Variability of shear wave velocity using different frequencies in acoustic radiation force impulse (ARFI) elastography: a phantom and normal liver study

Shear-Wave Elastography of the Achilles tendon: reliability analysis and impact of parameters modulating elasticity values

PURPOSE

Shear wave elastography (SWE) has seen many advancements in Achilles tendon evaluation in recent years, yet standardization of this technique is still problematic due to the lack of knowledge regarding the optimal way to perform the examination. The purpose of this study was to evaluate the effects of ankle position, probe frequency and physical effort on the shear modulus of the Achilles tendon, but also to determine the intra and inter-observer reliability of the technique.

METHODS

37 healthy volunteers were included; SWE protocol was performed by two examiners. We analyzed the shear modulus of the tendon with the ankle in neutral, maximum dorsiflexion and maximum plantar flexion using two different high frequency probes. Afterwards, the subjects performed a brief physical exercise and SWE measurements were repeated.

RESULTS

The L18-5 probe showed the highest ICC values (ICC = 0.798, 95% CI 0.660-0.880, p < 0.001) when positioned at 2 cm from the calcaneal insertion with the ankle in a neutral state. Conversely, utilizing the same L18-5 probe at 1 cm from the insertion during maximum plantar flexion of the ankle resulted in the lowest ICC (ICC = 0.422, 95% CI 0.032-0.655, p = 0.019). Significant variations in elasticity values were noted among different ankle positions and probe types, while no significant changes in elasticity were observed post-physical exercise.

CONCLUSION

Ankle position and probe frequency are factors that influence elasticity values of the Achilles tendon. An ankle position between 10 and 20 degrees of plantar flexion is the most suitable for SWE evaluation. However, more research focusing on Achilles tendon SWE is essential due to the challenges encountered in standardizing this region.

Cardiac 2-D Shear Wave Imaging Using a New Dedicated Clinical Ultrasound System: A Phantom Study

OBJECTIVE

The purpose of this study was to assess cardiac shear wave imaging implemented in a new MACH 30 ultrasound machine (SuperSonic Imaging, Aix-en-Provence, France) and interfaced with a linear probe and a phased array probe, in comparison with a previously validated Aixplorer system connected to a linear probe (SuperSonic Imaging) using Elasticity QA phantoms (Models 039 and 049, CIRS Inc., Norfolk, VA, USA).

METHODS

Quantile-quantile plots were used for distribution agreement. The accuracy of stiffness measurement was assessed by the percentage error and the mean percentage error (MPE), and its homogeneity, by the standard deviation of the MPE. A p value <0.01 was considered to indicate statistical significance.

RESULTS

The accuracy of dedicated cardiac sequences for linear probes was similar for the two systems with an MPE of 8 ± 14% versus 20 ± 21% (p = not significant) with the SuperSonic MACH 30 and Aixplorer, respectively, and was influenced by target stiffness and location of the measurement in the field of view, but without drift over time. The optimal transthoracic cardiac probe workspace was located between 4 and 10 cm, with an MPE of 29.5 ± 25% compared with 93.3 ± 130% outside this area (p < 0.0001). In this area, stiffness below 20 kPa was significantly different from the reference (p < 0.0001). The sectorial probe revealed no MPE difference in any of the measurement areas, with no significant lateral or axial gradient.

CONCLUSION

The new Supersonic MACH 30 system upgraded with a sectorial probe and specific cardiac settings provided homogenous stiffness measurements, especially when operating at depths between 4 and 10 cm. These phantom results may be useful in designing future in vivo studies.

Using ultrasound shear wave elastography to characterize peripheral nerve mechanics: a systematic review on the normative reference values in healthy individuals

Ultrasound shear wave elastography (SWE) is an emerging non-invasive imaging technique for peripheral nerve evaluation. Shear wave velocity (SWV), a surrogate measure of stiffness, holds promise as a biomarker for various peripheral nerve disorders. However, to maximize its clinical and biomechanical value, it is important to fully understand the factors that influence nerve SWV measurements. This systematic review aimed to identify the normal range of SWV for healthy sciatic and tibial nerves and to reveal the factors potentially affecting nerve SWV. An electronic search yielded 17 studies eligible for inclusion, involving 548 healthy individuals (age range, 17 to 72 years). Despite very good reliability metrics, the reported SWV values differed considerably across studies for the sciatic (1.9-9.9 m/s) and tibial (2.3-9.1 m/s) nerves. Factors such as measurement proximity to joint regions, limb postures inducing nerve axial stretching, and transducer alignment with nerve fiber orientation were associated with increased SWV. These findings suggest regional-specific nerve mechanical properties, non-linear elastic behaviour, and marked mechanical anisotropy. The impact of age and sex remains unclear and warrants further investigation. These results emphasize the importance of considering these factors when assessing and interpreting nerve SWE. While increased SWV has been linked to pathological changes affecting nerve tissue mechanics, the significant variability observed in healthy nerves highlights the need for standardized SWE assessment protocols. Developing guidelines for enhanced clinical utility and achieving a comprehensive understanding of the factors that influence nerve SWE assessments are critical in advancing the field.

Depth effect on point shear wave velocity elastography: Evidence in a chronic hepatitis C patient cohort

Background and Aims

This study investigated the depth-related bias and the influence of scan plane angle on performance of point-shear-wave elastometry in a chronic hepatitis C patient cohort.

Materials and Methods

We included 104 patients affected by chronic liver disease related to the hepatitis C virus. Liver surface nodularity was the reference to diagnose cirrhosis. The ultrasound platform was the Siemens S2000, equipped with point-shear-wave elastometry software. Measurements were obtained in left lateral decubitus from the liver surface to the maximum depth of 8 cm in two orthogonal scan planes according to a standard sampling plane. Scatterplot and box plots explored the depth-related bias graphically. The area under the receiver operating characteristic was used to determine the point-shear-wave elastometry diagnostic performance at progressive depths according to liver surface nodularity.

