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W2015890756 abstract "To date, two other ultrasound (US) techniques have been introduced in the clinical practive: contrast-enhanced US and elastography. The aim of this EJR special issue is to present current knowledge on ultrasound elastography in several clinical fields taking in account the limitations. The availability and application of elastographic technology is expanding rapidly, so this set of reviews can only present current knowledge in 2013, although future developments are anticipated.Various techniques for imaging tissue elasticity have been investigated since the early 1990's. They can be largely separated into two main groups: Strain imaging and shear-wave velocity measurement techniques.With strain imaging techniques, the tissue is compressed and the resulting strain is measured from the degree to which the tissue distorts. These are referred to as ‘static’ or ‘quasi-static’ methods. Usually the ultrasound probe is used to palpate the tissue. Alternatively physiological movements such as vessel or heart pulsations are used as the source of the displacement. Strain imaging techniques are based on the fact that stiffer tissues have very low strains and is the method used in real time elastography (RTE). The data is used to form an image using a grey-scale or colour-coded map to show the pattern of relative tissue stiffness, which can be assessed subjectively. In a variant of this approach, the rate of change of the strain is displayed; this method is used in echocardiography and for the gut.The strain image does not directly depict the elasticity coefficient of the tissues (or Young's modulus); there are technical reasons for this, the method does not allow for the measurement of the applied compression (stress). However, with regions of interest (ROIs) drawn over the target area and over an adjacent reference region, assumed to be normal tissue, the strain ratio can be calculated to provide a semi-quantitative measure. Currently there is no standardisation as to which colour should be used to map stiffer tissue and which to use for softer tissues. RTE was introduced into clinical practice first and uses blue as the colour to map stiffer tissue, but other implementations introduced more recently have used a red colour. To improve the clinical acceptance of the method and avoid mistakes in interpretation, a standardisation in colour coding is recommended.Shear-wave techniques display the distribution of the velocity of shear wave propagation (between 1 and 10 m/s), induced by a mechanical vibrator or other method. The method is based on the fact that stiffer tissue induces a higher shear wave propagation speed. A practical way to generate shear waves is to use a focussed ultrasound beam, the technique used in Acoustic Radiation Force Impulse (ARFI) imaging.In patients with chronic inflammatory liver disease the assessment of the grade of fibrosis is important for prognosis and for the management of antiviral treatment. Transient elastography (TE) and shear wave elastography (SWE) using ARFI were introduced into clinical routine practice some years ago as a method to estimate the degree of liver fibrosis. More recently SWE using Aixplorer (Supersonic) has been introduced as well. The main advantage is that the generation of the shear wave and measurement of shear wave velocity is largely independent of the operator, and both TE and SWE provide a numerical result that can be related to the degree of liver fibrosis. Patient-derived factors can influence the results, e.g., congestive heart failure, fasting state and others. It has also been shown that training is mandatory and results are more accurate when the operator has performed more than 500 previous studies.Transcutaneous elastographic techniques have also been studied as a method to characterise focal liver lesions and promising results have been reported.So far, most published data on thyroid applications focusses on strain elastography. However, studies with convincing results show a much higher proportion of malignant disease, than the incidence seen in the general population. This was highlighted in a recent meta-analysis that included 639 nodules with a 24% prevalence of malignant nodules, representing a highly selected surgical population. The mean sensitivity was 92% and the specificity 90% for the correct diagnosis of malignant thyroid nodules. More recently a number of papers on other different techniques provided preliminary results of different quantitative and semiquantitative methods to differentiate thyroid nodules. Details and references are summarised in the respective review by Cantisani et al. of this EJR Special Issue. It presents the current knowledge about the role of the different elastographic techniques to evaluate diffuse thyroid pathology and to differentiate thyroid nodules.The main application of elastography in the breast is as a complementary tool to conventional ultrasound to improve the differentiation between benign and malignant lesions. Elastography may increase diagnostic confidence to re-grade benign-appearing lesions on B-mode ultrasound that appear stiff on elastography, and consider them for biopsy, and conversely, to downgrade suspicious lesions that appear completely soft on elastography. The addition of elastography to conventional ultrasound assessment of breast masses has been endorsed by its recent inclusion in the ACR BI-RADS