WFUMB guidelines and recommendations for clinical use of ultrasound elastography: Part 2: breast

Auto strain ratio system for the quality control of breast strain elastography

PURPOSE

To determine the reproducibility, accuracy, and quantitative values of the auto strain ratio system (ASRS)-a newly developed strain elastography-based program.

MATERIALS AND METHODS

First, the accuracy of ASRS was verified using a breast phantom. A prospective clinical study was then performed in patients. Two hundred and one women (mean age 52.4 years ± SD 14.5) with 232 breast lesions (177 benign and 55 malignant) were enrolled in this study. We assessed the correlation between ASRS and manual strain ratio (MSR), calculating the diagnostic performance to determine the cut-off. The area under the receiver operating characteristic curve (AUC) was calculated.

RESULTS

ASRS was strongly correlated with the subtle differences in phantom stiffness (R = 0.87). In the clinical study, there was a significant correlation between MSR and ASRS with R = 0.79 (P < 0.001). ASRS (cut-off = 3.9) had a sensitivity of 81.8%, specificity of 88.7%, accuracy of 87.1%, positive predictive value of 69.2%, and negative predictive value of 94%. The AUC of ASRS was 0.89.

CONCLUSION

The findings from this study have demonstrated that it is possible to quantify strain elastography and control its accuracy. ASRS is expected to contribute to the standardization of breast elastography.

Assessing the mechanical properties of anisotropic soft tissues using guided wave elastography: Inverse method and numerical experiments

Determining the mechanical properties of soft biological tissues can be of great importance. For example, the microstructures of many soft tissues, such as those of the human Achilles tendon, have been identified as typical anisotropic materials. This paper proposes an inverse approach that uses guided wave elastography to determine the anisotropic elastic and hyperelastic parameters of thin-walled transversely isotropic biological soft tissues. This approach was developed from the theoretical solutions for the dispersion relations of guided waves, which were derived based on a constitutive model suitable for describing the deformation behavior of such tissues. The properties of these solutions were investigated; in particular, sensitivity to data errors was addressed by introducing the concept of the condition number. To further validate the proposed inverse approach, the guided wave elastography of thin-walled transversely isotropic soft tissues was investigated using numerical experiments. The results indicated that the four constitutive parameters (other than the tensile modulus along the direction of the fibers, E_L) could be determined with a good level of accuracy using this method.

Application of Ultrasound Elastography for Chronic Allograft Dysfunction in Kidney Transplantation

Interstitial fibrosis is the main characteristic of chronic allograft dysfunction, which remains the key factor affecting long-term allograft survival after kidney transplantation. Ultrasound elastography (UE), including real-time elastography, transient elastography, and acoustic radiation force impulse, has been applied widely in breast, thyroid, and liver diseases, especially in the assessment of liver fibrosis. Recently, numerous studies have reported the efficacy of UE methods in evaluating renal allograft fibrosis. This review aims to investigate the clinical applications, limitations, and future roles of UE in current clinical practice in light of changing management paradigms. In current clinical practice, UE methods, especially transient elastographic measurement, appear to be useful for ruling out fibrosis but do not have sufficient accuracy to distinguish between various stages of allograft fibrosis. Moreover, there remain considerable issues to be solved for the application of UE in kidney transplantation. Thus, UE methods cannot replace the crucial role of renal allograft biopsy in the diagnosis and evaluation of allograft fibrosis in kidney transplantation. Perhaps UE methods could be of more importance in the long-term observation and evaluation of allograft fibrosis during follow-up.

The diagnostic performance of shear wave speed (SWS) imaging for thyroid nodules with elasticity modulus and SWS measurement

To evaluate the diagnostic performance of a new technique of shear wave speed (SWS) imaging for the diagnosis of thyroid nodule with elasticity modulus and SWS measurement. 322 thyroid nodules in 322 patients (216 benign nodules, 106 malignant nodules) were included in this study. All the nodules received conventional ultrasound (US) and SWS imaging (Aplio500, Toshiba Medical Systems, Japan) before fine-needle aspiration (FNA) and/or surgery. The values of E-max and E-mean with elastic modulus (61.27 ± 36.31 kPa and 31.89 ± 19.11 kPa) or SWS (4.45 ± 1.49 m/s and 3.26 ± 2.71 m/s) in malignant nodules were significantly higher than those in benign lesions (29.18 ± 18.62 kPa and 15.85 ± 6.96 kPa, or 2.98 ± 0.85 m/s and 2.19 ± 0.42 m/s, all P < 0.001). No significant differences in area under the curve (AUC) between the SWS imaging parameters were found (all P > 0.05). In multivariate logistic regression analysis, E-max (m/s) with SWS was identified to be the strongest independent predictor for malignant nodules (odds ratio [OR] = 16.760), followed by poorly-defined margin (OR = 7.792), taller-than-wide shape (OR = 3.160), micro-calcification (OR = 2.422), and E-max (kPa) with elastic modulus (OR = 0.914). The AUC was 0.813 for E-max with SWS (m/s) and 0.796 for E-max with elastic modulus (kPa). With cut-off SWS value of 3.52 m/s in E-max, sensitivity of 69.8%, specificity of 81.5%, and accuracy of 77.6% were achieved. SWS imaging is a valuable tool in predicting thyroid malignancy. E-max with SWS measurement is the strongest independent predictor for thyroid malignancy.

Value of shear wave arrival time contour display in shear wave elastography for breast masses diagnosis

To evaluate the diagnostic performance of shear wave arrival time contour (SWATC) display for the diagnosis of breast lesions and to identify factors associated with the quality of shear wave propagation (QSWP) in breast lesions. This study included 277 pathologically confirmed breast lesions. Conventional B-mode ultrasound characteristics and shear wave elastography parameters were computed. Using the SWATC display, the QSWP of each lesion was assigned to a two-point scale: score 1 (low quality) and score 2 (high quality). Binary logistic regression analysis was performed to identify factors associated with QSWP. The area under the receiver operating characteristic curve (AUROC) for QSWP to differentiate benign from malignant lesions was 0.913, with a sensitivity of 91.9%, a specificity of 90.7%, a positive predictive value (PPV) of 74.0%, and a negative predictive value (NPV) of 97.5%. Compared with using the standard deviation of shear wave speed (SWS_SD) alone, SWS_SD combined with QSWP increased the sensitivity from 75.8% to 93.5%, but decreased the specificity from 95.8% to 89.3% (P < 0.05). SWS_SD was identified to be the strongest factor associated with the QSWP, followed by tumor malignancy and the depth of the lesion. In conclusion, SWATC display may be useful for characterization of breast lesions.

