Review of Ultrasound Elastography Quality Control and Training Test Phantoms

While the rapid development of ultrasound elastography techniques in recent decades has sparked its prompt implementation in the clinical setting adding new diagnostic information to conventional imaging techniques, questions still remain as to its full potential and efficacy in the hospital environment. A limited number of technical studies have objectively assessed the full capabilities of the different elastography approaches, perhaps due, in part, to the scarcity of suitable tissue-mimicking materials and appropriately designed phantoms available. Few commercially-available elastography phantoms possess the necessary test target characteristics or mechanical properties observed clinically, or indeed reflect the lesion-to-background elasticity ratio encountered during clinical scanning. Thus, while some phantoms may prove useful, they may not fully challenge the capabilities of the different elastography technniques, proving limited when it comes to quality control (QC) and/or training purposes. Although a variety of elastography tissue-mimicking materials, such as agar and gelatine dispersions, co-polymer in oil and poly(vinyl) alcohol cryogel, have been developed for specific research purposes, such work has yet to produce appropriately designed phantoms to adequately challenge the variety of current commercially-available elastography applications. Accordingly, there is a clear need for the further development of elastography TMMs and phantoms to keep pace with the rapid developments in elastography technology, to ensure the performance of these new diagnostic approaches are validated, and for clinical training purposes

Ultrasound Elastography

The comparison between methods, evaluation of portal hypertension and many other questions are still open issues in liver elastography. New elastographic applications are under evaluation and close to being used in clinical practice. Strain imaging has been incorporated into many disciplines and EFSUMB guidelines are under preparation. More research is necessary for improved evidence for clinical applications in daily practice. The Special Issue published papers on recent advances in development and application of Ultrasound Elastography

