Quantitative assessment of breast lesion viscoelasticity: initial clinical results using supersonic shear imaging

Shear wave trajectory detection in ultra-fast M-mode images for liver fibrosis assessment: A deep learning-based line detection approach

Stiffness measurement using shear wave propagation velocity has been the most common non-invasive method for liver fibrosis assessment. The velocity is captured through a trace recorded by transient ultrasonographic elastography, with the slope indicating the velocity of the wave. However, due to various factors such as noise and shear wave attenuation, detecting shear wave trajectory on wave propagation maps is a challenging task. In this work, we made the first attempt to use deep learning methods for shear wave trajectory detection on wave propagation maps. Specifically, we adopted five deep learning models in this task and evaluated them by using a well-acknowledged metric based on EA-Angular-Score (EAA) and task-specific metric based on Young s-Score (Ys) in the line-detection field. Furthermore, we proposed an end-to-end framework based on a Transformer and Hough transform, named Transformer-enhanced Hough Transform (TEHT). It took a wave propagation map as input image and directly output the slope of the shear wave trajectory. The framework extracts multi-scale local features from wave propagation maps, employs a deformable attention mechanism for feature fusion, identifies the target line using the Hough transform's voting mechanism, and calculates the contribution of each scale through channel attention. Wave propagation maps from 68 patients were utilized in this study, with manual annotation performed by a rater who was trained as a radiologist, serving as the reference value. The evaluation revealed that the SLNet model exhibited F-measure of EA and Ys values as 40.33 % and 40.72 %, respectively, while the TEHT model showed F-measure of EA and Ys values as 80.96 % and 98.00 %, respectively. TEHT yielded significantly better performance than other deep learning models. Moreover, TEHT demonstrated strong concordance with the gold standard, yielding R2 values of 0.967 and 0.968 for velocity and liver stiffness, respectively. The present study therefore suggests the application of the TEHT model for assessing liver fibrosis owing to its superiority among the five deep learning models.

Frame composite imaging method based on time-sharing latency excitation for ultrasound shear wave elastography

Ultrasound shear wave elastography is an imaging modality that noninvasively assesses mechanical properties of tissues. The results of elastic imaging are obtained by accurately estimating the propagation velocity of shear wave fronts. However, the acquisition rate of the shear wave acquisition device is limited by the hardware of the system. Therefore, increasing the collection rate of shear waves can directly improve the quality of shear wave velocity images. In addition, the problem of velocity reconstruction with relatively small elastic inclusions has always been a challenge in elastic imaging and a very important and urgent issue in early disease diagnosis. For the problem of elastography detection of the shape and boundary of inclusions in tissues, Time-sharing latency excitation frame composite imaging (TS-FCI) method is proposed for tissue elasticity measurement. The method fuses the shear wave motion data generated by time sharing and latency excitation to obtain a set of composite shear wave motion data. Based on the shear wave motion data, the local shear wave velocity image is reconstructed in the frequency domain to obtain the elastic information of the tissue. The experimental results show that the TS-FCI method has a velocity estimation error of 11 % and a contrast to noise ratio (CNR) of 3.81 when estimating inclusions with smaller dimensions (2.53 mm). Furthermore, when dealing with inclusions with small elastic changes (10 kPa), the velocity estimation error is 3 % and the CNR is 3.21. Compared to conventional time-domain and frequency-domain analysis methods, the proposed method has advantages. Results and analysis have shown that this method has potential promotional value in the quantitative evaluation of organizational elasticity.

Lumbar multifidus layers stiffness at L5-S1 level in prone and sitting posture measured by shear wave elastography

BACKGROUND

Multifidus is an important lumbar muscle with distinct superficial and deep fibers responsible for torque production and stabilization, respectively. Its mechanical properties change when transitioning from lying to sitting positions, necessitating enhanced stability. It holds crucial clinical relevance to assess these layers separately, especially in the sitting posture, which demands increased neuromuscular control compared to the prone position.

OBJECTIVE

To compare lumbar multifidus stiffness in lying versus sitting postures, analyzing both superficial and deep layers.

METHODS

Supersonic Shear Imaging captured elastographic images from 26 asymptomatic volunteers in prone and seated positions.

RESULTS

Left multifidus shear modulus in lying: 5.98 ± 1.80/7.96 ± 1.59 kPa (deep/superficial) and sitting: 12.58 ± 4.22/16.04 ± 6.65 kPa. Right side lying: 6.08 ± 1.97/7.80 ± 1.76 kPa and sitting: 13.25 ± 4.61/17.95 ± 7.12 kPa. No side differences (lying p= 0.99, sitting p= 0.43). However, significant inter-postural differences occurred.

CONCLUSION

Lumbar multifidus exhibits increased stiffness in sitting, both layers affected, with superior stiffness in superficial versus deep fibers. Applying these findings could enhance assessing multifidus stiffness changes, for classifying tension-induced low back pain stages.

Quantifying radiation-induced breast fibrosis by shear-wave elastography in patients with breast cancer: A 12-months-follow-up data of a prospective study

Purpose

To assess radiation-induced fibrosis (RIF) using shear-wave elastography (SWE) in patients with breast cancer who received radiotherapy (RT) after breast conserving surgery.

Methods

Forty-one patients were enrolled in a prospective study before RT. SWE and B-mode ultrasonography were performed to measure elasticity. For quantitative measurement, the maximum elasticity value was measured in the tumor bed and non-tumor bed of the treated breast, and contralateral breast before RT and at 3, and 12 months after RT. and RIF was recorded using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

Results

The mean ± standard deviation elasticity values for the tumor bed, non-tumor bed, and contralateral breast were 71.2 ± 74.9 kPa, 19.4 ± 9.8 kPa and 20.3 ± 10.0 kPa before RT; 28.7 ± 26.3 kPa, 15.1 ± 7.0 kPa, and 14.7 ± 6.3 kPa at 12 months after RT, respectively. The elasticity values for all three measurement areas before and 12 months after RT were significantly different (p < 0.001 for tumor bed, p = 0.002 for non-tumor bed, p = 0.001 for contralateral breast). At 12 months follow-up, the distribution of grades of RIF evaluated by CTCAE grade was grade 0 in 43.9 %, grade 1 in 48.8 %, and grade 2 in 7.3 %.

Conclusion

We demonstrated that SWE enables the evaluation of tissue stiffness to provide quantified information for the RIF of breast cancer. Further studies with long-term follow-up should provide more quantitative data.

Effect of rt-PA on Shear Wave Mechanical Assessment and Quantitative Ultrasound Properties of Blood Clot Kinetics In Vitro

OBJECTIVE

The consequences associated with blood clots are numerous and are responsible for many deaths worldwide. The assessment of treatment efficacy is necessary for patient follow-up and to detect treatment-resistant patients. The aim of this study was to characterize the effect of treatment on blood clots in vitro using quantitative ultrasound parameters.

METHODS

Blood from 10 pigs was collected to form three clots per pig in gelatin phantoms. Clots were subjected to 1) no treatment, 2) rt-PA (recombinant tissue plasminogen activator) treatment after 20 minutes of clotting, and 3) rt-PA treatment after 60 minutes of clotting. Clots were weighted before and after the experiment to assess the treatment effect by the mass loss. The clot kinetics was studied over 100 minutes using elastography (Young's modulus, shear wave dispersion, and shear wave attenuation). Homodyne K-distribution (HKD) parameters derived from speckle statistics were also studied during clot formation and dissolving (diffuse-to-total signal power ratio and intensity parameters).

RESULTS

Treated clots loosed significantly more mass than non-treated ones (P < .005). A significant increase in Young's modulus was observed over time (P < .001), and significant reductions were seen for treated clots at 20 or 60 minutes compared with untreated ones (P < .001). The shear wave dispersion differed for treated clots at 60 minutes versus no treatments (P < .001). The shear wave attenuation decreased over time (P < .001), and was different for clots treated at 20 minutes versus no treatments (P < .031). The HKD intensity parameter varied over time (P < .032), and was lower for clots treated at 20 and 60 minutes than those untreated (P < .001 and P < .02).

CONCLUSION

The effect of rt-PA treatment could be confirmed by a decrease in Young's modulus and HKD intensity parameter. The shear wave dispersion and shear wave attenuation were sensitive to late and early treatments, respectively. The Young's modulus, shear wave attenuation, and HKD intensity parameter varied over time despite treatment.

Biopathologic Characterization and Grade Assessment of Breast Cancer With 3-D Multiparametric Ultrasound Combining Shear Wave Elastography and Backscatter Tensor Imaging

OBJECTIVE

Despite recent improvements in medical imaging, the final diagnosis and biopathologic characterization of breast cancers currently still requires biopsies. Ultrasound is commonly used for clinical examination of breast masses. B-Mode and shear wave elastography (SWE) are already widely used to detect suspicious masses and differentiate benign lesions from cancers. But additional ultrasound modalities such as backscatter tensor imaging (BTI) could provide relevant biomarkers related to tissue organization. Here we describe a 3-D multiparametric ultrasound approach applied to breast carcinomas in the aims of (i) validating the ability of BTI to reveal the underlying organization of collagen fibers and (ii) assessing the complementarity of SWE and BTI to reveal biopathologic features of diagnostic interest.