Quality Measurement of Two-dimensional Shear Wave Speed Imaging for Breast Lesions: the Associated Factors and the Impact to Diagnostic Performance

This study aimed to identify the associated factors for quality measurement (QM) of shear wave speed (SWS) imaging and to validate the additional value of QM in the diagnosis of breast lesions. From September 2014 to February 2015, conventional ultrasound and SWS imaging were performed in 338 women with 361 breast lesions. Binary logistic regression was used to identify associated factors for QM. Sensitivity, specificity and the area under receiver operating characteristic (ROC) curve (AUC) among maximum SWS (SWS _max ), QM and SWS _max plus QM (SWS _max +QM) were compared to validate additional value of QM. Pathology confirmed 263 (72.9%) benign lesions and 98 (27.1%) malignancies. Maximum depth (Odds ratio [OR]: 1.398) and posterior features (OR: 1.206) were identified as independent associated factors for QM. Compared with SWS _max and QM, the sensitivity of SWS _max +QM increased from 67.3%, 64.3% to 83.7% whereas the specificity decreased from 90.5%, 72.6% to 65.4% (all P < 0.05). SWS _max had the highest AUC in comparison with QM and SWS _max +QM (0.849 vs. 0.685 vs. 0.745; P < 0.05). QM for breast lesions is associated with maximum depth and posterior features. Adding QM to SWS _max is useful for breast cancer screening and SWS _max alone is useful for breast cancer differentiation.

Do Histopathological Features and Microcalcification Affect the Elasticity of Breast Cancer?

OBJECTIVES

The aim of this study was to evaluate any association between histological grade, molecular subtypes of breast cancer, and strain elastography, and to investigate whether microcalcification affects the stiffness of tumor in breast cancers with the same histological grade.

METHODS

Between April 2015 and March 2016, 94 lesions of 94 patients with the diagnosis of invasive ductal carcinoma were included in the study. Strain elastography was performed on all patients before biopsy. Histological grades (Grades 1, 2, and 3), molecular subtypes (luminal A, luminal B, Her-2, and basal-like), and strain ratio (SR) were compared. In the same histological grades, patients were divided into two groups according to the presence of microcalcifications, and the groups were compared with each other.

RESULTS

Compared with Grades 1 (20.5) and 2 (23.7), Grade 3 (11.7) showed lower SR values (Grade 3-2, P = .01; Grade 3-1, P = .2). The groups with microcalcification had slightly higher SR in all histological grades, but not of statistical significance. In molecular subtypes, luminal A and B demonstrated higher SR, whereas HER2 and basal-like had lower SR (P > .05 for all group comparisons).

CONCLUSIONS

Grade 3 invasive ductal carcinomas are different from other grades with lower SR values. The presence of microcalcifications and molecular subtypes do not affect elasticity like a high histological grade does.

Ultrasound Strain Elastography for Breast Lesions: Computer-Aided Evaluation With Quantifiable Elastographic Features

OBJECTIVES

To develop and evaluate a set of quantifiable elastographic features based on ultrasound real-time strain elastography (SE) in differentiating between benign and malignant breast lesions.

METHODS

The SE and conventional B-mode ultrasound images of 226 breast lesions (81 malignant, 145 benign) were obtained from 226 consecutive women. By using a computer-aided tool, four elastographic features (elasticity score, lesion stiffness degree, lesion-to-fat strain ratio, and elastography-to-B-mode lesion area ratio) were respectively calculated and evaluated. Histopathologic results were used as the reference standard. B-mode Breast Imaging Reporting and Data System categorization was used to compare the performances between B-mode ultrasound and SE. Sensitivity, specificity, positive and negative predictive values, and receiver operating characteristic curve analyses were performed to evaluate the diagnostic performances for three data sets (conventional B-mode ultrasound alone, SE features alone, combined SE features).

RESULTS

Quantifiable SE features for malignant lesions all showed significantly higher values than those for benign lesions (all P < .001). The evaluation with any individual SE feature significantly improved the specificity in breast lesion differentiation compared with B-mode ultrasound (all P <.001). The logistic regression model combing SE features significantly improved the diagnostic performance compared with B-mode US, with significantly increased specificity (95.2% versus 54.5%; P < .001) and area under the receiver operating characteristic curve (0.988 versus 0.921, P < .001).

CONCLUSIONS

Computer-aided tool with SE provided further elasticity information for breast characterization. Evaluation using quantifiable SE features showed better diagnostic performance than conventional B-mode ultrasound in breast lesion differentiation.

[Value of ultrasound shear wave elasticity imaging in diagnosis of Hashimoto's thyroiditis]

OBJECTIVE

To investigate the correlation between Young's modulus of the thyroid tissue measured by in shear wave elastography (SWE) and the clinical manifestations of Hashimoto's thyroiditis in different stages.

METHODS

A total of 104 patients with the clinical diagnosis of Hashimoto's thyroiditis were enrolled in this study, including 26 with hyperthyroidism, 29 with normal thyroid function, 27 with subclinical hypothyroidism, 22 with clinical hypothyroidism, with 50 healthy volunteers serving as the healthy control group. All the subjects underwent SWE to obtain the Young's modulus value of the thyroid tissue. Univariate analysis of variance was used to compare the Young's modulus among the groups, and Pearson correlation analysis was used to analyze the correlation between the Young's modulus of the thyroid tissue and serum levels of thyroid microsomal antibody (TMAb) and thyroid globulin antibody (TGAb).

RESULTS

In the 4 groups of patients, the Young's modulus increased significantly in the order of hyperthyroidism group, normal thyroid function group, subclinical hypothyroidism group and clinical hypothyroidism group (F=60.983, P<0.01). The Young's modulus was significantly lower in hyperthyroidism group than in the other 3 groups (P<0.05), and was significantly lower in normal thyroid function group than in subclinical hypothyroidism group and clinical hypothyroidism group (P<0.05).

CONCLUSION

The Young's modulus of the thyroid tissue measured by shear wave elastography is related with the clinical manifestations of Hashimoto's thyroiditis in different stages, but the relevance needs to be further confirmed by multi-center, randomized, controlled studies involving a larger sample size.