Ultrasound shear wave imaging for diagnosis of nonalcoholic fatty liver disease

Pour le diagnostic et la stratification de la fibrose hépatique, la rigidité du foie est un biomarqueur quantitatif estimé par des méthodes d'élastographie. L'élastographie par ondes de cisaillement (« shear wave », SW) utilise des ultrasons médicaux non invasifs pour évaluer les propriétés mécaniques du foie sur la base des propriétés de propagation des ondes de cisaillement. La vitesse des ondes de cisaillement (« shear wave speed », SWS) et l'atténuation des ondes de cisaillement (« shear wave attenuation », SWA) peuvent fournir une estimation de la viscoélasticité des tissus. Les tissus biologiques sont intrinsèquement viscoélastiques et un modèle mathématique complexe est généralement nécessaire pour calculer la viscoélasticité en imagerie SW. Le calcul précis de l'atténuation est essentiel, en particulier pour une estimation précise du module de perte et de la viscosité. Des études récentes ont tenté d'augmenter la précision de l'estimation du SWA, mais elles présentent encore certaines limites. Comme premier objectif de cette thèse, une méthode de décalage de fréquence revisitée a été développée pour améliorer les estimations fournies par la méthode originale de décalage en fréquence [Bernard et al 2017]. Dans la nouvelle méthode, l'hypothèse d'un paramètre de forme décrivant les caractéristiques spectrales des ondes de cisaillement, et assumé initialement constant pour tous les emplacements latéraux, a été abandonnée permettant un meilleur ajustement de la fonction gamma du spectre d'amplitude. En second lieu, un algorithme de consensus d'échantillons aléatoires adaptatifs (« adaptive random sample consensus », A-RANSAC) a été mis en œuvre pour estimer la pente du paramètre de taux variable de la distribution gamma afin d’améliorer la précision de la méthode. Pour valider ces changements algorithmiques, la méthode proposée a été comparée à trois méthodes récentes permettant d’estimer également l’atténuation des ondes de cisaillements (méthodes de décalage en fréquence, de décalage en fréquence en deux points et une méthode ayant comme acronyme anglophone AMUSE) à l'aide de données de simulations ou fantômes numériques. Également, des fantômes de gels homogènes in vitro et des données in vivo acquises sur le foie de canards ont été traités. Comme deuxième objectif, cette thèse porte également sur le diagnostic précoce de la stéatose hépatique non alcoolique (NAFLD) qui est nécessaire pour prévenir sa progression et réduire la mortalité globale. À cet effet, la méthode de décalage en fréquence revisitée a été testée sur des foies humains in vivo. La performance diagnostique de la nouvelle méthode a été étudiée sur des foies humains sains et atteints de la maladie du foie gras non alcoolique. Pour minimiser les sources de variabilité, une méthode d'analyse automatisée faisant la moyenne des mesures prises sous plusieurs angles a été mise au point. Les résultats de cette méthode ont été comparés à la fraction de graisse à densité de protons obtenue de l'imagerie par résonance magnétique (« magnetic resonance imaging proton density fat fraction », MRI-PDFF) et à la biopsie du foie. En outre, l’imagerie SWA a été utilisée pour classer la stéatose et des seuils de décision ont été établis pour la dichotomisation des différents grades de stéatose. Finalement, le dernier objectif de la thèse consiste en une étude de reproductibilité de six paramètres basés sur la technologie SW (vitesse, atténuation, dispersion, module de Young, viscosité et module de cisaillement). Cette étude a été réalisée chez des volontaires sains et des patients atteints de NAFLD à partir de données acquises lors de deux visites distinctes. En conclusion, une méthode robuste de calcul du SWA du foie a été développée et validée pour fournir une méthode de diagnostic de la NAFLD.For diagnosis and staging of liver fibrosis, liver stiffness is a quantitative biomarker estimated by elastography methods. Ultrasound shear wave (SW) elastography utilizes noninvasive medical ultrasound to assess the mechanical properties of the liver based on the monitoring of the SW propagation. SW speed (SWS) and SW attenuation (SWA) can provide an estimation of tissue viscoelasticity. Biological tissues are inherently viscoelastic in nature and a complex mathematical model is usually required to compute viscoelasticity in SW imaging. Accurate computation of attenuation is critical, especially for accurate loss modulus and viscosity estimation. Recent studies have made attempts to increase the precision of SWA estimation, but they still face some limitations. As a first objective of this thesis, a revisited frequency-shift method was developed to improve the estimates provided by the original implementation of the frequency-shift method [Bernard et al 2017]. In the new method, the assumption of a constant shape parameter of the gamma function describing the SW magnitude spectrum has been dropped for all lateral locations, allowing a better gamma fitting. Secondly, an adaptive random sample consensus algorithm (A-RANSAC) was implemented to estimate the slope of the varying rate parameter of the gamma distribution to improve the accuracy of the method. For the validation of these algorithmic changes, the proposed method was compared with three recent methods proposed to estimate SWA (frequency-shift, two-point frequency-shift and AMUSE methods) using simulation data or numerical phantoms. In addition, in vitro homogenous gel phantoms and in vivo animal (duck) liver data were processed. As a second objective, this thesis also aimed at improving the early diagnosis of nonalcoholic fatty liver disease (NAFLD), which is necessary to prevent its progression and decrease the overall mortality. For this purpose, the revisited frequency-shift method was tested on in vivo human livers. The new method's diagnosis performance was investigated with healthy and NAFLD human livers. To minimize sources of variability, an automated analysis method averaging measurements from several angles has been developed. The results of this method were compared to the magnetic resonance imaging proton density fat fraction (MRI-PDFF) and to liver biopsy. SWA imaging was used for grading steatosis and cut-off decision thresholds were established for dichotomization of different steatosis grades. As a third objective, this thesis is proposing a reproducibility study of six SW-based parameters (speed, attenuation, dispersion, Young’s modulus, viscosity and shear modulus). The assessment was performed in healthy volunteers and NAFLD patients using data acquired at two separate visits. In conclusion, a robust method for computing the liver’s SWA was developed and validated to provide a diagnostic method for NAFLD

WFUMB Guidelines and Recommendations for Clinical Use of Ultrasound Elastography: Part 1: Basic Principles and Terminology

Abstract Conventional diagnostic ultrasound images of the anatomy (as opposed to blood flow) reveal differences in the acoustic properties of soft tissues (mainly echogenicity but also, to some extent, attenuation), whereas ultrasound-based elasticity images are able to reveal the differences in the elastic properties of soft tissues (e.g., elasticity and viscosity). The benefit of elasticity imaging lies in the fact that many soft tissues can share similar ultrasonic echogenicities but may have different mechanical properties that can be used to clearly visualize normal anatomy and delineate pathologic lesions. Typically, all elasticity measurement and imaging methods introduce a mechanical excitation and monitor the resulting tissue response. Some of the most widely available commercial elasticity imaging methods are 'quasi-static' and use external tissue compression to generate images of the resulting tissue strain (or deformation). In addition, many manufacturers now provide shear wave imaging and measurement methods, which deliver stiffness images based upon the shear wave propagation speed. The goal of this review is to describe the fundamental physics and the associated terminology underlying these technologies. We have included a questions and answers section, an extensive appendix, and a glossary of terms in this manuscript. We have also endeavored to ensure that the terminology and descriptions, although not identical, are broadly compatible across the WFUMB and EFSUMB sets of guidelines on elastography ( Bamber et al. 2013; Cosgrove et al. 2013 )