METHODS

Three-dimensional SWE and BTI were performed ex vivo on 64 human breast carcinoma samples using a linear ultrasound probe moved by a set of motors. Here we describe a 3-D multiparametric representation of the breast masses and quantitative measurements combining B-mode, SWE and BTI.

RESULTS

Our results reveal for the first time that BTI can capture the orientation of the collagen fibers around tumors. BTI was found to be a relevant marker for assessing cancer stages, revealing a more tangent tissue orientation for in situ carcinomas than for invasive cancers. In invasive cases, the combination of BTI and SWE parameters allowed for classification of invasive tumors with respect to their grade with an accuracy of 95.7%.

CONCLUSION

Our results highlight the potential of 3-D multiparametric ultrasound imaging for biopathologic characterization of breast tumors.

SWENet: A Physics-Informed Deep Neural Network (PINN) for Shear Wave Elastography

Shear wave elastography (SWE) enables the measurement of elastic properties of soft materials in a non-invasive manner and finds broad applications in various disciplines. The state-of-the-art SWE methods rely on the measurement of local shear wave speeds to infer material parameters and suffer from wave diffraction when applied to soft materials with strong heterogeneity. In the present study, we overcome this challenge by proposing a physics-informed neural network (PINN)-based SWE (SWENet) method. The spatial variation of elastic properties of inhomogeneous materials has been introduced in the governing equations, which are encoded in SWENet as loss functions. Snapshots of wave motions have been used to train neural networks, and during this course, the elastic properties within a region of interest illuminated by shear waves are inferred simultaneously. We performed finite element simulations, tissue-mimicking phantom experiments, and ex vivo experiments to validate the method. Our results show that the shear moduli of soft composites consisting of matrix and inclusions of several millimeters in cross-section dimensions with either regular or irregular geometries can be identified with excellent accuracy. The advantages of the SWENet over conventional SWE methods consist of using more features of the wave motions and enabling seamless integration of multi-source data in the inverse analysis. Given the advantages of SWENet, it may find broad applications where full wave fields get involved to infer heterogeneous mechanical properties, such as identifying small solid tumors with ultrasound SWE, and differentiating gray and white matters of the brain with magnetic resonance elastography.

Quantitative measurements of radiation-induced fibrosis for head and neck cancer: A narrative review

Objectives

To provide a comprehensive summary of the different modalities available to measure soft tissue fibrosis after radiotherapy in head and neck cancer patients.

Data Sources

PubMed, Scopus, and Web of Sciences.

Review Methods

A search was conducted using a list of medical subject headings and terms related to head and neck oncology, radiation fibrosis, and quantitative measurements, including bioimpedance, MRI, and ultrasound. Original research related to quantitative measurement of neck fibrosis post-radiotherapy was included without time constraints, while reviews, case reports, non-English texts, and inaccessible studies were excluded. Discrepancies during the review were resolved by discussing with the senior author until consensus was reached.

Results

A total of 284 articles were identified and underwent title and abstract screening. Seventeen articles had met our criteria for full-text review based on relevance, of which nine had met our inclusion criteria. Young's modulus (YM) and viscoelasticity measures have demonstrated efficacy in quantifying neck fibrosis, with fibrotic tissues displaying significantly higher YM values and altered viscoelastic properties such as increased stiffness rate-sensitivity and prolonged stress-relaxation post-radiation. Intravoxel incoherent motion offers detailed insights into tissue changes by assessing the diffusion of water molecules and blood perfusion, thereby differentiating fibrosed from healthy tissues. Shear wave elastography has proven to be an effective technique for quantifying radiation-induced fibrosis in the head and neck region by measuring shear wave velocity.

Conclusion

There are various modalities to measure radiation-induced fibrosis, each with its unique strengths and limitations. Providers should be aware of these implications and decide on methodologies based on their specific clinical workflow.

Level of Evidence

Step 5.

Effect of Hydrogel Stiffness on Chemoresistance of Breast Cancer Cells in 3D Culture

Chemotherapy is one of the most common strategies for cancer treatment, whereas drug resistance reduces the efficiency of chemotherapy and leads to treatment failure. The mechanism of emerging chemoresistance is complex and the effect of extracellular matrix (ECM) surrounding cells may contribute to drug resistance. Although it is well known that ECM plays an important role in orchestrating cell functions, it remains exclusive how ECM stiffness affects drug resistance. In this study, we prepared agarose hydrogels of different stiffnesses to investigate the effect of hydrogel stiffness on the chemoresistance of breast cancer cells to doxorubicin (DOX). Agarose hydrogels with a stiffness range of 1.5 kPa to 112.3 kPa were prepared and used to encapsulate breast cancer cells for a three-dimensional culture with different concentrations of DOX. The viability of the cells cultured in the hydrogels was dependent on both DOX concentration and hydrogel stiffness. Cell viability decreased with DOX concentration when the cells were cultured in the same stiffness hydrogels. When DOX concentration was the same, breast cancer cells showed higher viability in high-stiffness hydrogels than they did in low-stiffness hydrogels. Furthermore, the expression of P-glycoprotein mRNA in high-stiffness hydrogels was higher than that in low-stiffness hydrogels. The results suggested that hydrogel stiffness could affect the resistance of breast cancer cells to DOX by regulating the expression of chemoresistance-related genes.

Corneal biomechanics and diagnostics: a review

PURPOSE

Corneal biomechanics is an emerging field and the interest into physical and biological interrelations in the anterior part of the eye has significantly increased during the past years. There are many factors that determine corneal biomechanics such as hormonal fluctuations, hydration and environmental factors. Other factors that can affect the corneas are the age, the intraocular pressure and the central corneal thickness. The purpose of this review is to evaluate the factors affecting corneal biomechanics and the recent advancements in non-destructive, in vivo measurement techniques for early detection and improved management of corneal diseases.

METHODS

Until recently, corneal biomechanics could not be directly assessed in humans and were instead inferred from geometrical cornea analysis and ex vivo biomechanical testing. The current research has made strides in studying and creating non-destructive and contactless techniques to measure the biomechanical properties of the cornea in vivo.

RESULTS

Research has indicated that altered corneal biomechanics contribute to diseases such as keratoconus and glaucoma. The identification of pathological corneas through the new measurement techniques is imperative for preventing postoperative complications.

CONCLUSIONS

Identification of pathological corneas is crucial for the prevention of postoperative complications. Therefore, a better understanding of corneal biomechanics will lead to earlier diagnosis of ectatic disorders, improve current refractive surgeries and allow for a better postoperative treatment.

On the Role of Coherent Plane Wave Compounding in Shear Wave Elasticity Imaging: The Convolution Effect and Its Implications

OBJECTIVE

The clinical applicability of shear wave elasticity imaging (SWEI) has been confounded by its appreciable inter-system variability and unsatisfactory sensitivity. While SWEI relies on plane wave imaging (PWI) to achieve real-time rendering, it has been rarely noticed that PWI can affect SWEI's performance. This work is aimed at demonstrating that the use of coherent plane wave compounding (CPWC) can be a factor causing SWEI's underperformance.

METHODS

We presented a model to formally describe the slow-time behavior of CPWC in motion tracking. This model reveals that CPWC introduces temporal convolution on the observed motion, making the motion sampling process a low-pass filter (LPF). For validation, shear waves were produced in a phantom in the same way but sampled via PWI using different compounding numbers (CN) and pulse repetition frequencies (PRF), with the obtained signals compared with the inferences drawn from our model. Similar experiments were performed to reconstruct two small targets in the phantom in order to appraise the impact of CPWC on SWEI's sensitivity.

DISCUSSION

The validation experiment shows that the measurements match well with the model inferences, which verifies the LPF nature of CPWC. The phantom study also shows that either increasing CN or decreasing PRF can cause the loss of high-frequency motion information, leading to blurred target delineation by SWEI.

CONCLUSION

The convolution effect can help understand the variability of SWEI. Researchers should beware this effect when working on SWEI standardization. Clinicians using SWEI should also be cautious because this effect makes it harder to identify small lesions.

Role of Shear Wave Elastography in the Diagnosis of Peyronie Disease

OBJECTIVES

The present study aims to explore the role of shear wave elastography (SWE) in the diagnosis of Peyronie disease (PD).

METHODS

A total of 59 PD patients and 59 age-matched healthy adult men were included in this study. The B-mode ultrasound (US) and SWE were performed for all subjects, and the Young modulus (YM) values of the corresponding regions of the penis in the PD and control groups were recorded and compared.

RESULTS

The mean age of the included PD patients and age-matched controls was 53.81 years (SD 9.52, range 32-73). On B-mode US evaluation, 41 (69.5%) of 59 included PD patients were found to have penile plaques, and the remaining 18 (30.5%) patients had no evidence of penile plaque. After evaluation using SWE, the YM values in the penile plaque region of these 41 patients with penile dysplasia were found to be significantly higher (60.29 kPa ± 19.95) than those outside the plaque (in the same patient) (21.05 kPa ± 4.58) and in the same penile region of the control group (20.59 kPa ± 4.65) (P < .001). In the remaining 18 PD patients, the results showed that the YM value of the abnormal penile region in the PD patients (56.67 kPa ± 13.52) was significantly higher than the YM value outside the abnormal penile region in the same patients (22.79 kPa ± 4.31) and in the same penile region in the control group (19.87 kPa ± 3.48) (P < .001; P < .001).

