67 ± 1.88, MVI-negative: 6.42 ± 0.94, p = 0.009) were greater in MVI-positive HCCs. The density ratio (VETC-positive: 1.30 ± 0.19, VETC-negative: 1.10 ± 0.05, p = 0.006) was larger in VETC-positive HCCs.

CONCLUSION

Higher blood flow velocity and area of HCC lesions, and higher blood vessel complexity and density may be related to microscopic histological features. This relationship might provide a strategy of using URM for preoperative non-invasive diagnostic VETC, MVI, and histological grade in the future.

SNR analysis of multi-aperture ultrasound and photoacoustic imaging systems

Multi-aperture ultrasound and photoacoustic imaging systems improve the imaging quality in terms of contrast, field of view, and potentially resolution in comparison to single aperture setups. However, the behavior of signal-to-noise ratio (SNR) in these systems has not been well understood. In this study, we propose a low-parameter predictive model for signal analysis based on the Fourier diffraction theorem. Furthermore, an analytical approach for SNR estimation is devised for both coherent and incoherent compounding methods. The theory is evaluated in simulations and experiments. The results show a great agreement with the theoretical expectation of k-space model for both mono-static and bi-static signals. In addition, the evaluated noise power and peak SNR results follow the analytical expectations. As the number of compounded reconstructed datasets increases, the noise power increases linearly and non-linearly for coherent and incoherent methods, respectively. Still, as demonstrated in both theory and results, for correlated sources, the SNR increases linearly with the number of coherently compounded reconstructions, while it can remain unchanged or even reduced if incoherent compounding is employed. Moreover, for uncorrelated sources, it is shown that compounding different views from several spatially diverse apertures may lead to a decrease in SNR.

A Tracking Prior to Localization Workflow for Ultrasound Localization Microscopy

Ultrasound Localization Microscopy (ULM) has proven effective in resolving microvascular structures and local mean velocities at sub-diffraction-limited scales, offering high-resolution imaging capabilities. Dynamic ULM (DULM) enables the creation of angiography or velocity movies throughout cardiac cycles. Currently, these techniques rely on a Localization-and-Tracking (LAT) workflow consisting in detecting microbubbles (MB) in the frames before pairing them to generate tracks. While conventional LAT methods perform well at low concentrations, they suffer from longer acquisition times and degraded localization and tracking accuracy at higher concentrations, leading to biased angiogram reconstruction and velocity estimation. In this study, we propose a novel approach to address these challenges by reversing the current workflow. The proposed method, Tracking-and-Localization (TAL), relies on first tracking the MB and then performing localization. Through comprehensive benchmarking using both in silico and in vivo experiments and employing various metrics to quantify ULM angiography and velocity maps, we demonstrate that the TAL method consistently outperforms the reference LAT workflow. Moreover, when applied to DULM, TAL successfully extracts velocity variations along the cardiac cycle with improved repeatability. The findings of this work highlight the effectiveness of the TAL approach in overcoming the limitations of conventional LAT methods, providing enhanced ULM angiography and velocity imaging.

A 1.11 mm2 IVUS SoC With -Range Plane Wave Transmit Beamforming at 40 MHz

Intravascular ultrasound (IVUS) imaging catheters are significant tools for cardiovascular interventions, and their use can be expanded by realizing IVUS imaging guidewires and microcatheters. The miniaturization of these devices creates challenges in SNR due to the need for higher frequencies to provide adequate resolution. An integrated IVUS system with transmit beamforming can mitigate these limitations. This work presents the first practical highly integrated system-on-a-chip (SoC) with plane wave transmit beamforming at 40 MHz for IVUS on guidewire or microcatheters. The front-end circuitry has a 20-channel ultrasound transmitter (Tx) and receiver (Rx) array interfaced with a capacitive micromachined ultrasound transducer (CMUT) array. During each firing, all 20 Tx are excited with the same analog delay with respect to each other, which can be continuously adjusted between 0 and 10 ns in two directions, generating a steerable plane wave in a range of +/-50 for a phased array at 40 MHz. The unit delays are generated via a voltage-controlled delay line (VCDL), which only needs two external controls, one tuning the unit delay and the other determining the steering direction. The SoC is fabricated using a 180-nm high-voltage (HV) CMOS process and features a slender active area of 0.3 mm 3.7 mm. The proposed SoC consumes 31.3 mW during the receiving mode. The beamformer's functionality and the SoC's overall performance were validated through acoustic characterization and imaging experiments.