The diagnostic performances of conventional strain elastography (SE), acoustic radiation force impulse (ARFI) imaging and point shear-wave speed (pSWS) measurement for non-calcified thyroid nodules

BACKGROUND

Non-calcified thyroid nodules are relatively difficult to diagnose only relying on features of at conventional US images.

OBJECTIVE

To investigate the diagnostic performances of conventional strain elastography (SE), acoustic radiation force impulse (ARFI) SE and point shear-wave speed (pSWS) measurement for non-calcified thyroid nodules.

METHODS

A total of 201 non-calcified thyroid nodules in 195 patients were studied. They were examined with conventional ultrasound (US), conventional SE, ARFI SE and pSWS measurement. Their diagnostic performances and multivariable models were assessed with receiver operating characteristic (ROC) curve and logistic regression analyses respectively.

RESULTS

There were 156 benign and 45 malignant non-calcified nodules proven by histopathology or cystology. The mean diameters of the nodules were 21.2±10.8 mm. Areas under receiver operating characteristic curve (AUCs) of elastography features (ranged, 0.488-0.745) were all greater than that of US (ranged, 0.111-0.332). At multivariate analysis, there were three predictors of malignancy for non-calcified nodules, including pSWS of nodule (odds ratio [OR], 34.960; 95% CI, 11.582-105.529), marked hypoechogenicity (OR, 16.223; 95% CI, 1.761-149.454) and ARFI SE grade (OR, 10.900; 95% CI, 3.567-33.310). US+SE+pSWS owned the largest AUC (0.936; 95% CI, 0.887-0.985; P < 0.05), followed by US+pSWS (0.889; 95% CI, 0.823-0.955), and the poorest was US (0.727; 95% CI, 0.635-0.819).

CONCLUSIONS

ARFI SE and pSWS measurement had better diagnostic performances than conventional SE and US. When US combined with SE and pSWS measurement, it could achieve an excellent diagnostic performance and might contribute a better decision-making of FNA for non-calcified thyroid nodules.

Sonoelastomics for Breast Tumor Classification: A Radiomics Approach with Clustering-Based Feature Selection on Sonoelastography

A radiomics approach to sonoelastography, called "sonoelastomics," is proposed for classification of benign and malignant breast tumors. From sonoelastograms of breast tumors, a high-throughput 364-dimensional feature set was calculated consisting of shape features, intensity statistics, gray-level co-occurrence matrix texture features and contourlet texture features, which quantified the shape, hardness and hardness heterogeneity of a tumor. The high-throughput features were then selected for feature reduction using hierarchical clustering and three-feature selection metrics. For a data set containing 42 malignant and 75 benign tumors from 117 patients, seven selected sonoelastomic features achieved an area under the receiver operating characteristic curve of 0.917, an accuracy of 88.0%, a sensitivity of 85.7% and a specificity of 89.3% in a validation set via the leave-one-out cross-validation, revealing superiority over the principal component analysis, deep polynomial networks and manually selected features. The sonoelastomic features are valuable in breast tumor differentiation.

Semi-Quantitative Strain Ratio Determined Using Different Measurement Methods: Comparison of Strain Ratio Values and Diagnostic Performance Using One- versus Two-Region-of-Interest Measurement

We evaluated the agreement and diagnostic performance of strain ratio values using measurements made with one and two user-defined regions of interest (ROIs) on breast elastography. Two hundred forty-three breast masses of 226 women (mean age: 48.2 y) were included. Ultrasonography (US) and elastography images of the masses were recorded. Strain ratio was measured twice on the same elastography image; strain ratio 1, applying one ROI at the target mass for measurement, and strain ratio 2, applying one ROI at the target mass and another ROI as reference strain. The two strain ratio measurements were in substantial agreement, with an intra-class correlation coefficient of 0.655 (95% confidence interval: 0.577-0.722). Specificity, positive predictive value and accuracy (cutoffs: 2.66 and 2.35) were significantly improved for US combined with the two strain ratio measurements (all p values < 0.05). Strain ratios measured using one or two user-defined ROIs were in substantial agreement, both contributing to the improved diagnostic performance of breast US.

Shear-wave elastography in breast ultrasonography: the state of the art

Shear-wave elastography (SWE) is a recently developed ultrasound technique that can visualize and measure tissue elasticity. In breast ultrasonography, SWE has been shown to be useful for differentiating benign breast lesions from malignant breast lesions, and it has been suggested that SWE enhances the diagnostic performance of ultrasonography, potentially improving the specificity of conventional ultrasonography using the Breast Imaging Reporting and Data System criteria. More recently, not only has SWE been proven useful for the diagnosis of breast cancer, but has also been shown to provide valuable information that can be used as a preoperative predictor of the prognosis or response to chemotherapy.

Implementation of Elastography Score and Strain Ratio in Combination with B-Mode Ultrasound Avoids Unnecessary Biopsies of Breast Lesions

The aim of this study was to evaluate whether the combination of B-mode ultrasound, elastography score (ES) and strain ratio (SR) improves diagnostic performance with respect to breast lesions. One hundred thirty lesions were prospectively evaluated by B-mode ultrasound and strain elastography, followed by fine-needle aspiration cytology/biopsy in 117 woman who were scheduled for regular breast BUS. The median ES (4.5 vs. 2.9, p < 0.001) and SR (4.9 vs. 2.3, p < 0.001) were significantly higher for malignant than for benign lesions. A sensitivity of 90.5% and specificity of 93.2% for the ES (cutoff point = 3.8) and a sensitivity of 87.5% and specificity of 87.6% for the SR (cutoff point = 3.5) were obtained. Elastography combined with B-mode ultrasound improved the specificity, accuracy and positive predictive value. Receiver operating characteristic curves yielded a higher value for the combined technique for diagnosis of breast lesions. Routine use of such a diagnostic algorithm could reduce the number of unnecessary biopsies.

Ultrasound Elastography: Review of Techniques and Clinical Applications

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.

Mechanics of ultrasound elastography

Ultrasound elastography enables in vivo measurement of the mechanical properties of living soft tissues in a non-destructive and non-invasive manner and has attracted considerable interest for clinical use in recent years. Continuum mechanics plays an essential role in understanding and improving ultrasound-based elastography methods and is the main focus of this review. In particular, the mechanics theories involved in both static and dynamic elastography methods are surveyed. They may help understand the challenges in and opportunities for the practical applications of various ultrasound elastography methods to characterize the linear elastic, viscoelastic, anisotropic elastic and hyperelastic properties of both bulk and thin-walled soft materials, especially the in vivo characterization of biological soft tissues.

