Ultrasound Elastography: Review of Techniques and Clinical Applications

Quantitative and Qualitative Evaluation of Breast Cancer Prognosis: A Sonographic Elastography Study

Background

Breast cancer is one of the most commonly diagnosed cancers in women worldwide, and sonographic elastography has previously demonstrated good performance in detecting breast malignancies. However, the exact relationship between elastographic measures and clinical prognostic factors is still not well understood. Thus, the aim of this study was to evaluate any associations between major clinical prognostic factors and strain elastography and to validate the diagnostic value of elastography in breast cancer.

Material/Methods

A total of 373 subjects with breast masses, of which 196 were benign and 177 were malignant, were included in the study. All subjects underwent routine ultrasound examination and strain elastography before biopsy. The elastographic measures – strain ratio (SR) for qualitative measures and Tsukuba score (TS) for quantitative measures – were obtained and compared with prognostic factors, including nuclear grade, lymph node status, estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER-2). The SR demonstrated the best diagnostic performance in differentiation between malignant and benign lesions.

Results

With the best cut-off value at 2.42, the SR achieved a sensitivity of 96.0% and specificity of 98.5%. Moreover, higher SRs and TSs were associated with breast lesions with a high nuclear grade and lymph node metastasis and with being ER-negative, PR-negative, and HER-2 negative.

Conclusions

Elastography is a useful imaging technique in differentiating benign breast masses from malignant ones. The strong relationship between prognostic factors and elastographic measures also demonstrated its excellent performance in predicting the prognosis of breast malignancies.

Noninvasive liver fibrosis assessment in chronic viral hepatitis C: agreement among 1D transient elastography, 2D shear wave elastography, and magnetic resonance elastography

PURPOSE

To assess the agreement of one-dimensional transient elastography (1D-TE), two-dimensional shear wave elastography (2D-SWE), and magnetic resonance elastography (MRE) in a consecutive cohort of patients affected by hepatitis C virus (HCV) and to understand which patient-related factors are associated with disagreement.

METHODS

Ninety-one consecutive patients with current or previous chronic HCV infection were enrolled between March 2017 and September 2018. We assessed the correlation between stiffness measurements expressed in kilopascals (kPa). After converting kPa values in three groups of increasing fibrosis burden using validated cut-off values, we assessed the agreement among the different techniques. Factors influencing inter-modality disagreement were examined by employing multivariate logistic regression analysis.

RESULTS

Seventy-seven patients met the inclusion criteria and had reliable measurements by all stiffness imaging techniques. At the quantitative analysis, a strong correlation between stiffness measurements was found (Spearman's rho values ranging from 0.7 to 0.89 in all pairs of techniques). Complete concordance among MRE, 1D-TE, and 2D-SWE was found in 64.9% of patients, and the agreement was highest between MRE and 1D-TE, with κ value of 0.801. In only 2/77 patients (2.6%), there was complete disagreement. High body mass index (BMI) was the only factor significantly associated with inter-modality discordance.

CONCLUSIONS

MRE, 1D-TE, and 2D-SWE assigned the majority of patients to the same fibrosis group. The agreement was at least good, and there was a strong correlation between kPa values in all three pairs of techniques. Highest agreement was found between MRE and 1D-TE. High BMI was associated with discordance among the techniques.

The effect of ageing on shear wave elastography muscle stiffness in adults

Background

Skeletal muscle undergoes structural changes with ageing which may alter its biomechanical properties. Shear wave elastography (SWE) may detect these changes by measuring muscle stiffness.

Aims

To investigate muscle stiffness in healthy young, middle-aged and elderly cohorts using SWE and correlate it with muscle strength and mass.

Methods

Shear wave velocity (SWV) was measured in the quadriceps, hamstrings and biceps brachii of 26 young (range 20–35 years), 21 middle-aged (40–55) and 30 elderly (77–94) volunteers. The participants performed several muscle tests to evaluate their strength. The One-way ANOVA was used to test the muscle stiffness differences between the groups and the Pearson’s correlation coefficient to evaluate the relationship between SWV and muscle strength.

Results

The overall resting muscle SWV gradually decreased with age but was only significantly reduced in the elderly group (p < 0.001); with the exception of the vastus lateralis SWV where a significant difference was noted (p < 0.05) between young (1.77 m/s), middle-aged (1.64 m/s) and elderly (1.48 m/s). The elderly group had on average 16.5% lower muscle stiffness compared to the young. SWV significantly correlated with muscle mass (r = 0.316), walking time (r = − 0.560), number of chair stands (r = 0.522), handgrip strength (r = 0.436) and isokinetic knee strength (r = 0.640). Sex and BMI did not explain any significant variation in SWV.

Conclusions

Ageing was associated with a decline in skeletal muscle stiffness which positively correlates with muscle weakness. Further research is needed to evaluate the promising role of SWE as a biomarker for sarcopenia assessment and potential falls risk prediction in elderly individuals.

Electronic supplementary material

The online version of this article (10.1007/s40520-019-01139-0) contains supplementary material, which is available to authorized users.

Transvaginal Real-time Shear Wave Elastography in the Diagnosis of Cervical Disease

OBJECTIVES

To explore the value of shear wave elastography in the diagnosis of cervical disease.

METHODS

This work was a retrospective analysis of 246 cases of cervical lesions confirmed by transvaginal conventional ultrasound, shear wave elastography, and a cytologic test. The lesions were divided into 2 groups according to the final pathologic results: a malignant cervical group and a benign cervical group. In addition, the normal cervix was set as the control group.

RESULTS

The maximum and mean shear wave velocity values ± SD were 5.24 ± 1.11 and 4.91 ± 1.12 m/s for the malignant cervical group, 3.93 ± 0.39 and 3.53 ± 0.52 m/s for the benign cervical group, and 3.27 ± 0.31 and 2.86 ± 0.23 m/s for the normal cervix, respectively. The areas under the receiver operating characteristic curves for the maximum and mean shear wave velocity in the differential diagnosis of a normal cervix and benign cervical tumors were 0.909 and 0.878 (both P < .001), whereas in the differential diagnosis of benign and malignant cervical tumors, they were 0.909 and 0.895 (both P < .001).

CONCLUSIONS

Shear wave elastography can quantitatively analyze the elastic characteristics of cervical diseases, help differentially diagnose cervical diseases, accurately determine the extent of tumor invasion, and improve effective clinical staging and treatment.

Combining Total Variation Regularization with Window-Based Time Delay Estimation in Ultrasound Elastography

A major challenge of free-hand palpation ultrasound elastography (USE) is estimating the displacement of RF samples between pre- and post-compressed RF data. The problem of displacement estimation is ill-posed since the displacement of one sample by itself cannot be uniquely calculated. To resolve this problem, two categories of methods have emerged. The first category assumes that the displacement of samples within a small window surrounding the reference sample is constant. The second class imposes smoothness regularization and optimizes an energy function. Herein, we propose a novel method that combines both approaches, and as such, is more robust to noise. The second contribution of this work is the introduction of the L1 norm as the regularization term in our cost function, which is often referred to as the total variation (TV) regularization. Compared to previous work that used the L2 norm regularization, optimization of the new cost function is more challenging. However, the advantages of using the L1 norm are twofold. First, it leads to substantial improvement in the sharpness of displacement estimates. Second, to optimize the cost function with the L1 norm regularization, we use an iterative method that further increases the robustness. We name our proposed method tOtal Variation Regularization and WINDow-based time delay estimation (OVERWIND) and show that it is robust to signal decorrelation and generates sharp displacement and strain maps for simulated, experimental phantom and in-vivo data. In particular, OVERWIND improves strain contrast-to-noise ratio (CNR) by 27.26%, 144.05%, and 49.90% on average in simulation, phantom, and in-vivo data, respectively, compared to our recent Global Ultrasound Elastography (GLUE) method.