Results

Of the 104 patients, 68 were cirrhotics. Depth-related bias equally modified point-shear-wave elastometry in the two orthogonal scan planes. A better point-shear-wave elastometry diagnostic performance was observed between depths of 4 and 5 cm. The frontal scan plane assured better discrimination between cirrhotic patients and non-cirrhotic patients.

Conclusion

Depth is crucial for point-shear-wave elastometry performance. Excellent diagnostic performance at a depth between 4 and 5 cm can also be obtained with a smaller number of measurements than previously recommended.

Variability, Validity and Operator Reliability of Three Ultrasound Systems for Measuring Tissue Stiffness: A Phantom Study

Introduction

Ultrasound elastography is a method of measuring soft tissue stiffness to detect the presence of pathology. There are several ultrasound elastography devices on the market. The aim of this study was twofold. Firstly, to determine the validity of three different ultrasound systems used to measure tissue stiffness. Secondly, to determine the operator reliability and repeatability when using these three systems.

Materials and methods

Two observers undertook multiple stiffness measurements from a phantom model using three different ultrasound systems; the LOGIQ E9, the Aixplorer, and the Acuson S2000. The phantom model had four cylindrical-shaped inclusions (Type 1-4) of increasing stiffness values and diameter embedded within. The background phantom stiffness was fixed. The mean, standard deviation, and coefficient of variation (CV) were calculated from measured stiffness readings per diameter per inclusion. Intra-observer variability was assessed. The validity of the measured stiffness value was assessed by calculating the difference between the measured elasticities and actual phantom elasticities. Bland-Altman plots with limits of agreement were used to display the inter-observer agreement. The intraclass correlation coefficients (ICC) were used to measure intra-observer, inter-observer, and inter-system reliability.

Results

Each observer undertook 1020 measurements. All three systems generally underestimated the stiffness values for the inclusions; the higher the actual stiffness value, the more significant the underestimation. The percentage difference between measured stiffness and actual stiffness varied from -79.1% to 12.7%. The intra-observer variability was generally less than 5% for observers using the LOGIQ E9 and the Aixplorer systems but more than 10% over the stiffer inclusions (Types 3 and 4) for the Acuson system. There was 'almost perfect' intra-observer reliability and repeatability for both the LOGIQ E9 and the Aixplorer systems; this was 'moderate' for the Acuson system over specific inclusions. For all systems, there was 'almost perfect' inter-observer reliability and repeatability between Observer A and Observer B. The inter-system reliability and repeatability were 'almost perfect' between the LOGIQ E9 system and the Aixplorer system but 'poor' and 'moderate' when the Acuson system was matched with the LOGIQ E9 system and the Aixplorer system, respectively.

Conclusion

This study has demonstrated that the Acuson, LOGIQ E9, and Aixplorer ultrasound systems have low variability, high reproducibility, and good intra-observer and inter-observer reliability when used to measure tissue stiffness. However, they all underestimated the stiffness values during this in vitro study. This study also revealed that not all ultrasound systems are comparable when measuring tissue stiffness, with some having better inter-system reliability than others. Ongoing standardization of technology is required at the manufacturer level.

The values of elastic quantitative and semi-quantitative indexes measured from different frequencies in the establishment of prediction models for breast tumor diagnosis

Objective

To obtain the elastic quantitative and semi-quantitative indexes of solid breast masses using ultrasound linear array probes with two different frequencies, and to construct prediction models and evaluate their diagnostic values.

Methods

A total of 92 patients who were scheduled for surgical treatment on solid breast masses were enrolled in this study. Linear array probes with two frequencies, 9-3 MHz (L9 group) and 14-5 MHz (L14 group), were used for sound touch elastography and strain elastography before surgery, and the maximum elasticity value (Emax), average elasticity value (Emean), minimum elasticity value (Emin), standard deviation (SD)(in kPa), elasticity ratio (E), and strain ratio to fat (SRf) were recorded and calculated for the breast mass (A) and surrounding tissues (Shell). The elastic characteristic indexes of the L9 group and L14 group were compared, and the prediction models of these two groups were constructed using Logistic regression method.

Results

The diagnostic performance of the prediction model based on L9 group was better than the model based on L14 group (AUC: 0.904 vs. 0.810, P = 0.0343, z = 2.116) and the best single index EMax-shell-L9 (P = 0.0398, z = 2.056). The sensitivity of L9 based model was 85.19% and the specificity was 84.21%.

Conclusion

The prediction model based on quantitative and semi-quantitative elastic ultrasound indexes from L9-3 probe exhibited better performance, which could improve the diagnostic accuracy for malignant breast tumors.

Preclinical Three-Dimensional Vibrational Shear Wave Elastography for Mapping of Tumour Biomechanical Properties In Vivo

Preclinical investigation of the biomechanical properties of tissues and their treatment-induced changes are essential to support drug-discovery, clinical translation of biomarkers of treatment response, and studies of mechanobiology. Here we describe the first use of preclinical 3D elastography to map the shear wave speed (cs), which is related to tissue stiffness, in vivo and demonstrate the ability of our novel 3D vibrational shear wave elastography (3D-VSWE) system to detect tumour response to a therapeutic challenge. We investigate the use of one or two vibrational sources at vibrational frequencies of 700, 1000 and 1200 Hz. The within-subject coefficients of variation of our system were found to be excellent for 700 and 1000 Hz and 5.4 and 6.2%, respectively. The relative change in cs measured with our 3D-VSWE upon treatment with an anti-vascular therapy ZD6126 in two tumour xenografts reflected changes in tumour necrosis. U-87 MG drug vs vehicle: Δcs = −24.7 ± 2.5 % vs 7.5 ± 7.1%, (p = 0.002) and MDA-MB-231 drug vs vehicle: Δcs = −12.3 ± 2.7 % vs 4.5 ± 4.7%, (p = 0.02). Our system enables rapid (<5 min were required for a scan length of 15 mm and three vibrational frequencies) 3D mapping of quantitative tumour viscoelastic properties in vivo, allowing exploration of regional heterogeneity within tumours and speedy recovery of animals from anaesthesia so that longitudinal studies (e.g., during tumour growth or following treatment) may be conducted frequently.