Four-Dimensional (4D) Ultrasound Shear Wave Elastography Using Sequential Excitation

OBJECTIVE

Current shear wave elastography methods primarily focus on 2D imaging. To explore mechanical properties of biological tissues in 3D, a four-dimensional (4D, x, y, z, t) ultrasound shear wave elastography is required. However, 4D ultrasound shear wave elastography is still challenging due to the limitation of the hardware of standard ultrasound acquisition systems. In this study, we introduce a novel method to achieve 4D shear wave elastography, named sequential-based excitation shear wave elastography (SE-SWE). This method can achieve 4D elastography implemented by a 1024-element 2D array with a standard ultrasound 256-channel system.

METHODS

The SE-SWE method employs sequential excitation to generate shear waves, and utilizes a 2D array, dividing it into four sub-sections, to capture shear waves across multiple planes. This process involves sequentially exciting each sub-section to capture shear waves, followed by compounding the acquired data from these subsections.

RESULTS

The phantom studies showed strong concordance between the shear wave speeds (SWS) measured by SE-SWE and expected values, confirming the accuracy of this method and potential to differentiate tissues by stiffness. In ex vivo chicken breast experiments, SE-SWE effectively distinguished between orientations relative to muscle fibers, highlighting its ability to capture the anisotropic properties of tissues.

CONCLUSION

The SE-SWE method advances shear wave elastography significantly by using a 2D array divided into four subsections and sequential excitation, achieving high-resolution volumetric imaging at 1.6mm resolution.

SIGNIFICANCE

The SE-SWE method offers a straightforward and effective approach for 3D shear volume imaging of tissue biological properties.

4-D Vector Doppler Imaging Using Row-Column Addressed Array

Large aperture 4-D blood flow Doppler imaging with high temporal resolution remains an important challenge. Different from the conventional matrix-array strategy, we proposed a 4-D ultrasound vector Doppler (4D-UVD) imaging method using a $128+128$ row-column addressed (RCA) array and a 256-channel ultrasound platform. This method integrates ultrafast 2-D plane wave transmission sequence and least-squares multiangle Doppler velocity estimator. The accuracy of the proposed method was evaluated in both simulations and phantom experiments of parabolic flow. The simulated result shows that the root-mean-squared error (RMSE) of estimated velocity is less than 15%. In the phantom experiments, the relative mean bias $\overline {B}$ and the standard deviation (SD) $\overline {\sigma }$ of the velocity profiles are less than 7.9% and 6.9%, respectively, suggesting a high estimated precision. Furthermore, in vivo feasibility of the approach was demonstrated in the human carotid artery. The blood flow velocity of the carotid artery was continuously measured over seven cardiac cycles at a 1-kHz volume rate. The fluctuations of the estimated mean and peak velocities were highly consistent with the pulse waves measured using a gating pulse sensor, yielding synchronization coefficients of 0.85 and 0.87, respectively. It is thus concluded that the proposed method can achieve a large aperture 4-D vector flow imaging with high temporal resolution using an RCA probe.

Shear wave elastography primer for the abdominal radiologist

PURPOSE

Shear wave elastography (SWE) provides a means for adding information about the mechanical properties of tissues to a diagnostic ultrasound examination. It is important to understand the physics and methods by which the measurements are made to aid interpretation of the results as they relate to disease processes.

METHODS

The components of how ultrasound is used to generate shear waves and make measurements of the induced motion are reviewed. The physics of shear wave propagation are briefly described for elastic and viscoelastic tissues. Additionally, shear wave propagation in homogeneous and inhomogeneous cases is addressed.

RESULTS

SWE technology has been implemented by many clinical vendors with different capabilities. Various quality metrics are used to define valid measurements based on aspects of the shear wave signals or wave velocity estimates.