Usefulness of noninvasive methods including assessment of liver stiffness by 2-dimensional shear wave elastography for predicting esophageal varices

BACKGROUND

The aim of this study was to predict the presence of esophageal varices (EVs) by noninvasive tools combined with 2-dimensional shear wave elastography (2D-SWE), and to compare the diagnostic capabilities of 2D-SWE with those of transient elastography (TE).

METHODS

Between January 2015 and December 2017, 289 patients with compensated advanced chronic liver disease (cACLD) who underwent consecutive 2D-SWE and EGD were enrolled. Capabilities for predicting the presence of EVs of 2D-SWE and models combining 2D-SWE with other noninvasive tools (modified LS-spleen-diameter-to-platelet-ratio score [mLSPS], platelet-spleen ratio score) were compared. A subgroup analysis was performed on 177 patients who also underwent simultaneous TE.

RESULTS

The area under receiver operating characteristics (AUROCs) for detecting EVs for 2D-SWE alone vs. mLSPS, which included 2D-SWE, were 0.757 (95% confidence interval [CI], 0.701-0.810) and 0.813 (95% CI, 0.763-.857), respectively. The AUROCs for predicting varices needing treatment (VNT) for 2D-SWE and mLSPS were 0.712 (95% CI, 0.621-0.738) and 0.834 (95% CI, 0.785-0.875), respectively. For the 195 patients who underwent simultaneous TE and 2D-SWE, no differences in diagnostic performance were observed.

CONCLUSIONS

The diagnostic performance of 2D-SWE is similar to that of TE for predicting the presence of EVs. The mLSPS, which includes 2D-SWE, seemed to be useful for predicting EVs.

Intraoperative Ultrasonographic Elastography: A Semi-Quantitative Analysis of Brain Tumor Elasticity Patterns and Peritumoral Region

BACKGROUND

Ultrasonographic elastography imaging visualizes the elastic properties of tissues to distinguish pathologic and healthy areas. Real-time elastography measures relative tissue hardness by evaluating changes in local strain in response to external forces.

OBJECTIVE

We aimed to determine the elastographic patterns of different brain tumor types and establish differences between their peritumoral regions.

METHODS

We prospectively enrolled patients undergoing craniotomy along with intraoperative ultrasonographic elastography for supratentorial brain tumors in March 2018-May 2019. The elastograms were semi-quantitatively analyzed offline based on the mean tissue elasticity of the tumors, peritumoral regions, and healthy parenchyma.

RESULTS

We examined 37 lesions in 36 patients. The pathologic diagnoses comprised 11 meningiomas (29.7%), 4 low-grade gliomas (LGGs; 10.8%), 16 high-grade gliomas (HGGs; 43.2%), and 6 metastases (16.2%). The median MTE values observed after manual segmentation of the whole tumor were as follows: meningiomas, 119.9 (36.6); HGGs, 77.9 (18.9); LGGs, 91 (19.5); metastases, 103.9 (35.6); tumor types significantly differed (H = 18.2; P < 0.001). The peritumoral MTE values were as follows: meningiomas, 120.1 (36.3); HGGs, 86.3 (20.9); LGGs, 94.8 (7.38); and metastases, 116.3 (22). The intergroup differences were significant (H = 17.43; P < 0.001). Using receiver operating characteristic curves, we obtained an optimal cutoff point of 92.22 (whole tumors) and 109.6 (peritumoral regions). Values below these cutoff points were correlated with a high probability of being a glioma.

CONCLUSIONS

We objectively describe the elastographic patterns of different types of brain tumors (i.e., gliomas, metastases, and meningiomas). We have identified differences in both the tumors and the peritumoral areas of these histologic types.

Impact of hemodialysis on liver stiffness measured with real-time two-dimensional shear wave elastography

BACKGROUND AND AIMS

The impact of hemodialysis on liver stiffness is still unclear. The aim of the study was to assess liver fibrosis by real-time two-dimensional shear wave elastography (RT 2D-SWE) and to quantify the influence of net fluid withdrawal on liver stiffness during one hemodialysis session. The second aim was to investigate the influence of systolic blood pressure and time spent on dialysis (in years) on liver stiffness measurements.

METHODS

This before/after hemodialysis (HD) study in a group of end stage renal disease (ESRD) patients was carried out with patients on regular HD. Measurements of liver stiffness were done using RT 2D-SWE directly before and after a hemodialysis session.

RESULTS

In this study 27 patients with mean age 69.4 ± 14.75 years were included. Mean net fluid withdrawal volume per session was 2874.07 ± 778.35 ml. Mean pre-HD and post-HD liver stiffness measurements were 8.15 kPa (95% confidence interval, CI 7.61-8.68) and 6.70 kPa (95% CI 6.10-7.30 kPa), respectively. Mean liver stiffness reduction was 1.448 ± 1.14 kPa. The amount of fluid removed correlated with the decline in liver stiffness values after HD (ρ = 0.523, P = 0.003). There was a positive but statistically not significant correlation between time spent in HD and liver stiffness (ρ = 0.151, P = 0.623) CONCLUSION: Liver stiffness significantly declined after one session of HD. The change in liver stiffness was strongly correlated with the amount of net fluid withdrawal. Random liver stiffness measurements (LSM) by RT 2D-SWE does not precisely show the degree of fibrosis, Furthermore, it is presumed that postdialysis liver stiffness values likely reflect the real degree of liver fibrosis.

Role of Probiotics in Non-alcoholic Fatty Liver Disease: Does Gut Microbiota Matter?

Non-alcoholic fatty liver disease (NAFLD) is the hepatic consequence of metabolic syndrome, which often also includes obesity, diabetes, and dyslipidemia. The connection between gut microbiota (GM) and NAFLD has attracted significant attention in recent years. Data has shown that GM affects hepatic lipid metabolism and influences the balance between pro/anti-inflammatory effectors in the liver. Although studies reveal the association between GM dysbiosis and NAFLD, decoding the mechanisms of gut dysbiosis resulting in NAFLD remains challenging. The potential pathophysiology that links GM dysbiosis to NAFLD can be summarized as: (1) disrupting the balance between energy harvest and expenditure, (2) promoting hepatic inflammation (impairing intestinal integrity, facilitating endotoxemia, and initiating inflammatory cascades with cytokines releasing), and (3) altered biochemistry metabolism and GM-related metabolites (i.e., bile acid, short-chain fatty acids, aromatic amino acid derivatives, branched-chain amino acids, choline, ethanol). Due to the hypothesis that probiotics/synbiotics could normalize GM and reverse dysbiosis, there have been efforts to investigate the therapeutic effect of probiotics/synbiotics in patients with NAFLD. Recent randomized clinical trials suggest that probiotics/synbiotics could improve transaminases, hepatic steatosis, and reduce hepatic inflammation. Despite these promising results, future studies are necessary to understand the full role GM plays in NAFLD development and progression. Additionally, further data is needed to unravel probiotics/synbiotics efficacy, safety, and sustainability as a novel pharmacologic approaches to NAFLD.