Effect of Depth on Ultrasound Point Shear Wave Elastography in an Elasticity Phantom

Background: Phantom studies are widely used to assess variability in measurements. This study aimed to assess the reliability and accuracy of point Shear Wave elastography (pSWE) measurements of an elasticity phantom. Methods: Measurements were obtained by an experienced certified clinical sonographer at three different depth levels in kPa, using a curvilinear 5-1MHz transducer of the EPIQ7 ultrasound imaging system. Results: A total of 180 pSWE measurements were obtained at three different depth levels (three cm, five cm, and seven cm) of the phantom background. The mean CV of pSWE was low at all depths (3 cm: 8.8%; 5 cm: 7%; 7 cm: 7.2%). There was a significant difference between measurements at depths of 3 cm vs. 7 cm (MD: −0.85, 95% CI −1.5, −0.11, p = 0.024) and measurements at depths 5 cm vs. 7 cm (MD: −1.1, 95% CI −1.7, −0.47, p = 0.001). An overestimation of mean pSWE measurements at a depth of 7 cm was noted compared to the manufacturer’s value (2.7%, p = 0.006). Conclusions: Superficial phantom SWE measurements in this study had low variability compared to deep measurement. pSWE measurements at deep levels can be overestimated.

Evaluation of ultrasound point shear wave elastography reliability in an elasticity phantom

PURPOSE

To date, limited studies have specifically addressed the reliability of ultrasound point shear-wave elastography (pSWE). Therefore, the aim of the present study was to assess the reproducibility of ultrasound pSWE within and between operators using two ultrasound scanners.

METHODS

iU22 and EPIQ7 ultrasound scanners were used to assess the reliability of pSWE measurements of four inclusions [L I (8 kPa), L II (14 kPa), L III (48 kPa), and L IV (80 kPa)] at a depth of 3.5 cm in an elasticity phantom using a curvilinear 5-1 MHz transducer. The intraoperator, inter-operator, and inter-scanner reproducibility of pSWE was assessed using intraclass correlation coefficients (ICCs). Bland-Altman plots were used to establish bias and limits of agreement (LoA) between measurements. The accuracy of pSWE from manufacturer values was determined using the one-sample t-test.

RESULTS

Intra-operator agreement was excellent, with an ICC >0.90. The bias in measurements for operator A was -0.36±3.13 kPa (LoA, -6.47 to 5.75), and for operator B it was 1.97±6.29 kPa (LoA, -10.25 to 14.21). Inter-operator agreement was excellent, with an ICC of 0.95. The bias in measurements between operators was -0.42±5.00 kPa (LoA, -10.24 to 9.38). The inter-scanner agreement between EPIQ7 and iU22 was excellent, with an ICC of 0.96. The bias in measurements between scanners was 1.74±4.44 kPa (LoA, -6.95 to 10.45). There was significant overestimation for L I (17.75%) and L II (31.14%) and underestimation for L III (-15.28%) and L VI (-98.00%) relative to the manufacturer-reported values.

CONCLUSION

Phantom ultrasound pSWE was reproducible within and between operators, and between Philips ultrasound scanners; further studies using different ultrasound systems and transducers are required.

A Cross-Machine Comparison of Shear-Wave Speed Measurements Using 2D Shear-Wave Elastography in the Normal Female Breast

Quantitative measures of radiation-induced breast stiffness are required to support clinical studies of novel breast radiotherapy regimens and exploration of personalised therapy, however, variation between shear-wave elastography (SWE) machines may limit the usefulness of shear-wave speed (cs) for this purpose. Mean cs measured in four healthy volunteers’ breasts and a phantom using 2D-SWE machines Acuson S2000 (Siemens Medical Solutions) and Aixplorer (Supersonic Imagine) were compared. Shear-wave speed was measured in the skin region, subcutaneous adipose tissue and parenchyma. cs estimates were on average 2.3% greater when using the Aixplorer compared to S2000 in vitro. In vivo, cs estimates were on average 43.7%, 36.3% and 49.9% significantly greater (p << 0.01) when using the Aixplorer compared to S2000, for skin region, subcutaneous adipose tissue and parenchyma, respectively. In conclusion, despite relatively small differences between machines observed in vitro, large differences in absolute measures of shear wave speed measured were observed in vivo, which may prevent pooling of cross-machine data in clinical studies of the breast.

Technical feasibility and correlations between shear-wave elastography and histology in kidney fibrosis in children

BACKGROUND

Ultrasound elastography has been suggested for assessing organ fibrosis.

OBJECTIVE

To study the feasibility of shear-wave elastography in children with kidney disease and the correlation between elasticity and kidney fibrosis in order to reduce the indications for kidney biopsy and its complications.

MATERIALS AND METHODS

Four operators measured kidney elasticity in children with kidney diseases or transplants, all of whom also had a renal biopsy. We assessed the feasibility and the intraobserver variability of the elasticity measurements for each probe used and each kidney explored. Then we tested the correlation between elasticity measurements and the presence of fibrosis.

RESULTS

Overall, we analyzed 95 children and adolescents, 31 of whom had renal transplant. Measurements with the convex probe were possible in 100% of cases. Linear probe analysis was only possible for 20% of native kidneys and 50% of transplants. Intraobserver variabilities ranged from moderate to high, depending on the probe and kidney studied. Elasticity was higher with the linear probe than with the convex probe (P<0.001 for left kidney and P=0.03 for right kidney). Measurements did not differ from one kidney to another in the same child. Elasticity and fibrosis were both higher in transplant patients (P=0.02 with convex probe; P=0.01 with linear probe; P=0.04 overall). There was no correlation between elasticity and fibrosis.

CONCLUSION

Of the devices used in this work, kidney elastography was more accurately analyzed with a convex probe. Our study did not identify any correlation between elasticity and kidney fibrosis.

