Ultrasound Elastography Methods Research Articles

Ultrasonic surface acoustic wave elastography: A review of basic theories, technical developments, and medical applications.

Physiological and pathological changes in tissues often cause changes in tissue mechanical properties, making tissue elastography an effective modality in medical imaging. Among the existing elastography methods, ultrasound elastography is of great interest due to the inherent advantages of ultrasound imaging technology, such as low cost, portability, safety, and wide availability. However, most current ultrasound elastography methods are based on the bulk shear wave; they can image deep tissues but cannot image superficial tissues. To address this challenge, ultrasonic elastography methods based on surface acoustic waves have been proposed. In this paper, we present a comprehensive review of ultrasound-based surface acoustic wave elastography techniques, including their theoretical foundations, technical implementations, and existing medical applications. The goal is to provide a concise summary of the state-of-the-art of this field, hoping to offer a reliable reference for the further development of these techniques and foster the expansion of their medical applications.

Evaluation of Robustness of S-Transform Based Phase Velocity Estimation in Viscoelastic Phantoms and Renal Transplants.

Ultrasound shear wave elastography (SWE) methods are being used to differentiate healthy versus diseased tissue on the basis of their viscoelastic mechanical properties. Tissue viscoelasticity is often studied by analyzing shear wave phase velocity dispersion curves, which is the variation of phase velocity with frequency or wavelength. Recently, a unique approach using a generalized Stockwell transformation (GST-SFK) was proposed for the calculation of dispersion curves in viscoelastic media over expanded frequency band. In this work, the method's robustness was evaluated on data from five custom-made viscoelastic tissue-mimicking phantoms and sixty in vivo renal transplants. For each phantom, 15 shear wave motion data acquisitions were taken, while 10-13 acquisitions were acquired for renal transplants measured in the renal cortex. For each data-set mean and standard deviation (SD) of estimated phase velocity dispersion curves were studied. In addition, the viscoelastic parameters of the Zener model were examined, which were preceded by a convergence analysis. For viscoelastic phantoms scanned with a research ultrasound scanner, and for the in vivo renal transplants scanned with a clinical scanner, the decisive advantage of the GST-SFK method over the standard two-dimensional Fourier transform (2D-FT) method was shown. The GST-SFK method provided dispersion curve estimates with lower SD over a wider frequency band in comparison to the 2D-FT method. These advantages are relevant to the analysis of the mechanical properties of tissues in clinical practice to discriminate healthy from diseased tissue.

Comparing in vivo wave-based elastography with ex vivo mechanical testing in porcine vessels

Arterial stiffness predicts cardiovascular disease, the leading cause of death worldwide. Ultrasound elastography methods that measure wave velocity have promise for evaluating the stiffness of blood vessels in vivo. However, vessel geometry modulates wave velocity by inducing geometric dispersion. Here, we compare Young's modulus E estimates obtained using in vivo wave velocity measurements and techniques that either do or do not consider geometry to ex vivo reference E values from mechanical testing . An acoustic radiation force was applied to generate propagating waves in the right common carotid artery (N = 9) and external jugular vein (N = 10) of anesthetized pigs. Vessels were imaged with ultrafast ultrasound to measure wave motion. Group velocity cg was estimated from wave motion using a Radon transform. E was estimated from cg using a bulk media assumption which neglects geometry, as well as the Moens–Korteweg equation and a semi-analytical finite element model, which consider geometry. Pigs were euthanized and vessels were excised. Ring-shaped samples were extracted and tested in a uniaxial tension setup to obtain reference E values for comparison with E values obtained from wave-based techniques. Techniques considering geometry exhibited higher correlation with reference E values, underscoring the need to incorporate geometry for accurate vascular elastography assessments.

Evaluation of Myocardial Stiffness in Cardiac Amyloidosis Using Acoustic Radiation Force Impulse and Natural Shear Wave Imaging.