Masseter muscle thickness and elasticity in periodontitis

This study aimed to compare the thickness and elasticity of the masseter muscle between patients with gingivitis and patients with periodontitis. A total of 124 patients (63 gingivitis, 61 chronic periodontitis) were recruited at the start of the study, but only 84 patients were declared as final participants. Patients were divided into two groups: (1) patients suffering from gingivitis and (2) those with generalized chronic periodontitis. Clinical (PI, plaque index; GI, gingival index; PD, probing depth; CAL, clinical attachment loss; and BOP, bleeding on probing scores) and ultrasonographic (thickness and elasticity of the masseter muscle) measurements of periodontitis were performed. There were no significant differences in gender, age, body mass index, education status, income level, or marital status between the two groups (P > 0.05). The mean age ± SD for the gingivitis and periodontitis groups was 39.5 ± 10.8 years and 44.8 ± 8.8 years, respectively. There were significant differences between the two groups in the number of PI, GI, PD, CAL, and BOP scores. There were significant differences between the two groups when thickness of masseter during contraction and at rest was taken into account. The gingivitis group had significantly thicker masseter during both contraction and rest. On the other hand, when the elasticity of the masseter was evaluated, there were no significant differences found between the two groups and two sides for each group. Masseter muscle thickness in the periodontitis group was found to be decreased compared with that in the gingivitis group. Furthermore, loss of periodontal tissues due to periodontitis reduces the masticatory ability.

Noninvasive Multimodal Methods to Differentiate Inflamed vs Fibrotic Strictures in Patients With Crohn's Disease

Fibrotic strictures occur in 30% of patients with Crohn's disease (CD). However, there are no therapeutic agents that prevent or reverse fibrotic strictures. Strictures are treated by endoscopic dilatation procedures and surgical procedures, but there are high rates of recurrence. Two antifibrotic agents (nintedanib and pirfenidone) recently were approved for the treatment of idiopathic pulmonary fibrosis and inhibitors of Rho-associated protein kinases 1 and 2 reversed fibrosis in mice with chronic intestinal inflammation. Cross-sectional imaging techniques, such as magnetic resonance (MR) enterography, computed tomography enterography, and bowel ultrasound, are used to assess small-bowel and CD-related complications, including strictures. It is important to be able to determine the degree of inflammation and fibrosis in strictures to select the best therapy; this can be a challenge because inflammation and fibrosis co-exist to varying degrees in a damaged bowel segment. Delayed gadolinium enhancement, magnetization transfer MR imaging, and ultrasound elastography seem to be promising tools for assessing fibrosis in patients with CD. We review noninvasive techniques for fibrosis assessment, including analyses of genetic, epigenetic, and protein markers. We discuss the potential of imaging techniques such as diffusion-weighted and magnetization transfer MR imaging, strain elastography, shear-wave imaging, and positron emission tomography to guide therapeutic decisions for patients with stricturing CD.

Spatial localization of mechanical excitation affects spatial resolution, contrast, and contrast-to-noise ratio in acoustic radiation force optical coherence elastography

The notion that a spatially confined mechanical excitation would produce an elastogram with high spatial resolution has motivated the development of various elastography techniques with localized mechanical excitation. However, a quantitative investigation of the effects of spatial localization of mechanical excitation on the spatial resolution of elastograms is still lacking in optical coherence elastography (OCE). Here, we experimentally investigated the effect of spatial localization of acoustic radiation force (ARF) excitation on spatial resolution, contrast, and contrast-to-noise ratio (CNR) of dynamic uniaxial strain elastograms in dynamic ARF-OCE, based on a framework for analyzing the factors that influence the quality of the elastogram at different stages of the elastography workflow. Our results show that localized ARF excitation with a smaller acoustic focal spot size produced a strain elastogram with superior spatial resolution, contrast, and CNR. Our results also suggest that the spatial extent spanned by the displacement response in the sample may connect between the spatial localization of the mechanical excitation and the resulting elastogram quality. The elastography framework and experimental approach presented here may provide a basis for the quantitative analysis of elastogram quality in OCE that can be adapted and applied to different OCE systems and applications.

Placental elasticity assessment by point shear wave elastography in pregnancies with intrauterine growth restriction

Background Placental elasticity varies in different diseases. Our objective was to evaluate placental elasticity using point shear wave elastography (pSWE) in pregnancies with intrauterine growth restriction (IUGR). Methods A total of 66 pregnant women with IUGR and 81 healthy pregnant women were enrolled. Placental elasticity was measured using the transabdominal pSWE method. Ten measurements were made, and the mean was accepted as the mean placental elasticity value in each case. The results for IUGR pregnancies and controls were compared. Results The mean pSWE values were significantly higher in pregnancies with IUGR, which means that women with IUGR have stiffer placentas (P < 0.001). Furthermore, the pSWE values were significantly and positively correlated with Doppler indices and adverse perinatal outcomes. Conclusion The pregnancies with IUGR had stiffer placentas than the healthy controls. The utilization of pSWE for placental elasticity may be useful in the diagnosis and management of IUGR as a supplement to the existing ultrasonography methods.

Ultrasound shear wave elastography for measuring intracompartmental pressure of compartment syndrome using a turkey hind limb model

Diagnosis and treatment of acute compartment syndrome are quite challenging. It is well known that compartment pressure is an important factor for diagnosing fasciotomy. However, the current technology to measure the pressure using a needle-catheter is invasive and painful. Recently ultrasound elastography has been used to measure soft tissue elasticity based on shear wave propagation speed. Because the muscle's elasticity is affected by the pressure within the compartment, ultrasound elastography might be a possible tool for the compartment pressure evaluation. Ultrasound shear wave elastography and pressure were simultaneously measured using a clinical ultrasound system and clinically used catheter in a turkey anterior-lateral and anterior-deep compartment under elevated pressures of baseline, 10, 20, 30, 40, and 50 mmHg using vascular infusion technique. Shear wave propagation speed increased linearly in proportion to the increase in intra-compartmental pressure. Strong correlation was observed between measured pressure and mean shear wave speed in each compartment (anterior-lateral compartment, mean R² = 0.929, P < 0.001; anterior-deep compartment, mean R² = 0.97, P < 0.001). Compared with anterolateral compartment pressure, anterior-deep compartment pressure was the same at the baseline; however, it was significantly higher at intended anterolateral compartment pressures of 20 and 30 mmHg (P = 0.008, P = 0.016). By using ultrasound shear wave elastography, the compartment pressure can be accurately measured. This noninvasive technology can potentially help surgeons for the early detection, monitoring, and prognosis of intra-compartmental pressure.

Laser-speckle-contrast projection tomography for three-dimensional shear wave imaging

Laser-speckle-contrast shear wave (LSC-SW) imaging is an optical method for tracking the propagation of a transient shear wave. With high spatial resolution and sensitivity in detecting displacements, this method is suitable for performing mechanical measurements in vitro. Here, we present a LSC-SW tomographic imaging system for visualizing the propagating shear wave wavefront in four dimensions [i.e., three-dimensional (3D) space plus time]. The volumetric elasticity distribution of a sample is constructed by estimating the speeds of the shear waves propagating along multiple paths at different angles. The proposed method enables multidirectional estimations of the shear wave speed. The capabilities of the imaging system are demonstrated by evaluating isotropy (both homogeneous and heterogeneous) and anisotropy in semiturbid phantoms. The proposed system is suitable for the mechanical characterization of a 3D cell culture system, such as monitoring changes in fiber orientation during the remodeling of the extracellular matrix that is known to be strongly associated with the progression and characterization of tumors.

Portal pressure monitoring-state-of-the-art and future perspective

Portal hypertension is a serious symptom of chronic liver diseases, which can lead to many critical complications, such as the formation of varices related to upper digestive bleeding, ascites, infection, hepatic encephalopathy, renal failure, and even death. As a result, portal pressure monitoring has important prognostic and clinical implications. The hepatic venous pressure gradient measurement, a gold-standard method applied to monitor portal pressure, is invasive and only available in experienced centers. Over the past decade, noninvasive methods aimed at monitoring the portal pressure have been increasingly investigated, including serum markers, radiological features, ultrasound elastography, doppler and contrast-enhanced ultrasonography. In this study, we focused on both invasive and noninvasive methods for portal pressure monitoring and explored their roles in clinical setting. The advantages and limitations of various techniques for future research are also discussed.

