Effect of renal perfusion and structural heterogeneity on shear wave elastography of the kidney: an in vivo and ex vivo study

Advancing Boiling Histotripsy Dose in Ex Vivo And In Vivo Renal Tissues Via Quantitative Histological Analysis and Shear Wave Elastography

OBJECTIVE

In the context of developing boiling histotripsy (BH) as a potential clinical approach for non-invasive mechanical ablation of kidney tumors, the concept of BH dose (BHD) was quantitatively investigated in porcine and canine kidney models in vivo and ex vivo.

METHODS

Volumetric lesions were produced in renal tissue using a 1.5-MHz 256-element HIFU-array with various pulsing protocols: pulse duration tp = 1-10 ms, number of pulses per point ppp = 1-15. Two BHD metrics were evaluated: BHD1 = ppp, BHD2 = tp × ppp. Quantitative assessment of lesion completeness was performed by their histological analysis and assignment of damage score to different renal compartments (i.e., cortex, medulla, and sinus). Shear wave elastography (SWE) was used to measure the Young's modulus of renal compartments in vivo vs ex vivo, and before vs after BH treatments.

RESULTS

In vivo tissue required lower BH doses to achieve identical degree of fractionation as compared to ex vivo. Renal cortex (homogeneous, low in collagen) was equal or higher in stiffness than medulla (anisotropic, collagenous), 5.8-12.2 kPa vs 4.7-9.6 kPa, but required lower BH doses to be fully fractionated. Renal sinus (fatty, irregular, with abundant collagenous structures) was significantly softer ex vivo vs in vivo, 4.9-5.1 kPa vs 9.7-15.2 kPa, but was barely damaged in either case with any tested BH protocols. BHD1 was shown to be relevant for planning the treatment of renal cortex (sufficient BHD1 = 5 pulses in vivo and 10 pulses ex vivo), while none of the tested doses resulted in complete fractionation of medulla or sinus. Post-treatment SWE imaging revealed reduction of tissue stiffness ex vivo by 27-58%, increasing with the applied dose, and complete absence of shear waves within in vivo lesions, both indicative of tissue liquefaction.

CONCLUSION

The results imply that tissue resistance to mechanical fractionation, and hence required BH dose, are not solely determined by tissue stiffness but also depend on its composition and structural arrangement, as well as presence of perfusion. The SWE-derived reduction of tissue stiffness with increasing BH doses correlated with tissue damage score, indicating potential of SWE for post-treatment confirmation of BH lesion completeness.

Prediction of allograft function in pre-transplant kidneys using sound touch elastography (STE): an ex vivo study

BACKGROUND

The purpose of the study was to evaluate renal quality and predict posttransplant graft function using ex vivo sound touch elastography (STE).

METHODS

In this prospective study, 106 donor kidneys underwent ex vivo STE examination and biopsy from March 2022 to August 2023. The mean stiffness of the superficial cortex (STEsc), deep cortex (STEdc), and medulla (STEme) was obtained and synthesized into one index (STE) through the factor analysis method. Additionally, 100 recipients were followed up for 6 months. A random forest algorithm was employed to explore significant predictive factors associated with the Remuzzi score and allograft function. The performance of parameters was evaluated by using the area under the receiver operating characteristic curve (AUC).

RESULTS

STE had AUC values of 0.803 for diagnosing low Remuzzi and 0.943 for diagnosing high Remuzzi. Meanwhile, STE had an AUC of 0.723 for diagnosing moderate to severe ATI. Random forest algorithm identified STE and Remuzzi score as significant predictors for 6-month renal function. The AUC for STE in predicting postoperative allograft function was 0.717, which was comparable with that of the Remuzzi score (AUC = 0.756). Nevertheless, the specificity of STE was significantly higher than that of Remuzzi (0.913 vs 0.652, p < 0.001). Given these promising results, donor kidneys can be transplanted directly without the need for biopsy when STE ≤ 11.741.

CONCLUSIONS

The assessment of kidney quality using ex vivo STE demonstrated significant predictive value for the Remuzzi score and allograft function, which could help avoid unnecessary biopsy.

CRITICAL RELEVANCE STATEMENT

Pre-transplant kidney quality measured with ex vivo STE can be used to assess donor kidney quality and avoid unnecessary biopsy.

KEY POINTS

STE has significant value for diagnosing low Remuzzi and high Remuzzi scores. STE achieved good performance in predicting posttransplant allograft function. Assessment of kidney quality using ex vivo STE could avoid unnecessary biopsies.