Intra-System Reliability Assessment of 2-Dimensional Shear Wave Elastography

The availability of 2-Dimensional Shear Wave Elastography (2D-SWE) technology on modern medical ultrasound systems is becoming increasingly common. The technology is now being used to investigate a range of soft tissues and related pathological conditions. This work investigated the reliability of a single commercial 2D-SWE system using a tissue-mimicking elastography phantom to understand the major causes of intra-system variability. Sources of shear wave velocity (SWV) measurement variability relates to imaging depth, target stiffness, sampling technique and the operator. Higher SWV measurement variability was evident with increasing depth and stiffness of the phantom targets. The influence of the operator was minimal, and variations in sampling technique had little impact on the SWV.

A review of physical and engineering factors potentially affecting shear wave elastography

It has been recognized that tissue stiffness provides useful diagnostic information, as with palpation as a screening for diseases such as cancer. In recent years, shear wave elastography (SWE), a technique for evaluating and imaging tissue elasticity quantitatively and objectively in diagnostic imaging, has been put into practical use, and the amount of clinical knowledge about SWE has increased. In addition, some guidelines and review papers regarding technology and clinical applications have been published, and the status as a diagnostic technology is in the process of being established. However, there are still unclear points about the interpretation of shear wave speed (SWS) and converted elastic modulus in SWE. To clarify these, it is important to investigate the factors that affect the SWS and elastic modulus. Therefore, physical and engineering factors that potentially affect the SWS and elastic modulus are discussed in this review paper, based on the principles of SWE and a literature review. The physical factors include the propagation properties of shear waves, mechanical properties (viscoelasticity, nonlinearity, and anisotropy), and size and shape of target tissues. The engineering factors include the region of interest depth and signal processing. The aim of this review paper is not to provide an answer to the interpretation of SWS. It is to provide information for readers to formulate and verify the hypothesis for the interpretation. Therefore, methods to verify the hypothesis for the interpretation are also reviewed. Finally, studies on the safety of SWE are discussed.

Determination of reference ranges for normal upper trapezius elasticity during different shoulder abduction using shear wave elastography: a preliminary study

The purpose of this study was to determine the reference ranges of normal upper trapezius (UT) elasticity during different shoulder abduction using shear wave elastography (SWE). Mean shear wave velocity (SWV) of UT elasticity in eighty healthy participants were measured at left and right shoulder 0° abduction and 90° passive abduction (L0°, R0°, L90°, R90°) with SWE. The effects of potential factors (gender, UT thickness, age, and body mass index) on UT elasticity were analyzed. The reference ranges of normal UT elasticity were calculated by using the normal distribution method. UT elasticity was significantly different among various shoulder abduction (P < 0.0001). UT elasticity was significantly higher in males at both L90° (P < 0.05) and R90° (P < 0.01) than in females. The reference ranges of normal UT elasticity were 2.90-4.01 m/s at L0° and 3.01-4.29 m/s at R0°, and were 4.90-6.40 m/s in males and 4.40-6.20 m/s in females at L90°, 5.20-7.02 m/s in males and 4.71-6.80 m/s in females at R90°. Our results suggest that gender should be considered when determining the reference ranges of normal UT elasticity at L90° and R90° with SWE. These values may provide quantitative baseline measurements for the assessment of UT muscle strain in the future.

Quantitative Imaging in Pediatric Hepatobiliary Disease

Pediatric hepatobiliary imaging is important for evaluation of not only congenital or structural disease but also metabolic or diffuse parenchymal disease and tumors. A variety of ultrasonography and magnetic resonance imaging (MRI) techniques can be used for these assessments. In ultrasonography, conventional ultrasound imaging as well as vascular imaging, elastography, and contrast-enhanced ultrasonography can be used, while in MRI, fat quantification, T2/T2^* mapping, diffusion-weighted imaging, magnetic resonance elastography, and dynamic contrast-enhanced MRI can be performed. These techniques may be helpful for evaluation of biliary atresia, hepatic fibrosis, nonalcoholic fatty liver disease, sinusoidal obstruction syndrome, and hepatic masses in children. In this review, we discuss each tool in the context of management of hepatobiliary disease in children, and cover various imaging techniques in the context of the relevant physics and their clinical applications for patient care.

Stiffness-matched biomaterial implants for cell delivery: clinical, intraoperative ultrasound elastography provides a 'target' stiffness for hydrogel synthesis in spinal cord injury

Safe hydrogel delivery requires stiffness-matching with host tissues to avoid iatrogenic damage and reduce inflammatory reactions. Hydrogel-encapsulated cell delivery is a promising combinatorial approach to spinal cord injury therapy, but a lack of in vivo clinical spinal cord injury stiffness measurements is a barrier to their use in clinics. We demonstrate that ultrasound elastography – a non-invasive, clinically established tool – can be used to measure spinal cord stiffness intraoperatively in canines with spontaneous spinal cord injury. In line with recent experimental reports, our data show that injured spinal cord has lower stiffness than uninjured cord. We show that the stiffness of hydrogels encapsulating a clinically relevant transplant population (olfactory ensheathing cells) can also be measured by ultrasound elastography, enabling synthesis of hydrogels with comparable stiffness to canine spinal cord injury. We therefore demonstrate proof-of-principle of a novel approach to stiffness-matching hydrogel-olfactory ensheathing cell implants to ‘real-life’ spinal cord injury values; an approach applicable to multiple biomaterial implants for regenerative therapies.

Reproducibility of shear wave elastography among operators, machines, and probes in an elasticity phantom

PURPOSE

This study was aimed to investigate the reproducibility of shear wave elastography (SWE) among operators, machines, and probes in a phantom, and to evaluate the effect of depth of the embedded inclusions and the accuracy of the measurements.

METHODS

In vitro stiffness measurements were made of six inclusions (10, 40, and 60 kPa) embedded at two depths (1.5 cm and 5 cm) in an elastography phantom. Measurements were obtained by two sonographers using two ultrasound machines (the SuperSonic Imagine Aixplorer with the XC6-1, SL10-2 and SL18-5 probes, and the General Electric LOGIQ E9 with the 9L-D probe). Variability was evaluated using the coefficient of variation. Reproducibility was calculated using intraclass correlation coefficients (ICCs).