Diagnostic accuracy of Acoustic Radiation Force Impulse (ARFI) Elastography of liver and spleen to identify Noncirrhotic portal fibrosis (NCPF) from cirrhosis with portal hypertension and comparison with liver biopsy

OBJECTIVES: To assess the diagnostic accuracy of ARFI elastography of liver and spleen to identify patients with NCPF from cirrhosis with portal hypertension as compared to liver biopsy, to differentiate significant liver fibrosis from non-significant liver fibrosis in patients with portal hypertension and to predict clinically significant portal hypertension (CSPH) compared to HVPG and the presence of high risk EV. METHODS: Prospective study approved by IRB. Patients with pre-biopsy preliminary diagnosis of cryptogenic cirrhosis were included and underwent ARFI elastography of the liver and the spleen. The liver stiffness (LS), spleen stiffness (SS), spleen stiffness to liver stiffness ratio (SS/LS) shear wave velocity measurements were correlated with the grades of liver fibrosis on biopsy, clinical and biochemical parameters, HVPG and the presence of high risk varices (EV) on endoscopy. Patients with other causes of portal hypertension were also studied who did not undergo liver biopsy. Chi- square test, kappa and spearmen correlation were used to analyse the data. RESULTS: 48 cases with preliminary diagnosis of cryptogenic cirrhosis were studied. 39 cases had liver biopsy. 11 cases were proven to be NCPF on biopsy. 9 cases were clinically suspected to have NCPF who did not undergo liver biopsy were also studied. 58 cases of portal hypertension of any etiology were studied to assess the correlation of ARFI of the liver and the spleen for CSPH. LS had 36% sensitivity, 93% specificity, PPV of 90%, NPV of 78.8% and kappa of 0.28 and p value of 0.04 to identify NCPF from other liver cirrhosis which was statistically significant. The SS/ LS ratio had 70% sensitivity, 79.2% specificity, PPV of 58.3%, NPV of 86.4% with kappa of 0.46 and p value of 0.06 which was statistically not significant. Spearman correlation (rho) of the liver stiffness (LS) with the fibrosis grades on liver biopsy was 0.54 with p value of < 0.001 which was statistically significant. Both LS and SS were found to have low sensitivity with low kappa agreement and were statistically not significant to identify CSPH. CONCLUSIONS: ARFI elastography of the liver and the spleen in combination have good sensitivity to identify NCPF from cirrhosis with portal hypertension as compared to liver biopsy. The best elastography parameter was the SS/LS. There is good correlation with liver stiffness velocities and grades of liver fibrosis. ARFI has low sensitivity and low specificity to identify CSPH

Shear wave elastography to assess the effect of botulinum toxin in muscle hypertonia following stroke