CONCLUSION

There are many uses for SWE in abdominal imaging, but it is important to understand how the measurements are performed to gauge their utility for diagnosis of different conditions. Continued efforts to make the technology robust in complex clinical situations are ongoing, but many applications actively benefit from added information about tissue mechanical properties for a more holistic view of the patient for diagnosis or assessment of prognosis and treatment management.

Three-dimensional diffractive acoustic tomography

Acoustically probing biological tissues with light or sound, photoacoustic and ultrasound imaging can provide anatomical, functional, and/or molecular information at depths far beyond the optical diffusion limit. However, most photoacoustic and ultrasound imaging systems rely on linear-array transducers with elevational focusing and are limited to two-dimensional imaging with anisotropic resolutions. Here, we present three-dimensional diffractive acoustic tomography (3D-DAT), which uses an off-the-shelf linear-array transducer with single-slit acoustic diffraction. Without jeopardizing its accessibility by general users, 3D-DAT has achieved simultaneous 3D photoacoustic and ultrasound imaging with optimal imaging performance in deep tissues, providing near-isotropic resolutions, high imaging speed, and a large field-of-view, as well as enhanced quantitative accuracy and detection sensitivity. Moreover, powered by the fast focal line volumetric reconstruction, 3D-DAT has achieved 50-fold faster reconstruction times than traditional photoacoustic imaging reconstruction. Using 3D-DAT on small animal models, we mapped the distribution of the biliverdin-binding serpin complex in glassfrogs, tracked gold nanoparticle accumulation in a mouse tumor model, imaged genetically-encoded photoswitchable tumors, and investigated polyfluoroalkyl substances exposure on developing embryos. With its enhanced imaging performance and high accessibility, 3D-DAT may find broad applications in fundamental life sciences and biomedical research.

Fourier energy spectrum centroid: a robust and efficient approach for shear wave speed estimation inω-kspace

Objective.The propagation speed of a shear wave, whether externally or internally induced, in biological tissues is directly linked to the tissue's stiffness. The group shear wave speed (SWS) can be estimated using a class of time-of-flight (TOF) methods in the time-domain or phase speed-based methods in the frequency domain. However, these methods suffer from biased estimations or time-consuming computations, and they are especially prone to wave distortions inin vivocases. In this work, we present a parameter-free, robust, and efficient group SWS estimation method coined as Fourier energy spectrum centroid (FESC).Approach.The proposed FESC method is based on the center of mass inω-kspace. It was evaluated on data from computer simulations with additive Gaussian noise, a commercial elasticity phantom, anex vivopig liver, andin vivobiceps brachii muscles of three young healthy male subjects. The FESC method was compared with two 2D frequency-domain methods: Max-fre, which considers phase SWS at the peak ofk-space, and Fre-regre, which applies linear regression of phase SWS within a fixed bandwidth. Two additional benchmarks included time-domain methods based on cross-correlation (X-Corr) and radon sum transformation (RD).Main results.Statistical results showed that our FESC method and the RD method had comparable accuracy and robustness, outperforming the other benchmark methods. In the simulation and phantom studies, when the signal-to-noise ratio was higher than 25 dB, our FESC showed higher accuracy than RD. In thein vivostudy, our FESC method had better repeatability than RD. Furthermore, the proposed FESC method was 100 times faster than the runner-up method, X-Corr, and 3,000 times faster than the least efficient method, RD.Significance.All results indicated that our proposed Fourier-based method shows promise in reliably and efficiently providing reference values for group SWS in homogeneous bulk media.

A Novel Ultrasound Thermometry Method Based on Thermal Strain and Short and Constant Acoustic Bursts: Preliminary Study in Phantoms

In the field of ultrasound therapy, the estimation of temperature to monitor treatments is becoming essential. We hypothesize that it is possible to measure temperature directly using a constant acoustic power burst. Under the assumption that the acoustic attenuation does not change significantly with temperature, the thermal strain induced by such bursts presents a linear relation with temperature. A mathematical demonstration is given in the introduction. Then, simulations of ultrasound waves in a canine liver model were conducted at different temperatures (from 20 °C to 90 °C). Finally, experimental measurements on phantom samples were performed over the same temperature range. The simulation and experimental results both showed a linear relation between thermal strain and temperature. This relation may suggest the foundation of a new ultrasound-based thermometry method. The potential and limitations of the method are discussed.

