Shear Wave Elastography: A Review on the Confounding Factors and Their Potential Mitigation in Detecting Chronic Kidney Disease

The application of shear wave quantitative ultrasound elastography in chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a major public health problem, so it is particularly important to quantitatively assess and intervene in the degree of early renal damage in CKD.

OBJECTIVE

The objective of the research is to establish reference values for kidney elasticity by using real-time shear wave elastography (RT-SWE) technology to quantify Young's modulus values in the renal cortex of normal adults. The intention is to provide a foundation for evaluating renal function and structural changes in patients with CKD. Furthermore, this research investigates the role of RT-SWE in the early detection of renal fibrosis in CKD, providing insights into its diagnostic value for detecting pathological changes at an early stage.

METHODS

Between August 2019 and December 2021, we collected a sample of 100 healthy people (55 men with an average age of 43.5 ± 15.2 years and 45 women with an average age of 41.6 ± 19.8 years) for medical evaluations at our hospital's Department of Ultrasound Medicine. In addition, 97 individuals with CKD1-3 stage were considered. Following the removal of contraindications and relevant confounding variables, we included a final cohort of 80 individuals in the research (45 men and 35 females, with an average age of 39.1 ± 19.2 years). The RENAL mode was selected and a convex array probe S6-1 operating at a frequency of 3.5-5.5 MHz was used in the research, which made use of the French Supersonic AixPlorer ultrasonic diagnostic instrument. Renal RT-SWE elastography was performed after conventional two-dimensional and color Doppler ultrasonography. The study used RT-SWE technology to assess the mean Young's modulus of the cortex in healthy individuals (Emean), with data analysis and comparisons based on age and gender. Furthermore, the Emean values of CKD stage 1-3 patients were determined, and analyses were performed about 24-hour urine protein quantitative (24hUTP), serum creatinine concentration (SCr), and renal biopsy pathology, specifically the degree of interstitial fibrosis.

RESULTS

Healthy group: a) The average kPa values of the left kidney (4.2 ± 2.3), right kidney (4.3 + 2.5) kPa, both kidneys' average kPa values (4.3 ± 2.4) kPa, and the average kPa values of the left and right kidneys do not differ statistically (p= 0.986). b) There was no difference in the kPa values of healthy male and female kidneys (4.4 + 2.1 and 4.2 + 2.6, respectively. c) There was no difference in the renal kPa values of healthy adults aged 50 (4.4 ± 2.8) kPa and renal kPa of the 50-year-old population (4.2 + 2.1) kPa (p= 0.041). Case group: a) the group of patients with CKD1-3 stage and the group did not vary in their Emean values (both p< 0.05); b) There is a difference between CKD stages 1, 2, and 3 (p< 0.05), however, there is still no difference in the pyEmean value corrected for patient age between patients in stages 1 and 2 (p> 0.05).

CONCLUSION

The study reveals no significant differences in the Emean value of bilateral kidneys in normal people and no differences in the elasticity value of kidneys and gender. However, age-based differences were statistically significant. pyEmean may be useful for comparing CKD stage 1, 2, and 3 patients, and RT-SWE can assess early renal damage.

Effect of proteinuria at relapse on shear wave velocity assessed using ultrasound elastography in children with idiopathic nephrotic syndrome

PURPOSE

Shear wave velocity (SWV) is an ultrasound elastography technique that provides much information for kidney disease assessment. However, the factors that alter SWV are not fully understood; it is unclear whether the variation in SWV seen in proteinuria associated with disease progression is due to tissue or proteinuria. This study investigated the effect of proteinuria on SWV.

METHODS

This prospective observational study compared SWV at remission with SWV at relapse in children treated for idiopathic nephrotic syndrome (INS) between April 2020 and December 2023. All relapses without oral steroids during the observation period were measured. SWV at remission was defined as the date closest to relapse during which repeated measurements were taken approximately every 3 months after steroid discontinuation.

RESULTS

Eight patients were treated for INS with a median observation period of 21.9 months (11.8-27.1). Of the 15 relapses, five that met the definition were considered for the study. The median interval between the measurement at relapse and remission was 40 days (11-55). SWV was significantly lower at relapse than remission (2.40 ± 0.20 m/s vs. 2.14 ± 0.15 m/s, P < 0.01).

CONCLUSIONS

SWV decreased in the presence of severe proteinuria at relapse compared to the remission measurements. Although more cases need to be studied, the decrease in SWV may reflect the mechanism by which protein leaks into the urine, not just a direct change caused by the presence of proteinuria.