Introduction Sonoelastography is a method capable of evaluating the mechanical properties of soft tissues by ultrasound (US). A further development of this technique is shear wave elastography (SWE), which provides a quantitative evaluation of the elastic properties - in terms of tissutal stiffness - by measuring the propagation velocities of the directional shear waves, produced by an ultrasound pulse. Spasticity often appears in stroke patients in the affected limbs. It corresponds to velocity-dependent muscle hypertonia in relation to the hyperexcitability of the stretch reflex. Over time, the paretic muscles develop intrinsic alterations with consequent muscle shortening and increased fibrosis related to reduced use and immobilization. Intramuscular injections of botulinum toxin A (BoNT-A) is an effective treatment which reduces muscle activity by inhibiting the release of acetylcholine at the neuromuscular junction level and is therefore able to reduce neuromediated muscle hypertonicity. The study aims to evaluate the effectiveness of SWE to appreciate changes in stiffness in spastic muscles after treatment with BoNT-A and possibly detect differences between affected muscles and unaffected contralateral ones related to fibrous-fatty remodeling. Materials &amp; Methods 14 adult patients (5F; age: 58,4\ub114,1 years, m\ub1SD; range:46-78) affected by spasticity were recruited after ischemic or hemorrhagic stroke diagnosed for at least 3 months and with a time interval from the last injection of at least 4 months, if already treated with BoNT-A. They patients underwent a physical examination in which muscle hypertonia was assessed using the modified Ashworth scale (MAS). The assessments were carried out on a sample muscle among the spastic ones favoring the greater volume and better accessibility to the ultrasound probe. SWE was also performed on the homologue non-paretic contralateral muscle. Spasticity was measured as the average electromyographic activity recorded during stretching (reflex by stretching) of the selected muscle at a reproducible speed, according to a previously validated methodology. The SWE evaluation was carried out with US scans across and along the direction of muscular fibers - as assessed by conventional US - covering the entire belly of the selected muscle to obtain a comprehensive estimate of the muscle stiffness both with the maximum shortened and elongated muscle position. Muscle fibrosis was also estimated on conventional B-mode US using the modified Heckmatt scale. All evaluations were performed shortly before botulinum toxin infiltration (T0) and one month later (T1). Clinical, electromyographic and ultrasound evaluation were performed by three different blinded examiners. Depending on data distribution, non-parametric statistical tests for paired data were performed for comparison; Spearman\u2019s r was calculated to assess data correlations. Results A total of 224 SWE values resulted considering both time points. Overall, SWE measurements on paretic muscles assessed with a longitudinal positioning of the probe showed statistically significant reduction at T1 versus T0 both in non stretched conditions (p=0.001) and in stretched conditions (p=0.0029). After BoNT-A injection, a significant reduction in MAS (p=0.009), spastic dystonia (p=0.0043), spasticity (p=0.0019) and longitudinal SWE measurements, both in non stretched conditions (p=0.001) and in stretched conditions (p=0.0029), was observed. No significant changes in SWE parameters were observed on non-paretic versus contralateral muscle . All SWE measurements were higher in the paretic limb than in the contralateral one (p&lt;0.01); higher SWE measurements resulted along the direction of muscular fibers versus across them (p&lt;0.01). Cohen\u2019s d estimate a larger effect on EMG values than longitudinal SWE ones (either in non stretched and in stretched condition), with narrower 95%CI for SWE measurements. No changes resulted by the modified Heckmatt scale US assessments; there was a positive correlation (r: 0.46-0.84) between MHS scores and SWE values. Conclusion This is the first study evaluating the effect of BoNT-A on muscle hypertonia following stroke, assessed by mean of SWE and compared with the stretch reflex. The treatment resulted in a reduction of MAS, stretch reflex and muscular stiffness, in relation to the reduction of the neuro-mediated hypertonia. We have therefore shown that SWE is able to appreciate a reduction in neuro-mediated stiffness. Abolishing the neuro-mediated contribution by keeping the limb in a shortened position and moreover after BoNT-A injection, the SWE values resulted higher in the paretic muscle than in the healthy muscle in the same position. Hence, SWE-driven comparison between the spastic muscle and the contralateral unaffected homologous one is able to disclose the amount of stiffness due only to intrinsic muscular involutive remodeling. Alongside sEMG, SWE could therefore constitute an added-value to clinicians who manage spasticity for the assessment of responses to treatments and monitoring therapeutic interventions

Ultrasound Elastography

Elastography, the science of creating noninvasive images of mechanical characteristics of tissues, has been rapidly evolving in recent years. The advantage of this technique resides in the ability to rapidly detect and quantify the changes in the stiffness of soft tissues resulting from specific pathological or physiological processes. Ultrasound elastography is nowadays applied especially on the liver and breast, but the technique has been increasingly used for other tissues including the thyroid, lymph nodes, spleen, pancreas, gastrointestinal tract, kidney, prostate, and the musculoskeletal and vascular systems. This book presents some of the applications of strain and shear-wave ultrasound elastography in hepatic, pancreatic, breast, and musculoskeletal conditions

Liver Biopsy

Liver biopsy is recommended as the gold standard method to determine diagnosis, fibrosis staging, prognosis and therapeutic indications in patients with chronic liver disease. However, liver biopsy is an invasive procedure with a risk of complications which can be serious. This book provides the management of the complications in liver biopsy. Additionally, this book provides also the references for the new technology of liver biopsy including the non-invasive elastography, imaging methods and blood panels which could be the alternatives to liver biopsy. The non-invasive methods, especially the elastography, which is the new procedure in hot topics, which were frequently reported in these years. In this book, the professionals of elastography show the mechanism, availability and how to use this technology in a clinical field of elastography. The comprehension of elastography could be a great help for better dealing and for understanding of liver biopsy

Nondestructive measurement of fruit and vegetable quality

We review nondestructive techniques for measuring internal and external quality attributes of fruit and vegetables, such as color, size and shape, flavor, texture, and absence of defects. The different techniques are organized according to their physical measurement principle. We first describe each technique and then list some examples. As many of these techniques rely on mathematical models and particular data processing methods, we discuss these where needed. We pay particular attention to techniques that can be implemented online in grading lines