CONCLUSIONS

In conclusion, this study showed that SWE as a non-invasive technique is useful in identifying and differentiating penile plaques in PD patients and is a simple, rapid and complementary method to B-mode US.

Modified multi-Rayleigh model-based statistical analysis of ultrasound envelope for quantification of liver steatosis and fibrosis

PURPOSE

Quantitative diagnosis of the degree of fibrosis progression is currently a focus of attention for fatty liver in nonalcoholic steatohepatitis (NASH). However, previous studies have focused on either lipid droplets or fibrotic tissue, and few have reported the evaluation of both in patients whose livers contain adipose and fibrous features. Our aim was to evaluate fibrosis tissue and lipid droplets in the liver.

METHODS

We used an analytical method combining the multi-Rayleigh (MRA) model and a healthy liver structure filter (HLSF) as a technique for statistical analysis of the amplitude envelope to estimate fat and fibrotic volumes in clinical datasets with different degrees of fat and fibrosis progression.

RESULTS

Fat mass was estimated based on the non-MRA fraction corresponding to the signal characteristics of aggregated lipid droplets. Non-MRA fraction has a positive correlation with fat mass and is effective for detecting moderate and severe fatty livers. Progression of fibrosis was estimated using MRA parameters in combination with the HLSF. The proposed method was used to extract non-healthy areas with characteristics of fibrotic tissue. Fibrosis in early fatty liver suggested the possibility of evaluation. On the other hand, fat was identified as a factor that reduced the accuracy of estimating fibrosis progression in moderate and severe fatty livers.

CONCLUSION

The proposed method was used to simultaneously evaluate fat mass and fibrosis progression in early fatty liver, suggesting the possibility of quantitative evaluation for discriminating between lipid droplets and fibrous tissue in the early fatty liver.

Experimental study on monitoring microwave ablation efficacy by real-time shear wave elastography in ex vivo porcine brain

Objective: Glioma constitutes the most common primary malignant tumor in the central nervous system. In recent years, microwave ablation (MWA) was expected to be applied in the minimally invasive treatment of brain tumors. This study aims to evaluate the feasibility and accuracy of microwave ablation in ex vivo brain tissue by Shear Wave Elastography (SWE) to explore the application value of real-time SWE in monitoring the process of MWA of brain tissue.Methods: Thirty ex vivo brain tissues were treated with different microwave power and ablation duration. The morphologic and microscopic changes of MWA tissues were observed, and the diameter of the ablation areas was measured. In this experiment, SWE is used to quantitatively evaluate brain tissue's degree of thermal injury immediately after ablation.Results: This study It is found that the ablation range measured by SWE after ablation is in good consistency with the pathological range [ICCSWEL1-L1 = 0.975(95% CI:0.959 - 0.985), ICCSWEL2-L2 = 0.887(95% CI:0.779 - 0.938)]. At the same time, the SWE value after ablation is significantly higher than before (mean ± SD,9.88 ± 2.64 kPa vs.23.6 ± 13.75 kPa; p < 0.001). In this study, the SWE value of tissues in different pathological states was further analyzed by the ROC curve (AUC = 0.86), and the threshold for distinguishing normal tissue from tissue after ablation was 13.7 kPa. The accuracy of evaluating ablation tissue using SWE can reach 84.72%, providing data support for real-time quantitative observation of the ablation range.Conclusion: In conclusion the accurate visualization and real-time evaluation of the organizational change range of the MWA process can be realized by real-time SWE.

Visualization of Human Hand Tendon Mechanical Anisotropy in 3-D Using High- Frequency Dual-Direction Shear Wave Imaging

High-resolution ultrasound shear wave elastography has been used to determine the mechanical properties of hand tendons. However, because of fiber orientation, tendons have anisotropic properties; this results in differences in shear wave velocity (SWV) between ultrasound scanning cross sections. Rotating transducers can be used to achieve full-angle scanning. However, this technique is inconvenient to implement in clinical settings. Therefore, in this study, high-frequency ultrasound (HFUS) dual-direction shear wave imaging (DDSWI) based on two external vibrators was used to create both transverse and longitudinal shear waves in the human flexor carpi radialis tendon. SWV maps from two directions were obtained using 40-MHz ultrafast imaging at the same scanning cross section. The anisotropic map was calculated pixel by pixel, and 3-D information was obtained using mechanical scanning. A standard phantom experiment was then conducted to verify the performance of the proposed HFUS DDSWI technique. Human studies were also conducted where volunteers assumed three hand postures: relaxed (Rel), full fist (FF), and tabletop (TT). The experimental results indicated that both the transverse and longitudinal SWVs increased due to tendon flexion. The transverse SWV surpassed the longitudinal SWV in all cases. The average anisotropic ratios for the Rel, FF, and TT hand postures were 1.78, 2.01, and 2.21, respectively. Both the transverse and the longitudinal SWVs were higher at the central region of the tendon than at the surrounding region. In conclusion, the proposed HFUS DDSWI technique is a high-resolution imaging technique capable of characterizing the anisotropic properties of tendons in clinical applications.

Dynein-Powered Cell Locomotion Guides Metastasis of Breast Cancer

The principal cause of death in cancer patients is metastasis, which remains an unresolved problem. Conventionally, metastatic dissemination is linked to actomyosin-driven cell locomotion. However, the locomotion of cancer cells often does not strictly line up with the measured actomyosin forces. Here, a complementary mechanism of metastatic locomotion powered by dynein-generated forces is identified. These forces arise within a non-stretchable microtubule network and drive persistent contact guidance of migrating cancer cells along the biomimetic collagen fibers. It is also shown that the dynein-powered locomotion becomes indispensable during invasive 3D migration within a tissue-like luminal network formed by spatially confining granular hydrogel scaffolds (GHS) made up of microscale hydrogel particles (microgels). These results indicate that the complementary motricity mediated by dynein is always necessary and, in certain instances, sufficient for disseminating metastatic breast cancer cells. These findings advance the fundamental understanding of cell locomotion mechanisms and expand the spectrum of clinical targets against metastasis.

Impact of Region-of-Interest Size on the Diagnostic Performance of Shear Wave Elastography in Differentiating Thyroid Nodules

This study investigated the impact of different region-of-interest (ROI) sizes (Max, 1 mm, and 2 mm) on shear wave elastography (SWE) in differentiating between malignant and benign thyroid nodules. The study cohort comprised 129 thyroid nodules (50 malignant, 79 benign) and 78 normal subjects. Diagnostic efficacy was assessed through pairwise comparisons of area under the curve (AUC) values in receiver operating characteristic analysis by using DeLong's test. Our results indicated significant differences in all SWE elasticity metrics between the groups, with malignant nodules exhibiting higher values than benign nodules (p < 0.05). Smaller ROIs (1 and 2 mm) were found to outperform the max ROI in terms of diagnostic accuracy, particularly for the Emax and Emin elasticity metrics. Emax(1mm) had the highest diagnostic accuracy, with an AUC of 0.883, sensitivity of 74.0%, and specificity of 86.1%. This study underscores the significant influence of ROI size selection on the diagnostic performance of SWE, offering valuable insights for future research and clinical applications in thyroid nodule assessment.

Load sharing between synergistic muscles characterized by a ligand-binding approach and elastography

The skeletal muscle contraction is determined by cross-bridge formation between the myosin heads and the actin active sites. When the muscle contracts, it shortens, increasing its longitudinal shear elastic modulus ([Formula: see text]). Structurally, skeletal muscle can be considered analogous to the molecular receptors that form receptor-ligand complexes and exhibit specific ligand-binding dynamics. In this context, this work aims to apply elastography and the ligand-binding framework to approach the possible intrinsic mechanisms behind muscle synergism. Based on the short-range stiffness principle and the acoustic-elasticity theory, we define the coefficient [Formula: see text], which is directly related to the fraction saturation of molecular receptors and links the relative longitudinal deformation of the muscle to its [Formula: see text]. We show that such a coefficient can be obtained directly from [Formula: see text] estimates, thus calculating it for the biceps brachii, brachioradialis, and brachialis muscles during isometric elbow flexion torque (τ) ramps. The resulting [Formula: see text] curves were analyzed by conventional characterization methods of receptor-ligand systems to study the dynamical behavior of each muscle. The results showed that, depending on muscle, [Formula: see text] exhibits typical ligand-binding dynamics during joint torque production. Therefore, the above indicates that these different behaviors describe the longitudinal shortening pattern of each muscle during load sharing. As a plausible interpretation, we suggested that this could be related to the binding kinetics of the cross-bridges during their synergistic action as torque increases. Likewise, it shows that elastography could be useful to assess contractile processes at different scales related to the change in the mechanical properties of skeletal muscle.