Fibrosis in Chronic Kidney Disease: Pathophysiology and Therapeutic Targets

Chronic kidney disease (CKD) is a slowly progressive condition characterized by decreased kidney function, tubular injury, oxidative stress, and inflammation. CKD is a leading global health burden that is asymptomatic in early stages but can ultimately cause kidney failure. Its etiology is complex and involves dysregulated signaling pathways that lead to fibrosis. Transforming growth factor (TGF)-β is a central mediator in promoting transdifferentiation of polarized renal tubular epithelial cells into mesenchymal cells, resulting in irreversible kidney injury. While current therapies are limited, the search for more effective diagnostic and treatment modalities is intensive. Although biopsy with histology is the most accurate method of diagnosis and staging, imaging techniques such as diffusion-weighted magnetic resonance imaging and shear wave elastography ultrasound are less invasive ways to stage fibrosis. Current therapies such as renin-angiotensin blockers, mineralocorticoid receptor antagonists, and sodium/glucose cotransporter 2 inhibitors aim to delay progression. Newer antifibrotic agents that suppress the downstream inflammatory mediators involved in the fibrotic process are in clinical trials, and potential therapeutic targets that interfere with TGF-β signaling are being explored. Small interfering RNAs and stem cell-based therapeutics are also being evaluated. Further research and clinical studies are necessary in order to avoid dialysis and kidney transplantation.

Quantitative Optical Coherence Elastography of the Optic Nerve Head In Vivo

OBJECTIVE

Optical coherence elastography (OCE) was used to demonstrate the relationship between the elasticity of the optic nerve head (ONH) and different intraocular pressure (IOP) levels in an in-vivo rabbit model for the first time.

METHOD

Both ex-vivo and in-vivo rabbit ONH were imaged using OCE system. A mechanical shaker initiated the propagation of elastic waves, and the elasticity of the ONH was determined by tracking the wave propagation speed. The elasticity of the ONH under varying IOP levels was reconstructed based on the wave speed. Notably, the ONH exhibited increased stiffness with elevated IOP.

RESULTS

In the in-vivo rabbit models, the Young's modulus of ONH increased from 14 kPa to 81 kPa with the IOP increased from 15 mmHg to 35 mmHg. This revealed a positive correlation between the Young's modulus of the ONH and intraocular pressure.

CONCLUSION

The OCE system proved effective in measuring the mechanical properties of ONH at different IOP levels, with validation in an in-vivo rabbit model.

SIGNIFICANCE

Considering ONH plays a critical role in vision and eye diseases, the capability to image and quantify in vivo ONH biomechanical properties has great potential to advance vision science research and improve the clinical management of glaucoma patients.

Shear wave elastography in chronic kidney disease - the physics and clinical application

Chronic kidney disease is a leading public health problem worldwide. The global prevalence of chronic kidney disease is nearly five hundred million people, with almost one million deaths worldwide. Estimated glomerular filtration rate, imaging such as conventional ultrasound, and histopathological findings are necessary as each technique provides specific information which, when taken together, may help to detect and arrest the development of chronic kidney disease, besides managing its adverse outcomes. However, estimated glomerular filtration rate measurements are hampered by substantial error margins while conventional ultrasound involves subjective assessment. Although histopathological assessment is the best tool for evaluating the severity of the renal pathology, it may lead to renal insufficiency and haemorrhage if complications occurred. Ultrasound shear wave elastography, an emerging imaging that quantifies tissue stiffness non-invasively has gained interest recently. This method applies acoustic force pulses to generate shear wave within the tissue that propagate perpendicular to the main ultrasound beam. By measuring the speed of shear wave propagation, the tissue stiffness is estimated. This paper reviews the literature and presents our combined experience and knowledge in renal shear wave elastography research. It discusses and highlights the confounding factors on shear wave elastography, current and future possibilities in ultrasound renal imaging and is not limited to new sophisticated techniques.

Association of renal elasticity evaluated by real-time shear wave elastography with renal fibrosis in patients with chronic kidney disease

OBJECTIVE

Renal fibrosis is a final common pathological hallmark in the progression of chronic kidney disease (CKD). Non-invasive evaluation of renal fibrosis by mapping renal stiffness obtained by shear wave elastography (SWE) may facilitate the clinical therapeutic regimen for CKD patients.