2D shear wave elastography: measurement acquisition and reliability criteria in noninvasive assessment of liver fibrosis

PURPOSE

The objective was to evaluate the accuracy of 2D shear wave elastography (SWE) in predicting stages of liver fibrosis using five individual versus grouped measurements and different reliability criteria.

MATERIALS AND METHODS

This is a prospective study of 109 patients who underwent hepatic 2D SWE (Canon Aplio 500) prior to liver biopsy for varied indications. Liver fibrosis was staged using the METAVIR scoring system (F = 0-4). Propagation mapping was used to guide ten SWE measurements from the liver parenchyma: five individual measurements and five grouped measurements. IQR/median, SD/median, and SD/mean were examined as quality criteria for patient inclusion at various thresholds (IQR/median ≤ 0.15, 0.2, 0.3, 0.4, 0.5; SD/median ≤ 0.15, 0.2, 0.3; SD/mean ≤ 0.2, 0.3, 0.5). Threshold for clinically significant fibrosis (F ≥ 2) was determined with receiver operating characteristic (ROC) analysis.

RESULTS

There was high agreement between individual and grouped measurements without statistically significant differences (intraclass correlation coefficient = 0.82; p = 0.26-0.96). When no quality criterion was used (n = 103), the optimal threshold was 11.3 kPa [AUROC 0.78, 95% CI (0.69, 0.88)] with sensitivity and specificity of 80% and 66%, respectively. All quality criteria were associated with equal or higher AUROC ranging from 0.78 to 0.87. IQR/median ≤ 0.5 (n = 88) achieved the highest sensitivity of 85% and only excluded a small subset of patients. The AUROC and specificity were 0.83 [95% CI (0.74, 0.92)] and 72%, respectively.

SIGNIFICANCE

Quality criterion IQR/median ≤ 0.5 increases sensitivity and specificity in prediction of clinically significant liver fibrosis while excluding only a small subset of patients. Grouped measurements are comparable to individual measurements and may help increase procedural efficiency.

Inter-platform reproducibility of liver stiffness measured with two different point shear wave elastography techniques and 2-dimensional shear wave elastography using the comb-push technique

PURPOSE

The purpose of this study was to compare the technical success rate and reliability of measurements made using three shear wave elastography (SWE) techniques and to assess the inter-platform reproducibility of the resultant liver stiffness measurements.

METHODS

This prospective study included 54 patients with liver disease. Liver stiffness (LS) measurements were obtained using 2-point SWE techniques (Virtual Touch Quantification and S-Shearwave) and 2-dimensional (2D) SWE, with transient elastography (TE) serving as the reference standard. The technical success rates and measurement reliability of the three techniques were compared. LS values measured using the three SWE techniques and TE were compared using Spearman correlation coefficients and 95% Bland-Altman limits of agreement. Intra-class correlation coefficients (ICC) were used to analyze the inter-platform reproducibility of LS measurements.

RESULTS

The three SWE techniques and TE showed similar technical success rates (P=0.682) but demonstrated significant differences in the reliability of LS measurements (P=0.006) and mean LS measurements (P<0.001). Despite strong correlations (r=0.73-0.94) between SWE systems, various degrees of inter-platform reproducibility (ICC, 0.58-0.92) were observed for the three SWE techniques. The best agreement was observed between S-Shearwave and TE (ICC, 0.92), and the worst agreement was observed between 2D-SWE and TE (ICC, 0.58). In the BlandAltman analysis, a tendency toward lower LS values with the three SWE techniques than with TE in patients with F3 and F4 disease was observed.

CONCLUSION

Significant inter-system variability was observed in LS measurements made using the three SWE techniques. Therefore, LS values measured using different SWE techniques should not be used interchangeably for longitudinal follow-up.

Which Confounders Have the Largest Impact in Shear Wave Elastography of Muscle and How Can They be Minimized? An Elasticity Phantom, Ex Vivo Porcine Muscle and Volunteer Study Using a Commercially Available System

The goal of the study was to investigate the quantitative impact of region of interest (ROI), software choice, muscle fiber orientation and preload tension on shear wave velocity (SWV). First, SWV was assessed in an isotropic elasticity phantom and ex vivo porcine muscle using a commercially available clinical ultrasound system. Secondly, SWV was acquired in relaxed and stretched calf muscles of healthy volunteers (dorsal extension of the talocrural joint), for both parallel and transverse probe direction to the fibers, as well as for different ROIs and software versions. The effect of intermediate probe-fiber alignments was also analyzed. Finally, the impact of confounding factors on SWV reproducibility was minimized with a second force-controlled volunteer study, in which the calf was isometrically loaded, and fiber orientation and ROI were well-defined. 2046 in vivoSWE images were acquired to analyze SWV reproducibility with different confounder settings. In healthy volunteers, the main variance-contributing factors were in order of importance muscle tension, fiber orientation, horizontal ROI size and insertion depth. Regression analysis showed significantly reduced SWV with increasing insertion depth for each study material. Parallel probe-fiber orientation, muscle stretch and increasing horizontal ROI size led to significantly higher SWV. Based on the results of the study, we provide recommendations to minimize the impact of confounders in musculoskeletal elastography and discuss the main confounding mechanisms and trade-offs between confounding variables. Coefficients of variation can be significantly reduced with a controlled protocol, if the confounders are clinically taken into account.

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

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

Reducing Unnecessary Biopsy of Breast Lesions: Preliminary Results with Combination of Strain and Shear-Wave Elastography

The aim of our study was to compare strain elastography (SE), acoustic radiation force impulse-inducing Virtual Touch Imaging ([VTI] Siemens Medical Solutions, Mountain View, CA, USA), Virtual Touch Imaging Quantification ([VTIQ] Siemens Medical Solutions) and combined methods in the evaluation of ultrasound (US) Breast Imaging-Reporting and Data System (BI-RADS) category 4 lesions to explore an applicable way to reduce unnecessary biopsy by reducing false positives of conventional US without yielding false-negative cases. A total of 267 patients with 278 BI-RADS category 4 lesions (151 benign and 127 malignant) were evaluated with conventional B-mode US, SE, VTI and VTIQ implemented on a Siemens Acuson S2000 US system. Diagnostic performance, including area under the receiver operating characteristic curve, sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were evaluated. Overall, VTI alone exhibited the highest NPV (91.74%), although combined elastic methods exhibited higher NPV than single methods, with the highest NPV at 100% when the VTI, SE and VTIQ methods were combined. Compared with conventional US, PPV increased from 45.7% (127 of 278) to 63.18% (127 of 201) when adding combined elastography (VTI + SE +VTIQ). In addition, 52.5% (63/120) and 50.8% (61/120) of BI-RADS 4 A lesions were downgraded when using combined methods (VTI + SE and VTI + SE + VTIQ, respectively) without missing any cancer. However, 2 intraductal papillomas and 1 phyllodes tumor were not identified. In conclusion, the combination of different elastic methods have the potential to downgrade BI-RADS 4A lesions to reduce false-positive biopsies without increasing the risk of missing cancers.