Kidney cortex shear wave motion simulations based on segmented biopsy histology

BACKGROUND AND OBJECTIVE

Biopsy stands as the gold standard for kidney transplant assessment, yet its invasive nature restricts frequent use. Shear wave elastography (SWE) is emerging as a promising alternative for kidney transplant monitoring. A parametric study involving 12 biopsy data sets categorized by standard biopsy scores (3 with normal histology, 3 with interstitial inflammation (i), 3 with interstitial fibrosis (ci), and 3 with tubular atrophy (ct)), was conducted to evaluate the interdependence between microstructural variations triggered by chronic allograft rejection and corresponding alterations in SWE measurements.

METHODS

Heterogeneous shear wave motion simulations from segmented kidney cortex sections were performed employing the staggered-grid finite difference (SGFD) method. The SGFD method allows the mechanical properties to be defined on a pixel-basis for shear wave motion simulation. Segmentation techniques enabled the isolation of four histological constituents: glomeruli, tubules, interstitium, and fluid. Baseline ex vivo Kelvin-Voigt mechanical properties for each constituent were drawn from established literature. The parametric evaluation was then performed by altering the baseline values individually. Shear wave velocity dispersion curves were measured with the generalized Stockwell transform in conjunction with slant frequency-wavenumber analysis (GST-SFK) algorithm. By fitting the curve within the 100-400 Hz range to the Kelvin-Voigt model, the rheological parameters, shear elasticity (µ1) and viscosity (µ2), were estimated. A time-to-peak algorithm was used to estimate the group velocity. The resultant in silico models emulated the heterogeneity of kidney cortex within the shear wave speed (SWS) reconstructions.

RESULTS

The presence of inflammation showed considerable spatial composition disparities compared to normal cases, featuring a 23 % increase in interstitial area and a 19 % increase in glomerular area. Concomitantly, there was a reduction of 12 % and 47 % in tubular and fluid areas, respectively. Consequently, mechanical changes induced by inflammation predominate in terms of rheological differentiation, evidenced by increased elasticity and viscosity. Mild tubular atrophy showed significant elevation in group velocity and µ1. Conversely, mild and moderate fibrosis exhibited negligible alterations across all parameters, compatible with relatively limited morphological impact.

CONCLUSIONS

This proposed model holds promise in enabling patient-specific simulations of the kidney cortex, thus facilitating exploration into how pathologies altering cortical morphology correlates to modifications in SWE-derived rheological measurements. We demonstrated that inflammation caused substantial changes in measured mechanical properties.

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.

Integrating shear wave elastography and estimated glomerular filtration rate to enhance diagnostic strategy for renal fibrosis assessment in chronic kidney disease

Background

Assessing renal fibrosis non-invasively in patients with chronic kidney disease (CKD) remains a considerable clinical challenge. This study aimed to investigate the diagnostic efficacy of different approaches that combine shear wave elastography (SWE) and estimated glomerular filtration rate (eGFR) in distinguishing between mild fibrosis and moderate-to-severe fibrosis in CKD patients.

Methods

In this prospective study, 162 patients underwent renal SWE examinations and renal biopsies. Using SWE, the right renal cortex stiffness was measured, and the corresponding SWE value was recorded. Four diagnostic patterns were used to combine eGFR and SWE value: in isolation, in series, in parallel, and in integration. The receiver operating characteristic (ROC) curve was established, and the area under the ROC curve (AUC) was calculated to quantify diagnostic performance. Sensitivity, specificity, and accuracy were computed.

Results

The eGFR demonstrated sensitivity of 68.2% and specificity of 83.8%, whereas the SWE value displayed sensitivity of 84.1% and specificity of 62.2%, yielding a similar AUC (78.2% and 77.8%, respectively). Combining in series improved specificity to 97.3%, superior to other diagnostic patterns (all P values <0.01), but compromised sensitivity to 58.0%. When combined in parallel, the sensitivity increased to 94.3%, exceeding any other strategies (all P values <0.05), but the specificity dropped to 48.7%. The integrated strategy, incorporating eGFR with SWE value via the logistic regression algorithm, exhibited an AUC of 85.8%, outperforming all existing approaches (all P values <0.01), with balanced sensitivity, specificity, and accuracy of 86.4%, 74.3%, and 80.9%, respectively.

Conclusions

Using an integrated strategy to combine eGFR and SWE value could improve diagnostic performance in distinguishing between mild renal fibrosis and moderate-to-severe renal fibrosis in patients with CKD, thereby helping clinicians perform a more accurate clinical diagnosis.