Combined ARFI and Shear Wave Imaging of Prostate Cancer: Optimizing Beam Sequences and Parameter Reconstruction Approaches

This study demonstrates the implementation of a shear wave reconstruction algorithm that enables concurrent acoustic radiation force impulse (ARFI) imaging and shear wave elasticity imaging (SWEI) of prostate cancer and zonal anatomy. The combined ARFI/SWEI sequence uses closely spaced push beams across the lateral field of view and simultaneously tracks both on-axis (within the region of excitation) and off-axis (laterally offset from the excitation) after each push beam. Using a large number of push beams across the lateral field of view enables the collection of higher signal-to-noise ratio (SNR) shear wave data to reconstruct the SWEI volume than is typically acquired. The shear wave arrival times were determined with cross-correlation of shear wave velocity signals in two dimensions after 3-D directional filtering to remove reflection artifacts. To combine data from serially interrogated lateral push locations, arrival times from different pushes were aligned by estimating the shear wave propagation time between push locations. Shear wave data acquired in an elasticity lesion phantom and reconstructed using this algorithm demonstrate benefits to contrast-to-noise ratio (CNR) with increased push beam density and 3-D directional filtering. Increasing the push beam spacing from 0.3 to 11.6 mm (typical for commercial SWEI systems) resulted in a 53% decrease in CNR. In human in vivo data, this imaging approach enabled high CNR (1.61-1.86) imaging of histologically-confirmed prostate cancer. The in vivo images had improved spatial resolution and CNR and fewer reflection artifacts as a result of the high push beam density, the high shear wave SNR, the use of multidimensional directional filtering, and the combination of shear wave data from different push beams.

Reconstructing the Spatial Distribution of the Relative Shear Modulus in Quasi-static Ultrasound Elastography: Plane Stress Analysis

Quasi-static ultrasound elastography (QSUE) is an imaging technique that mainly provides axial strain maps of tissues when the latter are subjected to compression. In this article, a method for reconstructing the relative shear modulus distribution within a linear elastic and isotropic medium, in QSUE, is introduced. More specifically, the plane stress inverse problem is considered. The proposed method is based on the variational formulation of the equilibrium equations and on the choice of adapted discretization spaces, and only requires displacement fields in the analyzed media to be determined. Results from plane stress and 3-D numerical simulations, as well as from phantom experiments, showed that the method is able to reconstruct the different regions within a medium, with shear modulus contrasts that unambiguously reveal whether inclusions are stiffer or softer than the surrounding material. More specifically, for the plane stress simulations, inclusion-to-background modulus ratios were found to be very accurately estimated, with an error lower than 3%. For the 3-D simulations, for which the plane stress conditions are no longer satisfied, these ratios were, as expected, less accurate, with an error that remained lower than 10% for two of the three cases analyzed but was around 34% for the last case. Concerning the phantom experiments, a comparison with a shear wave elastography technique from a clinical ultrasound scanner was also made. Overall, the inclusion-to-background shear modulus ratios obtained with our approach were found to be closer to those given by the phantom manufacturer than the ratios provided by the clinical system.

Nondestructive ultrasound evaluation of microstructure-related material parameters of skeletal muscle: An in silico and in vitro study

Direct and nondestructive assessment of material properties of skeletal muscle in vivo shall advance our understanding of intact muscle mechanics and facilitate personalized interventions. However, this is challenged by intricate hierarchical microstructure of the skeletal muscle. We have previously regarded the skeletal muscle as a composite of myofibers and extracellular matrix (ECM), formulated shear wave propagation in the undeformed muscle using the acoustoelastic theory, and preliminarily demonstrated that ultrasound-based shear wave elastography (SWE) could estimate microstructure-related material parameters (MRMPs): myofiber stiffness μ_f, ECM stiffness μ_m, and myofiber volume ratio V_f. The proposed method warrants further validation but is hampered by the lack of ground truth values of MRMPs. In this study, we presented analytical and experimental validations of the proposed method using finite-element (FE) simulations and 3D-printed hydrogel phantoms, respectively. Three combinations of different physiologically relevant MRMPs were used in the FE simulations where shear wave propagations in the corresponding composite media were simulated. Two 3D-printed hydrogel phantoms with the MRMPs close to those of a real skeletal muscle (i.e., μ_f=2.02kPa, μ_m=52.42kPa, and V_f=0.675,0.832) for ultrasound imaging were fabricated by an alginate-based hydrogel printing protocol that we modified and optimized from the freeform reversible embedding of suspended hydrogels (FRESH) method in literature. Average percent errors of (μ_f,μ_m,V_f) estimates were found to be (2.7%,7.3%,2.4%)in silico and (3.0%,8.0%,9.9%)in vitro. This quantitative study corroborated the potential of our proposed theoretical model along with ultrasound SWE for uncovering microstructural characteristics of the skeletal muscle in an entirely nondestructive way.

A Systematic Temporal Assessment of Changes in Tendon Stiffness Following Rotator Cuff Repair

OBJECTIVES

How the material properties of the human supraspinatus tendon change following arthroscopic rotator cuff repair is undetermined. Shear wave elastography ultrasound is a relatively new, noninvasive measure of tissue stiffness. We aimed to evaluate any temporal changes in stiffness and/or thickness of supraspinatus tendons in humans following primary arthroscopic rotator cuff repair.

METHODS

Shear wave elastography was performed at three predetermined regions by a single sonographer at 1-, 6-, 12-, 24-, and 52 weeks postoperatively in 50 consecutive single-row inverted mattress primary arthroscopic rotator cuff repairs. One-way ANOVA with Tukey's correction and Spearman's correlation tests was performed.

RESULTS

Of 50 patients, two retore by 1-week and were excluded. Two patients retore at 6 weeks, two at 12 weeks, and one at 24 weeks. The mean tendon stiffness in 48 patients at the tendon footprint increased by 21% (1.32 m/s) at 6 months (P < .001), with the lateral tendon stiffening before the medial tendon. Tendon thickness decreased by 11% (0.6 mm) at 6 weeks (P = .008), then stabilized to 24 weeks. Tendons that were less elastographically stiff at 1 week were more likely to be thinner at 6-weeks (r = .38, P = .010).

CONCLUSIONS

The data supports the hypothesis that rotator cuff tendons repaired using the single-row inverted-mattress technique take 6 weeks to heal to bone. Unlike in other tendons, there was no hypertrophic healing response. Prior to 6 weeks, the tendon may stretch/thin-out, particularly if its material properties, as assessed by shear wave elastography, are inferior. The material properties of the tendon improved at the tendon insertion site first, then medially out to 12 months post-repair.

High frequency ultrasound vibrational shear wave elastography for preclinical research

Preclinical evaluation of novel therapies using models of cancer is an important tool in cancer research, where imaging can provide non-invasive tools to characterise the internal structure and function of tumours. The short propagation paths when imaging tumours and organs in small animals allow the use of high frequencies for both ultrasound and shear waves, providing the opportunity for high-resolution shear wave elastography and hence its use for studying the heterogeneity of tissue elasticity, where heterogeneity may be a predictor of tissue response. Here we demonstrate vibrational shear wave elastography (VSWE) using a mechanical actuator to produce high frequency (up to 1000 Hz) shear waves in preclinical tumours, an alternative to the majority of preclinical ultrasound SWE studies where an acoustic radiation force impulse is required to create a relatively low-frequency broad-band shear-wave pulse. We implement VSWE with a high frequency (17.8 MHz) probe running a focused line-by-line ultrasound imaging sequence which as expected was found to offer improved detection of 1000 Hz shear waves over an ultrafast planar wave imaging sequence in a homogenous tissue-mimicking phantom. We test the VSWE in anex vivotumour xenograft, demonstrating the ability to detect shear waves up to 10 mm from the contactor position at 1000 Hz. By reducing the kernel size used for shear wave speed estimation to 1 mm we are able to produce shear wave speed images with spatial resolution of this order. Finally, we present VSWE data from xenograft tumoursin vivo, demonstrating the feasibility of the technique in mice under isoflurane sedation. Mean shear wave speeds in the tumours are in good agreements with those reported by previous authors. Characterising the frequency dependence of shear wave speed demonstrates the potential to quantify the viscoelastic properties of tumoursin vivo.

2D-SWE of the Metacarpophalangeal Joint Capsule in Horses

(1) Two-dimensional shear wave elastography (2D-SWE) employs an ultrasound impulse to produce transversely oriented shear waves, which travel through the surrounding tissue according to the stiffness of the tissue itself. The study aimed to assess the reliability of 2D-SWE for evaluating the elastosonographic appearance of the distal attachment of the fetlock joint capsule (DJC) in sound horses and in horses with osteoarthritis (OA) (2). According to a thorough evaluation of metacarpophalangeal joint (MCPJ), adult horses were divided in a sound Group (H) and in OA Group (P). Thereafter, a 2D-SWE of MCPJs was performed. Shear wave velocity (m/sec) and Young’s modulus (kPa) were calculated independently by two operators at each selected ROI. Statistical analysis was performed with R software. (3) Results: 2D-SWE had good–excellent inter-CC and intra-CC in both groups. Differences in m/s and kPa between Groups H and P were found in transverse scans with lower values in Group P. No correlation with age or DJC thickness was found. (4) Conclusions: 2D-SWE was repeatable and reproducible. In Group H, DJC was statistically stiffer than in Group P only in transverse scan. The technique showed poor sensitivity and specificity in differentiating fetlocks affected by OA.