Noninvasive staging of pressure ulcers using photoacoustic imaging

Ulcers including pressure ulcers and diabetic foot ulcers damage the skin and underlying tissue in people with compromised blood circulation. They are classified into four stages of severity and span from mild reddening of the skin to tissue damage and muscle/bone infections. Here, we used photoacoustic imaging as a noninvasive method for detecting early tissue damage that cannot be visually observed while also staging the disease using quantitative image analysis. We used a mouse model of pressure ulcers by implanting subdermal magnets in the dorsal flank and periodically applying an external magnet to the healed implant site. The magnet-induced pressure was applied in cycles, and the extent of ulceration was dictated by the number of cycles. We used both laser- and light-emitting diode (LED)-based photoacoustic imaging tools with 690 nm excitation to evaluate the change in photoacoustic signal and depth of injury. Using laser-based photoacoustic imaging system, we found a 4.4-fold increase in the photoacoustic intensity in stage I vs. baseline (no pressure). We also evaluated the depth of injury using photoacoustics. We measured a photoacoustic ulcer depth of 0.38 ± 0.09 mm, 0.74 ± 0.11 mm, 1.63 ± 0.4 mm, and 2.7 ± 0.31 mm (n = 4) for stages I-IV, respectively. The photoacoustic depth differences between each stage were significant (p < 0.05). We also used an LED-based photoacoustic imaging system to detect early stage (stage I) pressure ulcers and observed a 2.5-fold increase in photoacoustic signal. Importantly, we confirmed the capacity of this technique to detect dysregulated skin even before stage I ulcers have erupted. We also observed significant changes in photoacoustic intensity during healing suggesting that this approach can monitor therapy. These findings were confirmed with histology. These results suggest that this photoacoustic-based approach might have clinical value for monitoring skin diseases including pressure ulcers.

Monitoring Breast Cancer Response to Neoadjuvant Chemotherapy Using Ultrasound Strain Elastography

Strain elastography was used to monitor response to neoadjuvant chemotherapy (NAC) in 92 patients with biopsy-proven, locally advanced breast cancer. Strain elastography data were collected before, during, and after NAC. Relative changes in tumor strain ratio (SR) were calculated over time, and responder status was classified according to tumor size changes. Statistical analyses determined the significance of changes in SR over time and between response groups. Machine learning techniques, such as a naïve Bayes classifier, were used to evaluate the performance of the SR as a marker for Miller-Payne pathological endpoints. With pathological complete response (pCR) as an endpoint, a significant difference (P < .01) in the SR was observed between response groups as early as 2 weeks into NAC. Naïve Bayes classifiers predicted pCR with a sensitivity of 84%, specificity of 85%, and area under the curve of 81% at the preoperative scan. This study demonstrates that strain elastography may be predictive of NAC response in locally advanced breast cancer as early as 2 weeks into treatment, with high sensitivity and specificity, granting it the potential to be used for active monitoring of tumor response to chemotherapy.

Diagnostic Performance of Ultrasound Shear Wave Elastography in Solid Small (≤4 cm) Renal Parenchymal Masses

The aim of the study was to analyze the diagnostic performance of shear wave elastography (SWE) in differentiating between malignant and benign solid renal parenchymal masses ≤4 cm, compared with conventional ultrasound. A total of 20 healthy volunteers and 117 patients had been included in this study. Conventional ultrasound and SWE were performed in all volunteers and patients. The elasticity of healthy cortex and the elastic parameters of tumors such as mean elasticity (E_mean), minimum elasticity (E_min), maximum elasticity (E_max), standard deviation and elasticity ratio of the lesion to surrounding cortex (E_ratio) were measured on SWE images. Diagnostic performance of SWE was compared with that of conventional ultrasound. The cortical elasticity values of healthy right and left kidneys were 4.7 ± 1.7 and 4.5 ± 1.5 kPa, respectively. Of the 117 renal tumors, 68 were renal cell carcinomas (RCCs) and 49 were benign. E_mean, E_min and E_ratio were significantly lower in RCCs compared with benign lesions: E_mean 7.2 ± 2.5 kPa versus 10.0 ± 2.4 kPa, E_min 2.5 ± 2.4 kPa versus 5.6 ± 2.3 kPa, E_ratio 1.6 ± 0.5 versus 2.2 ± 0.6 (all p values < 0.001). The cutoff values of 9.15 kPa for E_mean, 3.55 kPa for E_min and 1.99 for E_ratio had the highest areas under the receiver operating characteristics curve (0.801 for E_mean, 0.832 for E_min and 0.806 for E_ratio). Combining E_mean, E_min and E_ratio with conventional ultrasound improved the specificity for predicting RCCs to 87.8%, but the sensitivity was not increased.

Usefulness of noninvasive shear wave elastography for the assessment of hepatic fibrosis in dogs with hepatic disease

BACKGROUND

Two-dimensional shear wave elastography (2D-SWE) can noninvasively evaluate hepatic elastic modulus as shear wave velocity (SWV). Additionally, it may predict the presence of clinical relevant hepatic fibrosis (≥F2) in dogs with hepatic disease.

OBJECTIVES

To investigate whether SWV measured by 2D-SWE can differentiate between dogs with (≥F2) and without (F0-1) clinically relevant hepatic fibrosis.

ANIMALS

Twenty-eight client-owned dogs with hepatic disease and 8 normal healthy Beagle dogs were enrolled.

METHODS

In this cross-sectional prospective study, SWVs were measured using 2D-SWE in all dogs. Hepatic fibrosis stages and necroinflammatory activity grades were histopathologically evaluated using a histological scoring scheme that was adapted from the Ishak schema used in human medicine.

RESULTS

Median SWVs were significantly higher in dogs with clinically relevant hepatic fibrosis (2.04 m/s; range, 1.81-2.26 m/s) than in healthy dogs (1.51 m/s; range, 1.44-1.66 m/s; P = .007), and dogs without clinically relevant hepatic fibrosis (1.56 m/s; range, 1.37-1.67 m/s; P < .001). However, no significant difference was found in the SWVs between dogs without clinically relevant hepatic fibrosis and healthy dogs (P = .99). Furthermore, median SWVs were not significantly different among dogs with necroinflammatory activity, those without necroinflammatory activity, and healthy dogs (Kruskal-Wallis test, P = .12).

CONCLUSIONS AND CLINICAL IMPORTANCE

The 2D-SWE may be useful for predicting the presence of hepatic fibrosis in dogs with hepatic disease.

Differentiating cervical metastatic lymphadenopathy and lymphoma by shear wave elastography

Shear wave elastography (SWE) is a recent technological advance of ultrasonography (US) to assess tissue stiffness. The purpose of this study is to assess tissue stiffness of malignant cervical lymph nodes (LN) with SWE, to reveal diagnostic performance of SWE in differentiating metastatic LN from lymphoma, and to assess inter-observer agreement of SWE. We assessed 62 malignant LN (24 lymphomas and 38 metastatic LN) and their median speed was 6.34 m/s and median elasticity was 69.7 kPa. Add of SWE with conventional US improved diagnostic accuracy of differentiating metastasis from lymphoma (16.13, 8.07 and 11.3% for three radiologists). Kendall’s Coefficient of Concordance of three readers for analyzing SWE patterns was 0.86. SWE can be a useful tool to discriminate metastatic cervical LN from lymphoma with improvement of diagnostic accuracy when using with conventional US.

Experimental pancreatic cancer develops in soft pancreas: novel leads for an individualized diagnosis by ultrafast elasticity imaging

Rapid, easy and early pancreatic cancer diagnosis and therapeutic follow up continue to necessitate an increasing attention towards the development of effective treatment strategies for this lethal disease. The non invasive quantitative assessment of pancreatic heterogeneity is limited. Here, we report the development of a preclinical imaging protocol using ultrasonography and shear wave technology in an experimental in situ pancreatic cancer model to measure the evolution of pancreatic rigidity.

Methods: Intrapancreatic tumors were genetically induced by mutated Kras and p53 in KPC mice. We evaluated the feasiblity of a live imaging protocol by assessing pancreas evolution with Aixplorer technology accross 36 weeks. Lethality induced by in situ pancreatic cancer was heterogeneous in time.