Breast Lesion Elastography Region of Interest Selection and Quantitative Heterogeneity: A Systematic Review and Meta-Analysis

In this systematic review and meta-analysis, we report measured elasticities of benign and malignant breast pathologies from shear wave elastography (SWE), quantitatively confirm the effect of the selected region of interest (ROI) on these measures and test the hypothesis that a metric of heterogeneity based on the mean and maximum elasticity can improve specificity of diagnosis. The elasticities of benign, malignant and specific pathologic states are reported from 22 publications encompassing 2989 patients, identified from a structured search of the literature from May to September 2015. Twelve articles were included in a meta-analysis that grouped results by the method of ROI selection to discriminate between different pathologies. We observe a significant correlation between the method of selection of ROI for malignant mean (p < 0.001) and maximum (p = 0.027) elasticities, but no correlation with benign measures. We define a quantitative heterogeneity parameter, the "stiffness gradient," computed from the mean and maximum measured elasticities. The stiffness gradient out-performed the current standard maximum elasticity metric in stratifying malignancy risk by a margin of 15% for the partial ROI, and 42% for the maximized ROI. An anecdotal example of improved differentiation using the stiffness gradient on pathology-specific lesions is also provided. These results quantitatively indicate that the method of ROI selection in SWE not only has a significant impact on the resulting mean reported elasticity of a lesion, but may provide some insight into lesion heterogeneity. Our results suggest that further exploration of quantitative heterogeneity is warranted to improve the specificity of diagnosis.

Application of 3D and 2D quantitative shear wave elastography (SWE) to differentiate between benign and malignant breast masses

As breast cancer tissues are stiffer than normal tissues, shear wave elastography (SWE) can locally quantify tissue stiffness and provide histological information. Moreover, tissue stiffness can be observed on three-dimensional (3D) colour-coded elasticity maps. Our objective was to evaluate the diagnostic performances of quantitative features in differentiating breast masses by two-dimensional (2D) and 3D SWE. Two hundred ten consecutive women with 210 breast masses were examined with B-mode ultrasound (US) and SWE. Quantitative features of 3D and 2D SWE were assessed, including elastic modulus standard deviation (E_SD^E) measured on SWE mode images and E_SD^U measured on B-mode images, as well as maximum elasticity (E_max). Adding quantitative features to B-mode US improved the diagnostic performance (p < 0.05) and reduced false-positive biopsies (p < 0.0001). The area under the receiver operating characteristic curve (AUC) of 3D SWE was similar to that of 2D SWE for E_SD^E (p = 0.026) and E_SD^U (p = 0.159) but inferior to that of 2D SWE for E_max (p = 0.002). Compared with E_SD^U, E_SD^E showed a higher AUC on 2D (p = 0.0038) and 3D SWE (p = 0.0057). Our study indicates that quantitative features of 3D and 2D SWE can significantly improve the diagnostic performance of B-mode US, especially 3D SWE E_SD^E, which shows considerable clinical value.

Elastographic measurement of the cervix during pregnancy: Current status and future challenges

The cervix is a cylindrical structure that is proximally connected to the uterus and distally to the vaginal cavity. The Bishop score has been used to evaluate the cervix during pregnancy. However, alternatives have been evaluated because the Bishop score is uncomfortable for patients, relies on a subjective examination, and lacks internal os data. Elastography has been used to assess the cervix, as it can estimate tissue stiffness. Recent articles on elastography for cervical assessment during pregnancy have focused on its usefulness for prediction of preterm birth and successful labor induction. There is a clinical need for cervical elastography, as an evaluation of biomechanical factors, because cervical length only assesses morphological changes. However, until now, cervical elastography has been studied in the limited field, and not shown a uniformed methodological technique. In this review, the current status, limitations, and future possibility of cervical elastography were discussed. Future studies should focus on overcoming the limitations of cervical elastography. Although the cervical elastography is presently an incompletely defined technique, it needs to be improved and evaluated as a method for use in combination with cervical length.

Qualitative and quantitative analysis with a novel shear wave speed imaging for differential diagnosis of breast lesions

To evaluate the diagnostic performance of a new two-dimensional shear wave speed (SWS) imaging (i.e. Toshiba shear wave elastography, T-SWE) in differential diagnosis of breast lesions. 225 pathologically confirmed breast lesions in 218 patients were subject to conventional ultrasound and T-SWE examinations. The mean, standard deviation and ratio of SWS values (m/s) and elastic modulus (KPa) on T-SWE were computed. Besides, the 2D elastic images were classified into four color patterns. The area under the receiver operating characteristic (AUROC) curve analysis was performed to evaluate the diagnostic performance of T-SWE in differentiation of breast lesions. Compared with other quantitative T-SWE parameters, mean value expressed in KPa had the highest AUROC value (AUROC = 0.943), with corresponding cut-off value of 36.1 KPa, sensitivity of 85.1%, specificity of 96.6%, accuracy of 94.2%, PPV of 87.0%, and NPV of 96.1%. The AUROC of qualitative color patterns in this study obtained the best performance (AUROC = 0.957), while the differences were not significant except for that of Eratio expressed in m/s (AUROC = 0.863) (P = 0.03). In summary, qualitative color patterns of T-SWE obtained the best performance in all parameters, while mean stiffness (36.05 KPa) provided the best diagnostic performance in the quantitative parameters.

Ultrasonic Shear Wave Elasticity Imaging Sequencing and Data Processing Using a Verasonics Research Scanner

Ultrasound elasticity imaging has been developed over the last decade to estimate tissue stiffness. Shear wave elasticity imaging (SWEI) quantifies tissue stiffness by measuring the speed of propagating shear waves following acoustic radiation force excitation. This paper presents the sequencing and data processing protocols of SWEI using a Verasonics system. The selection of the sequence parameters in a Verasonics programming script is discussed in detail. The data processing pipeline to calculate group shear wave speed (SWS), including tissue motion estimation, data filtering, and SWS estimation, is demonstrated. In addition, the procedures for calibration of beam position, scanner timing, and transducer face heating are provided to avoid SWS measurement bias and transducer damage.