METHODS

A cohort of 162 patients diagnosed with CKD, who underwent renal biopsy, was prospectively and consecutively recruited between April 2019 and December 2021. The assessment of renal cortex stiffness was performed using SWE imaging. The patients were classified into different groups based on pathological renal fibrosis (mild group: n = 74; moderate-to-severe group: n = 88). Binary logistic regression model and generalized additive model were conducted to investigate the association of renal elasticity with renal fibrosis.

RESULTS

Compared with the mildly impaired group, the moderate-to-severe group showed a significant decline in renal elasticity (P < .001). In the fully adjusted model, each 10 kPa drop in renal elasticity was associated with a 3.5-fold increment in the risk of moderate-to-severe renal fibrosis (fully adjusted odds ratio, 4.54; 95% CI, 2.41-8.57). Particularly, participants in the lowest elasticity group (≤29.92 kPa) had a 20-fold increased chance of moderate-to-severe renal fibrosis than those in the group with highest elasticity (≥37.93 kPa). An inverse linear association was observed between renal elasticity increment and moderate-to-severe renal fibrosis risk.

CONCLUSION

There is a negative linear association between increased renal elasticity and moderate-to-severe renal fibrosis risk among CKD patients. Patients with diminished renal stiffness have a higher risk of moderate-to-severe renal fibrosis.

ADVANCES IN KNOWLEDGE

CKD patients with reduced renal stiffness have a higher likelihood of moderate-to-severe renal fibrosis.

Imaging fibrosis in pediatric kidney transplantation: A pilot study

BACKGROUND

Noninvasive alternatives to biopsy for assessment of interstitial fibrosis and tubular atrophy (IFTA), the major determinant of kidney transplant failure, remain profoundly limited. Elastography is a noninvasive technique that propagates shear waves across tissues to measure their stiffness. We aimed to test utility of elastography for early detection of IFTA in pediatric kidney allografts.

METHODS

We compared ultrasound (USE) and MR elastography (MRE) stiffness measurements, performed on pediatric transplant recipients referred for clinically indicated biopsies, and healthy controls.

RESULTS

Ten transplant recipients (median age 16 years) and eight controls (median age 16.5 years) were enrolled. Three transplant recipients had "stable" allografts and seven had Banff Grade 1 IFTA. Median time from transplantation to biopsy was 12 months. Mean estimated glomerular filtration rate was 61.5 mL/min/1.73m2 by creatinine-cystatin-C CKiD equation at time of biopsy. Mean stiffness, calculated through one-way ANOVA, was higher for IFTA allografts (23.4 kPa USE/5.6 kPa MRE) than stable allografts (13.7 kPa USE/4.4 kPa MRE) and controls (9.1 kPa USE/3.6 kPa MRE). Pearson's coefficient between USE and MRE stiffness values was strong (r = .97). AUC for fibrosis prediction in transplanted kidneys was high for both modalities (0.91 USE and 0.89 MRE), although statistically nonsignificant (p > .05). Stiffness cut-off values for USE and MRE were 13.8 kPa and 4.6 kPa, respectively. Both values yielded a sensitivity of 100% but USE specificity (72%) was slightly higher than MRE (67%).

CONCLUSION

Elastography shows potential for detection of low-grade IFTA in allografts although a larger sample is imperative for clinical validation.

The role of shear viscosity as a biomarker for improving chronic kidney disease detection using shear wave elastography: A computational study using a validated finite element model

The application of ultrasound shear wave elastography for detecting chronic kidney disease, namely renal fibrosis, has been widely studied. A good correlation between tissue Young's modulus and the degree of renal impairment has been established. However, the current limitation of this imaging modality pertains to the linear elastic assumption used in quantifying the stiffness of renal tissue in commercial shear wave elastography systems. As such, when underlying medical conditions such as acquired cystic kidney disease, which may potentially influence the viscous component of renal tissue, is present concurrently with renal fibrosis, the accuracy of the imaging modality in detecting chronic kidney disease may be affected. The findings in this study demonstrate that quantifying the stiffness of linear viscoelastic tissue using an approach similar to those implemented in commercial shear wave elastography systems led to percentage errors as high as 87%. The findings presented indicate that use of shear viscosity to detect changes in renal impairment led to a reduction in percentage error to values as low as 0.3%. For cases in which renal tissue was affected by multiple medical conditions, shear viscosity was found to be a good indicator in gauging the reliability of the Young's modulus (quantified through a shear wave dispersion analysis) in detecting chronic kidney disease. The findings show that percentage error in stiffness quantification can be reduced to as low as 0.6%. The present study demonstrates the potential use of renal shear viscosity as a biomarker to improve the detection of chronic kidney disease.