Results: The developed method successfully detected tumor mass from 26 weeks onwards at minimal 0.029 cm³ size. Elastography measurements using shear wave methodology had a wide detection range from 4.7kPa to 166.1kPa. Protumorigenic mutations induced a significant decrease of the rigidity of pancreatic tissue before tumors developed in correlation with the detection of senescent marker p16-positive cells. An intratumoral increased rigidity was quantified and found surprisingly heterogeneous. Tumors also presented a huge inter-individual heterogeneity in their rigidity parameters; tumors with low and high rigidity at detection evolve very heterogeneously in their rigidity parameters, as well as in their volume. Increase in rigidity in tumors detected by ultrafast elasticity imaging coincided with detection of tumors by echography and with the detection of the inflammatory protumoral systemic condition by non invasive follow-up and of collagen fibers by post-processing tumoral IHC analysis.

Conclusion: Our promising results indicate the potential of the shear wave elastography to support individualization of diagnosis in this most aggressive disease.

Diagnostic value of endoscopic ultrasound elastography for benign and malignant digestive system tumors

Objective:

To investigate the effect of endoscopic ultrasound real-time tissue elastography in differential diagnosis of benign and malignant digestive system tumors.

Methods:

Forty-two patients with solid tumors of digestive system who were admitted to our hospital between October 2017 and October 2018 were selected. All patients were diagnosed by endoscopic ultrasound real-time tissue elastography. Elastography score was used. The strain ratios (SR) of the lesion and the surrounding control tissues were measured and compared.

Results:

Lesions with elastography score no more than two points were evaluated as benign, while lesions with elastography score no less than three points were evaluated as malignant. The difference of the elastography score between the benign lesion group and malignant lesion group was statistically significant (P<0.05). The sensitivity, specificity and accuracy of endoscopic ultrasound elastography in the diagnosis of malignant tumors of digestive system were 91.4%, 88.9% and 87.5%, respectively. The SR of the benign lesions ranged from 0.01 to 7.34, with a median SR of 7.33; the SR of the malignant lesions ranged from 1.01 to 47.66, with a median SR of 20.07. The SR of the benign lesions was significantly lower than that of the malignant lesions (P<0.05).

Conclusion:

Elastography of benign and malignant tissues of digestive tract tumors has different image characteristics. Endoscopic ultrasound real-time tissue elastography is effective in differential diagnosis of digestive tract tumors as it can effectively determine whether a tumor is benign or malignant and improve diagnostic accuracy.

Ultrasound elastography in the evaluation of thyroid nodules: evolution of a promising diagnostic tool for predicting the risk of malignancy

The elastic properties of tissue have always been of interest in clinical practice. In the past, the identification of structures that were stiffer on physical palpation would raise the suspicion that "there was something wrong". With the development and advancement of medicine, there proved to be a true correlation in the prediction of malignancy of a lesion: malignant disease tends to stiffen the affected tissue, either by increased cell proliferation or fibrosis. Palpation is the oldest method for the detection of thyroid nodules, which is informed by the knowledge that malignant thyroid lesions tend to be much harder than benign ones. Unfortunately, palpation is a highly subjective method that is dependent on the size and location of the lesion, as well as on the skill of the physician. In cases where these nodules are very small or are located in deep regions, their detection by palpation is difficult or even impossible. In addition, although a malignant lesion differs in terms of elasticity, it may not have echogenic properties, preventing its detection by conventional ultrasound. Imaging that indicates the stiffness or deformation of tissues, through the use of ultrasound elastography techniques, adds new information related to their structural formation. In this article, we review the basic physical principles of elastography and the evolution of the method for the evaluation of thyroid nodules, as well as the limitations of and future perspectives for its use.

Point Shear Wave Elastography Using Machine Learning to Differentiate Renal Cell Carcinoma and Angiomyolipoma

The question of whether ultrasound point shear wave elastography can differentiate renal cell carcinoma (RCC) from angiomyolipoma (AML) is controversial. This study prospectively enrolled 51 patients with 52 renal tumors (42 RCCs, 10 AMLs). We obtained 10 measurements of shear wave velocity (SWV) in the renal tumor, cortex and medulla. Median SWV was first used to classify RCC versus AML. Next, the prediction accuracy of 4 machine learning algorithms-logistic regression, naïve Bayes, quadratic discriminant analysis and support vector machines (SVMs)-was evaluated, using statistical inputs from the tumor, cortex and combined statistical inputs from tumor, cortex and medulla. After leave-one-out cross validation, models were evaluated using the area under the receiver operating characteristic (ROC) curve (AUC). Tumor median SWV performed poorly (AUC = 0.62; p = 0.23). Except logistic regression, all machine learning algorithms reached statistical significance using combined statistical inputs (AUC = 0.78-0.98; p < 7.1 × 10-3). SVMs demonstrated 94% accuracy (AUC = 0.98; p = 3.13 × 10-6) and clearly outperformed median SWV in differentiating RCC from AML (p = 2.8 × 10-4).

Handheld probe for quantitative micro-elastography

Optical coherence elastography (OCE) has been proposed for a range of clinical applications. However, the majority of these studies have been performed using bulky, lab-based imaging systems. A compact, handheld imaging probe would accelerate clinical translation, however, to date, this had been inhibited by the slow scan rates of compact devices and the motion artifact induced by the user's hand. In this paper, we present a proof-of-concept, handheld quantitative micro-elastography (QME) probe capable of scanning a 6 × 6 × 1 mm volume of tissue in 3.4 seconds. This handheld probe is enabled by a novel QME acquisition protocol that incorporates a custom bidirectional scan pattern driving a microelectromechanical system (MEMS) scanner, synchronized with the sample deformation induced by an annular PZT actuator. The custom scan pattern reduces the total acquisition time and the time difference between B-scans used to generate displacement maps, minimizing the impact of motion artifact. We test the feasibility of the handheld QME probe on a tissue-mimicking silicone phantom, demonstrating comparable image quality to a bench-mounted setup. In addition, we present the first handheld QME scans performed on human breast tissue specimens. For each specimen, quantitative micro-elastograms are co-registered with, and validated by, histology, demonstrating the ability to distinguish stiff cancerous tissue from surrounding soft benign tissue.

Reduction in stiffness of proximal leg muscles during the first 6 months of glucocorticoid therapy for giant cell arteritis: A pilot study using shear wave elastography

AIM

To investigate muscle stiffness changes in patients treated for giant cell arteritis (GCA) with high-dose oral glucocorticoids.

METHODS

Using ultrasound elastography, shear wave velocity (SWV) was measured in the quadriceps, hamstrings and biceps brachii muscles of 14 patients with GCA (4 male, mean age ± SD, 68.2 ± 4.3 years) within the first 2 weeks of initiating glucocorticoid treatment (baseline) and repeated after 3 and 6 months treatment. Muscle strength and performance tests were performed at each visit. Baseline measures were compared with those from 14 healthy controls. Linear mixed models were used to test for change in patient measures over time.

RESULTS

At baseline, muscle SWV in patients was not significantly different from controls. With glucocorticoid treatment, there was a reduction in SWV in the leg but not the arm muscles. SWV decreased by a mean of 14% (range 8.3%-17.3%; P = .001) after 3 months and 18% (range 10.2%-25.3%; P < .001) after 6-months in the quadriceps and hamstrings during the resting position. The baseline, 3 and 6 months mean SWV (±SD) for the vastus lateralis were 1.62 ± 0.16 m/s, 1.40 ± 0.10 m/s and 1.31 ± 0.06 m/s, respectively (P < .001). In the patient group as a whole, there was no significant change in muscle strength. However, there were moderate correlations (r = .54-.69) between exhibiting weaker muscle strength at follow-up visits and a greater reduction in SWV.

CONCLUSION

Glucocorticoid therapy in patients with GCA was associated with a significant reduction in proximal leg muscle stiffness during the first 6 months. Future research should study a larger sample of patients for a longer duration to investigate if diminished muscle stiffness precedes signs of glucocorticoid-induced myopathy.