Increased myocardial stiffness (MS) is an important hallmark of cardiac amyloidosis (CA) caused by myocardial amyloid deposition. Standard echocardiography metrics assess MS indirectly via downstream effects of cardiac stiffening. The ultrasound elastography methods acoustic radiation force impulse (ARFI) and natural shear wave (NSW) imaging assess MS more directly. This study compared MS in 12 healthy volunteers and 13 patients with confirmed CA using ARFI and NSW imaging. Parasternal long-axis acquisitions of the interventricular septum were obtained using a modified Acuson Sequoia scanner and a 5V1 transducer. ARFI-induced displacements were measured through the cardiac cycle, and ratios of diastolic-over-systolic displacement were calculated. NSW speeds from aortic valve closure were extracted from echocardiography-tracked displacement data. ARFI stiffness ratios were significantly lower in CA patients than controls (mean ± standard deviation: 1.47 ± 0.27 vs. 2.10 ± 0.47, p < 0.001), and NSW speeds were significantly higher in CA patients than controls (5.58 ± 1.10 m/s vs. 3.79 ± 1.10 m/s, p < 0.001). A linear combination of the two metrics exhibited greater diagnostic potential than either metric alone (area under the curve=0.97 vs. 0.89 and 0.88). MS was measured to be significantly higher in CA patients using both ARFI and NSW imaging. Together, these methods have potential utility to aid in clinical diagnosis of diastolic dysfunction and infiltrative cardiomyopathies.

A single-center, retrospective, cross-sectional study comparing the number of non-diagnostic measurements ratio in the pSWE and SSI ultrasound elastography methods.

The point shear wave elastography and supersonic shear imaging methods were compared regarding incorrect measurements during the liver examinations. A report-based, single-center, retrospective analysis of 425 liver elastography examinations was performed. A lower success ratio was observed for the point shear wave elastography method, as well as the older and obese patients pre-dominated in non-diagnostic studies. In our center experience, it is easier to obtain diagnostic data using the supersonic shear imaging method. However, further investigation of the subject is needed.

A Case-Control Study of 40 Patients with Piriformis Muscle Syndrome to Evaluate Diagnostic Findings Using Two-Dimensional Ultrasound and Shear Wave Elastography.

BACKGROUND Piriformis muscle syndrome (PMS) is a neuropathy caused by compression of the sciatic nerve by the piriformis muscle. This case-control study included 40 patients with PMS and aimed to evaluate the diagnostic findings using two-dimensional ultrasound and shear wave elastography (SWE), as non-invasive and cost-effective diagnostic methods. MATERIAL AND METHODS In order to evaluate the value of two-dimensional ultrasound diagnosis, a new imaging technique called shear wave elastography (SWE) was used in the screening of PMS, with a total of 40 PMS patients and 40 healthy individuals participating in our study. We analyzed the correlation and area under the curve (AUC) of changes in thickness (mm) and Young's modulus (kpa) of the bilateral piriformis muscle (PM). RESULTS We found that PM thickness and Young's modulus on the lesion sides were significantly higher in PMS patients than in controls (P<0.05). Also, we determined that there was a positive correlation between PM thickness and Young's modulus (r=0.454, P<0.05). Using two-dimensional ultrasonic diagnosis and the SWE technique, a specificity of 95.8% and sensitivity of 78.8% were demonstrated in the clinical diagnosis of PM. CONCLUSIONS Two-dimensional ultrasound with SWE technology has demonstrated its superior sensitivity and specificity in diagnosing PMS in the clinic.

A Scholte wave based ultrasound elastography method for imaging superficial tissue

Pathological changes in tissues are often related to changes in tissue mechanical properties, making elastography an important tool for medical applications. Among the existing elastography methods, ultrasound elastography is of great interest due to the inherent advantages of ultrasound imaging technology, such as low cost, portability, safety, and wide availability. However, the current ultrasound elastography methods, including shear wave elastography, can readily image deep tissue but cannot assess superficial tissue. To address this challenge, we proposed an ultrasonic Scholte-wave-based approach for imaging the elasticity of superficial tissue. The feasibility of the proposed technique was tested using a gelatin phantom with a cylindrical inclusion. In the tests, Scholte (surface) and shear (bulk) waves were simultaneously generated by the same excitation but propagated in the superficial and deeper regions of the phantom, respectively. In this study, we first demonstrated that the elasticity of superficial tissue could be evaluated by utilizing the generated Scholte wave alone and further showed that a comprehensive elasticity imaging of the tissue extending from the superficial to deep regions can be achieved by combining the proposed Scholte wave technique and the conventional shear wave technique.