Motion-Compensated Interpolation in Echocardiography: A Lie Advection-Based Approach

To better understand cardiac structures and dynamics via echocardiography, it is essential to have cardiac image sequences with sufficient spatio-temporal resolution. However, in echocardiography, there is an inherent tradeoff between temporal and spatial resolution, which limits the ability to acquire images with both high temporal and spatial resolution simultaneously. Motion-compensated interpolation, a post-acquisition technique, enhances the temporal resolution without compromising the spatial resolution. This paper introduces a novel motion-compensated interpolation algorithm based on the advection equation in fluid mechanics. Considering the incompressibility of cardiac tissue, we derive a solution in terms of Lie series for the advection problem. Subsequently, we construct a bidirectional advection energy model to estimate the optimal velocity fields that can simultaneously advect two cardiac images towards each other. The process continues until they converge at a midpoint where the image similarity peaks. To preserve the topology of the cardiac structures and ensure that image deformations are diffeomorphic, the advection process is carried out gradually with a smooth velocity field. To reduce the contribution of the blood signal in optimizing for the best tissue advection velocity, a nonlocal regularization pre-processing is applied to echocardiography data. Our algorithm, tested on 2D and 3D echocardiography, outperforms existing motion-compensated interpolation algorithms in estimating cardiac motions. It preserves cardiac topology during image deformations and reduces interpolation artifacts, especially in low frame rate recordings. By training a neural network on the data generated by our algorithm, we achieved over 75 times faster computation without compromising image quality.

Continuous Emission Ultrasound: A New Paradigm to Ultrafast Ultrasound Imaging

Current imaging techniques in echography rely on the pulse-echo (PE) paradigm which provides a straight-forward access to the in-depth structure of tissues. They inherently face two major challenges: the limitation of the pulse repetition frequency, directly linked to the imaging framerate, and, due to the emission scheme, their blindness to the phenomena that happen in the medium during the majority of the acquisition time. To overcome these limitations, we propose a new paradigm for ultrasound imaging, denoted by continuous emission ultrasound imaging (CEUI) (Liebgott et al., 2023), for a single input single output (SISO) device. A continuous insonification of the medium is done by the probe using a coded waveform inspired from the radar and sonar literature. A framework coupling a sliding window approach (SWA) and pulse compression methods processes the recorded echoes to rebuild a motion-mode (M-mode) image from the medium with a high temporal resolution compared to state-of-the-art ultrafast imaging methods. A study on realistic simulated data, with regards to the motion of the medium, has been carried out and, achieved results assess an unequivocal improvement of the slow time frequency up to, at least, two orders of magnitude compared to ultrafast US imaging methods. This enhancement leads, therefore, to a ten times improvement in the temporal separability of the imaging system. In addition, it demonstrates the capability of CEUI to catch relatively short and quick events, in comparison to the imaging period of PE methods, at any instant of the acquisition.

TinyProbe: A Wearable 32-Channel Multimodal Wireless Ultrasound Probe

The need for continuous monitoring of cardiorespiratory activity, blood pressure, bladder, muscle motion analysis, and more is pushing for research and development of wearable ultrasound (US) devices. In this context, there is a critical need for highly configurable, energy-efficient wearable US systems with wireless access to raw data and long battery life. Previous exploratory works have primarily relied on bulky commercial research systems or custom-built prototypes with limited and narrowly focused field applicability. This article presents TinyProbe, a novel multimodal wearable US platform. TinyProbe integrates a 32-channel US receive (RX)/transmit (TX) front-end, including TX beamforming ( excitations, 16 delay profiles) and analog-to-digital conversion (up to 30 Ms/s, 10 bit), with a Wi-Fi link (21.6 Mb/s, UDP), for wireless raw data access, all in a compact ( mm) and lightweight (35 g) design. Using advanced power-saving techniques and optimized electronics design, TinyProbe achieves a power consumption of <1 W for imaging modes (32 ch., 33 Hz) and <1.3 W for high-PRF Doppler mode (2 ch., 1400 Hz). This results in a state-of-the-art power efficiency of 44.9 mW/Mb/s for wireless US systems, ensuring multihour operation with a compact 500 mAh Li-Po battery. We validate TinyProbe as a versatile, general-purpose wearable platform in multiple in vivo imaging scenarios, including muscle and bladder imaging, and blood flow velocity measurements.