Kelvin-Voigt Parameters Reconstruction of Cervical Tissue-Mimicking Phantoms Using Torsional Wave Elastography

The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography (TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP) approach, is presented and experimentally validated against Shear Wave Elastography (SWE). The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were fabricated at different proportion to test the new reconstruction technique. The PIP approach was used for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain (FDTD) KV wave propagation model. Additionally, SWE tests were realized in order to characterize the viscoelastic properties of each batch of gelatine. Finally, validation was carried out by comparing the KV parameters inferred from the PIP with those reconstructed from the shear wave dispersion curve obtained from the SWE measurements. In order to test the degree of agreement between both techniques, a Student's T-test and a Pearson's correlation study were performed. The results indicate that the proposed method is able to reconstruct the KV viscoelastic properties of the cervical tissue, for both the epithelial and connective layers, as well as the thickness of the first layer with acceptable accuracy.

Ultrasound elastography for the evaluation of peripheral nerves: A systematic review

Peripheral nerve disorders are commonly encountered in clinical practice. Electrodiagnostic studies remain the cornerstone of the evaluation of nerve disorders. More recently, ultrasound has played an increasing complementary role in the neuromuscular clinic. Ultrasound elastography is a technique that measures the elastic properties of tissues. Given the histological changes that occur in diseased peripheral nerves, nerve ultrasound elastography has been explored as a noninvasive way to evaluate changes in nerve tissue composition. Studies to date suggest that nerve stiffness tends to increase in the setting of peripheral neuropathy, regardless of etiology, consistent with loss of more compliant myelin, and replacement with connective tissue. The aim of this systematic review is to summarize the current literature on the use of ultrasound elastography in the evaluation of peripheral neuropathy. Limitations of ultrasound elastography and gaps in current literature are discussed, and prospects for future clinical and research applications are raised.

Accuracy and precision of ultrasound shear wave elasticity measurements according to target elasticity and acquisition depth: A phantom study

OBJECTIVE

To investigate the accuracy and precision of ultrasound shear wave elasticity measurements as a function of target elasticity and acquisition depth.

MATERIALS AND METHODS

Using five ultrasound systems (VTQ, VTIQ, EPIQ 5, Aixplorer, and Aplio 500), two operators independently measured shear wave elasticities in two phantoms containing five different target elasticities (8±3, 14±4, 25±6, 45±8, and 80±12 kPa) at depths of 15, 30, 35, and 60 mm. Accuracy was assessed by evaluating measurement errors and the proportions of outliers, while factors affecting accuracy were assessed using logistic regression analysis. Measurement errors were defined as differences between the measured values and 1) the margins of the target elasticity, and 2) the median values of the target elasticity. Outliers were defined as measured values outside the margins of the target elasticity. Precision was assessed by calculating the reproducibility of measurements using the within-subject coefficient of variation (wCV).

RESULTS

Mean measurement errors and the proportions of outliers were higher for high than for low target elasticities (p<0.001), but did not differ in relation to acquisition depth, either within an elastography system or across the different systems. Logistic regression analysis showed that target elasticity (p<0.001) significantly affected accuracy, whereas acquisition depth (p>0.05) did not. The wCV for the 80±12 kPa target (31.33%) was significantly higher than that for lower elasticity targets (6.96-10.43 kPa; p<0.001). The wCV did not differ across acquisition depths. The individual elastography systems showed consistent results.

CONCLUSIONS

Targets with high elasticity showed lower accuracy and lower precision than targets with low elasticity, while acquisition depth did not show consistent patterns in either accuracy or precision.

Prediction of Postprostatectomy Biochemical Recurrence Using Quantitative Ultrasound Shear Wave Elastography Imaging

Objectives: To determine the prognostic significance of tissue stiffness measurement using transrectal ultrasound shear wave elastography in predicting biochemical recurrence following radical prostatectomy for clinically localized prostate cancer.

Patients and Methods: Eligible male patients with clinically localized prostate cancer and extraperitoneal laparoscopic radical prostatectomy between November 2013 and August 2017 were retrospectively selected. Information of potential biochemical recurrence predictors, including imaging (ultrasound shear wave elastography and magnetic resonance imaging), clinicopathological characteristics, and preoperative prostate specific antigen (PSA) levels were obtained. Recurrence-free survival (Kaplan–Meier curve) and a multivariate model were constructed using Cox regression analysis to evaluate the impact of shear wave elastography as a prognostic marker for biochemical recurrence.

Results: Patients experienced biochemical recurrence in an average of 26.3 ± 16.3 months during their follow-up. A cutoff of 144.85 kPa for tissue stiffness measurement was estimated for recurrence status at follow-up with a sensitivity of 74.4% and a specificity of 61.7%, respectively (p < 0.05). In univariate analysis, shear wave elastography performed well in all preoperative factors compared to biopsy Gleason Score, PSA and magnetic resonance imaging; in multivariate analysis with postoperative pathological factors, shear wave elastography was statistically significant in predicting postoperative biochemical recurrence, which improved the C-index of predictive nomogram significantly (0.74 vs. 0.70, p < 0.05).

Conclusions: The study revealed that quantitative ultrasound shear wave elastography-measured tissue stiffness was a significant imaging marker that enhanced the predictive ability with other clinical and histopathological factors in prognosticating postoperative biochemical recurrence following radical prostatectomy for clinically localized prostate cancer.

Do functional changes occur in the bladder due to bladder outlet obstruction? - ICI-RS 2018

Studies on bladder dysfunction (BD), more specifically functional‐urodynamic changes in the bladder as a result of bladder outlet obstruction (BOO) have been summarized for this TT. Based on available, but limited evidence from human studies a three‐stage model can be hypothesized to characterize BOO‐induced bladder remodeling: hypertrophy, compensation (increased detrusor contractility during the voiding phase, often in combination with filling phase detrusor overactivity) followed by the phase of decompensation [detrusor underactivity]. The time between the start of compensation and eventual decompensation seems to be determined by age of onset, severity, and type of obstruction and clinical mitigating factors such as vascular and metabolic problems. Understanding the relative contributions of these factors may allow the development of personalized timelines and probabilities for these obstructed patients.

Imaging the Vocal Folds: A Feasibility Study on Strain Imaging and Elastography of Porcine Vocal Folds

Vocal folds are an essential part of human voice production. The biomechanical properties are a good indicator for pathological changes. In particular, as an oscillation system, changes in the biomechanical properties have an impact on the vibration behavior. Subsequently, those changes could lead to voice-related disturbances. However, no existing examination combines biomechanical properties and spatial imaging. Therefore, we propose an image registration-based approach, using ultrasound in order to gain this information synchronously. We used a quasi-static load to compress the tissue and measured the displacement by image registration. The strain distribution was directly calculated from the displacement field, whereas the elastic properties were estimated by a finite element model. In order to show the feasibility and reliability of the algorithm, we tested it on gelatin phantoms. Further, by examining ex vivo porcine vocal folds, we were able to show the practicability of the approach. We displayed the strain distribution in the tissue and the elastic properties of the vocal folds. The results were superimposed on the corresponding ultrasound images. The findings are promising and show the feasibility of the suggested approach. Possible applications are in improved diagnosis of voice disorders, by measuring the biomechanical properties of the vocal folds with ultrasound. The transducer will be placed on the vocal folds of the anesthetized patient, and the elastic properties will be measured. Further, the understanding of the vocal folds’ biomechanics and the voice forming process could benefit from it.

Current Imaging Techniques for Noninvasive Staging of Hepatic Fibrosis

OBJECTIVE. The purpose of this article is to discuss quantitative methods of CT, MRI, and ultrasound (US) for noninvasive staging of hepatic fibrosis. Hepatic fibrosis is the hallmark of chronic liver disease (CLD), and staging by random liver biopsy is invasive and prone to sampling errors and subjectivity. Several noninvasive quantitative imaging methods are under development or in clinical use. The accuracy, precision, technical aspects, advantages, and disadvantages of each method are discussed. CONCLUSION. The most promising methods are the liver surface nodularity score using CT and measurement of liver stiffness using MR elastography or US elastography.