Point of Care Ultrasound: A WFUMB Position Paper

Over the last decade, the use of portable ultrasound scanners has enhanced the concept of point of care ultrasound (PoC-US), namely, "ultrasound performed at the bedside and interpreted directly by the treating clinician." PoC-US is not a replacement for comprehensive ultrasound, but rather allows physicians immediate access to clinical imaging for rapid and direct solutions. PoC-US has already revolutionized everyday clinical practice, and it is believed that it will dramatically change how ultrasound is applied in daily practice. However, its use and teaching are different from continent to continent and from country to country. This World Federation for Ultrasound in Medicine and Biology position paper discusses the current status and future perspectives of PoC-US. Particular attention is given to the different uses of PoC-US and its clinical significance, including within emergency and critical care medicine, cardiology, anesthesiology, rheumatology, obstetrics, neonatology, gynecology, gastroenterology and many other applications. In the future, PoC-US will be more diverse than ever and be included in medical student training.

Inability of shear-wave elastography to distinguish malignant from benign prostate tissue - a comparison of biopsy, whole-mount sectioning and shear-wave elastography

Aim

This study was designed to assess the possible usefulness of shear-wave elastography in differentiating between benign and malignant tissue in prostate neoplasia.

Patients and methods

A total of 120 prostate tissue samples were obtained from 10 patients treated by radical prostatectomy and investigated pre-operatively by ultrasound elastography followed by directed biopsy. After resection, whole-mount sectioning and histological examination was performed. The predictions based on shear-wave elastography were compared with biopsy and histological results.

Results

The comparison between the results of shear-wave elastography and those of biopsy was performed by receiver operating characteristic analysis, which suggested an optimum cut-off tissue elasticity value of 50 kPa, in agreement with earlier studies aimed at distinguishing between benign and malignant tissue. However, the diagnostic selectivity (and thus the diagnostic power) was poor (area under the curve 0.527, which hardly differs from the value of 0.500 that would correspond to a complete lack of predictive power); furthermore, application of this cut-off value to the samples led to a sensitivity of only 74% and a specificity of only 43%. An analogous comparison between the results of shear-wave elastography and those of whole-mount histology, which itself is more reliable than biopsy, gave an even poorer diagnostic selectivity (sensitivity of 62%, specificity of 35%). Meaningful association with Gleason score was not found for D’Amico risk groups (p = 0.35).

Conclusions

The (negative) findings of this investigation add to the dissonance among results of studies investigating the possible value of shear-wave elastography as a diagnostic tool to identify malignant neoplasia. There is a clear need for further research to elucidate the diversity of study results and to identify the usefulness, if any, of the method in question.

Deep learning based classification of breast tumors with shear-wave elastography

This study aims to build a deep learning (DL) architecture for automated extraction of learned-from-data image features from the shear-wave elastography (SWE), and to evaluate the DL architecture in differentiation between benign and malignant breast tumors. We construct a two-layer DL architecture for SWE feature extraction, comprised of the point-wise gated Boltzmann machine (PGBM) and the restricted Boltzmann machine (RBM). The PGBM contains task-relevant and task-irrelevant hidden units, and the task-relevant units are connected to the RBM. Experimental evaluation was performed with five-fold cross validation on a set of 227 SWE images, 135 of benign tumors and 92 of malignant tumors, from 121 patients. The features learned with our DL architecture were compared with the statistical features quantifying image intensity and texture. Results showed that the DL features achieved better classification performance with an accuracy of 93.4%, a sensitivity of 88.6%, a specificity of 97.1%, and an area under the receiver operating characteristic curve of 0.947. The DL-based method integrates feature learning with feature selection on SWE. It may be potentially used in clinical computer-aided diagnosis of breast cancer.

Combination of shear wave elastography and Ki-67 index as a novel predictive modality for the pathological response to neoadjuvant chemotherapy in patients with invasive breast cancer

PURPOSE

This study evaluated shear wave elastography (SWE) and SWE combined with the Ki-67 index as novel predictive modalities for the pathological response of invasive breast cancer to neoadjuvant chemotherapy (NAC).

METHODS

The prospective study recruited 66 eligible patients from July 2014 to November 2015. Tumour stiffness, which corresponds with tumour progression and invasiveness, was assessed by quantitative SWE 1 d before biopsy (time point t0, elasticity E0), 1 d before next NAC cycle (t1-t5, E1-E5), and 1 d before surgery (t6, E6). The relative changes in SWE parameters after the first and second NAC cycles were considered as the variables [ΔE (t1), ΔE (t2)]. The pathological response was classified according to the residual cancer burden (RCB) protocol. Correlations between RCB scores and variables were evaluated. The predictive diagnostic performances of SWE parameters, Ki-67 index, and the predictive RCB (predRCB) score determined by a linear regression model were compared.

RESULTS

Some immunohistochemical and molecular factors and SWE parameters were significantly different among the three RCB groups. The ΔE_mean (t2) and Ki-67 had significantly better diagnostic performance than other parameters regarding predicting the pathological response (the RCB-I response and RCB-III resistance). However, the correlation between ΔE_mean (t2) and Ki-67 index was significantly weaker as a diagnostic predictor (r = 0.29). We generated a new predictive modality, predRCB, which is a multivariable linear regression model that combines ΔE_mean (t2) and the Ki-67 index. The predRCB modality showed better diagnostic performance than SWE parameters and Ki-67 index alone.

CONCLUSION

Our findings highlight the potential utility for adding the Ki-67 index to the SWE results, which may improve the predictive power of SWE and facilitate personalising the treatment regimens of patients with breast cancer. These results should be validated in the future by performing a multicentre prospective study with a larger cohort.

Comparison of strain and shear-wave ultrasounic elastography in predicting the pathological response to neoadjuvant chemotherapy in breast cancers

OBJECTIVE

To compare the diagnostic performances of strain elastography (SE) and shear-wave elastography (SWE) for predicting response to neoadjuvant chemotherapy (NACT) in patients with breast cancer.

METHODS

This prospective study recruited 71 eligible patients from June 2014 to May 2016. All patients provided written informed consent. Tumour stiffness was assessed by the SE strain ratio (R), SWE maximum elasticity (E_max) and SWE mean elasticity (E_mean). Ultrasonic elastography (UE) assessments were performed at each NACT cycle (t1 - t6). For the purpose of predicting, the relative changes in elastographic parameters after the first and second NACT cycles were considered as the variables [Δ(t1) and Δ(t2)]. The area under the receiver operating characteristics (AUC) curve was compared.