A novel tissue mechanics-based method for improved motion tracking in quasi-static ultrasound elastography.

Most cancers are associated with biological and structural changes that lead to tissue stiffening. Therefore, imaging tissue stiffness using quasi-static ultrasound elastography (USE) can potentially be effective in cancer diagnosis. USE techniques developed for stiffness image reconstruction use noisy displacement data to obtain the stiffness images. In this study, we propose a technique to substantially improve the accuracy of the displacement data computed through ultrasound tissue motion tracking techniques, especially in the lateral direction. The proposed technique uses mathematical constraints derived from fundamental tissue mechanics principles to regularize displacement and strain fields obtained using Global Ultrasound Elastography (GLUE) and Second-Order Ultrasound Elastography (SOUL) methods. The principles include a novel technique to enforce (1) tissue incompressibility using 3D Boussinesq model and (2) deformation compatibility using the compatibility differential equation. The technique was validated thoroughly using metrics pertaining to Signal-to-Noise-Ratio (SNR), Contrast-to-Noise-Ratio (CNR) and Normalized Cross Correlation (NCC) for four tissue-mimicking phantom models and two clinical breast ultrasound elastography cases. The results show substantial improvement in the displacement and strain images generated using the proposed technique. The tissue-mimicking phantom study results indicate that the proposed method is superior in improving image quality compared to the GLUE and SOUL techniques as it shows an average axial strain SNR and CNR improvement of 44% and 63%, and lateral strain SNR and CNR improvement of 130% and 435%, respectively. The results of the phantom study also indicate higher accuracy of displacement images obtained using the proposed technique, including improvement ranges of 7-84% and 26-140% for axial and lateral displacement images, respectively. For the clinical cases, the results indicate average improvement of 48% and 64% in SNR and CNR, respectively, in the axial strain images, and average improvement of 40% and 41% in SNR and CNR, respectively, in the lateral strain images. The proposed method is very effective in producing improved estimate of tissue displacement and strain images, especially with the lateral displacement and strain where the improvement is highly remarkable. While the method shows promise for clinical applications, further investigation is necessary for rigorous assessment of the method's performance in the clinic.

Elastography Assisted BI-RADS in the Preoperative Breast Magnetic Resonance Imaging 4a Lesions in China.

A considerable number of benign lesions, especially category 4a lesions on Breast Imaging Reporting and Data System Magnetic Resonance Imaging (BI-RADS-MRI), were biopsied according to BI-RADS-MRI, which was a diagnostic imaging challenge. This study aimed to evaluate the diagnostic performance of ultrasound elastography (UE) assisted Breast Imaging Reporting and Data System (BI-RADS) for BI-RADS-MRI category 4a lesions. Between January 2017 and December 2019, 228 breast lesions categorized as BI-RADS-MRI 4a were included. Conventional ultrasound (US) and UE were performed to evaluate each lesion. Pathology results were used as the gold standard. The diagnostic performances of different UE methods and our re-assessment proposal were evaluated. When BI-RADS-MRI category 4a, BI-RADS-US category 3-4a, the stiffness of soft or intermediate in elasticity assessment according to the fifth edition of the BI-RADS atlas, strain ratio < 1.335, age ≤ 52 years, and the maximum diameter of lesion ≤20 mm were simultaneously met, an ultrasound-guided empty needle biopsy was not recommended, but short-term ultrasound follow-up for 3-6 months was recommended, and biopsy was performed after changes in evaluation. In this way, 95 of 228 BI-RADS-MRI category 4a lesions avoided biopsies, and the number of patients with biopsies decreased by 41.7%. UE offers benefits in the characterization of BI-RADS-MRI category 4a lesions. Ultrasound and elastography can help optimize therapy recommendations for BI-RADS-MRI category 4a lesions by our re-assessment proposal.