Reproducibility of 2 Liver 2-Dimensional Shear Wave Elastographic Techniques in the Fasting and Postprandial States

OBJECTIVES

The purpose of this study was to compare the reliability and agreement of 2 methods of 2-dimensional (2D) shear wave elastography (SWE) on liver stiffness in healthy volunteers. We also assessed effects of the prandial state and operator experience on measurements.

METHODS

Two operators, 1 experienced and 1 novice, independently examined 20 healthy volunteers with 2D SWE on 2 ultrasound machines (Aixplorer [SuperSonic Imagine, Aix-en-Provence, France] and Aplio 500 [Canon Medical Systems Corporation, Otawara, Japan]). Volunteers were scanned 8 times by the operators using both machines in fasting and postprandial states. Agreement was evaluated by a Bland-Altman analysis, and the correlation was assessed by the Pearson correlation and intraclass correlation coefficients (ICCs). An analysis of variance was conducted to determine the contribution of the machine, prandial state, and operator experience to the variability.

RESULTS

Agreement assessed by Bland-Altman plots showed no statistically significant difference in measured liver stiffness between the machines (mean difference, -0.8%; 95% confidence interval, -3.7%, 2.1%), with a critical difference of 1.36 kPa. The correlation was good to excellent for both the crude overall Pearson coefficient and the ICC, both measuring 0.88 (95% confidence interval, 0.82, 0.92). Subclass ICCs for the fasting state, postprandial state, novice operator, and experienced operator were 0.89, 0.88, 0.90, and 0.86, respectively. The 2-way mixed effect analysis of variance showed that the volunteers accounted for 86.3% of variation in median liver stiffness, with no statistically significant contribution from operator experience, the prandial state, or the machine (P = .108, .067, and .296, respectively).

CONCLUSIONS

Our study showed that the 2D SWE techniques had a high degree of reliability and agreement in measurement of liver stiffness in a healthy population. Operator experience and the prandial state did not impart significant variability to stiffness measurements.

Reliability of ultrasound strain elastography in the assessment of the quadriceps and patellar tendon in healthy adults

Objective

To report the intra- and inter-operator reliability of ultrasound strain elastography measures in the assessment of quadriceps and patellar tendons.

Materials and methods

Forty tendons were investigated of 20 healthy volunteers. Five anatomical sites were examined and analysed by three operators of differing levels of experience. Ultrasound was performed over two measures, employing three sonoelastography measurement techniques using a GE S8 with linear probe (L6-15 MHz). The percentage of exact agreement, Cohen's kappa and ICC_2,1 were performed to assess intra- and inter-operator reliability.

Results

The patellar tendon is more reliably measured across all techniques compared to the quadriceps tendon, particularly the distal region. Colour scoring was the most reliable method of sonoelastography. Colour scoring intra- and inter-operator reliability was better for patella tendon sites across all operators (60-95% agreement range), and greatest for experienced operators. Elasticity index intra-operator reliability was greatest for the most experienced operator compared with the least (ICC range 0.35-0.72 and ICC 0.17-0.60). Elasticity ratio intra-operator reliability of the patella tendon was fair-excellent for the experienced operator (ICC range 0.43-0.91), excluding the mid patellar region (ICC 0.13). Poor-fair inter-operator reliability was observed for elasticity ratio (ICC range 0.0-0.54) and elasticity index (ICC range 0.0-0.57).

Conclusions

Strain elastography of the patellar tendon is more reliable than the quadriceps tendon. Intra- and inter-operator reliability was better when undertaken by more experienced operators. Colour scoring was more reliable than elasticity ratio and index methods. Poor-fair intra- and inter-operator reliability of the elasticity ratio and elasticity index was observed.

Multiparametric ultrasound in the evaluation of kidney disease in elderly

After the age of 30 years, GFR progressively declines at an average rate of 8 mL/min/1.73 m/decade. A problem of advanced age is that the evaluation of renal function on the basis of indicators valid in young adults, such as creatininemia, is unreliable. In fact, many patients with chronic renal failure may have serum creatinine levels within the normal range even if they have a significant reduction in renal function. Ultrasound has become a routine method of investigation in renal disease: kidney size and parenchymal echogenicity are considered markers of renal function, so US is useful in assessing the presence and degree of renal failure. CEUS is useful in the evaluation of kidney disease in the elderly: the increased hemodynamic resistance of renal microvessels reduces perfusion in the renal cortex, so fewer microbubbles enter the renal cortex. EcoColor and EcoDoppler are also useful in the evaluation of senile alterations: here, the distribution of color-signals, as compared to that in the young adult population, appears more attenuated, limited to intersegmental and interlobar districts. Among the ecoDoppler parameters, the resistance index can be considered a marker of renal damage progression, with attention needing to paid to possible concomitant confounding factors. Ultrasonography, color-Doppler and CEUS are a non-invasive and convenient modality for managing kidney disease; their integration with anamnestic, objective and laboratory data permits fast and reliable clinical, diagnostic, and therapeutic classification. It also allows early therapeutic intervention and, ultimately, improvements in patient management.

Comparison of Shear Wave Elastography and Conventional Ultrasound in Assessing Kidney Function as Measured Using 51Cr-ethylenediaminetetraacetic Acid and 99Tc-Dimercaptosuccinic Acid

The purpose of this study was to assess the potential of shear wave elastography (SWE) as an indicator of abnormal kidney function defined by radiolabeled glomerular filtration rate (GFR). Fifty-seven patients referred for ⁵¹Cr-ethylenediaminetetraacetic acid GFR and ^99mTc-dimercaptosuccinic acid renal scintigraphy were included. Young's modulus (YM) measured with SWE and kidney length, volume, cortical thickness and parenchymal echogenicity measured with conventional ultrasound were correlated with patients' GFR and renal scintigraphy results. Spearman correlation coefficients between SWE and GFR were negative for the right (r = -0.635, p < 0.0001) and left (r = -0.817, p < 0.0001) kidneys. Positive correlations between left renal cortical thickness (r = 0.381, p = 0.04) and left kidney volume (r = 0.356, p = 0.019) with GFR were reported. SWE correctly predicted the dominant functioning kidney in 94.7% of cases. The area under the receiver operating characteristic curve for SWE (0.800) was superior to that for conventional ultrasound (0.252-0.415). The cutoff value of ≥5.52 kPa suggested a kidney function ≤60 mL/min/1.73 m² (82.4% sensitivity and 76.2% specificity). SWE has advantages over conventional ultrasound in assessing kidney function and distinguishing the dominant functioning kidney.

Propagation Imaging in the Demonstration of Common Shear Wave Artifacts

In this article, we describe our experience with shear wave propagation imaging (SWPI) as an adjunct to 2-dimensional (2D) shear wave elastography (SWE) in a cohort of patients being evaluated for diffuse liver disease. Two-dimensional SWE has been extensively studied in previous publications; however, 2D SWE using propagation images has not been widely described in the literature to date. We observed that when certain artifacts occurred on the color elastograms, highly characteristic changes to shear wave propagation contours were seen, which can help clarify the cause of the artifacts. To our knowledge, the use of SWPI to explain the etiology of artifacts has never been published before. The artifacts described in this article include the capsule reverberation artifact, penetration limitation or dropout artifact, artifact due to blood vessels, shadowing artifact, tissue motion artifact, and near-field distortion/precompression artifact. Hence, the purpose of this article is to show examples of common artifacts seen on 2D SWE as depicted on corresponding SWPI to demonstrate that both types of image displays are complementary to each other.