Shear wave elastography: A noninvasive approach for assessing acute kidney injury in critically ill patients

Traditional markers, such as serum creatinine and blood urea nitrogen, frequently show delayed elevations following acute kidney injury (AKI), limiting their utility for prompt detection and timely intervention in AKI management. Shear wave elastography (SWE) exhibits potential for AKI diagnosis by measuring tissue stiffness. Our study aimed to evaluate the diagnostic performance of SWE in detecting AKI by measuring the stiffness of kidney tissue. Between July 2022 and December 2022, a total of 103 consecutive participants who met the eligibility criteria were prospectively enrolled, underwent SWE measurements, and were classified into AKI or non-AKI groups based on the 2012 Kidney Disease: Improving Global Outcomes (KDIGO) criteria. A receiver operating characteristic (ROC) curve was drawn to examine the feasibility of differentiating between AKI and non-AKI patients and assessing diagnostic performance. The effects of tissue anisotropy on SWE measurements were also examined. Our results revealed that patients in the AKI group exhibited significantly increased stiffness values in specific kidney regions compared with those in the non-AKI group. For the diagnosis of AKI, the optimal cut-off values were identified as 9.9 kPa, 2.9 kPa, and 4.4 kPa for the upper pole medulla, middle cortex, and middle medulla, respectively, in the longitudinal plane. Correspondingly, the areas under the ROC curves for these regions were 0.737 (95% confidence interval [CI]: 0.637, 0.822), 0.736 (95% CI: 0.637, 0.821), and 0.784 (95% CI: 0.688, 0.861). Additionally, we observed a significant variability in stiffness values due to tissue anisotropy, specifically in the segments of the upper pole cortex, and medulla across both longitudinal and transverse planes. SWE serves as a noninvasive approach for the quantification of tissue stiffness and shows promise as an adjunctive tool for the assessment of AKI.

Renal elasticity and perfusion changes on ultrasonography in an early-stage diabetic rat model

Background

Renal hemodynamic changes in early diabetes occur before the onset of significant structural abnormalities or clinical manifestations, and timely detection of these changes has clinical significance. This study aimed to evaluate renal elasticity and perfusion changes in an early-stage diabetic rat model by shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS), and to explore the potential correlations between renal elasticity and perfusion parameters.

Methods

A total of 18 male Sprague-Dawley rats were randomly divided into three groups: a control group (group 1, n=6), a diabetic group (group 2, n=6), and a diabetic group receiving drug therapy (group 3, n=6). An intraperitoneal injection of streptozotocin (STZ) for 2 days combined with a high-fat diet (HFD) was used as the early-stage diabetic rat model. The diabetic rats in group 3 were treated with canagliflozin and losartan for 6 weeks, whereas the rats in groups 1 and 2 were given equal amounts of purified water. Renal stiffness on SWE and perfusion parameters on CEUS were measured and compared among the three groups, then the rats were sacrificed, and serum, urine, and renal histopathology were evaluated to confirm the development of early diabetes.

Results

The early-stage diabetic rats without significant pathological changes exhibited bigger kidneys and higher blood glucose (all P<0.05). Among the CEUS parameters, peak enhancement (PE), wash-in area under the curve (WiAUC), wash-in perfusion index (WiPI), wash-out AUC (WoAUC), wash-in and wash-out AUC (WiWoAUC), rise time (RT), and time to peak (TTP) of diabetic rats in group 2 were significantly increased (all P<0.05), and the hyperperfusion ameliorated significantly after drug treatment. The renal elasticity measured by SWE varied in accordance with certain perfusion parameters, and was strongly positively correlated with WiAUC (r=0.701, P<0.001), WoAUC (r=0.647, P<0.001), and WiWoAUC (r=0.655, P<0.001), and moderately positively correlated with PE (r=0.539, P=0.001), WiPI (r=0.555, P<0.001), RT (r=0.425, P=0.010), and TTP (r=0.439, P=0.007).

Conclusions

Renal elasticity and perfusion changes in the early stage of diabetes, and renal elasticity was positively associated with delayed and increased perfusion.

Application of Real-Time Sound Touch Elastography for Evaluating Chronic Kidney Disease of Transplanted Kidneys

BACKGROUND

If chronic allograft nephropathy can be detected early and treated, the long-term survival rate of the transplanted kidney may be effectively improved.

PURPOSE

To compare the application value of real-time sound touch elastography (STE), strain elastography, and color Doppler flow imaging in evaluating chronic kidney disease of transplanted kidneys.