Analysis of influencing factors of shear wave elastography of the superficial tissue: A phantom study

Shear wave elastography (SWE) is widely used in clinical work. But there is no standard protocol and operation specification for SWE acquisition methods, which impacts the diagnosis and clinical staging. This study aimed to investigate the influence factors of diameter, depth, and stiffness on SWE using different probes at superficial depths and discuss SWE differences with two machines at superficial depths. We performed SWE on two elastic phantoms that each phantom contained six subjects with two stiffness (41.06 ± 4.62 kpa and 57.30 ± 4.31 kpa), three diameters (10, 15, and 18 mm), and two depths (15 and 25 mm). A total of 240 measurements were obtained by using two ultrasound machines (SuperSonic Imagine Aixplorer and Mindray Resona 7) and 4 probes (SL15-4 and SL10-2, L11-3, and L14-5). The measurements were compared among 4 probes, 3 diameters, and 2 depths. There was no significant difference in SWE measurements among the probes from the same machine. The SWE measurements were affected by diameter, and the degree of influence was related to the stiffness. The SWE measurements were unaffected at a 15–25 mm depth range.

Improved two-point frequency shift power method for measurement of shear wave attenuation

Quantitative assessment of mechanical properties of biological soft tissues is frequently evaluated using a noninvasive modality, called ultrasound shear wave elastography (SWE). SWE typically exerts an acoustic radiation force (ARF) to produce shear waves propagating in the lateral direction for which velocities and attenuations are measured. The tissue viscoelasticity is commonly studied by investigating the shear wave phase velocity curves. Viscoelastic tissue properties can also be characterized through utilizing various shear wave attenuation techniques. In this study, we propose an improved method for measuring the shear wave attenuation, called two-point frequency shift power (2P-FSP), which is an improved version of the two-point frequency shift (2P-FS) method. The technique is fully data driven and does not use a rheological model for mathematical modeling. The 2P-FSP method utilizes the power spectra frequency shift of shear waves measured at two spatial positions, which provides robustness to noise. The conceptual basis for the 2P-FSP is provided and tested with numerical and experimental data. We investigated how the location of the first signal and the distance interval between the two locations influence the shear wave attenuation measurement in the 2P-FSP technique. We utilized the 2P-FSP method on numerical phantom data generated using a finite-difference-based method in tissue-mimicking viscoelastic media. Moreover, we tested the 2P-FSP method with data from custom-made tissue-mimicking viscoelastic phantom experiments, and ex vivo porcine liver. We compared results from the proposed technique with results from 2P-FS and analytical values in the case of simulations. The results showed that the 2P-FSP method provides improved results over the 2P-FS technique for lower signal-to-noise ratio (SNR) and locations farther from the push location considered, and can be used to measure attenuation of viscoelastic soft tissues.

Role of Shear-Wave Elastography in Achilles Tendon in Psoriatic Arthritis and Its Correlation with Disease Severity Score, Psoriasis Area and Severity Index

Purpose  The aim of this study was to compare accuracy of shear-wave elastography (SWE) with gray scale (GS) ultrasound and power Doppler (pD) for diagnosing Achilles tendinopathy in psoriatic patients with and without arthritis and correlation with achillodynia and disease severity score, psoriasis area and severity index (PASI).

Methods  A total of 100 Achilles tendons were evaluated where 56% were cases of psoriatic arthritis with achillodynia; 44% were controls of psoriasis without arthritis in this prospective study. Evaluation was done with GS, pD, SWE at proximal, mid, and distal third of the tendon. Qualitative (color maps) and quantitative data, elastic modulus, kilopascal (kPa), were generated. Pearson's correlation was done to see association between kPa, PASI and clinical symptoms, achillodynia, scored using visual analog scale (VAS).

Results  Significant negative correlation was seen between duration of arthritis, VAS and PASI with SWE values with r  = −0.34, −0.47, and −0.41, respectively. SWE could identify abnormal tendons in 71/100 (71%) in the overall study, 53/56 (94.6%) in cases, and 18/44 (40.9%) in control. The statistical significance was set at p  ≤ 0.05. In comparison, conventional ultrasound, GS, and pD together could identify 13/56 (23.21%) in cases and no abnormal tendon was identified in the control group.

Conclusion  SWE is a reliable, noninvasive, and valuable tool to detect early tendinopathy and monitor progression of disease.

Effectiveness of Quantitative Shear Wave Elastography for the Prediction of Axillary Lymph Node Metastasis

Objective

Invasive breast cancer can be metastasized through axillary lymph nodes (LNs). This study was to evaluate the effectiveness of quantitative shear wave elastography (SWE) to predict axillary LN metastasis, which also provides prognostic implication of SWE as a histopathologic element of invasive breast cancer.

Methods

72 prospectively enrolled patients received B-mode ultrasound (BUS) and SWE, and the elasticity index (EI) of SWE at the stiffest part of lymph nodes (LNs) was measured. EI of SWE was closely associated with pathologic results and the histopathologic elements. The receiver operating characteristics (ROC) curve was drawn to evaluate the optimal cut-off value for the assessment of disease severity.

Results

A significantly longer short-axis diameter and a larger maximal cortex were observed in malignant LNs than that in healthy LNs. The absence of the hilum was associated with metastatic LNs. The EI of SWE varied markedly between the benign and malignant LNs. The combination of E_{max and} BUS showed higher area under the curve (AUC) than BUS alone to predict metastatic LNs (0.7762 vs. 0.7230). EI of SWE in malignant lymph nodes those with extranodal extension are higher than those without extranodal extension.

Conclusions

Quantitative SWE provides a viable alternative for the assessment of axillary LN and shows great potential to predict pathological prognostic elements of metastatic axillary LNs in invasive breast cancer. Joint use of SWE and BUS allows examination of the predictive outcome of BUS for axillary lymph node metastasis in invasive breast cancer.

Shear Wave Elastography Implementation on a Portable Research Ultrasound System: Initial Results

Ultrasound shear wave elastography (SWE) has emerged as a promising technique that enables the quantitative estimation of soft tissue stiffness. However, its practical implementation is complicated and presents a number of engineering challenges, including high-energy burst transmission, high-frame rate data acquisition and high computational requirements to process huge datasets. Therefore, to date, SWE has only been available for high-end commercial systems or bulk and expensive research platforms. In this work, we present a low-cost, portable and fully configurable 256-channel research system that is able to implement various SWE techniques. We evaluated its transmit capabilities using various push beam patterns and developed algorithms for the reconstruction of tissue stiffness maps. Three different push beam generation methods were evaluated in both homogeneous and heterogeneous experiments using an industry-standard elastography phantom. The results showed that it is possible to implement the SWE modality using a portable and cost-optimized system without significant image quality losses.

The Revisited Frequency-Shift Method for Shear Wave Attenuation Computation and Imaging

Ultrasound (US) shear wave (SW) elastography has been widely studied and implemented on clinical systems to assess the elasticity of living organs. Imaging of SW attenuation reflecting viscous properties of tissues has received less attention. A revisited frequency shift (R-FS) method is proposed to improve the robustness of SW attenuation imaging. Performances are compared with the FS method that we originally proposed and with the two-point frequency shift (2P-FS) and attenuation measuring US SW elastography (AMUSE) methods. In the proposed R-FS method, the shape parameter of the gamma distribution fitting SW spectra is assumed to vary with distance, in contrast to FS. Second, an adaptive random sample consensus (A-RANSAC) line fitting method is used to prevent outlier attenuation values in the presence of noise. Validation was made on ten simulated phantoms with two viscosities (0.5 and 2 Pa [Formula: see text]) and different noise levels (15 to -5 dB), two experimental homogeneous gel phantoms, and six in vivo liver acquisitions on awake ducks (including three normal and three fatty duck livers). According to the conducted experiments, R-FS revealed mean reductions in coefficients of variation (CV) of 62.6% on simulations, 62.5% with phantoms, and 62.3% in vivo compared with FS. Corresponding reductions compared with 2P-FS were 45.4%, 77.1%, and 62.0%, respectively. Reductions in normalized root-mean-square errors for simulations were 63.9% and 48.7% with respect to FS and 2P-FS, respectively.