RESULTS

For shallow inclusions, low variability was observed between operators (range, 0.9% to 5.4%). However, the variability increased significantly for deep inclusions (range, 2.4% to 80.8%). The measurement difference between the operators was 1%-15% for superficial inclusions and 3%-43% for deep inclusions. Inter-operator reproducibility was almost perfect (ICC>0.90). The measurement difference between machines was 0%-15% for superficial inclusions and 38.6%-82.9% for deep inclusions. For superficial inclusions, the reproducibility among the three probes was excellent (ICC>0.97). The mean stiffness values of the 10 kPa inclusion were overestimated by 16%, while those of the 40 kPa and 60 kPa inclusions were underestimated by 42% and 48%, respectively.

CONCLUSION

Phantom SWE measurements were only reproducible among operators, machines, and probes at superficial depths. SWE measurements acquired in deep regions should not be used interchangeably among operators, machines, or probes.

Normal values of shear wave velocity in liver tissue of healthy children measured using the latest acoustic radiation force impulse technology

BACKGROUND

Several studies have demonstrated the feasibility and effectiveness of using ultrasound elastography to assess liver tissue stiffness. Virtual touch imaging quantification (VTIQ) based on acoustic radiation force impulse imaging has been developed as a latest and noninvasive method for assessing liver stiffness in children.

AIM

To determine the standard value in healthy children, and to identify possible factors that might influence the VTIQ measurement.

METHODS

With the ethical approval, 202 children between 1 month and 15 years old were included in this study. None of them had any liver or systematic diseases. All children had a normal ultrasound scan and normal body mass index (BMI) range. The subjects were divided into four age and BMI groups. The effects of gender, age, liver lobe, measurement depth, and BMI on liver elasticity were investigated.

RESULTS

A significant correlation was found between age and shear wave velocity (SWV) value. At measurement depths of 1.5 cm and 2.0 cm in the left lobe, there were significant differences among the age groups. SWV values were significantly negatively correlated with the measurement depth. Gender, liver lobe, and BMI showed no significant effect on the SWV values. Age and BMI may influence the quality of the elastogram.

CONCLUSION

VTIQ is a noninvasive technique that is feasible to measure liver stiffness in children. The afore-mentioned velocity value obtained utilizing VTIQ method could be used as reference value for normal liver stiffness in children.

Evaluation of rat liver with ARFI elastography: In vivo and ex vivo study

OBJECTIVE

The aim of this study was to compare in vivo vs ex vivo liver stiffness in rats with acoustic radiation force impulse (ARFI) elastography using the histological findings as the gold standard.

METHODS

Eighteen male Wistar rats aged 16-18 months were divided into a control group (n = 6) and obese group (n = 12). Liver stiffness was measured with shear wave velocity (SWV) using the ARFI technique both in vivo and ex vivo. The degree of fibrosis, steatosis and liver inflammation was evaluated in the histological findings. Pearson's correlation coefficient was applied to relate the SWV values to the histological parameters.

RESULTS

The SWV values acquired in the ex vivo study were significantly lower than those obtained in vivo (P < 0.004). A significantly higher correlation value between the degree of liver fibrosis and the ARFI elastography assessment was observed in the ex vivo study (r = 0.706, P < 0.002), than the in vivo study (r = 0.623, P < 0.05).

CONCLUSION

Assessment of liver stiffness using ARFI elastography yielded a significant correlation between SWV and liver fibrosis in both the in vivo and ex vivo experiments. We consider that by minimising the influence of possible sources of artefact we could improve the accuracy of the measurements acquired with ARFI.

Correlation between acoustic radiation force impulse (ARFI)-based tissue elasticity measurements and perfusion parameters acquired by perfusion CT in cirrhotic livers: a proof of principle

PURPOSE

To investigate whether liver stiffness measured by acoustic radiation force impulse (ARFI) sonoelastography always correlates with the liver perfusion parameters quantified by perfusion CT in patients with known liver cirrhosis.

METHODS

Sonoelastography and perfusion CT were performed in 50 patients (mean age 65.5; range 45-87 years) with liver cirrhosis, who were classified according to Child-Pugh into class A (30/50, 60%), B (17/50, 34%), and C (3/50, 6%). For standardized ARFI measurements in the left liver lobe at a depth of 4 cm, a convex 6-MHz probe was used. CT examinations were performed using 80 kV, 100 mAs, and 50 ml of iodinated contrast agent injected at 5 ml/s. Using standardized region-of-interest measurements, we quantified arterial, portal venous, and total liver perfusion.

RESULTS

There was a significant linear correlation between tissue stiffness and arterial liver perfusion (p = 0.015), and also when limiting the analysis to patients with histology (p = 0.019). In addition, there was a positive correlation between the total blood supply (arterial + portal-venous liver perfusion) to the liver and tissue stiffness (p = 0.001; with histology, p = 0.027). Shear wave velocity increased with higher Child-Pugh stages (p = 0.013).

CONCLUSION

The degree of tissue stiffness in cirrhotic livers correlates expectedly-even if only moderately-with the magnitude of arterial liver perfusion and total liver perfusion. As such, liver elastography remains the leading imaging tool in assessing liver fibrosis.

Reference Values for Shear Wave Elastography of Neck and Shoulder Muscles in Healthy Individuals

Purpose

to establish reference values for ultrasound shear-wave elastography for pericranial muscles in healthy individuals (m. trapezius, m. splenius capitis, m. semispinalis capitis, m. sternocleidomastoideus and m. masseter). Also to evaluate day-to-day variations in the shear-wave speeds and evaluate the effect of the pennation of the muscle fibers, ie scanning parallel or perpendicularly to the fibers.