Effect of Quantitative and Semi-quantitative Elastography Methods for the Management of Borderline Lesions on Ultrasonography.

Elastography (strain or shear-wave) is a method that estimates tissue stiffness. The aim of this study is to evaluate the quantitative and semi-quantitative ultrasound elastography methods for the diagnosis of BI-RADS 4a and BI-RADS 3 lesions, which are borderline for biopsy and follow-up. 175 consecutive women with 193 ultrasound-visible breast lesions were classified on Conventional B-mode Ultrasonography (CUS) according to the BI-RADS scoring system. Quantitative and semiquantitative values from ultrasound elastography in the form of strain Elastography Ratio (SER), shear Wave Elastography (SWE) and Shear Wave Elastography Ratio (SWER) were obtained. The lesions categorized as BI-RADS 4a and BI-RADS 3 on ultrasound were subsequently re-categorized according to the elastography values. Except for the 13 BI-RADS 2 lesions, the remaining 180 lesions were biopsied. Pathology showed 83 lesions to be benign and 97 to be malignant. The sensitivity and specificity of the CUS were 96.9% and 75.0%, respectively with an accuracy of 86.0%. Cut-off points calculated based on ROC curves were 56.8 kPa for SWE, 3.53 for SWER and 3.81 for SER. When we downgraded BIRADS 4a lesions based on elastography results, the specificity (CUS+SER 96.9%, CUS+SWE 91.7%, and CUS+SWER 90.6%) and the accuracy (CUS+SER 95.3%, CUS+SWE 92.7%, and CUS+SWER 92.2%) were shown to be better than CUS. When we upgraded BI-RADS 3 lesions based on elastography results, the sensitivity of combined sets of SWE (99,0%) and SWER (100,0%) was better than CUS. The rate of false-negative biopsies can be decreased with the combined use of elastography and ultrasonography.

Quantitative Ultrasound Elastography Methods in Focal Liver Lesions Including Hepatocellular Carcinoma: From Diagnosis to Prognosis.

The ability of ultrasound elastography to diagnose focal liver lesions and determine their prognoses including hepatocellular carcinoma (HCC) is unclear. At present, radiofrequency ablation and liver resection are the most common treatments for HCC. However, the survival rate remains disappointing because of recurrences and postoperative liver failure, necessitating the development of noninvasive approaches. There is currently no systematic definition of an elastic technique for measuring liver stiffness to predict the recurrence of HCC after radiofrequency ablation and postoperative liver failure. In this review, recent advances in ultrasound elastography for the diagnosis and prognosis of focal liver lesions are discussed including HCC.

Shear wave elastography and transient elastography in HCV patients after direct-acting antivirals.

To compare the ultrasound (US) and pulse shear wave elastography (pSWE, Elast PQ®) methods with transient elastography (TE), clinical scores and laboratory tests, during the follow-up of HCV patients receiving direct-acting antiviral drugs (DAA). Our prospective study from June 2016 to December 2017 included 22 consecutively enrolled HCV-positive patients (59.7 ± 12.3years, 11 male) which were subjected to antiviral therapy. All patients underwent B-mode ultrasound, color-Doppler, pSWE and TE five times: before therapy (T0), at the end of therapy (post-Tx), and at 12, 24, 48 weeks post-therapy. The liver stiffness (LS) values obtained with pSWE and TE and the data coming from US assessment and clinical evaluation were compared. We obtained a statistically significant reduction of LS values (kPa) measured by pSWE, between T0 (14.3 ± 9.3), post-Tx (11.8 ± 10.5), 12weeks (7.5 ± 3.3), 24weeks (8 ± 3.8) and 48weeks (8.5 ± 4.6) (p = 0.02). The reduction of kPa measured by TE was not significant between T0 (14.7 ± 9.3), post-Tx (12 ± 9.5), 12weeks (11.6 ± 7.7), 24weeks (10.3 ± 6) and 48weeks (10.8 ± 7.5) (p > 0.05). Multivariate baseline analysis showed significant independent association among measurement of TE stiffness with cirrhosis, type of vein hepatic flow and showed significant independent association between delta-pSWE measurement (difference between stiffness measurements at the baseline and 12months after treatment) with staging of fibrosis (p = 0.006) and sustained virologic response after 12weeks of treatment (SVR12, p = 0.017). The pSWE method has shown better ability than TE to identify a reduction in LS. Therefore, pSWE allow to evaluate stiffness reduction in HCV patient during DAA treatment follow-up, which is related to SVR12.