Image quality improvement in single plane-wave imaging using deep learning

In ultrasound image diagnosis, single plane-wave imaging (SPWI), which can acquire ultrasound images at more than 1000 fps, has been used to observe detailed tissue and evaluate blood flow. SPWI achieves high temporal resolution by sacrificing the spatial resolution and contrast of ultrasound images. To improve spatial resolution and contrast in SPWI, coherent plane-wave compounding (CPWC) is used to obtain high-quality ultrasound images, i.e., compound images, by coherent addition of radio frequency (RF) signals acquired by transmitting plane waves in different directions. Although CPWC produces high-quality ultrasound images, their temporal resolution is lower than that of SPWI. To address this problem, some methods have been proposed to reconstruct a ultrasound image comparable to a compound image from RF signals obtained by transmitting a small number of plane waves in different directions. These methods do not fully consider the properties of RF signals, resulting in lower image quality compared to a compound image. In this paper, we propose methods to reconstruct high-quality ultrasound images in SPWI by considering the characteristics of RF signal of a single plane wave to obtain ultrasound images with image quality comparable to CPWC. The proposed methods employ encoder-decoder models of 1D U-Net, 2D U-Net, and their combination to generate the high-quality ultrasound images by minimizing the loss that considers the point spread effect of plane waves and frequency spectrum of RF signals in training. We also create a public large-scale SPWI/CPWC dataset for developing and evaluating deep-learning methods. Through a set of experiments using the public dataset and our dataset, we demonstrate that the proposed methods can reconstruct higher-quality ultrasound images from RF signals in SPWI than conventional method.

High resolution ultrasonic imaging of extended targets via combined match field and time delay beamforming

Ultrasound imaging using an active sensing array has been extensively studied in both time domain and frequency domain. Subspace decomposition methods in match field beamforming such as the multiple signal classification (MUSIC) algorithm can achieve subwavelength resolution of distinct point scatterers. However, when the size of the target is on the order of one wavelength or larger, the MUSIC type algorithms suffer from poor performance due to a tangled eigen structure. This paper proposes an adaptive match field beamformer that does not require subspace decomposition to achieve high resolution imaging of extended targets. Specifically, the broadband coherent white noise constraint (C-WNC) algorithm is utilized to achieve high focusing ability of extended targets by exploiting the cross-frequency coherence in an active sensing scheme. The dynamic range bias in the adaptive beamformer benefits the C-WNC algorithm to achieve high contrast regardless of the SNR. Both simulations and experiments show that the C-WNC images retain their resolution cells on the tips of the extended target with sizes ranging from a wavelength to sizes as large as the physical aperture width. A robust imaging scheme is then proposed to obtain high quality images by combining C-WNC images with a statistically stable delay-multiply-and-sum (DMAS) algorithm to create high-contrast and high-resolution images of extended targets in both azimuth and axial range directions.

Unveiling the potential of ultrasound in brain imaging: Innovations, challenges, and prospects