Materials and Methods

10 healthy individuals (5 males and 5 females) had their pericranial muscles examined with shear-wave elastography in two orthogonal planes on two different days for their dominant and non-dominant side. Mean shear wave speeds from 5 ROI’s in each muscle, for each scan plane for the dominant and non-dominant side for the two days were calculated. The effect of the different parameters – muscle pennation, gender, dominant vs non-dominant side and day was evaluated.

Results

The effect of scan plane in relation to muscle pennation was statistically significant (p<0.0001). The mean shear-wave speed when scanning parallel to the muscle fibers was significantly higher than the mean shear-wave speed when scanning perpendicularly to the fibers. The day-to-day variation was statistically significant (p=0.0258), but not clinically relevant. Shear-wave speeds differed significantly between muscles. Mean shear wave speeds (m/s) for the muscles in the parallel plane were: for masseter 2.45 (SD:+/−0.25), semispinal 3.36 (SD:+/−0.75), splenius 3.04 (SD:+/−0.65), sternocleidomastoid 2.75 (SD:+/−0.23), trapezius 3.20 (SD:+/−0.27) and trapezius lateral 3.87 (SD:+/−3.87).

Conclusion

The shear wave speed variation depended on the direction of scanning. Shear wave elastography may be a method to evaluate muscle stiffness in patients suffering from chronic neck pain.

Influencing Factors of 2D Shear Wave Elastography of the Muscle - An Ex Vivo Animal Study

OBJECTIVE

To evaluate measurement confounders on 2D shear wave elastography (2D-SWE) elastography of muscle.

MATERIALS AND METHODS

Ex vivo , porcine muscle was examined with a GE LOGIQ E9 ultrasound machine with a 9 L linear (9 MHz) and C1-6 convex probe (operating at 2.5 or 6 MHz). The influence of different confounders on mean shear wave velocity (SWVmean) was analyzed: probes, pressure applied by probe, muscle orientation, together with the impact of different machine settings such as frequency, placement depth and size of region of interest (ROI). The mean of twelve repeated SWVmean measurements (m/s) and coefficient of variation (CV; standard deviation/mean in %) were assessed for each test configuration.

RESULTS

Reproducibility (CV) and maximum possible tissue depth of the linear probe were inferior to the convex probe. With the linear probe, there was a linear decrease of SWVmean with placement depth from 4.56 m/s to 1.81 m/s. A significant increase of SWVmean (p<0.001) was observed for larger ROI widths (range 3.96 m/s to 6.8 m/s). A change in the machine operation mode ('penetration' instead of 'general') led to a significant increase of SWVmean (p=0.04). SWVmean in the longitudinal direction of muscle was significantly higher than in cross section (p<0.001) (e. g. 4.56 m/s versus 3.42 m/s). An increase of linear probe pressure significantly increased muscle SWVmean from 5.29 m/s to 7.21 m/s (p<0.001).

CONCLUSIONS

2D-SWE of muscle is influenced by a wealth of parameters. Therefore, standardization of measurement is advisable before application in clinical research studies and routine patient assessment.

Clinical value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension

AIM

To explore the relationship of liver and spleen shear wave velocity in patients with liver cirrhosis combined with portal hypertension, and assess the value of liver and spleen shear wave velocity in predicting the prognosis of patients with portal hypertension.

METHODS

All 67 patients with liver cirrhosis diagnosed as portal hypertension by hepatic venous pressure gradient in our hospital from June 2014 to December 2014 were enrolled into this study. The baseline information of these patients was recorded. Furthermore, 67 patients were followed-up at 20 mo after treatment, and liver and spleen shear wave velocity were measured by acoustic radiation force impulse at the 1^st week, 3^rd month and 9^th month after treatment. Patients with favorable prognosis were assigned into the favorable prognosis group, while patients with unfavorable prognosis were assigned into the unfavorable prognosis group. The variation and difference in liver and spleen shear wave velocity in these two groups were analyzed by repeated measurement analysis of variance. Meanwhile, in order to evaluate the effect of liver and spleen shear wave velocity on the prognosis of patients with portal hypertension, Cox’s proportional hazard regression model analysis was applied. The ability of those factors in predicting the prognosis of patients with portal hypertension was calculated through receiver operating characteristic (ROC) curves.

RESULTS

The liver and spleen shear wave velocity in the favorable prognosis group revealed a clear decline, while those in the unfavorable prognosis group revealed an increasing tendency at different time points. Furthermore, liver and spleen shear wave velocity was higher in the unfavorable prognosis group, compared with the favorable prognosis group; the differences were statistically significant (P < 0.05). The prognosis of patients with portal hypertension was significantly affected by spleen hardness at the 3^rd month after treatment [relative risk (RR) = 3.481]. At the 9^th month after treatment, the prognosis was affected by liver hardness (RR = 5.241) and spleen hardness (RR = 7.829). The differences between these two groups were statistically significant (P < 0.05). The ROC analysis revealed that the area under the curve (AUC) of spleen hardness at the 3^rd month after treatment was 0.644, while the AUCs of liver and spleen hardness at the 9^th month were 0.579 and 0.776, respectively. These might predict the prognosis of patients with portal hypertension.

CONCLUSION

Spleen hardness at the 3^rd month and liver and spleen shear wave velocity at the 9^th month may be used to assess the prognosis of patients with portal hypertension. This is hoped to be used as an indicator of predicting the prognosis of patients with portal hypertension.