Shear Wave Elastography for Assessment of Biopsy-Proven Renal Fibrosis: A Systematic Review and Meta-analysis

The purpose of this meta-analysis was to evaluate the diagnostic performance of shear wave elastography (SWE) for the staging of renal fibrosis in patients with chronic kidney disease (CKD). Classification of CKD into mild, moderate and severe fibrosis was based on renal biopsy pathology (glomerulosclerosis, tubulointerstitial injury and vascular sclerosis). The Cochrane Library, Medline, PubMed, Web of Science, EMBASE and CNKI databases were searched from January 1, 2009, to April 20, 2022. Pooled sensitivity, specificity, diagnostic odds ratio and area under the receiver operating characteristic curve (AUROC) were calculated using random effects models. A total of 1394 patients from 14 studies were included in the final analysis. For mild, moderate and severe renal fibrosis, SWE had a sensitivity of 0.79 (95% confidence interval [CI]: 0.67-0.88), 0.73 (95% CI: 0.65-0.80) and 0.87 (95% CI: 0.71-0.95); a specificity of 0.82 (95% CI: 0.75-0.87), 72% (95% CI: 0.67-0.77) and 0.83 (95% CI: 0.80-0.86); an AUROC of 0.87 (95% CI: 0.84-0.90), 0.78 (95% CI: 0.75-0.82) and 0.86 (95% CI: 0.82-0.88); and a diagnostic odds ratio of 17 (95% CI: 7-43), 7 (95% CI: 4-12) and 34 (95% CI: 13-88), respectively. Meta-regressions revealed that the publication date, system used and number of valid measurements of SWE were the main causes of heterogeneity. SWE is a good technique for diagnosing mild and severe renal fibrosis, as well as a fair technique for diagnosing moderate fibrosis.

Ultrasound shear wave elastography for the evaluation of renal pathological changes in adult patients

OBJECTIVE

Many studies have conflicting findings in using shear wave elastography (SWE) to assess renal fibrosis. This study reviews the use of SWE to evaluate pathological changes in native kidneys and renal allografts. It also tries to elucidate the confounding factors and care taken to ensure the results are consistent and reliable.

METHODS

The review was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Literature search was conducted in Pubmed, Web of Science and Scopus database up to 23 October 2021. To evaluate risk and bias applicability, the Cochrane risk-of bias tool and GRADE was used. The review was registered under PROSPERO CRD42021265303.

RESULTS

A total of 2921 articles were identified. 104 full texts were examined and 26 studies included in systematic review. 11 studies performed on native kidneys and 15 studies on transplanted kidney. A wide range of impact factors was found that affect the accuracy of SWE of renal fibrosis in adult patients.

CONCLUSIONS

Compared to point SWE, two-dimensional SWE with elastogram could enable better selection of the region of interest in kidneys, leading to reproducible results. Tracking waves were attenuated as the depth from skin to region of interest increased, therefore, SWE is not recommended for overweight or obese patients. Variable transducer forces might also affect SWE reproducibility, thus, training of operators to ensure consistent operator-dependent transducer forces may be helpful.

ADVANCES IN KNOWLEDGE

This review provides a holistic insight on the efficiency of using SWE in evaluating pathological changes in native and transplanted kidneys, thereby contributing to the knowledge of its utilisation in clinical practice.

Measurement of renal congestion and compliance following intravenous fluid administration using shear wave elastography

Objective

Ultrasound shear wave elastography (SWE) is a novel technique that may provide non-invasive measurements of renal compliance. We aimed to investigate the relationship between intravenous (IV) fluid administration and change in SWE measurements. We hypothesised that following IV fluid administration in healthy volunteers, global kidney stiffness would increase and that this increase in stiffness could be quantified using SWE. Our second hypothesis was that graduated doses of IV fluids would result in a dose-dependent increase in global kidney stiffness measured by SWE.

Design

Randomised prospective study.

Setting

Intensive Care Unit.

Participants

Healthy volunteers aged 18-40 years.

Interventions

Participants were randomised to receive 20 ml/kg, 30 ml/kg, or 40 ml/kg of normal saline. The volume of fluid infused was based on the actual body weight recorded.

Main outcome measures

We recorded average SWE stiffness (kPa with standard deviation of the mean), median SWE stiffness (kPa), and the interquartile range.