RESULTS

ΔE_mean(t2) and R2 displayed the best diagnostic performances within their own modalities (AUC = 0.93 and 0.90 for predicting favourable response to NACT; AUC = 0.92 and 0.78 for predicting NACT resistance, respectively). There were no significant differences in AUCs for ΔE_mean(t2) and some UE parameters (P > 0.05). By contrast, ΔE_mean(t2) was significantly superior to all other SE parameters for predicting resistance (P < 0.05).

CONCLUSIONS

SE and SWE exhibited similar performances for predicting favourable NACT responses; SWE was better than SE for predicting NACT resistance.

KEY POINTS

• Elastography parameters after the second NACT cycle showed the best diagnostic performances. • SWE and SE yielded similar diagnostic performances in predicting favourable responses. • SWE performed better than SE in predicting the pathological resistance to NACT. • Discrepant results may be due to the breast thickness and lesion depth.

Calcification of thyroid nodules increases shear-wave speed (SWS) measurement: using multiple calcification-specific SWS cutoff values outperforms a single uniform cutoff value in diagnosing malignant thyroid nodules

Conventional ultrasound cannot satisfactorily distinguish malignant and benign thyroid nodules. Shear-wave elastography (SWE) can evaluate tissue stiffness and complement conventional ultrasound in diagnosing malignant nodules. However, calcification of nodules may affect the results of SWE. The purposes of this study are to compare the differences of shear-wave speed (SWS) measurement among different calcification groups and compare the diagnostic performance between using a single uniform SWS cutoff value and multiple individual calcification-specific cutoff values using technique of point SWS measurement. We retrospectively identified 517 thyroid nodules (346 benign and 171 malignant nodules) examined by conventional ultrasound and point SWS measurement. There were 177 non-calcified, 159 micro-calcified and 181 macro-calcified nodules. The diagnostic performance was evaluated by receiver operating characteristic (ROC) curve and area under the curve (AUC) was computed. The mean SWS in malignant nodules more than doubled that of benign nodules (4.81±2.03 m/s vs. 2.29±0.99 m/s, p<0.001). The mean SWS of nodules progressively increased from the non-calcification (2.60±1.49 m/s), to micro-calcification (3.27±1.85 m/s) and to macro-calcification (3.68±2.26 m/s) groups (p<0.001), which was true in both the benign and malignant nodules. If we used individual SWS cutoff values for non- (SWS >2.42 m/s), micro- (SWS >2.88 m/s) and macro-calcification (SWS >3.59 m/s) nodules in the whole group, the AUC was 0.859 (95% confidence interval [CI], 0.826-0.888), which was significantly better than the AUC of 0.816 (95% CI, 0.780-0.848) if a single uniform cutoff value (SWS >2.72 m/s) was applied to all the nodules regardless of calcification status (p=0.011). The cutoff values of SWS for different calcified nodules warrant future prospective validation.

AdipoScan: A Novel Transient Elastography-Based Tool Used to Non-Invasively Assess Subcutaneous Adipose Tissue Shear Wave Speed in Obesity

We describe a novel device called the AdipoScan that was adapted from the FibroScan to specifically assess shear wave speed (SWS) in human abdominal subcutaneous adipose tissue (scAT). Measurement reproducibility was assessed on tissue-mimicking phantoms with and without repositioning, with resultant coefficients of variation of 1% and 0%, respectively, as well as in vivo (14% and 7%, respectively). The applicability of the AdipoScan was tested on 19 non-obese volunteers, and a scAT thickness >2 cm was found to be mandatory to perform a valid measurement. Abdominal scAT SWS was assessed in 73 severely obese subjects, all candidates for bariatric surgery. Subcutaneous AT SWS was positively associated with scAT fibrosis and obesity-related co-morbidities such as hypertension, glycemic status, dyslipidemia and liver dysfunction. These results suggest that the AdipoScan could be a useful non-invasive tool to evaluate scAT fibrosis and metabolic complications in obesity. Further investigation is required to evaluate the relevance of using the AdipoScan to predict patient weight trajectories and metabolic outcomes after bariatric surgery.

Anisotropic Properties of Breast Tissue Measured by Acoustic Radiation Force Impulse Quantification

The goal of our study was to investigate the anisotropy of normal breast glandular and fatty tissue with acoustic radiation force impulse (ARFI) quantification. A total of 137 breasts in 137 women were enrolled. These breasts were divided into the duct-apparent group and the duct-inapparent group, divided into the ligament-apparent group and the ligament-inapparent group. Shear wave velocity (SWV) in the radial (SWV(r)) and anti-radial (SWV(a-r)) directions was measured. The elastic anisotropy of glandular tissue and fatty tissue was evaluated as the ratio between SWV(r) and SWV(a-r). The SWV ratio was 1.30 ± 0.45 for glandular tissue and 1.27 ± 0.53 for fatty tissue in the total group. In glandular tissue, the SWV ratio of the duct-apparent group was higher than that of the duct-inapparent group (p = 0.011). In both glandular and fatty tissue, the SWV ratio was higher in the ligament-apparent group than in the ligament-inapparent group (p < 0.05 for both). SWV(r) was higher than SWV(a-r) in both glandular tissue and fatty tissue in all groups (p < 0.05 for all) except in breast fatty tissue in the ligament-inapparent group (p = 0.913). It is concluded that both breast glandular tissue and fatty tissue exhibited anisotropy of elastic behavior. To improve the diagnostic power of elastography in breast lesions, the elastic anisotropy of glandular tissue and fatty tissue should be taken into account in calculating strain ratio or elasticity ratio.

Ultrasound-based imaging methods of the kidney-recent developments

In recent years, several novel ultrasound (US)-based techniques have emerged for kidney diagnostic imaging, including tissue stiffness assessment with elastography, Ultrasensitive Doppler techniques, and contrast-enhanced ultrasonography to assess renal microvascularization. Renal elastography has become available with the development of noninvasive quantitative techniques, following the rapidly growing field of liver fibrosis diagnosis. With the increased incidence of chronic kidney disease, noninvasive diagnosis of renal fibrosis can be of critical value. However, it is difficult to simply extend the application of US elastography from one organ to the other due to anatomic and technical issues. Today, renal elastography appears to be a promising application that, however, still requires optimization and validation. New ultrasensitive Doppler techniques improve the detection of slow blood flow and can be used alone or after administration of US contrast agents. These microbubble-based agents are extremely well tolerated and can be administered even in cases of impaired renal function. Despite the lack of approval, they improve the characterization of atypical renal masses, complex cystic renal masses, and peripheral vascular disorders. Dynamic contrast-enhanced US is based on quantification of the signal intensity from region of interest and mathematical fits of the time-intensity curves. Perfusion-related parameters can be extracted for the monitoring of vascular changes in the renal parenchyma and in tumors in order to evaluate drug response. This estimation of renal perfusion depends on many parameters that should be kept constant for follow-up studies, and, when possible, an internal reference should be used to normalize the measurements.