Diagnostic Performance of MR Elastography and Vibration-controlled Transient Elastography in the Detection of Hepatic Fibrosis in Patients with Severe to Morbid Obesity

Purpose To evaluate the diagnostic performance and examination success rate of magnetic resonance (MR) elastography and vibration-controlled transient elastography (VCTE) in the detection of hepatic fibrosis in patients with severe to morbid obesity. Materials and Methods This prospective and HIPAA-compliant study was approved by the institutional review board. A total of 111 patients (71 women, 40 men) participated. Written informed consent was obtained from all patients. Patients underwent MR elastography with two readers and VCTE with three observers to acquire liver stiffness measurements for liver fibrosis assessment. The results were compared with those from liver biopsy. Each pathology specimen was evaluated by two hepatopathologists according to the METAVIR scoring system or Brunt classification when appropriate. All imaging observers were blinded to the biopsy results, and all hepatopathologists were blinded to the imaging results. Examination success rate, interobserver agreement, and diagnostic accuracy for fibrosis detection were assessed. Results In this obese patient population (mean body mass index = 40.3 kg/m²; 95% confidence interval [CI]: 38.7 kg/m², 41.8 kg/m²]), the examination success rate was 95.8% (92 of 96 patients) for MR elastography and 81.3% (78 of 96 patients) or 88.5% (85 of 96 patients) for VCTE. Interobserver agreement was higher with MR elastography than with biopsy (intraclass correlation coefficient, 0.95 vs 0.89). In patients with successful MR elastography and VCTE examinations (excluding unreliable VCTE examinations), both MR elastography and VCTE had excellent diagnostic accuracy in the detection of clinically significant hepatic fibrosis (stage F2-F4) (mean area under the curve: 0.93 [95% CI: 0.85, 0.97] vs 0.91 [95% CI: 0.83, 0.96]; P = .551). Conclusion In this obese patient population, both MR elastography and VCTE had excellent diagnostic performance for assessing hepatic fibrosis; MR elastography was more technically reliable than VCTE and had a higher interobserver agreement than liver biopsy. ^© RSNA, 2016 Online supplemental material is available for this article. An earlier incorrect version of this article appeared online. This article was corrected on January 25, 2017.

ARFI: from basic principles to clinical applications in diffuse chronic disease-a review

Abstract

The many factors influencing the shear wave velocity (SWV) measured with Acoustic Radiation Force Impulse (ARFI) are examined in order to define the most correct examination technique. In particular, attention is given to the information achieved by experimental models, such as phantoms and animal studies. This review targets the clinical applications of ARFI in the evaluation of chronic diffuse disease, especially of liver and kidneys. The contribution of ARFI to the clinical workout of these patients and some possible perspectives are described.

Teaching Points

• Stiffness significantly varies among normal and abnormal biological tissues.

• In clinical applications physical, geometrical, anatomical and physiological factors influence the SWV.

• Elastographic techniques can quantify fibrosis, which is directly related to stiffness.

• ARFI can be useful in chronic diffuse disease of liver and kidney.

Comparison of shear wave velocities on ultrasound elastography between different machines, transducers, and acquisition depths: a phantom study

OBJECTIVES

To investigate consistency in shear wave velocities (SWVs) on ultrasound elastography using different machines, transducers and acquisition depths.

METHODS

The SWVs were measured using an elasticity phantom with a Young's modulus of 16.9 kPa, with three recently introduced ultrasound elastography machines (A, B and C from different vendors) and two transducers (low and high frequencies) at four depths (2, 3, 4 and 5 cm). Mean SWVs from 15 measurements and coefficient of variations (CVs) were compared between three machines, two transducers and four acquisition depths.

RESULTS

The SWVs using the high frequency transducer were not acquired at 5 cm depth in machine B, and a high frequency transducer was not available in machine C. The mean SWVs in the three machines were different (p ≤ 0.002). The CVs were 0-0.09 in three machines. The mean SWVs between the two transducers were different (p < 0.001) except at 4 and 5 cm depths in machine A. The SWVs were affected by the acquisition depths in all conditions (p < 0.001).

CONCLUSION

There is considerable difference in SWVs on ultrasound elastography depending on different machines, transducers and acquisition depths. Caution is needed when using the cutoff values of SWVs in different conditions.

KEY POINTS

• The shear wave velocities (SWVs) are different between different ultrasound elastography machines • The SWVs are also different between different transducers and acquisition depths • Caution is needed when using the cutoff SWVs measured under different conditions.

Clinical perspective on renal elasticity quantification by acoustic radiation force impulse: Where we are and where we are going

Recent interests have focused on the exploration of the mechanical properties (elasticity, stiffness and deformity) of parenchymatous organs using tissue strain imaging techniques and elastosonography. Measures of the mechanical properties of the kidneys have given conflicting results. There are various conditions that affect the variability of renal parenchymal measures, the main target of the investigations. They can be classified as intrinsic (depending upon the patient), extrinsic (depending upon the operator) and mixed (both intrinsic and extrinsic). Indeed, the mechanical properties of the kidney depend on various conditions that alter its histology, mainly the amount of fibrosis in the renal parenchymal interstitium. Anatomical factors play an important role because the kidney is a highly anisotropic organ with important differences when considering the cortex and the medulla. Physical factors include the frequency of the probe, compression and distance from source to target. Many factors can affect measurements and it is necessary to find an accurate technique in order to avoid mistakes and to obtain reproducible data. Indeed, it is imperative to define a standardized examination technique in order to get comparable results. Therefore, the utility of acoustic radiation force imaging technique to predict only renal fibrosis or progression of chronic kidney disease is of dubious value because several variables - blood perfusion and urinary pressure - can contribute to a given measure, even with a standardized method able to minimize intra- and inter-operator variability.

Shear wave elastography in chronic kidney disease: a pilot experience in native kidneys

Background

There currently is a need for a non-invasive measure of renal fibrosis. We aim to explore whether shear wave elastography (SWE)-derived estimates of tissue stiffness may serve as a non-invasive biomarker that can distinguish normal and abnormal renal parenchymal tissue.

Methods

Participants with CKD (by estimated GFR) and healthy volunteers underwent SWE. Renal elasticity was estimated as Young’s modulus (YM) in kilopascals (kPa). Univariate Wilcoxon rank-sum tests were used.

Results

Twenty-five participants with CKD (median GFR 38 mL/min; quartile 1, quartile 3 28, 42) and 20 healthy controls without CKD underwent SWE performed by a single radiologist. CKD was associated with increased median YM (9.40 [5.55, 22.35] vs. 4.40 [3.68, 5.70] kPa; p = 0.002) and higher median intra-subject inter-measurement estimated YM’s variability (4.27 [2.89, 9.90] vs. 1.51 [1.21, 2.05] kPa; p < 0.001).

