Ultrasound Shear Wave Elastography, Shear Wave Dispersion and Attenuation Imaging of Pediatric Liver Disease with Histological Correlation

The Effect of Steatosis on Shear-Wave Velocity and Viscoelastic Properties Related to Liver Fibrosis Progression in Rat Models

OBJECTIVE

Hepatic fibrosis has recently been evaluated using ultrasonography or magnetic resonance elastography. Although the shear wave velocity (SWV) obtained using point shear wave elastography (pSWE) provides a valuable measure of fibrosis, underlying steatosis may affect its measurement.

METHODS

Using hepatic fibrosis samples, this study evaluated the effect of steatosis on the shear wave velocity of pSWE (Vs) and viscoelastic properties (assessed by dynamic mechanical analysis) of rat liver. Fifty rats with various grades of steatosis and fibrosis underwent open abdominal in vivo Vs measurements using a commercial ultrasound scanner. The mechanical properties of hepatic tissue were also characterized under ex vivo conditions using dynamic mechanical analysis and the Zener model of viscoelasticity.

RESULTS

Fibrosis and steatosis progression influenced Vs and elasticity. The SWV computed using the Zener model and Vs showed a substantial correlation (r > 0.8). Fibrosis progression increased SWV. Steatosis was also related to SWV. Steatosis progression obscured the SWV change associated with fibrosis progression.

CONCLUSION

We conclude that steatosis progression affects the evaluation of fibrosis progression. This finding could aid discrimination of non-alcoholic steatohepatitis from non-alcoholic fatty liver disease using SWV.

Resonance, Velocity, Dispersion, and Attenuation of Ultrasound-Induced Shear Wave Propagation in Blood Clot In Vitro Models

OBJECTIVE

Improve the characterization of mechanical properties of blood clots. Parameters derived from shear wave (SW) velocity and SW amplitude spectra were determined for gel phantoms and in vitro blood clots.

METHODS

Homogeneous phantoms and phantoms with gel or blood clot inclusions of different diameters and mechanical properties were analyzed. SW amplitude spectra were used to observe resonant peaks. Parameters derived from those resonant peaks were related to mimicked blood clot properties. Three regions of interest were tested to analyze where resonances occurred the most. For blood experiments, 20 samples from different pigs were analyzed over time during a 110-minute coagulation period using the Young modulus, SW frequency dispersion, and SW attenuation.

RESULTS

The mechanical resonance was manifested by an increase in the number of SW spectral peaks as the inclusion diameter was reduced (P < .001). In blood clot inclusions, the Young modulus increased over time during coagulation (P < .001). Descriptive spectral parameters (frequency peak, bandwidth, and distance between resonant peaks) were linearly correlated with clot elasticity values (P < .001) with R2  = .77 for the frequency peak, .60 for the bandwidth, and .48 for the distance between peaks. The SW dispersion and SW attenuation reflecting the viscous behavior of blood clots decreased over time (P < .001), mainly in the early stage of coagulation (first minutes).

CONCLUSION

The confined soft inclusion configuration favored SW mechanical resonances potentially challenging the computation of spectral-based parameters, such as the SW attenuation. The impact of resonances can be reduced by properly selecting the region of interest for data analysis.

Shear wave elastography and shear wave dispersion correlated to biopsy at the scheduled follow-up of pediatric liver grafts

BACKGROUND

It is unknown how shear wave dispersion (SWD) is displayed in pediatric liver transplant recipients and not fully elucidated how ultrasound shear wave elastography (2D-SWE) display within this cohort, which is important to determine to improve noninvasive surveillance of these patients. The study aimed to compare SWE and SWD values with histopathology in pediatric liver recipients.

METHODS

Forty-eight pediatric liver recipients were examined with SWE in conjunction with an elective liver biopsy (clinically without complication). Additionally, SWD values were measured in 21 children. SWE and SWD values were compared to histologically determined fibrosis graded as none-to-mild (F0-1) and moderate-to-severe (F2-4), and inflammation graded as low (grade 0-1) and high (grade 2-4).

RESULTS

Two children were excluded due to SWE IQR/median > 30% kPa. The mean age across 46 included patients was 10.9 years (range 1.4-18). The number of patients and median (range) SWE value (kPa) for each stage of fibrosis were: F0-1 [n = 23; 5.8 (3.2-16.1)], F2 [n = 22; 6.0 (4.5-25.9)], F3 [n = 1; 33.3], and F4 [n = 0]. Significantly higher SWE values and greater variability were registered in F2-4 vs. F0-1 (p = .05). Grade of fibrosis correlated weakly to SWE values (r = .3; p = .05), but not to SWD values (r = .2; p = .27). In patients with low-grade inflammation, median SWD was 13.7 m/s KHz (10.7-17.6). Only one patient had high-grade inflammation.

