Elastography-based imaging techniques have received substantial attention in recent years for non-invasive assessment of tissue mechanical properties. These techniques take advantage of changed soft tissue elasticity in various pathologies to yield qualitative and quantitative information that can be used for diagnostic purposes. Measurements are acquired in specialized imaging modes that can detect tissue stiffness in response to an applied mechanical force (compression or shear wave). Ultrasound-based methods are of particular interest due to its many inherent advantages, such as wide availability including at the bedside and relatively low cost. Several ultrasound elastography techniques using different excitation methods have been developed. In general, these can be classified into strain imaging methods that use internal or external compression stimuli, and shear wave imaging that use ultrasound-generated traveling shear wave stimuli. While ultrasound elastography has shown promising results for non-invasive assessment of liver fibrosis, new applications in breast, thyroid, prostate, kidney and lymph node imaging are emerging. Here, we review the basic principles, foundation physics, and limitations of ultrasound elastography and summarize its current clinical use and ongoing developments in various clinical applications.

Ultrasound Elastography: Review of Techniques and Clinical Applications

The clinical part of these Guidelines and Recommendations produced under the auspices of the European Federation of Societies for Ultrasound in Medicine and Biology EFSUMB assesses the clinically used applications of all forms of elastography, stressing the evidence from meta-analyses and giving practical advice for their uses and interpretation. Diffuse liver disease forms the largest section, reflecting the wide experience with transient and shear wave elastography . Then follow the breast, thyroid, gastro-intestinal tract, endoscopic elastography, the prostate and the musculo-skeletal system using strain and shear wave elastography as appropriate. The document is intended to form a reference and to guide clinical users in a practical way.

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EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography.Part 2: Clinical Applications

Ultrasonography has been widely used for diagnosis since it was first introduced in clinical practice in the 1970's. Since then, new ultrasound modalities have been developed, such as Doppler imaging, which provides new information for diagnosis. Elastography was developed in the 1990's to map tissue stiffness, and reproduces/replaces the palpation performed by clinicians. In this paper, we introduce the principles of elastography and give a technical summary for the main elastography techniques: from quasi-static methods that require a static compression of the tissue to dynamic methods that uses the propagation of mechanical waves in the body. Several dynamic methods are discussed: vibro-acoustography, Acoustic Radiation Force Impulsion (ARFI), transient elastography, shear wave imaging, etc. This paper aims to help the reader at understanding the differences between the different methods of this promising imaging modality that may become a significant tool in medical imaging.

Ultrasound elastography: Principles and techniques

The breast section of these Guidelines and Recommendations for Elastography produced under the auspices of the World Federation of Ultrasound in Medicine and Biology (WFUMB) assesses the clinically used applications of all forms of elastography used in breast imaging. The literature on various breast elastography techniques is reviewed, and recommendations are made on evidence-based results. Practical advice is given on how to perform and interpret breast elastography for optimal results, with emphasis placed on avoiding pitfalls. Artifacts are reviewed, and the clinical utility of some artifacts is discussed. Both strain and shear wave techniques have been shown to be highly accurate in characterizing breast lesions as benign or malignant. The relationship between the various techniques is discussed, and recommended interpretation based on a BI-RADS-like malignancy probability scale is provided. This document is intended to be used as a reference and to guide clinical users in a practical way.

WFUMB Guidelines and Recommendations for Clinical Use of Ultrasound Elastography: Part 2: Breast

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).

WFUMB guidelines and recommendations for clinical use of ultrasound elastography: Part 1: basic principles and terminology.

Purpose: To evaluate the diagnostic performance of real-time freehand elastography by using the extended combined autocorrelation method (CAM) to differentiate benign from malignant breast lesions, with pathologic diagnosis as the reference standard. Materials and Methods: This study was approved by the University of Tsukuba Human Subjects Institutional Review Board; all patients gave informed consent. Conventional ultrasonography (US) and real-time US elastography with CAM were performed in 111 women (mean age, 49.4 years; age range, 27–91 years) who had breast lesions (59 benign, 52 malignant). Elasticity images were assigned an elasticity score according to the degree and distribution of strain induced by light compression. The area under the curve and cutoff point, both of which were obtained by using a receiver operating characteristic curve analysis, were used to assess diagnostic performance. Mean scores were examined by using a Student t test. Sensitivity, specificity, and accuracy were compared b...

Breast disease: clinical application of US elastography for diagnosis.

We have previously reported our real-time elasticity imaging system and a preliminary application to breast tissue diagnosis. We now propose several post processing algorithms to stabilize the elasticity imaging, introduce a method for scoring its clinical usefulness, and report the current status of the scoring method on breast tissue diagnosis. Our newly implemented post processing algorithms are: (1) frame-to-frame smoothing; (2) adaptive contrast optimization; (3) noisy-frame rejection; (4) noisy-region reduction. Using these algorithms, more than 20% of intensity fluctuations (SD) in strain images can be reduced. Our newly introduced scoring method is based on the imaging pattern of the low-strain region inside the hypoechoic region in the B-mode image. We classify 5 grades of elasticity score ranging from 1 (no strain-zero brightness region; benign) to 5 (broader strain-zero brightness region; malignant). As the result of applying 137 patients with breast diseases, this method provides a sensitivity of 87%, a specificity of 91%, and an accuracy of 89%.

Diagnostic results for breast disease by real-time elasticity imaging system

目的：男性乳癌は稀な疾患である．男性最多乳腺疾患である女性化乳房症との鑑別には乳房超音波検査が有用であるが，形態のみでは診断に苦慮することがある．今回Bモードに血流と硬さ評価を加えた超音波所見を後ろ向きに比較検討した．対象と方法：2000年1月から2019年10月に乳房腫瘤や疼痛を主訴に受診し，超音波検査を行い，男性乳癌または老年期女性化乳房症の診断となった92例を対象とした．Bモードにて形態をnodular，dendritic，diffuse glandularの3つに，血流は視覚的に4段階に，硬さはTsukuba elasticity score（スコア）の5段階に分類し比較した．女性化乳房症の形態ごとの特徴について検討した．結果と考察：男性乳癌は6例，女性化乳房症は86例であった．Bモードでは男性乳癌は全例nodularで，女性化乳房症はnodular28例（32.6％），dendritic17例（19.8％），diffuse glandular 41例（47.7％）であった．血流評価は男性乳癌5/6例（83.3％），女性化乳房症21/34例（61.8％）がhypervascularまたはvascularであった（P＝0.399）．硬さ評価では男性乳癌はスコア5が3/5例（60％），女性化乳房症は46/49例（93.9％）がスコア1と2であり，両群間に有意差を認めた（P<0.005）．血流と硬さ評価のArea Under the Curveは0.7と0.994であった．女性化乳房症のnodular，dendriticは10/15例（66.7％），8/11例（72.7％）がhypervascularまたはvascularであった．Diffuse glandularの35/41例（85.4％）は血流が未評価であった．女性化乳房症の形態ごとで硬さ評価に明らかな特徴差はなかった．結論：男性乳癌と女性化乳房症の鑑別診断には超音波による形態評価に加え，硬さ評価が有用である． 

Ako Itoh

Papers

Breast disease: clinical application of US elastography for diagnosis.

Diagnostic results for breast disease by real-time elasticity imaging system

Is adding vascularity and elastography adjunct to B-mode ultrasound useful in distinguishing male breast carcinoma and gynecomastia?