Conclusions

SWE-derived estimates of renal stiffness and intra-subject estimated stiffness variability are higher in patients with CKD than in healthy controls. Renal fibrosis is a plausible explanation for the observed difference in YM. Further studies are required to determine the relationship between YM, estimated renal stiffness, and renal fibrosis severity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-015-0120-7) contains supplementary material, which is available to authorized users.

Contrast-enhanced ultrasonography for the evaluation of liver fibrosis after biliary obstruction

AIM: To investigate perfusion change in contrast-enhanced ultrasonography (CEUS) to evaluate liver fibrosis based on biliary obstruction using an animal model.

METHODS: New Zealand white rabbits (3-4 kg) underwent bile duct ligation to form a biliary obstruction model. We performed liver CEUS and laboratory tests on the day before the operation (day 0) and every 7 postoperative days until the rabbits were sacrificed. After CEUS, signal intensity of liver parenchyma with a time-intensity curve was analyzed. Perfusion parameters were automatically calculated from region-of-interests, including peak signal intensity, mean transit time, area under the curve and time to peak. Histological grades of liver fibrosis were assessed according to the Metavir score system immediately after sacrifice. Generalized estimating equations were used to analyze the association between liver fibrosis grades and perfusion parameters for statistical analysis. The perfusion parameters were measured on the last day and the difference between day 0 and the last day were evaluated.

RESULTS: From the nine rabbits, histological grades of liver fibrosis were grade 1 in one rabbit, grade 2 and 3 in three rabbits each, and grade 4 in two rabbits. Among the four CEUS parameters, only the peak signal intensity measured on the last day demonstrated a significant association with liver fibrosis grades (OR = 1.392, 95%CI: 1.114-1.741, P = 0.004). The difference in peak signal intensity between day 0 and the last day also demonstrated an association with liver fibrosis (OR = 1.191, 95%CI: 0.999-1.419, P = 0.051). The other parameters tested, including mean transit time, area under the curve, and time to peak, showed no significant correlation with liver fibrosis grades.

CONCLUSION: This animal study demonstrates that CEUS can be used to evaluate liver fibrosis from biliary obstruction using peak signal intensity as a parameter.

Effect of depth on shear-wave elastography estimated in the internal and external cervical os during pregnancy

AIM

To investigate the effect of depth on cervical shear-wave elastography.

METHODS

Shear-wave elastography was applied to estimate the velocity of propagation of the acoustic force impulse (shear wave) in the cervix of 154 pregnant women at 11-36 weeks of gestation. Shear-wave speed (SWS) was evaluated in cross-sectional views of the internal and external cervical os in five regions of interest: anterior, posterior, lateral right, lateral left, and endocervix. Distance from the center of the ultrasound (US) transducer to the center of each region of interest was registered.

RESULTS

In all regions, SWS decreased significantly with gestational age (P=0.006). In the internal os, SWS was similar among the anterior, posterior, and lateral regions and lower in the endocervix. In the external os, the endocervix and anterior regions showed similar SWS values, lower than those from the posterior and lateral regions. In the endocervix, these differences remained significant after adjustment for depth, gestational age, and cervical length. SWS estimations in all regions of the internal os were higher than those of the external os, suggesting denser tissue.

CONCLUSION

Depth from the US probe to different regions in the cervix did not significantly affect the SWS estimations.

Noninvasive diagnosis of cirrhosis: A review of different imaging modalities

Progressive hepatic fibrosis can lead to cirrhosis, so its early detection is fundamental. Staging fibrosis is also critical for prognosis and management. The gold standard for these aims is liver biopsy, but it has several drawbacks, as it is invasive, expensive, has poor acceptance, is prone to inter observer variability and sampling errors, has poor repeatability, and has a risk of complications and mortality. Therefore, non-invasive imaging tests have been developed. This review mainly focuses on the role of transient elastography, acoustic radiation force impulse imaging, and magnetic resonance-based methods for the noninvasive diagnosis of cirrhosis.

Accuracy of visual scoring and semi-quantification of ultrasound strain elastography--a phantom study

Purpose

The aim of this study was to evaluate the performance of strain elastography in an elasticity phantom and to assess which factors influenced visual scoring, strain histograms and strain ratios. Furthermore this study aimed to evaluate the effect of observer experience on visual scorings.

Materials and Methods

Two operators examined 20 targets of various stiffness and size (16.7 to 2.5 mm) in an elasticity phantom at a depth of 3.5 cm with a 5–18 MHz transducer. Two pre-settings were used yielding 80 scans. Eight evaluators, four experienced, four inexperienced, performed visual scorings. Cut-offs for semi-quantitative methods were established for prediction of target stiffness. Data was pooled in two categories allowing calculations of sensitivity and specificity. Statistical tests chi-square test and linear regression as relevant.

Results

Strain ratios and strain histograms were superior to visual scorings of both experienced and inexperienced observers (p = 0.025, strain histograms vs. experienced observers, p<0.001, strain histograms vs. inexperienced observers, p = 0.044 strain ratios vs. experienced observers and p = 0.002 strain ratios vs. inexperienced observers). No significant difference in predicting target stiffness between strain ratios and strain histograms (p = 0.83) nor between experienced and inexperienced observers (p = 0.054) was shown when using four categories. When pooling data in two groups (80 kPa/45 kPa vs. 14/8 kPa) the difference between the observers became significant (p<0.001). Target size had a significant influence on strain ratios measurements (p = 0.017) and on visual scorings (p<0.001) but not on the strain histograms(p = 0.358). Observer experience had significant effect on visual scorings(p = 0.003).

Conclusion

Strain ratios and strain histograms are superior to visual scoring in assessing target stiffness in a phantom. Target size had a significant impact on strain ratios and visual scoring, but not on strain histograms. Experience influenced visual scorings but the difference between experienced and inexperienced observers was only significant when looking at two classes of target stiffness.