Neural-network-based Motion Tracking for Breast Ultrasound Strain Elastography: An Initial Assessment of Performance and Feasibility.

Accurate tracking of tissue motion is critically important for several ultrasound elastography methods. In this study, we investigate the feasibility of using three published convolution neural network (CNN) models built for optical flow (hereafter referred to as CNN-based tracking) by the computer vision community for breast ultrasound strain elastography. Elastographic datasets produced by finite element and ultrasound simulations were used to retrain three published CNN models: FlowNet-CSS, PWC-Net, and LiteFlowNet. After retraining, the three improved CNN models were evaluated using computer-simulated and tissue-mimicking phantoms, and in vivo breast ultrasound data. CNN-based tracking results were compared with two published two-dimensional (2D) speckle tracking methods: coupled tracking and GLobal Ultrasound Elastography (GLUE) methods. Our preliminary data showed that, based on the Wilcoxon rank-sum tests, the improvements due to retraining were statistically significant (p < 0.05) for all three CNN models. We also found that the PWC-Net model was the best neural network model for data investigated, and its overall performance was on par with the coupled tracking method. CNR values estimated from in vivo axial and lateral strain elastograms showed that the GLUE algorithm outperformed both the retrained PWC-Net model and the coupled tracking method, though the GLUE algorithm exhibited some biases. The PWC-Net model was also able to achieve approximately 45 frames/second for 2D speckle tracking data investigated.

Monitoring Liver Stiffness Changes during Controlled Hyperthermia and Microwave Ablation Using Point Shear-Wave Elastography.