Ultrasound. The accuracy and the limitation of different elastographic techniques applied to date in the breast pathology evaluation are herein presented and discussed by Ricci et al.The endocavitary use focusses on the technique of RTE, which currently is the only technique that has been applied to endoscopic ultrasound (EUS), whereas other techniques have been used for the transabdominal approach. D’Onofrio et al. illustrate this current knowledge in their article. Inflammation and neoplastic infiltration lead to changes in normal tissue structure causing a hardening of the tissue with an alteration of its elasticity. The elasticity modulus can be defined as the measurement of ‘stress’ applied to tissue structures, relative to the ‘strain’ or deformation produced. With RTE, the compression-induced tissue deformation within a region of interest (ROI) is measured and the resultant strain is displayed as a transparent colour overlay on the B-Mode image. The measurement of displacement is made using a sophisticated algorithm based on the Extended Combined Autocorrelation Method.The application of RTE to study the pancreas, gastrointestinal tract and lymph nodes has been a more recent development, but results from early studies look promising. RTE-EUS has also been used to evaluate subepithelial lesions. On RTE, malignant subepithelial tumours typically show a heterogeneously stiffer pattern. Tumour staging is also a very promising application. Anorectal elastography may be helpful for the evaluation of sphincter defects.In all elastographic methods, tissue becomes stiffer as it is compressed. This is a very important factor: pre-stress can result in misleadingly high stiffness readings, especially in superficial tissues. A light touch on the skin with the transducer is one of the key requirements in order to obtain accurate, reproducible results.Future developments should include evaluating elastography-guided biopsy of the pancreas, lymph nodes and subepithelial lesions. The additional value of elastography combined with other techniques such as contrast-enhanced ultrasound, fusion imaging or 3D elastography examinations might also be feasible.Most studies of the GI tract have used the endoscopic approach, as the percutaneous access can be limited. The appearance of the layers of the GI tract wall as demonstrated on B-mode ultrasound is well known. Between 3 and 9 layers can be observed depending on the transducer frequency; most often 5 layers will be seen. When examining the GI tract, it is preferable to use higher frequency transducers of at least 7 MHz to enable optimal visualisation of the wall layers, thickened bowel walls and target lesions. The article by Gilja et al. focuses on possible indications for elastography in evaluating intestinal diseases. Acute and chronic inflammation, which is of importance when it comes to a therapeutic strategy, might be differentiated by analyzing the stiffness of the bowel wall.Promising results have also been reported for many other applications, although only few papers have been published to date. In symptomatic chronic Achilles tendinopathy, mucoid degeneration and partial ruptures are represented by well-delineated soft regions. In surgically repaired Achilles tendon ruptures, regions of increased stiffness are a consequence of tendon healing. Stiffness and shear wave measurements are also interesting in evaluating the normal muscles and trigger points in fibromyalgia. Testicular neoplasia might be characterised by elastography. This is of importance when it comes to a differential diagnosis of e.g., Leydig cell tumours which can be managed with tissue-sparing surgical techniques. RTE-EUS of the adrenal glands has been described in reviews but there are no published prospective studies. Malignant infiltrations tend to be stiffer than fatty deposits, benign tumours and inflammatory processes. Endobronchial applications (EBUS) of elastography-guided lymph node staging and elastography targeted lymph node biopsy are promising techniques that have recently become available. Early studies of the usefulness of RTE for examination of the prostate showed inconsistent results, but more recently its use has become established for routine use in some centres. Tumours of the peripheral gland are displayed as stiffer areas and can be targeted to obtain histological confirmation. However, chronic inflammation and atrophy may also lead to tissue hardening thus reducing the specificity of the method. RTE is also feasible for gynaecology applications: pre- and post-menopausal stiffness of the cervix uteri does not differ significantly, whilst malignant cervical tumours can be delineated as stiff (blue).Limitations and artefacts have to be addressed as well. They are discussed in all the referenced papers. Limited depth of penetration; erratic or very strong compression of the tissues; irregular surfaces of the body, for example due to bony projections; insufficient surrounding ‘normal tissue’ or insufficient contrast between the elastic properties of the tissues are all considered limitations.Future developments should include the evaluation of elastography targeted biopsy techniques. Treatment monitoring with antiangiogenic therapy may also be a feasible application of elastography techniques. Other important issues include the application of new technologies in paediatric patients and adequate reimbursement. To date, two other ultrasound (US) techniques have been introduced