CONCLUSIONS

Uncomplicated transplanted liver grafts in a small pediatric cohort revealed slightly increased SWE and SWD values compared to previously reported values in healthy children. This likely reflect both the fibrotic and inflammatory elements in the grafts; however, other confounders impacting the liver's viscoelastic properties are also probable factors.

Shear Wave Dispersion in Chronic Liver Disease: From Physical Principles to Clinical Usefulness

The development of new applications in ultrasound (US) imaging in recent years has strengthened the role of this imaging technique in the management of different pathologies, particularly in the setting of liver disease. Improved B-mode imaging (3D and 4D), contrast-enhanced US (CEUS) and especially US-based elastography techniques have created the concept of multiparametric ultrasound (MP-US), a term borrowed from radiological sectional imaging. Among the new elastography techniques, shear wave dispersion is a newly developed imaging technology which enables the assessment of the shear waves' dispersion slope. The analysis of the dispersion qualities of shear waves might be indirectly related to the tissue viscosity, thus providing biomechanical information concerning the pathologic state of the liver such as necroinflammation. Some of the most recent US devices have been embedded with software that evaluate the dispersion of shear waves/liver viscosity. In this review, the feasibility and the clinical applications of liver viscosity are reviewed based on the preliminary findings of both animal and human studies.

Fontan-associated liver disease: Diagnosis, surveillance, and management

The Fontan operation is a lifesaving procedure for patients with functional single-ventricle congenital heart disease, where hypoplastic left heart syndrome is the most frequent anomaly. Hemodynamic changes following Fontan circulation creation are now increasingly recognized to cause multiorgan affection, where the development of a chronic liver disease, Fontan-associated liver disease (FALD), is one of the most important morbidities. Virtually, all patients with a Fontan circulation develop liver congestion, resulting in fibrosis and cirrhosis, and most patients experience childhood onset. FALD is a distinctive type of congestive hepatopathy, and its pathogenesis is thought to be a multifactorial process driven by increased nonpulsatile central venous pressure and decreased cardiac output, both of which are inherent in the Fontan circulation. In the advanced stage of liver injury, complications of portal hypertension often occur, and there is a risk of developing secondary liver cancer, reported at young age. However, FALD develops with few clinical symptoms, a surprisingly variable degree of severity in liver disease, and with little relation to poor cardiac function. The disease mechanisms and modifying factors of its development are still not fully understood. As one of the more important noncardiac complications of the Fontan circulation, FALD needs to be diagnosed in a timely manner with a structured monitoring scheme of disease development, early detection of malignancy, and determination of the optimal time point for transplantation. There is also a clear need for consensus on the best surveillance strategy for FALD. In this regard, imaging plays an important role together with clinical scoring systems, biochemical workups, and histology. Patients operated on with a Fontan circulation are generally followed up in cardiology units. Ultimately, the resulting multiorgan affection requires a multidisciplinary team of healthcare personnel to address the different organ complications. This article discusses the current concepts, diagnosis, and management of FALD, with special emphasis on the role of different imaging techniques in the diagnosis and monitoring of disease progression, as well as current recommendations for liver disease surveillance.

Factors other than fibrosis that increase measured shear wave velocity

Shear wave elastography (SWE) is now becoming an indispensable diagnostic tool in the routine examination of liver diseases. In particular, accuracy is required for shear wave propagation velocity measurement, which is directly related to diagnostic accuracy. It is generally accepted that the liver shear wave propagation velocity reflects the degree of fibrosis, but there are still few reports on other factors that increase the shear wave propagation velocity. In this study, we reviewed such factors in the literature and examined their mechanisms. Current SWE measures propagation velocity based on the assumption that the medium has a homogeneous structure, uniform density, and is purely elastic. Otherwise, the measurement is subject to error. The other (confounding) factors that we routinely experience are primarily: (1) Conditions that appear to increase the viscous component; and (2) Conditions that appear to increase tissue density. Clinically, the former includes acute hepatitis, congested liver, biliary obstruction, etc, and the latter includes diffuse infiltration of malignant cells, various storage diseases, tissue necrosis, etc. In any case, it is important to evaluate SWE in the context of the entire clinical picture.