Finite element model of mechanical imaging of the breast

Purpose: Malignant breast lesions can be distinguished from benign lesions by their mechanical properties. This has been utilized for mechanical imaging in which the stress distribution over the breast is measured. Mechanical imaging has shown the ability to identify benign or normal cases and to reduce the number of false positives from mammography screening. Our aim was to develop a model of mechanical imaging acquisition for simulation purposes. To that end, we simulated mammographic compression of a computer model of breast anatomy and lesions. Approach: The breast compression was modeled using the finite element method. Two finite element breast models of different sizes were used and solved using linear elastic material properties in open-source virtual clinical trial (VCT) software. A spherical lesion (15 mm in diameter) was inserted into the breasts, and both the location and stiffness of the lesion were varied extensively. The average stress over the breast and the average stress at the lesion location, as well as the relative mean pressure over lesion area (RMPA), were calculated. Results: The average stress varied 6.2-6.5 kPa over the breast surface and 7.8-11.4 kPa over the lesion, for different lesion locations and stiffnesses. These stresses correspond to an RMPA of 0.80 to 1.46. The average stress was 20% to 50% higher at the lesion location compared with the average stress over the entire breast surface. Conclusions: The average stress over the breast and the lesion location corresponded well to clinical measurements. The proposed model can be used in VCTs for evaluation and optimization of mechanical imaging screening strategies.

Quantifying viscosity and elasticity using holographic imaging by Rayleigh wave dispersion

Viscoelasticity is an important diagnostic parameter to investigate physiological dysfunctions in biological tissues. This Letter reports the quantification of viscoelastic parameters by Rayleigh wave tracing on the surface of tissue-mimicking phantoms using holographic imaging. The Rayleigh wave is induced by an electromechanical actuator on the surface of oil-in-gelatin phantoms and a biological tissue sample followed by holographic imaging and reconstruction of the wave. The frequency-dependent velocity dispersion is fitted to a Voigt model for the quantification of viscous and elastic moduli. The viscoelastic parameters calculated by the proposed method are validated by comparing the results from a conventional mechanical rheometer.

Diagnostic Accuracy of Shear-Wave Elastography for Breast Lesion Characterization in Women: A Systematic Review and Meta-Analysis

PURPOSE

The aim of this study was to assess the diagnostic accuracy of 2-D shear-wave elastography (SWE) for differentiating benign and malignant breast lesions in women with abnormal findings on mammography.

METHODS

Included in this review are studies of diagnostic accuracy published before June 2021 using 2-D SWE to evaluate female breast lesions. Included studies were required to include at least 50 lesions, report quantitative shear-wave speed (SWS) thresholds, and include a reference standard of either biopsy or 2-year stability. Included studies used the mean, maximum, minimum, or SD of SWS for classification. A systematic search of PubMed, Scopus, Embase, Ovid-MEDLINE, the Cochrane Library, and Web of Science was performed. Bias and applicability of the studies were assessed using Quality Assessment of Diagnostic Accuracy Studies 2. A hierarchical summary receiver operating characteristic model was used to arrive at the summary statistics.

RESULTS

Eighty-seven prospective and retrospective studies were included, encompassing 17,810 women (mean age 42.3 ± 10.4 years) with 19,043 lesions (7,623 malignant). Summary sensitivities and specificities, respectively, were 0.86 (95% confidence interval [CI], 0.83-0.88) and 0.87 (95% CI, 0.84-0.88) for mean SWS, 0.83 (95% CI, 0.80-0.85) and 0.88 (95% CI, 0.86-0.90) for the maximum, 0.86 (95% CI, 0.74-0.93) and 0.81 (95% CI, 0.69-0.89) for the minimum, and 0.82 (95% CI, 0.77-0.86) and 0.88 (95% CI, 0.85-0.91) for the SD. Alternatively, the areas under the receiver operating characteristic curve were 0.93 (95% CI, 0.91-0.94), 0.92 (95% CI, 0.90-0.94), 0.90 (95% CI, 0.82-0.96), and 0.92 (95% CI, 0.88-0.94), respectively.

CONCLUSIONS

This review demonstrates the discriminative power of SWE in the diagnosis of breast cancer. Using the resulting likelihood ratios, SWE may prove beneficial in downgrading BI-RADS® 4a or upgrading BI-RADS 3 lesions. However, current society guidelines do not provide definitive recommendations regarding the use of SWE and its counterpart strain elastography (SE). Comparison with our results suggests that SE alone or a combination of SE and SWE may provide better diagnostic performance than SWE alone and serve as an adjunct to current diagnostic techniques.

Evaluation of Different Types of Breast Lesions With Apparent Diffusion Coefficient and Shear Wave Elastography Values: Comparison of Shear Wave Elastography and Apparent Diffusion Coefficient in Breast Lesions

Objective:

The aim of this study was to compare the stiffness of different histological types of breast lesions by obtaining shear wave elastography (SWE) and apparent diffusion coefficient (ADC) values, and to determine the contribution of these two methods to the diagnosis.

Materials and Methods:

In total, 70 patients with biopsy-proven breast lesions were included in the study. The mean SWE values of breast lesions were recorded and ADC values of these lesions were calculated. Receiver operating characteristic (ROC) curve analyses and the diagnostic accuracies of SWE-ADC values were determined.

Results:

The mean SWE values were 45.47 ± 25.11 kPa and 3.51 ± 1.04 m/s in benign group, and 161.11 ± 219.34 kPa and 5.96 ± 1.06 m/s in malignant group, respectively. The mean ADC values were 1.38 ± 0.32 (×10–3 mm2/s) in benign group and 0.96 ± 0.22 (×10–3 mm2/s) in malignant group, respectively. When the diagnostic performances of both imaging modalities on mass stiffness are evaluated, statistically significant negative correlations were found between SWE lesion values and ADC lesion values.

Conclusion:

Evaluation of tissue elasticity has recently been used frequently in the diagnosis of breast diseases. SWE-ADC values, which are negatively correlated in the diagnosis of breast masses, may prove to be a powerful alternative diagnostic tool that can be used interchangeably, as appropriate.

Advanced Neuroimaging Role in Traumatic Brain Injury: A Narrative Review

Traumatic brain injury (TBI) is a common source of morbidity and mortality among civilians and military personnel. Initial routine neuroimaging plays an essential role in rapidly assessing intracranial injury that may require intervention. However, in the context of TBI, limitations of routine neuroimaging include poor visualization of more subtle changes of brain parenchymal after injury, poor prognostic ability and inability to analyze cerebral perfusion, metabolite and mechanical properties. With the development of modern neuroimaging techniques, advanced neuroimaging techniques have greatly boosted the studies in the diagnosis, prognostication, and eventually impacting treatment of TBI. Advances in neuroimaging techniques have shown potential, including (1) Ultrasound (US) based techniques (contrast-enhanced US, intravascular US, and US elastography), (2) Magnetic resonance imaging (MRI) based techniques (diffusion tensor imaging, magnetic resonance spectroscopy, perfusion weighted imaging, magnetic resonance elastography and functional MRI), and (3) molecular imaging based techniques (positron emission tomography and single photon emission computed tomography). Therefore, in this review, we aim to summarize the role of these advanced neuroimaging techniques in the evaluation and management of TBI. This review is the first to combine the role of the US, MRI and molecular imaging based techniques in TBI. Advanced neuroimaging techniques have great potential; still, there is much to improve. With more clinical validation and larger studies, these techniques will be likely applied for routine clinical use from the initial research.

Elastography and Doppler May Bring a New Perspective to TIRADS, Altering Conventional Ultrasonography Dominance

RATIONALE AND OBJECTIVES

The main aim of ultrasonography (US) examining thyroid nodules is to differentiate malignant nodules from benign nodules. Several professional societies and groups of investigators have defined guidelines such as Thyroid Imaging Reporting and Data System (TIRADS) to provide the standardized language and approach to thyroid nodules. This study is aimed to investigate the compatibility of such classification systems with the pathological diagnosis of nodules and evaluate the contribution of the Shear-wave elastography (SWE) and Doppler ultrasonography (DUS) findings.

MATERIALS AND METHODS

This is a prospective study. Patients with thyroid US exams between December 2017 and April 2019 were included. In the study, eligible 210 nodules from 210 patients were enrolled. For stratification, the conventional B-mode US, SWE and DUS were performed. According to Kwak, American College of Radiology (ACR), and European (EU)-TIRADS, Nodules were classified separately, and a new scoring system whose the criteria was put defined in the study has developed.

RESULTS

For SWE; Emean cut-off value was 33 kPa with a sensitivity and specificity of 95,6% (95% CI: 0,85-0,98) and 95% (95% CI:0,90-0,97) respectively (p <0.001). For spectral DUS; resistivity index (RI) cut-off value was 0.64 with a sensitivity and specificity of 73,3% (95% CI:0,59-0,83) and 80% (95% CI:0,73-0,85) respectively (p <0.001). Kwak TIRADS, American College of Radiology TIRADS, EU-TIRADS, and new system were compared by ROC curve analysis. The new system has the highest sensitivity, specificity, PPV, NPV, accuracy, and AUC compared to others.

CONCLUSIONS

The new scoring system has shown that SWE and DUS findings may alter the categorization in TIRADS and increase sensitivity and specificity.

Visualization of Human Skeletal Muscle Anisotropy by Using Dual-Direction Shear Wave Imaging

OBJECTIVE

Ultrasound (US) shear wave elasticity imaging (SWEI) is a mature technique for diagnosing the elasticity of isotropic tissues. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be diagnosed correctly using SWEI because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, SWEI has been studied for measuring the anisotropic properties of muscles by rotating the transducer; however, this is difficult for clinical practice.