in the clinical practive: contrast-enhanced US and elastography. The aim of this EJR special issue is to present current knowledge on ultrasound elastography in several clinical fields taking in account the limitations. The availability and application of elastographic technology is expanding rapidly, so this set of reviews can only present current knowledge in 2013, although future developments are anticipated. Various techniques for imaging tissue elasticity have been investigated since the early 1990's. They can be largely separated into two main groups: Strain imaging and shear-wave velocity measurement techniques. With strain imaging techniques, the tissue is compressed and the resulting strain is measured from the degree to which the tissue distorts. These are referred to as ‘static’ or ‘quasi-static’ methods. Usually the ultrasound probe is used to palpate the tissue. Alternatively physiological movements such as vessel or heart pulsations are used as the source of the displacement. Strain imaging techniques are based on the fact that stiffer tissues have very low strains and is the method used in real time elastography (RTE). The data is used to form an image using a grey-scale or colour-coded map to show the pattern of relative tissue stiffness, which can be assessed subjectively. In a variant of this approach, the rate of change of the strain is displayed; this method is used in echocardiography and for the gut. The strain image does not directly depict the elasticity coefficient of the tissues (or Young's modulus); there are technical reasons for this, the method does not allow for the measurement of the applied compression (stress). However, with regions of interest (ROIs) drawn over the target area and over an adjacent reference region, assumed to be normal tissue, the strain ratio can be calculated to provide a semi-quantitative measure. Currently there is no standardisation as to which colour should be used to map stiffer tissue and which to use for softer tissues. RTE was introduced into clinical practice first and uses blue as the colour to map stiffer tissue, but other implementations introduced more recently have used a red colour. To improve the clinical acceptance of the method and avoid mistakes in interpretation, a standardisation in colour coding is recommended. Shear-wave techniques display the distribution of the velocity of shear wave propagation (between 1 and 10 m/s), induced by a mechanical vibrator or other method. The method is based on the fact that stiffer tissue induces a higher shear wave propagation speed. A practical way to generate shear waves is to use a focussed ultrasound beam, the technique used in Acoustic Radiation Force Impulse (ARFI) imaging. In patients with chronic inflammatory liver disease the assessment of the grade of fibrosis is important for prognosis and for the management of antiviral treatment. Transient elastography (TE) and shear wave elastography (SWE) using ARFI were introduced into clinical routine practice some years ago as a method to estimate the degree of liver fibrosis. More recently SWE using Aixplorer (Supersonic) has been introduced as well. The main advantage is that the generation of the shear wave and measurement of shear wave velocity is largely independent of the operator, and both TE and SWE provide a numerical result that can be related to the degree of liver fibrosis. Patient-derived factors can influence the results, e.g., congestive heart failure, fasting state and others. It has also been shown that training is mandatory and results are more accurate when the operator has performed more than 500 previous studies. Transcutaneous elastographic techniques have also been studied as a method to characterise focal liver lesions and promising results have been reported. So far, most published data on thyroid applications focusses on strain elastography. However, studies with convincing results show a much higher proportion of malignant disease, than the incidence seen in the general population. This was highlighted in a recent meta-analysis that included 639 nodules with a 24% prevalence of malignant nodules, representing a highly selected surgical population. The mean sensitivity was 92% and the specificity 90% for the correct diagnosis of malignant thyroid nodules. More recently a number of papers on other different techniques provided preliminary results of different quantitative and semiquantitative methods to differentiate thyroid nodules. Details and references are summarised in the respective review by Cantisani et al. of this EJR Special Issue. It presents the current knowledge about the role of the different elastographic techniques to evaluate diffuse thyroid pathology and to differentiate thyroid nodules. The main application of elastography in the breast is as a complementary tool to conventional ultrasound to improve the differentiation between benign and malignant lesions. Elastography may increase diagnostic confidence to re-grade benign-appearing lesions on B-mode ultrasound that appear stiff on elastography, and consider them for biopsy, and conversely, to downgrade suspicious lesions that appear completely soft on elastography. The addition of elastography to conventional ultrasound assessment of breast masses has been endorsed by its recent inclusion in the ACR BI-RADS Ultrasound. The accuracy and the limitation of different elastographic techniques applied to date in the breast pathology evaluation are herein