Within medical imaging, ultrasound serves as a crucial tool, particularly in the realms of brain imaging and disease diagnosis. It offers superior safety, speed, and wider applicability compared to Magnetic Resonance Imaging (MRI) and X-ray Computed Tomography (CT). Nonetheless, conventional transcranial ultrasound applications in adult brain imaging face challenges stemming from the significant acoustic impedance contrast between the skull bone and soft tissues. Recent strides in ultrasound technology encompass a spectrum of advancements spanning tissue structural imaging, blood flow imaging, functional imaging, and image enhancement techniques. Structural imaging methods include traditional transcranial ultrasound techniques and ultrasound elastography. Transcranial ultrasound assesses the structure and function of the skull and brain, while ultrasound elastography evaluates the elasticity of brain tissue. Blood flow imaging includes traditional transcranial Doppler (TCD), ultrafast Doppler (UfD), contrast-enhanced ultrasound (CEUS), and ultrasound localization microscopy (ULM), which can be used to evaluate the velocity, direction, and perfusion of cerebral blood flow. Functional ultrasound imaging (fUS) detects changes in cerebral blood flow to create images of brain activity. Image enhancement techniques include full waveform inversion (FWI) and phase aberration correction techniques, focusing on more accurate localization and analysis of brain structures, achieving more precise and reliable brain imaging results. These methods have been extensively studied in clinical animal models, neonates, and adults, showing significant potential in brain tissue structural imaging, cerebral hemodynamics monitoring, and brain disease diagnosis. They represent current hotspots and focal points of ultrasound medical research. This review provides a comprehensive summary of recent developments in brain imaging technologies and methods, discussing their advantages, limitations, and future trends, offering insights into their prospects.

Cubic nonlinearity and surface shock waves in soft tissue-like materials

The cubic nonlinearity of shear wave propagation plays a significant role in brain injury biomechanics. However, soft materials, like the brain, also support the propagation of surface waves, which produce a combination of longitudinal and transverse deformation. The order of the nonlinearity of surface waves in soft materials is still unknown. Here, we directly observe nonlinear Scholte waves propagating in an interface formed by an incompressible gelatin tissue-mimicking phantom and a water layer using ultrasound imaging operated as fast as 16667 frames per second. A two-dimensional correlation-based tracking algorithm was utilized to extract movies of the movement produced by the surface wave. Our results show that the initially nearly monochromatic wave becomes progressively distorted with the propagation due to nonlinearity. The distortion of the wave and its frequency spectrum indicate a high content of odd harmonics when compared with even harmonics. Additionally, by fitting our experimental data to a minimalist one-dimensional model based on the wave speed variation as a function of the perturbation amplitude, we found a cubic nonlinear parameter 46 times larger than the quadratic nonlinear parameter. Overall, the wave distortion, the harmonic development, and the dependence of the wave speed with the amplitude prove that cubic nonlinearity is essential to modeling nonlinear Scholte wave propagation.

High volume-rate echocardiography for simultaneous imaging of electromechanical activation and cardiac strain of the whole heart in a single heartbeat in humans

BACKGROUND

Imaging both electrical and mechanical cardiac function can better characterize cardiac disease and improve patient care. Currently, there is no noninvasive technique that can simultaneously image both electrical and mechanical function of the whole heart at the point of care. Here, our aim is to demonstrate that high volume-rate echocardiography can simultaneously map cardiac electromechanical activation and end-systolic cardiac strain of the whole heart in a single heartbeat.

METHOD

A 32x32 ultrasound matrix array connected to four synchronized ultrasound scanners were used for transthoracic high volume-rate imaging (840 volumes/s) in sixteen young volunteers (28.1±4.2 y.o.). An electromechanical activation map of the whole heart and volumetric end-systolic atrial and ventricular strain images were obtained.

RESULTS

The whole heart activation sequence was found to be consistent across volunteers and in agreement with previously reported normal electrical activation sequences. The mean electromechanical activation time was 72.6±15.2 ms in the atria, 132.4±19.7 ms in the ventricles and 154.5±19.6 ms in the whole heart. Volumetric right and left atrial as well as right and left ventricular strains were also consistent across all volunteers, with a mean end-systolic global longitudinal strain of 26.8±6.5% in the atria and -16.6±3.4% in the ventricles.

CONCLUSIONS

This initial feasibility study demonstrates that noninvasive high-volume rate imaging of the heart in a single heartbeat is feasible and can provide electromechanical activation and systolic strains simultaneously in all four cardiac chambers. This technique can be further developed and used at the point of care to assist for screening, diagnosis, therapy guidance and follow-up of heart disease patients.