Shear wave elastography with a new reliability indicator

Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Endobronchial ultrasound elastography

Elastographic techniques have recently become available as advanced diagnostic tools for tissue characterization. Strain elastography is a real-time technique used with transcutaneous ultrasound (US) and endoscopic US. Convincing evidence is available demonstrating a significant value of strain elastography for the discrimination of benign and malignant lymph nodes (LNs). This paper reviews preliminary data demonstrating the feasibility of performing real-time elastography during endobronchial US (EBUS) and a potential application of this technique for selection of LNs for EBUS-guided transbronchial needle aspiration in patients with lung cancer and extrathoracic malignancies.

Recent technological advancements in breast ultrasound

Ultrasound is becoming increasingly common as an imaging tool for the detection and characterization of breast tumors. This paper provides an overview of recent technological advancements, especially those that may have an impact in clinical applications in the field of breast ultrasound in the near future. These advancements include close to 100% fractional bandwidth high frequency (5-18MHz) 2D and 3D arrays, automated breast imaging systems to minimize the operator dependence and advanced processing techniques, such as those used for detection of microcalcifications. In addition, elastography and contrast-enhanced ultrasound examinations that are expected to further enhance the clinical importance of ultrasound based breast tumor screening are briefly reviewed. These techniques have shown initial promise in clinical trials and may translate to more comprehensive clinical adoption in the future.

Semi-Quantitative Strain Ratio in the Differential Diagnosis of Breast Masses: Measurements Using One Region-of-Interest

The purpose of this study was to evaluate the diagnostic performances of semi-quantitative strain ratio measured by using one region-of-interest (ROI) on breast US elastography images. Two hundred one breast masses of 165 women (mean age: 47.2 y) were included. Ultrasonography (US) and elastography images of the masses were obtained and prospectively analyzed according to elasticity pattern, strain ratio, and final Breast Imaging-Reporting and Data System (BI-RADS) assessments. Of the 201 breast masses, 127 (63.2%) were benign and 74 (36.8%) were malignant. Elastography pattern and strain ratio (cut-off of 1.44) had significantly higher specificity than gray-scale US, 39.4% and 61.4% versus 29.1%, respectively (all p < 0.05). Area under the receiver operating characteristics curve (Az) was highest for gray-scale US (0.646), without statistical significances, than for elastography pattern (0.596, p = 0.159) or strain ratio (0.625, p = 0.610). Semi-quantitative strain ratio measured from one ROI has comparable diagnostic performances to gray-scale US, which may contribute to more accurate differential diagnosis of breast masses seen on US.

Preclinical evaluation of acoustic radiation force impulse measurements in regions of heterogeneous elasticity

Purpose

The purpose of this study was to compare the reliability of ultrasound-based shear wave elastography in regions of homogeneous versus heterogeneous elasticity by using two different probes.

Methods

Using acoustic radiation force impulse (ARFI) elastography, we measured the shear wave velocity (SWV) in different lesions of an elastography phantom with the convex 4C1 probe and the linear 9L4 probe. The region of interest (ROI) was positioned in such a way that it was partly filled by one of the lesions (0%, 25%, 50%, 75%, and 100%) and partly by the background of the phantom (100%, 75%, 50%, 25%, and 0%, respectively).

Results

The success rate was 98.5%. The measured value and the reference value of SWV correlated significantly (r=0.89, P<0.001). Further, a comparison of the two probes revealed that there was no statistical difference in either the mean or the variance values. However, the deviation of SWV from the reference was higher in the case of the 9L4 probe than in the case of the 4C1 probe, both overall and in measurements in which the ROI contained structures of different elasticity (P=0.021 and P=0.002). Taking into account all data, for both probes, we found that there was a greater spread and deviation of the SWV from the reference value when the ROI was positioned in structures having different elastic properties (standard deviation, 0.02±0.01 m/sec vs. 0.04±0.04 m/sec; P=0.010; deviation from the reference value, 0.21±0.12 m/sec vs. 0.38±0.27 m/sec; P=0.050).

Conclusion

Quantitative ARFI elastography was achievable in structures of different elasticity; however, the validity and the reliability of the SWV measurements decreased in comparison to those of the measurements performed in structures of homogeneous elasticity. Therefore, a convex probe is preferred for examining heterogeneous structures.

Applications of acoustic radiation force impulse quantification in chronic kidney disease: a review

Acoustic radiation force impulse (ARFI) imaging is an emerging technique with great promise in the field of elastography. Previous studies have validated ARFI quantification as a method of estimating fibrosis in chronic liver disease. Similarly, fibrosis is the principal process underlying the progression of chronic kidney disease, which is the major cause of renal failure. However, the quantification of tissue stiffness using ARFI imaging is more complex in the kidney than in the liver. Moreover, not all previous studies are comparable because they employed different procedures. Therefore, subsequent studies are warranted, both in animal models and in clinical patients, in order to better understand the histopathological mechanisms associated with renal elasticity and to further improve this imaging method by developing a standardized guidelines for its implementation.

Critical comparison of elastography methods to assess chronic liver disease

Staging of liver fibrosis and diagnosis, or exclusion, of early compensated liver cirrhosis are important in the treatment decisions and surveillance of patients with chronic liver disease. Good diagnostic accuracy, increased availability and the possibility to perform follow-up examinations led to the implementation of noninvasive methods into clinical practice. Noninvasive tests are increasingly included in national and international guidelines, leaving liver biopsy reserved for patients with unexplained discordance or suspected additional aetiologies of liver disease. In addition to staging of liver fibrosis, data on the prognostic value of these methods have increased in the past few years and are of great importance for patient care. This Review focuses on elastography methods for noninvasive assessment of liver fibrosis, disease severity and prognosis. Although liver elastography started with transient elastography, at present all large ultrasonography companies offer an elastography technique integrated in their machines. The goal of this Review is to summarize the methodological problems of noninvasive tests in general, in addition to providing an overview on currently available techniques and latest developments in liver elastography.