METHODS

In this study, a novel dual-direction shear wave imaging (DDSWI) technique was proposed for visualizing the mechanical anisotropy of muscles without rotation. Longitudinal and transverse shear waves were created by a specially designed external vibrator and supersonic pushing beam, respectively; the SWVs were then tracked using ultrafast US imaging. Subsequently, the SWV maps of two directions were obtained at the same scanning cross section, and the mechanical anisotropy was represented as the ratio between them at each pixel.

RESULTS

The performance of DDSWI was verified using a standard phantom, and human experiments were performed on the gastrocnemius and biceps brachii. Experimental results of phantom revealed DDSWI exhibited a high precision of <0.81 % and a low bias of <3.88 % in SWV measurements. The distribution of anisotropic properties in muscle was visualized with the anisotropic ratios of 1.54 and 2.27 for the gastrocnemius and biceps brachii, respectively.

CONCLUSION

The results highlight the potential of this novel anisotropic imaging in clinical applications because the conditions of musculoskeletal fiber orientation can be easily and accurately evaluated in real time by DDSWI.

A New Plane Wave Compounding Scheme Using Phase Compensation for Motion Detection

Plane wave (PW) transmission has enabled multiple new applications, such as shear wave elastography, ultrafast Doppler imaging, and functional ultrasound imaging. PW compounding (PWC), which coherently sums the echo signals from multiple PW transmits with different angles, is widely used to improve B-mode image quality. When the motion between two speckle images is estimated, PWC suffers from an inherent displacement estimation error. This is derived theoretically and experimentally demonstrated in this work. We show that the phase difference between the acquired data with PW emissions with different angles is related to this error. When the absolute value of the phase difference is larger than π /2, the displacement estimation error occurs. A new scheme, named initial-phase-compensated PWC (IPCPWC), is proposed, which compensates the phase of echo signals from each PW transmit and maintains the absolute value of the phase difference smaller than π /2. The increased signal-to-noise ratio and reduced jitter of IPCPWC in motion data are demonstrated using tissue mimicking phantoms compared with PWC.

Ultrasonic Elastography of the Rectus Femoris, a Potential Tool to Predict Sarcopenia in Patients With Chronic Obstructive Pulmonary Disease

Purpose: Skeletal muscle dysfunction is common in patients with chronic obstructive pulmonary disease (COPD) and is associated with a poor prognosis. Abnormal muscle quantity of the lower limbs is a manifestation of skeletal muscle dysfunction in patients with COPD. Shear wave ultrasound elastography (SWE) is a novel and possible tool to evaluate qualitative muscle parameters. This study explores the feasibility of SWE to measure the stiffness of the rectus femoris and evaluates its value in predicting sarcopenia in patients with COPD.

Methods: Ultrasound examination of the rectus femoris was performed to determine the mean elasticity index (SWE_mean), cross-sectional area (RF_csa), and thickness (RF_thick) using grayscale ultrasonography (US) and SWE in 53 patients with COPD and 23 age-matched non-COPD healthy controls. The serum levels of circulating biomarkers (GDF15, resistin, and TNF-α) were measured using ELISA. The definition of sarcopenia followed the guidelines from the Asian Working Group for Sarcopenia. Receiver operating characteristic (ROC) curve analysis of the SWE_mean, RF_thick, and RF_csa was used to evaluate their predictive ability for sarcopenia.

Results: The intraobserver and interobserver repeatability of SWE performance was excellent (all correlation coefficients > 0.95; p < 0.05). The SWE_mean of the rectus femoris in patients with COPD (8.98 ± 3.12 kPa) was decreased compared with that in healthy controls (17.00 ± 5.14 kPa) and decreased with advanced global initiative for chronic obstructive lung disease (GOLD) stage. Furthermore, SWE_mean was found to be independent of sex, height, and body mass, and a lower SWE_mean in patients with COPD was positively associated with reduced pulmonary function, worse physical function, poor exercise tolerance, decreased muscle strength, and worse dyspnea index score. The correlation between physical function [five-repetition sit-to-stand test (5STST)], muscle function, and SWE_mean was higher than those of RF_thick and RF_csa. In addition, SWE_mean was negatively correlated with serum GDF15 levels (r = −0.472, p < 0.001), serum resistin levels (r = −0.291, p = 0.035), and serum TNF-α levels (r = −0.433, p = 0.001). Finally, the predictive power of SWE_mean [area under the curve (AUC): 0.863] in the diagnosis of sarcopenia was higher than that of RF_thick (AUC: 0.802) and RF_csa (AUC: 0.816).

Conclusion: Compared with grayscale US, SWE was not affected by the patient’s height, weight, or BMI and better represented skeletal muscle function and physical function. Furthermore, SWE is a promising potential tool to predict sarcopenia in patients with COPD.

Controllable Angle Shear Wavefront Reconstruction Based on Image Fusion Method for Shear Wave Elasticity Imaging

The generation and measurement of shear waves are critical in ultrasonic elasticity imaging. Generally, the resulting wavefront direction is very important for accurately measuring the shear speed and estimating the medium elasticity. In this article, the proposed method can generate a compound shear wavefront with the same direction as speed reconstruction and zero angles between the wavefront and the focus direction, which can improve the estimation accuracy of shear wave velocity. Also, this method, called time-division multipoint excitation image fusion (TDMPEIF), can reconstruct the shear wave propagation images acquired at different depths of a medium according to the frame sequence to produce the shear waves front with a regulable angle. Moreover, the shear wave speed and the elasticity of a medium can be mapped quantitatively with this method. The results demonstrate that the TDMPEIF can improve the quality of the shear wave velocity images, which has wide application value and good promotion prospects for quantitative evaluation of tissue elasticity.

Nonlinear Characterization of Tissue Viscoelasticity With Acoustoelastic Attenuation of Shear Waves

Shear-wave elastography (SWE) measures shear-wave speed (SWS), which is related to the underlying shear modulus of soft tissue. SWS in soft tissue changes depending on the amount of external strain that soft tissue is subjected to due to the acoustoelastic (AE) phenomenon. In the literature, variations of SWS as a function of applied uniaxial strain were used for nonlinear characterization, assuming soft tissues to be elastic, although soft tissues are indeed viscoelastic in nature. Hence, nonlinear characterization using SWS alone is insufficient. In this work, we use SWS together with shear-wave attenuation (SWA) during incremental quasi-static compressions in order to derive biomechanical characterization based on the AE theory in terms of well-defined storage and loss moduli. As part of this study, we also quantify the effect of applied strain on measurements of SWS and SWA since such confounding effects need to be taken into account when using SWS and/or SWA, e.g., for staging a disease state, while such effects can also serve as an additional imaging biomarker. Our results from tissue-mimicking phantoms with varying oil percentages and ex vivo porcine liver experiments demonstrate the feasibility of our proposed methods. In both experiments, SWA was observed to decrease with applied strain. For 10% compression in ex vivo livers, shear-wave attenuation decreased, on average, by 28% (93 Np/m), while SWS increased, on average, by 20% (0.26 m/s).

Shear Wave Elasticity Imaging Using Nondiffractive Bessel Apodized Acoustic Radiation Force

The acoustic radiation force impulse (ARFI) has been widely used in transient shear wave elasticity imaging (SWEI). For SWEI based on focused ARFI, the highest image quality exists inside the focal zone due to the limitation of the depth of focus and diffraction. Consequently, the areas outside the focal zone and in the near field present poor image quality. To address the limitations of the focused beam, we introduce Bessel apodized ARFI that enhances image quality and improves the depth of focus. The objective of this study is to evaluate the feasibility of SWEI based on Bessel ARF in simulation and experiment. We report measurements of elastogram image quality and depth of field in tissue-mimicking phantoms and ex vivo liver tissue. Our results demonstrate improved depth of field, image quality, and shear wave speed (SWS) estimation accuracy using Bessel push beams. As a result, Bessel ARF enlarges the field of view of elastograms. The signal-to-noise ratio (SNR) of Bessel SWEI is improved 26% compared with focused SWEI in homogeneous phantom. The estimated SWS by Bessel SWEI is closer to the measured SWS from a clinical scanner with an error of 0.3% compared to 2.4% with a focused beam. In heterogeneous phantoms, the contrast-to-noise ratios (CNRs) of shallow and deep inclusions are improved by 8.79 and 3.33 dB, respectively, under Bessel ARF. We also compare the results between Bessel SWEI and supersonic shear imaging (SSI), and the SNR of Bessel SWEI is improved by 8.1%. Compared with SSI, Bessel SWEI shows more accurate SWS estimates in high stiffness inclusions. Finally, Bessel SWEI can generate higher quality elastograms with less energy than conventional SSI.