Results

Ninety-eight percent of participants (44/45) demonstrated an increase in global kidney stiffness following administration of IV fluids. The average SWE pre fluid administration was 7.572 kPa ± 2.38 versus 14.9 kPa ± 4.81 post fluid administration (p < 0.001). In subgroup analysis, there were significant changes in global kidney stiffness pre and post fluid administration with each volume (ml/kg) of fluid administered. Average percentage change in global kidney stiffness from baseline was compared between the three groups. There was no significant difference when comparing groups 1 and 2 (197.1% increase ± 49.5 vs 216.1% ± 72.0, p ¼ 0.398), groups 2 and 3 (216.1% increase ± 72.0 vs 197.8% ± 59.9, p ¼ 0.455), or groups 1 and 3 (197.1% increase ± 49.5 vs 197.8% ± 59.9, p ¼ 0.972).

Conclusions

Fluid administration results in immediately visible and quantifiable changes in global kidney stiffness across all infused volumes of fluid.

Predicting Progression of Kidney Injury Based on Elastography Ultrasound and Radiomics Signatures

Background: Shear wave elastography ultrasound (SWE) is an emerging non-invasive candidate for assessing kidney stiffness. However, its prognostic value regarding kidney injury is unclear. Methods: A prospective cohort was created from kidney biopsy patients in our hospital from May 2019 to June 2020. The primary outcome was the initiation of renal replacement therapy or death, while the secondary outcome was eGFR < 60 mL/min/1.73 m2. Ultrasound, biochemical, and biopsy examinations were performed on the same day. Radiomics signatures were extracted from the SWE images. Results: In total, 187 patients were included and followed up for 24.57 ± 5.52 months. The median SWE value of the left kidney cortex (L_C_median) is an independent risk factor for kidney prognosis for stage 3 or over (HR 0.890 (0.796−0.994), p < 0.05). The inclusion of 9 out of 2511 extracted radiomics signatures improved the prognostic performance of the Cox regression models containing the SWE and the traditional index (chi-square test, p < 0.001). The traditional Cox regression model had a c-index of 0.9051 (0.8460−0.9196), which was no worse than the machine learning models, Support Vector Machine (SVM), SurvivalTree, Random survival forest (RSF), Coxboost, and Deepsurv. Conclusions: SWE can predict kidney injury progression with an improved performance by radiomics and Cox regression modeling.

Clinical studies of magnetic resonance elastography from 1995 to 2021: Scientometric and visualization analysis based on CiteSpace

BACKGROUND

To assess the knowledge framework around magnetic resonance elastography (MRE) and to explore MRE research hotspots and emerging trends.

METHODS

The Science Citation Index Expanded of the Web of Science Core Collection was searched on 22 October 2021 for MRE-related studies published between 1995 and 2021. Excel 2016 and CiteSpace V (version 5.8.R3) were used to analyze the downloaded data.

RESULTS

In all, 1,236 articles published by 726 authors from 540 institutions in 40 countries were included in this study. The top 10 authors published 57.6% of all included articles. The 3 most productive countries were the USA (n=631), Germany (n=202), and France (n=134), and the 3 most productive institutions were the Mayo Clinic (n=240), Charité (n=131), and the University of Illinois (n=56). The USA and the Mayo Clinic had the highest betweenness centrality among countries and institutions, respectively, and played an important role in the field of MRE. In this study, the 24,347 distinct references were clustered into 48 categories via reasonable clustering using specific keywords, forming the knowledge framework. Among the 294 co-occurring keywords, "hepatic fibrosis", "stiffness", "skeletal muscle", "acoustic strain wave", "in vivo", and "non-invasive assessment" were research hotspots. "Diagnostic performance", "diagnostic accuracy", "hepatic steatosis", "chronic hepatitis B", "radiation force impulse", "children", and "echo" were frontier topics.

CONCLUSIONS

Scientometric and visualized analysis of MRE can provide information regarding the knowledge framework, research hotspots, frontier areas, and emerging trends in this field.

Polydatin attenuates tubulointerstitial fibrosis in diabetic kidney disease by inhibiting YAP expression and nuclear translocation