Influence of age, sex, body mass index, alcohol, and smoking on shear wave velocity (p-SWE) of the pancreas

Purpose

A variety of elastographic techniques have been developed to facilitate the non-invasive assessment of tissue properties. The goal of the study was to examine the influence of gender, age, BMI, alcohol consumption, and smoking in healthy volunteers.

Methods

Of the 263 participants who met all the study inclusion criteria, 234 had successful measurements. The examination was performed with the Siemens Acuson S3000 (Siemens Healthcare, Erlangen, Germany), using the 6C1 curved array transducer with the virtual touch tissue quantification (VTQ) method.

Results

The values determined with the curved array in the head of the pancreas were 1.44 ± 0.39 m/s for women and 1.19 ± 0.29 m/s for men; in the body, the results were 1.49 ± 0.37 m/s for women and 1.26 ± 0.30  m/s for men; in the tail, the corresponding values were 1.29 ± 0.36 m/s for women and 1.05 ± 0.30 m/s for men. Comparison of gender showed that men have significantly lower mean values than women. There were significantly higher values in all parts of the organ with the increasing age of the participants (p < 0.0001). For BMI, there was a significant correlation with the values only when considering the BMI in continuous form. Alcohol consumption and smoking did not have any significant effects.

Conclusions

ARFI-VTQ is qualified for use on pancreatic tissue. Further studies are required to examine the influence of other factors in larger populations.

Quantitative Assessment of Left Ventricular Diastolic Stiffness Using Cardiac Shear Wave Elastography: A Pilot Study

OBJECTIVES

The purpose of this study was to systematically investigate the feasible echocardiographic views for human transthoracic cardiac shear wave elastography (SWE) and the impact of myocardial anisotropy on myocardial stiffness measurements.

METHODS

A novel cardiac SWE technique using pulse inversion harmonic imaging and time-aligned sequential tracking was developed for this study. The technique can measure the quantitative local myocardial stiffness noninvasively. Ten healthy volunteers were recruited and scanned by the proposed technique 3 times on 3 different days.

RESULTS

Seven combinations of echocardiographic views and left ventricular (LV) segments were found to be feasible for LV diastolic stiffness measurements: basal interventricular septum under parasternal short- and long-axis views; mid interventricular septum under parasternal short- and long-axis views; anterior LV free wall under parasternal short- and long-axis views; and posterior LV free wall under a parasternal short-axis view. Statistical analyses showed good repeatability of LV diastolic stiffness measurements among 3 different days from 70% of the participants for the basal interventricular septum and posterior LV free wall short-axis views. On the same LV segment, the mean diastolic shear wave speed measurements from the short-axis view were statistically different from the long-axis measurements: 1.82 versus 1.29 m/s for the basal interventricular septum; 1.81 versus 1.45 m/s for mid interventricular septum; and 1.96 versus 1.77 m/s for the anterior LV free wall, indicating that myocardial anisotropy plays a substantial role in LV diastolic stiffness measurements.

CONCLUSIONS

These results establish the preliminary normal range of LV diastolic stiffness under different scan views and provide important guidance for future clinical studies using cardiac SWE.

Comparison of sonoelastography with sonourethrography and retrograde urethrography in the evaluation of male anterior urethral strictures

OBJECTIVE

Retrograde urethrography (RUG) is the most common and preferred imaging modality for imaging of the anterior urethral strictures despite its well-known limitations and disadvantages. Sonourethrography (SUG) was introduced in 1988 to overcome the limitations of RUG and to provide more accurate results. As proper selection of imaging modality is very important for planning the treatment, various advances in this area are required. One of the major factors for recurrence of stricture disease is spongiofibrosis. Sonoelastography (SE) is a newer technique, tried in various other pathologies. In this study, we have used this technique for the first time to assess its efficacy in the evaluation of anterior urethral stricture disease by comparison with RUG and SUG.

MATERIAL AND METHODS

Between August 2014 and May 2015, 77 patients with clinical features of anterior urethral stricture disease were included in the study and evaluated by RUG followed by SUG and SE for stricture location, length, depth of spongiofibrosis and periurethral pathologies. The results were then correlated with operative and histopathological findings.

RESULTS

Overall diagnostic accuracy of SE, SUG, and RGU for the estimation of stricture location, and length were estimated 92.68% vs. 91.54%, 79% vs. 78.87% and 80.48% vs. 43.66%, respectively, while for depth of spongiofibrosis SE, and SUG had accuracy rates of 87.3%, 48%, respectively. The mean length measured on SE was nearest to the mean intra-operative stricture length (21.34+11.8 mm). SE findings significantly correlated with the colour of bladder mucosa on cystoscopic examination (p=0.003) whereas the association was non-significant (p=0.127) for difficulty in incision. While a nonsignificant correlation existed between SUG findings related both to the colour of the bladder mucosa and difficulty in incision on cystoscopy, SE findings had a significant association (p<0.001) with histopathology findings for severe degree of fibrosis.

CONCLUSION

Sonoelastography estimates stricture site and length better in comparison with RUG and SUG. It estimates degree of spongiofibrosis which serves as an important prognostic factor for stricture recurrence more accurately than SUG.

Elastography for the pancreas: Current status and future perspective

Elastography for the pancreas can be performed by either ultrasound or endoscopic ultrasound (EUS). There are two types of pancreatic elastographies based on different principles, which are strain elastography and shear wave elastography. The stiffness of tissue is estimated by measuring the grade of strain generated by external pressure in the former, whereas it is estimated by measuring propagation speed of shear wave, the transverse wave, generated by acoustic radiation impulse (ARFI) in the latter. Strain elastography is difficult to perform when the probe, the pancreas and the aorta are not located in line. Accordingly, a fine elastogram can be easily obtained in the pancreatic body but not in the pancreatic head and tail. In contrast, shear wave elastography can be easily performed in the entire pancreas because ARFI can be emitted to wherever desired. However, shear wave elastography cannot be performed by EUS to date. Recently, clinical guidelines for elastography specialized in the pancreas were published from Japanese Society of Medical Ultrasonics. The guidelines show us technical knacks of performing elastography for the pancreas.