HomeRadiology: Imaging CancerVol. 1, No. 2 Previous Research HighlightsFree AccessMonitoring Liver Stiffness Changes during Controlled Hyperthermia and Microwave Ablation Using Point Shear-Wave ElastographyLuke WilkinsLuke WilkinsLuke WilkinsPublished Online:Nov 29 2019https://doi.org/10.1148/rycan.2019194013MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked InEmail Take-Away Points■ Major focus: To investigate the changes in liver stiffness following controlled hyperthermia and microwave ablation in an ex vivo bovine model using point shear-wave elastography.■ Key result: Point shear-wave elastography can provide an elasticity threshold predictive of coagulative necrosis development during microwave ablation in an ex vivo liver model.■ Impact: While there are current limitations, there are opportunities for incorporation of more advanced, real-time imaging techniques to more accurately predict zones of coagulative necrosis in tumor ablation.Noninvasive monitoring of thermal ablation can greatly decrease the risk of complications while ensuring treatment efficacy. While some thermal ablation systems have the capacity to provide real-time temperature feedback, it is typically restricted to the temperature at the device level and does not provide information on tissue temperature within the remainder of the treatment cavity. Crocetti et al explore the use of elastography as a potential method to provide real-time temperature monitoring.There are several US elastographic techniques. In point shear-wave elastography (pSWE), an acoustic radiation force is induced within the tissue. The disturbance created within the tissue moves through the tissue as a shear wave. By monitoring the corresponding tissue displacements created by the shear wave under B-mode imaging, inferences can be made regarding the stiffness of the underlying tissue. This is important for thermal ablation as it is well-known that coagulation (protein denaturation and tissue dehydration) occurs at 60°C. However, the effect of thermal-induced changes in the mechanical properties of the liver tissue has not yet been fully investigated. This article sought to investigate the changes in liver stiffness in controlled hyperthermia and microwave ablation (MWA) in an ex vivo animal model.The authors used five samples of ex vivo bovine liver that were uniformly heated to temperatures ranging from 40 to 100°C. B-mode US imaging and pSWE were then performed simultaneously. In addition, MWA was performed in 11 liver samples at 60 W. Shear wave velocity (SWV) was then measured in the regions of interest (ROIs) at 10–40 mm from the antenna. Histopathologic examination was performed to correlate mean values of SWV to treatment associated changes (within, border, or outside necrotic area). The article reports that a steep transition in liver stiffness was observed at 63.0°C ± 2.4. Through this first phase of experiments, the authors determined that the mean SWV at 60°C was 2.5 m/sec (defined as Avg60). For the next set of experiments, the threshold was defined as Avg60 + 0.5 m/sec or 3 m/sec. Eight of nine experiments showed that following stoppage of ablation when the predetermined ROI reached threshold SWV of 3 m/sec, the ROI was within the necrotic area at histologic examination. While this is notable, there was no correlation between SWV values for outside, border, and within necrosis. This markedly limits current clinical applicability of this technology. Future research may allow more accurate methods for detecting changes in tissue stiffness that would be able to predict tissue still outside the necrotic zone.Highlighted ArticleCrocetti L, Calcagni F, Gherarducci G, et al. Monitoring of thermal-induced changes in liver stiffness during controlled hyperthermia and microwave ablation in an ex vivo bovine model using point shear wave elastography. Cardiovasc Interv Radiol 2019;42(5):744–750. doi: https://doi.org/10.1007/s00270-018-02152-yHighlighted ArticleCrocetti L, Calcagni F, Gherarducci G, et al. Monitoring of thermal-induced changes in liver stiffness during controlled hyperthermia and microwave ablation in an ex vivo bovine model using point shear wave elastography. Cardiovasc Interv Radiol 2019;42(5):744–750. doi: https://doi.org/10.1007/s00270-018-02152-y Crossref, Medline, Google ScholarArticle HistoryPublished online: Nov 29 2019 FiguresReferencesRelatedDetailsCited ByRecommended Articles Elastography in Chronic Liver Disease: Modalities, Techniques, Limitations, and Future DirectionsRadioGraphics2016Volume: 36Issue: 7pp. 1987-2006US Elastography in Hepatic Fibrosis—Radiology In TrainingRadiology2021Volume: 299Issue: 2pp. 264-271Quantitative Elastography Methods in Liver Disease: Current Evidence and Future DirectionsRadiology2018Volume: 286Issue: 3pp. 738-763US Time-Harmonic Elastography: Detection of Liver Fibrosis in Adolescents with Extreme Obesity with Nonalcoholic Fatty Liver DiseaseRadiology2018Volume: 288Issue: 1pp. 99-106Update to the Society of Radiologists in Ultrasound Liver Elastography Consensus StatementRadiology2020Volume: 296Issue: 2pp. 263-274See More RSNA Education Exhibits Ultrasound Elastography Methods: Physical Principles, Techniques, and IndicationsDigital Posters2018Spleen Elastography and Portal Hypertension: An Overview and the Nitty-GrittiesDigital Posters2018Ultrasound Elastography in Children: How We Do it and What is it Helpful For?Digital Posters2019 RSNA Case Collection Hepatic AdenomatosisRSNA Case Collection2021 Cholecystitis and CholedocholithiasisRSNA Case Collection2020Radioembolization of Liver Metastasis RSNA Case Collection2020 Vol. 1, No. 2 Metrics Downloaded 178 times Altmetric Score PDF download

Ultrasound Elastography Use in Lower Extremity Lymphedema: A Systematic Review of the Literature.