A Cross-Machine Comparison of Shear-Wave Speed Measurements Using 2D Shear-Wave Elastography in the Normal Female Breast

Quantitative measures of radiation-induced breast stiffness are required to support clinical studies of novel breast radiotherapy regimens and exploration of personalised therapy, however, variation between shear-wave elastography (SWE) machines may limit the usefulness of shear-wave speed (cs) for this purpose. Mean cs measured in four healthy volunteers’ breasts and a phantom using 2D-SWE machines Acuson S2000 (Siemens Medical Solutions) and Aixplorer (Supersonic Imagine) were compared. Shear-wave speed was measured in the skin region, subcutaneous adipose tissue and parenchyma. cs estimates were on average 2.3% greater when using the Aixplorer compared to S2000 in vitro. In vivo, cs estimates were on average 43.7%, 36.3% and 49.9% significantly greater (p << 0.01) when using the Aixplorer compared to S2000, for skin region, subcutaneous adipose tissue and parenchyma, respectively. In conclusion, despite relatively small differences between machines observed in vitro, large differences in absolute measures of shear wave speed measured were observed in vivo, which may prevent pooling of cross-machine data in clinical studies of the breast.

Ultrasonic technologies in imaging and drug delivery

Ultrasonic technologies show great promise for diagnostic imaging and drug delivery in theranostic applications. The development of functional and molecular ultrasound imaging is based on the technical breakthrough of high frame-rate ultrasound. The evolution of shear wave elastography, high-frequency ultrasound imaging, ultrasound contrast imaging, and super-resolution blood flow imaging are described in this review. Recently, the therapeutic potential of the interaction of ultrasound with microbubble cavitation or droplet vaporization has become recognized. Microbubbles and phase-change droplets not only provide effective contrast media, but also show great therapeutic potential. Interaction with ultrasound induces unique and distinguishable biophysical features in microbubbles and droplets that promote drug loading and delivery. In particular, this approach demonstrates potential for central nervous system applications. Here, we systemically review the technological developments of theranostic ultrasound including novel ultrasound imaging techniques, the synergetic use of ultrasound with microbubbles and droplets, and microbubble/droplet drug-loading strategies for anticancer applications and disease modulation. These advancements have transformed ultrasound from a purely diagnostic utility into a promising theranostic tool.

Characterization of Suspicious Microcalcifications on Mammography Using 2D Shear-Wave Elastography

Our aim was to investigate the correlations between the findings of two-dimensional shear-wave elastography (2D-SWE) and the histopathologic results of microcalcifications (MCs) visualized using ultrasonography (USG). Fifty people with suspicious MCs without accompanying mass were evaluated. They underwent USG and 2D-SWE before USG-guided tru-cut biopsy. SWE values and histopathologic features were compared statistically. The variables between groups were analyzed using the Mann-Whitney U test. Receiver operating characteristic analysis was performed and cut-off values determined to discriminate malignancy, invasiveness and high grade. Pathology confirmed 27 malignant lesions (18 invasive ductal carcinomas, one invasive lobular and eight ductal carcinomas in situ) and 23 benign ones. There was a statistically significant difference between the SWE values of malignant and benign MCs (p < 0.001). The diagnostic performance of SWE for malignancy, invasiveness and high grade were as follows, repectively: sensitivity (93%, 83%, 88%), specificity (91%, 88%, 53%), positive predictive value (93%, 94%, 44%), negative predictive value (91%, 70%, 90%) and area under the curve (0.952, 0.885, 0.776). Cut-off values were determined as 57 kPa for malignancy, 124 kPa for invasiveness and 124.5 kPa for high grade. In conclusion, SWE is a useful method in clinical practice for characterizing MCs that can be visualized with USG.

Application Value of Real-Time Shear Wave Elastography in Diagnosing the Depth of Infiltrating Muscular Layer of Endometrial Cancer

OBJECTIVE

To explore the clinical value of real-time shear wave ultrasonic elastography in diagnosing the depth of infiltrating muscularis of endometrial cancer.

METHODS

Seventy-one patients with stage I endometrial cancer infiltrating the myometrium and 37 patients with normal physical examination were enrolled and divided into three groups: endometrial cancer superficial muscle infiltration group, endometrial cancer deep muscle infiltration group, and normal control group. After completing 2-dimensional ultrasound examination, each patient switched to the real-time shear wave elastography mode to measure the elasticity values Emax, Emean, and Esd.

RESULTS

For control group, comparison of elastic modulus values between superficial muscular layer near the intimal surface and the deep muscular layer near the serosa surface showed no difference (P > 0.05). For endometrial cancer superficial muscular infiltration group, significant difference was found regarding the elastic modulus values of infiltrated muscular layer and uninfiltrated muscular layer (Emax and Emean) without difference for Esd (P > 0.05). A significant difference of elastic modulus was observed between control group and deep myometrial infiltration group (P < 0.05) without difference of Emean or Emax but with difference of Esd. The accuracy in diagnosing muscular layer infiltration was 78.9% for Emax cutoff and 82.5% for Emean cutoff. The rate of using Emax ≥32.22 kPa or Emean ≥27.54 kPa as the ultrasound standard for diagnosing myometrium infiltration was 92.9%. The accuracy for the diagnosis of muscular layer infiltration was 96.1% for Emax cutoff, 94.1% for Emean cutoff and 86.3% for Esd cutoff.

CONCLUSION

Real-time shear wave elastography is helpful to determine the depth of infiltrating myometrium of endometrial cancer.

Evaluation of Hand Tendon Elastic Properties During Rehabilitation Through High-Frequency Ultrasound Shear Elastography

Tendon injuries lead to tendon stiffness, which impairs skeletal muscle movement. Most studies have focused on patellar or Achilles tendons by using ultrasound elastography. Only a few studies have measured the stiffness of hand tendons because their thickness is only 1-2 mm, rendering clinical ultrasound elastography unsuitable for mapping hand tendon stiffness. In this study, a high-frequency ultrasound shear elastography (HFUSE) system was proposed to map the shear wave velocity (SWV) of hand flexor tendons. A handheld vibration system that was coaxially mounted with an external vibrator on a high-frequency ultrasound (HFUS) array transducer allowed the operators to scan hand tendons freely. To quantify the performance of HFUSE, six parameters were comprehensively measured from homogeneous, two-sided, and three-sided gelatin phantom experiments: bias, precision, lateral resolution, contrast, contrast-to-noise ratio (CNR), and accuracy. HFUSE demonstrated an excellent resolution of [Formula: see text] to distinguish the local stiffness of thin phantom (thickness: 1.2 mm) without compromising bias, precision, contrast, CNR, and accuracy, which has been noted with previous systems. Human experiments involved four patients with hand tendon injuries who underwent ≥2 months of rehabilitation. Using HFUSE, two-dimensional SWV images of flexor tendons could be clearly mapped for healthy and injured tendons, respectively. The findings demonstrate that HFUSE can be a promising tool for evaluating the elastic properties of the injured hand tendon after surgery and during rehabilitation and thus help monitor progress.

Surface wave elastography is a reliable method to correlate muscle elasticity, torque, and electromyography activity level

The shear elastic modulus is one of the most important parameters to characterize the mechanical behavior of soft tissues. In biomechanics, ultrasound elastography is the gold standard for measuring and mapping it locally in skeletal muscle in vivo. However, their applications are limited to the laboratory or clinic. Thus, low-frequency elastography methods have recently emerged as a novel alternative to ultrasound elastography. Avoiding the use of high frequencies, these methods allow obtaining a mean value of bulk shear elasticity. However, they are frequently susceptible to diffraction, guided waves, and near field effects, which introduces biases in the estimates. The goal of this work is to test the performance of the non-ultrasound surface wave elastography (NU-SWE), which is portable and is based on new algorithms designed to correct the incidence of such effects. Thus, we show its first application to muscle biomechanics. We performed two experiments to assess the relationships of muscle shear elasticity versus joint torque (experiment 1) and the electromyographic activity level (experiment 2). Our results were comparable regarding previous works using the reference ultrasonic methods. Thus, the NU-SWE showed its potentiality to get wide the biomechanical applications of elastography in many areas of health and sports sciences.

A Robust and Fast Method for 2-D Shear Wave Speed Calculation

We developed a new method, called the tangent plane method (TPM), for more efficiently and accurately estimating 2-D shear wave speed (SWS) from any direction of wave propagation. In this technique, we estimate SWS by solving the Eikonal equation because this approach is more robust to noise. To further enhance the performance, we computed the tangent plane of the arrival time surface. To evaluate the approach, we performed simulations and also conducted phantom studies. Simulation studies showed that TPM was more robust to noise than the conventional methods such as 2-D cross correlation (CC) and the distance method. The contrast/CNR for an inclusion (69 kPa; manufacturer provided stiffness) of a phantom is 0.54/4.17, 0.54/1.82, and 0.46/1.22. SWS results [mean and standard deviation (SD)] were 4.41 ± 0.49, 4.62 ± 0.85, and 3.66 ± 0.99 m/s, respectively, while the manufacturer's reported value (mean and range) is 4.81 ± 0.49 m/s. This shows that TPM has the higher CNR and lower SD than other methods. To increase the computation speed, an iterative version of TPM (ITPM) was also developed, which calculated the time-of-flight iteratively. ITPM reduced the computation time to 3.6%, i.e., from 748 to 27 s. In vivo case analysis demonstrated the feasibility of using the conventional ultrasound scanner for the proposed 2-D SWS algorithms.