presented and discussed by Ricci et al. The endocavitary use focusses on the technique of RTE, which currently is the only technique that has been applied to endoscopic ultrasound (EUS), whereas other techniques have been used for the transabdominal approach. D’Onofrio et al. illustrate this current knowledge in their article. Inflammation and neoplastic infiltration lead to changes in normal tissue structure causing a hardening of the tissue with an alteration of its elasticity. The elasticity modulus can be defined as the measurement of ‘stress’ applied to tissue structures, relative to the ‘strain’ or deformation produced. With RTE, the compression-induced tissue deformation within a region of interest (ROI) is measured and the resultant strain is displayed as a transparent colour overlay on the B-Mode image. The measurement of displacement is made using a sophisticated algorithm based on the Extended Combined Autocorrelation Method. The application of RTE to study the pancreas, gastrointestinal tract and lymph nodes has been a more recent development, but results from early studies look promising. RTE-EUS has also been used to evaluate subepithelial lesions. On RTE, malignant subepithelial tumours typically show a heterogeneously stiffer pattern. Tumour staging is also a very promising application. Anorectal elastography may be helpful for the evaluation of sphincter defects. In all elastographic methods, tissue becomes stiffer as it is compressed. This is a very important factor: pre-stress can result in misleadingly high stiffness readings, especially in superficial tissues. A light touch on the skin with the transducer is one of the key requirements in order to obtain accurate, reproducible results. Future developments should include evaluating elastography-guided biopsy of the pancreas, lymph nodes and subepithelial lesions. The additional value of elastography combined with other techniques such as contrast-enhanced ultrasound, fusion imaging or 3D elastography examinations might also be feasible. Most studies of the GI tract have used the endoscopic approach, as the percutaneous access can be limited. The appearance of the layers of the GI tract wall as demonstrated on B-mode ultrasound is well known. Between 3 and 9 layers can be observed depending on the transducer frequency; most often 5 layers will be seen. When examining the GI tract, it is preferable to use higher frequency transducers of at least 7 MHz to enable optimal visualisation of the wall layers, thickened bowel walls and target lesions. The article by Gilja et al. focuses on possible indications for elastography in evaluating intestinal diseases. Acute and chronic inflammation, which is of importance when it comes to a therapeutic strategy, might be differentiated by analyzing the stiffness of the bowel wall. Promising results have also been reported for many other applications, although only few papers have been published to date. In symptomatic chronic Achilles tendinopathy, mucoid degeneration and partial ruptures are represented by well-delineated soft regions. In surgically repaired Achilles tendon ruptures, regions of increased stiffness are a consequence of tendon healing. Stiffness and shear wave measurements are also interesting in evaluating the normal muscles and trigger points in fibromyalgia. Testicular neoplasia might be characterised by elastography. This is of importance when it comes to a differential diagnosis of e.g., Leydig cell tumours which can be managed with tissue-sparing surgical techniques. RTE-EUS of the adrenal glands has been described in reviews but there are no published prospective studies. Malignant infiltrations tend to be stiffer than fatty deposits, benign tumours and inflammatory processes. Endobronchial applications (EBUS) of elastography-guided lymph node staging and elastography targeted lymph node biopsy are promising techniques that have recently become available. Early studies of the usefulness of RTE for examination of the prostate showed inconsistent results, but more recently its use has become established for routine use in some centres. Tumours of the peripheral gland are displayed as stiffer areas and can be targeted to obtain histological confirmation. However, chronic inflammation and atrophy may also lead to tissue hardening thus reducing the specificity of the method. RTE is also feasible for gynaecology applications: pre- and post-menopausal stiffness of the cervix uteri does not differ significantly, whilst malignant cervical tumours can be delineated as stiff (blue). Limitations and artefacts have to be addressed as well. They are discussed in all the referenced papers. Limited depth of penetration; erratic or very strong compression of the tissues; irregular surfaces of the body, for example due to bony projections; insufficient surrounding ‘normal tissue’ or insufficient contrast between the elastic properties of the tissues are all considered limitations. Future developments should include the evaluation of elastography targeted biopsy techniques. Treatment monitoring with antiangiogenic therapy may also be a feasible application of elastography techniques. Other important issues include the application of new technologies in paediatric patients and adequate reimbursement." @default.
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W2015890756 title "Current status and perspectives of elastography" @default.
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