Lower extremity lymphedema (LEL) is mainly assessed clinically. Ultrasound elastography (UE) is a promising imaging tool to assess this disorder. We conducted a systematic literature review to describe the studies evaluating the use of UE in LEL. The PubMed database was queried for studies that evaluated the use of UE in LEL. The keywords “elastography” AND “lymphedema” were used for the search. Original articles in English were included in our study, whereas reviews were excluded. Our search resulted in 12 articles, 4 of which met the inclusion criteria. UE methods included free-hand real-time tissue elastography and UE with transducer in B mode. The imaging parameters applied were the tissue strains and the area of red region, respectively. All studies tested UE use in the assessment of LEL, and only one considered its use for staging. All studies but one found a difference in strain parameters for assessment of patients with LEL. Our systematic review has shown that UE appears to be a great tool in the assessment of LEL in moderate-to-advanced stages of disease. However, further studies using new effective methods are needed to evaluate patients with early lymphedema.

Fast Approximate Time-Delay Estimation in Ultrasound Elastography Using Principal Component Analysis.

Time delay estimation (TDE) is a critical and challenging step in all ultrasound elastography methods. A growing number of TDE techniques require an approximate but robust and fast method to initialize solving for TDE. Herein, we present a fast method for calculating an approximate TDE between two radio frequency (RF) frames of ultrasound. Although this approximate TDE can be useful for several algorithms, we focus on GLobal Ultrasound Elastography (GLUE), which currently relies on Dynamic Programming (DP) to provide this approximate TDE. We exploit Principal Component Analysis (PCA) to find the general modes of deformation in quasi-static elastography, and therefore call our method PCA-GLUE. PCA-GLUE is a data-driven approach that learns a set of TDE principal components from a training database in real experiments. In the test phase, TDE is approximated as a weighted sum of these principal components. Our algorithm robustly estimates the weights from sparse feature matches, then passes the resulting displacement field to GLUE as initial estimates to perform a more accurate displacement estimation. PCA-GLUE is more than ten times faster than DP in estimation of the initial displacement field and yields similar results.

Performance of a THED system for ruling in/ruling out Liver Cirrhosis as compared with Transient Elastography

Introduction While most ultrasound elastography methods employ transient stimulation methods, the new time harmonic elastography (THED) relies on time-harmonic vibrations in the same manner as magnetic resonance elastography. The aim of our study was to assess the performance of the THED system for ruling in/out liver cirrhosis (LC) considering transient elastography (TE) as the reference method, as well as and the correlation of THED values with TE. Material & Method We evaluated by THED a group of 70 patients. Each subject has been fasting for more than 6 hours before evaluation. 10 valid LS measurements were performed in the same day, both by THED and by TE. We used the TE cut-off values published by Tsochatzis (1): significant fibrosis (F ≥ 2)- 7.0kPa and for LC (F = 4)- 12kPa as reference values. Quality criteria recommended by the manufacturer: SR ≥ 60%, IQR Results From the 70 patients, 34 were women and 36 men. Mean age 55.2 ± 11.7, mean BMI 27.8 ± 6.2 kg/m2. Of the 70 patients, 15.8% (11/70) were F4, 25.7% (18/70) were F2-3, 58.5 % (41/70) were F0-1.We had 100% feasibility for all the patients that were previously evaluated by TE. The cut-off for ruling out LC by THED measurements on our study group was 2 m/s (11.9 kPa). AUROC = 0.83, 95%CI (0.73-0.91), P Conclusions In our study, the cut-of values to rule-out and rule-in LC by LS measurements with THED system were 11.9 kPa, respectively. There was a strong correlation between the LS values obtained by the two elastographic methods.

Narrowband Shear Wave Generation Using Sinusoidally Modulated Acoustic Radiation Force.