RADD-CycleGAN: unsupervised reconstruction of high-quality ultrasound image based on CycleGAN with residual attention and dual-domain discrimination

Plane wave (PW) imaging is fast, but limited by poor imaging quality. Coherent PW compounding (CPWC) improves image quality but decrease frame rate. In this study, we propose a modified CycleGAN model that combines a residual attention module with a space-frequency dual-domain discriminator, termed RADD-CycleGAN, to rapidly reconstruct high-quality ultrasound images. To enhance the ability to reconstruct image details, we specially design a process of hybrid dynamic and static channel selection followed by the frequency domain discriminator. The low-quality images are generated by the 3-angle CPWC, while the high-quality images are generated as real images (ground truth) by the 75-angle CPWC. The training set includes unpaired images, whereas the images in the test set are paired to verify the validity and superiority of the proposed model. Finally, we respectively design ablation and comparison experiments to evaluate the model performance. Compared with the basic CycleGAN, our proposed method reaches a better performance, with a 7.8% increase in the peak signal-to-noise ratio and a 22.2% increase in the structural similarity index measure. The experimental results show that our method achieves the best unsupervised reconstruction from low quality images in comparison with several state-of-the-art methods.

A unified framework combining coherent compounding, harmonic imaging and angular coherence for simultaneous high-quality B-mode and tissue Doppler in ultrafast echocardiography

Various methods have been proposed to enhance image quality in ultrafast ultrasound. Coherent compounding can improve image quality using multiple steered diverging transmits when motion occurring between transmits is corrected for. Harmonic imaging, a standard technique in conventional focused echocardiography, has been adapted for ultrafast imaging, reducing clutter. Coherence-based approaches have also been shown to increase contrast in clinical settings by enhancing signals from coherent echoes and reducing clutter. Herein, we introduce a simple, unified framework that combines motion-correction, harmonic imaging, and angular-coherence, showing for the first time that their benefits can be combined in real-time. Validation was conducted through in vitro testing on a spinning disk model and in vivo on 4 volunteers. In vitro results confirmed the unified framework capability to achieve high contrast in large-motion contexts up to 17 cm/s. In vivo testing highlighted proficiency in generating images of high quality during low and high tissue velocity phases of the cardiac cycle. Specifically, during ventricular filling, the unified framework increased the gCNR from 0.47 to 0.87 when compared against coherent compounding.

High-Frame-Rate Ultrasound Velocimetry in the Healthy Femoral Bifurcation: A Comparative Study Against 4-D Flow Magnetic Resonance Imaging

OBJECTIVE

Local flow dynamics impact atherosclerosis yet are difficult to quantify with conventional ultrasound techniques. This study investigates the performance of ultrasound vector flow imaging (US-VFI) with and without ultrasound contrast agents in the healthy femoral bifurcation.

METHODS

High-frame-rate ultrasound data with incremental acoustic outputs were acquired in the femoral bifurcations of 20 healthy subjects before (50V) and after contrast injection (2V, 5V and 10V). 2-D blood-velocity profiles were obtained through native blood speckle tracking (BST) and contrast tracking (echo particle image velocimetry [echoPIV]). As a reference, 4-D flow magnetic resonance imaging (4-D flow MRI) was acquired. Contrast-to-background ratio and vector correlation were used to assess the quality of the US-VFI acquisitions. Spatiotemporal velocity profiles were extracted, from which peak velocities (PSV) were compared between the modalities. Furthermore, root-mean-square error analysis was performed.

RESULTS

US-VFI was successful in 99% of the cases and optimal VFI quality was established with the 10V echoPIV and BST settings. A good correspondence between 10V echoPIV and BST was found, with a mean PSV difference of -0.5 cm/s (limits of agreement: -14.1-13.2). Both US-VFI techniques compared well with 4-D flow MRI, with a mean PSV difference of 1.4 cm/s (-18.7-21.6) between 10V echoPIV and MRI, and 0.3 cm/s (-23.8-24.4) between BST and MRI. Similar complex flow patterns among all modalities were observed.

CONCLUSION

2-D blood-flow quantification of femoral bifurcation is feasible with echoPIV and BST. Both modalities showed good agreement compared to 4-D flow MRI. For the femoral tract the administration of contrast was not needed to increase the echogenicity of the blood for optimal image quality.