The activation of Yes-associated protein (YAP) pathway is mutually causal with the increase of extracellular matrix (ECM) stiffness. Polydatin (PD) has been proved to have anti-fibrosis effect in diabetic kidney disease (DKD), but it is still a mystery whether PD participates in YAP-related mechano-transduction. Therefore, this study intends to solve the following two problems: 1) To construct an in vitro system of polyacrylamide hydrogels (PA gels) based on the true stiffness of kidneys in healthy and DKD rats, and observe the effect of PD on pathological matrix stiffness-induced YAP expression in renal fibroblasts; 2) Compared with verteporfin (VP), a pharmacological inhibitor of YAP, to explore whether the therapeutic effect of PD on DKD in vivo model is related to the regulation of YAP. In this study, the in vitro system of PA gels with 3 kPa, 12 kPa and 30 kPa stiffness was constructed and determined for the first time to simulate the kidney stiffness of healthy rats, rats with DKD for 8 weeks and 16 weeks, respectively. Compared with the PA gels with 3 kPa stiffness, the PA gels with 12 kPa and 30 kPa stiffness significantly increased the expression of YAP, α-smooth muscle actin (α-SMA) and collagen I, and the production of reactive oxygen species (ROS) in renal fibroblasts, and the PA gels with 30 kPa stiffness were the highest. PD significantly inhibited the above-mentioned changes of fibroblasts induced by pathological matrix stiffness, suggesting that the inhibition of PD on fibroblast-to-myofibroblast transformation and ECM production was at least partially associated with regulating YAP-related mechano-transduction pathway. Importantly, the inhibitory effect of PD on YAP expression and nuclear translocation in kidneys of DKD rats is similar to that of VP, but PD is superior to VP in reducing urinary protein, blood glucose, blood urea nitrogen and serum creatinine, as well as decreasing the expression of α-SMA and collagen I, ROS overproduction and renal fibrosis. Our results prove for the first time from the biomechanical point of view that PD is a potential therapeutic strategy for delaying the progression of renal fibrosis by inhibiting YAP expression and nuclear translocation.

Evaluation of renal fibrosis in patients with chronic kidney disease by shear wave elastography: a comparative analysis with pathological findings

PURPOSE

To explore the elastic values obtained by shear wave elastography (SWE) in assessing renal fibrosis in chronic kidney disease (CKD).

METHODS

One hundred and twenty-four patients with CKD who underwent renal biopsy were prospectively enrolled between April 2019 and June 2021. SWE was performed to measure the renal cortex stiffness, presented as SWE parameters, including the minimum, mean, and maximum elasticity (namely Emin, Emean, and Emax). Then, the patients with different kidney pathological impairment (mild, moderate, and severe groups) were compared in SWE elasticity and the discriminative capacity was also analyzed.

RESULTS

For the pathology impaired grade, SWE parameter was significantly reduced in the moderately and severely impaired group than the mild one. Emax parameter achieved the best discriminative ability toward differentiating moderate-severe impairment from mild one, yielding an area under the curve (AUC) of 0.764 (95%CI: 0.681-0.848). Regarding interstitial fibrosis/tubular atrophy and global glomerular sclerosis, the Emax values were significantly reduced across the group of patients with moderate grade compared to those with mild grade. Patients in severe group were also with reduced elastic value than those in mild one, while the difference was non-significant in interstitial fibrosis/tubular atrophy but a borderline statistical significance was achieved in global glomerular sclerosis. For grade of vessel wall thickening, patients in moderate (33.04 ± 9.86 kPa, P = 0.009) and severe (31.42 ± 9.16 kPa, P < 0.001) group were with significantly lower elastic value compared with those in the mild one (39.58 ± 9.67 kPa). The SWE parameter was linearly reduced as grade of vessel wall thickening elevated (P for trend: < 0.001).

CONCLUSION

SWE derived elastic values reduced as pathology grade of renal fibrosis or grade of vessel wall thickening progresses in patients with CKD, which may be attributed to renal hypo-perfusion rather than tubulo-interstitial fibrosis progression.

Novel Uses of Ultrasound to Assess Kidney Mechanical Properties

Ultrasound is a key imaging tool for evaluating the kidney. Over the last two decades, methods to measure the mechanical properties of soft tissues have been developed and used in clinical practice, although use in the kidney has not been as widespread as for other applications. The mechanical properties of the kidney are determined by the structure and composition of the renal parenchyma and perfusion characteristics. Because pathologic processes change these factors, the mechanical properties change and can be used for diagnostic purposes and for monitoring treatment or disease progression. Ultrasound-based elastography methods for evaluating the mechanical properties of the kidney use focused ultrasound beams to perturb the kidney and then high frame-rate ultrasound methods are used to measure the resulting motion. The motion is analyzed to estimate the mechanical properties. This review will describe the principles of these methods and discuss several seminal studies related to characterizing the kidney. Additionally, an overview of the clinical use of elastography methods in native and kidney allografts will be provided. Perspectives on future developments and uses of elastography technology along with other complementary ultrasound imaging modalities will be provided.