Most transient ultrasound elastography methods use high-intensity ultrasound "push" pulses that generate a shear wave with a wide frequency spectrum. However, it is difficult to control how the energy of the wave is distributed within that spectrum. For this reason, the shear-wave group velocity may not match that of harmonic methods like magnetic resonance elastography (MRE). The objective of this study was to introduce a narrowband shear wave generation method produced by "push" pulses with sinusoidally modulated intensity. The method, named harmonic shear wave imaging (HSWI), successively transmits a series of push pulses with a periodic change in duration. The excited shear waves form a continuous shear wave with a known main frequency that can be controlled by the user. Push pulses are interleaved with imaging pulses so only one clinical transducer is used to generate and record the shear waves. The proposed method was compared to MRE and a transient shear wave elastography method using phantoms and in vivo measurements. It was found that HSWI produces narrowband waves with a speed that closely matches that measured by MRE. Measurement of the acoustic output parameters indicated that the acoustic intensities in HSWI are suitable for clinical applications. The ability of HSWI to generate narrowband shear waves using a single linear array transducer makes it amenable for clinical translation. HSWI can potentially use the same thresholds as MRE for diagnosis of diseases affecting the stiffness of soft tissues.

Spatial domain reconstruction for imaging speed-of-sound with pulse-echo ultrasound: simulation and in vivo study

Despite many uses of ultrasound, some pathologies such as breast cancer still cannot reliably be diagnosed in either conventional B-mode ultrasound imaging nor with more recent ultrasound elastography methods. Speed-of-sound (SoS) is a quantitative imaging biomarker, which is sensitive to structural changes due to pathology, and hence could facilitate diagnosis. Full-angle ultrasound computed tomography (USCT) was proposed to obtain spatially-resolved SoS images, however, its water-bath setup involves practical limitations. To increase clinical utility and for widespread use, recently, a limited-angle Fourier-domain SoS reconstruction was proposed, however, it suffers from significant image reconstruction artifacts. In this work, we present a SoS reconstruction strategy, where the forward problem is formulated using differential time-of-flight measurements based on apparent displacements along different ultrasound wave propagation paths, and the inverse problem is solved in spatial-domain using a proposed total-variation scheme with spatially-varying anisotropic weighting to compensate for geometric bias from limited angle imaging setup. This is shown to be robust to missing displacement data and easily allow for incorporating any prior geometric information. In numerical simulations, SoS values in inclusions are accurately reconstructed with 90% accuracy up to a noise level of 50%. With respect to Fourier-domain reconstruction, our proposed method improved contrast ratio from 0.37 to 0.67 for even high noise levels such as 50%. Numerical full-wave simulation and our preliminary in vivo results illustrate the clinical applicability of our method in a breast cancer imaging setting. Our proposed method requires single-sided access to the tissue and can be implemented as an add-on to conventional ultrasound equipment, applicable to a range of transducers and applications.

Clinical applications of spleen ultrasound elastography - a review.

In the last few years, notable technical progress has taken place in ultrasound elastography. Qualitative methods have been replaced by quantitative ones, such as: transient elastography, acoustic radiation force impulse and shear wave elastography. Owing to the fact that the spleen is superficially located, it is possible to obtain reliable measuring accuracy of its hardness using sonoelastography. Lately, many researchers have been investigating how spleen elasticity changes in patients infected with hepatitis B virus or hepatitis C virus and in patients suffering from liver fibrosis, portal hypertension, esophageal varices or myelofibrosis. In this article, we review the role and current status of accessible qualitative ultrasound elastography methods, including recent advances in the evaluation of spleen stiffness and its clinical utility. As study results demonstrate, spleen stiffness correlates with liver fibrosis and is helpful in determining the level of fibrosis in the METAVIR scoring system. In patients infected with hepatitis B virus or hepatitis C virus, spleen stiffness increases even when liver elasticity remains unaltered. Furthermore, it is useful in diagnosing portal hypertension or predicting existence of esophageal varices. Moreover, in patients suffering from biliary atresia after Kasai portoenterostomy, spleen sonoelastography may be helpful in selecting patients for liver transplantation as well as for choosing the best strategy for portal vein reconstruction before liver transplantation. In myelofibrosis, spleen stiffness correlates with bone marrow fibrosis and may be used to assess the response to treatment. Spleen sonoelastography is also useful in the monitoring of transjugular intrahepatic portosystemic shunt function.