MATERIALS AND METHODS

A total of 101 patients with renal transplantation were divided into a normal group (serum creatinine <134 mol/L, 58 patients) and a chronic allograft nephropathy group after renal transplantation over 6 months (serum creatinine >134 mol/L, 43 patients). The maximum elastic modulus (Emax) was determined, and receiver operator characteristics were used to compare the diagnostic efficacy of STE ultrasound.

RESULTS

Emean, Emax, B/A (the strain rate of the internal oblique muscle tissue/ the strain rate of the central renal cortex) of cortical standard strain ratio in strain elastography, and resistance index (RI) between normal and chronic allograft nephropathy groups have statistical significance (P < .05). Emax is superior to B/A and arcuate artery RI in the chronic cortex in the diagnosis of renal dysfunction, and the area under the receiver operator characteristics curve is 0.88. The estimated glomerular filtration rate was negatively correlated with renal cortex Emax, B/A, and arcuate artery RI, among which Emax was the strongest (r = - 0.713, P < .001). The renal cortical Emax cut-off was 30.95 kPa, the sensitivity was 92%, the specificity was 88%, and the accuracy was 88%.

CONCLUSION

The STE technique to evaluate chronic renal dysfunction after renal transplantation is more sensitive than traditional strain-type elastography and hemodynamic parameters, with renal function decline, renal cortex Emax, renal cortical B/A, and arcuate artery RI gradually increased, and renal cortex Emax was particularly obvious.

Utility of shear wave-based ultrasound elastography in chronic kidney disease and related pathological quantitative analysis

OBJECTIVES

The purpose of this study was to investigate the effects of tissue fibrosis and microvessel density on shear wave-based ultrasound elastography (SWUE) of chronic kidney disease (CKD). In addition, we were looking to see whether SWUE could predict stage of CKD, correlating with the histology on kidney biopsy.

METHODS

Renal tissue sections from 54 patients diagnosed with suspected CKD were subjected to immunohistochemistry (CD31 and CD34), and the degree of tissue fibrosis was assessed using Masson staining. Before renal puncture, both kidneys were examined using SWUE. Comparative analysis was used to assess the correlation between SWUE and microvessel density, and between SWUE and the degree of fibrosis.

RESULTS

Fibrosis area according to Masson staining (p < 0.05) and integrated optical density (IOD) (p < 0.05) were positively correlated with CKD stage. The percentage of positive area (PPA) and IOD for CD31 and CD34 were not correlated with CKD stage (p > 0.05). When stage 1 CKD was removed, PPA and IOD for CD34 were negatively correlated with CKD stage (p < 0.05). Masson staining fibrosis area and IOD were not correlated with SWUE (p > 0.05), PPA and IOD for CD31 and CD34 were not correlated with SWUE (p > 0.05) and, finally, no correlation between SWUE and CKD stage was found (p > 0.05).

CONCLUSION

The diagnostic value of SWUE for CKD staging was very low. The utility of SWUE in CKD was affected by many factors and its diagnostic value was limited.

KEY POINTS

• There was no correlation between SWUE and the degree of fibrosis, or between SWUE and microvessel density among patients with CKD. • There was no correlation between SWUE and CKD stage and the diagnostic value of SWUE for CKD staging was very low. • The utility of SWUE in CKD is affected by many factors and its value was limited.

Secreted phosphoprotein 1 exacerbates renal ischemia-reperfusion injury by inhibiting PI3K/AKT signaling pathway

BACKGROUND

Renal ischemia-reperfusion injury (IRI) is a prevalent reason for acute kidney injury and a key clinical issue for patients under anesthesia and about to have surgery. We aim to investigate the Secreted phosphoprotein 1 (SPP1) role in renal IRI and the underlying mechanisms.

METHODS

Using Gene Expression Omnibus (GEO) database helped in analyzing the SPP1 expression in renal IRI. We established two models, a mouse renal ischemia-reperfusion (I/R) besides a hypoxia-reoxygenation (H/R) HK-2 cell. Renal tubular lesions were measured using H&E staining. Depending on the TUNEL assay, immunohistochemistry, qRT-PCR, as well as western blot, we applied the assessment of apoptosis and apoptosis-associated protein levels. At the same time, a western blot was performed for assessing PI3K/AKT pathway-associated proteins.

RESULTS

GEO data and experimental validation revealed elevated SPP1 content in the kidney tissues of renal I/R mice more than in sham mice. In vitro and in vivo studies revealed an increase in cell apoptosis due to SPP1 overexpression, but the opposite is true when SPP1 is silenced. SPP1 downregulation led to high p-PI3K and p-AKT protein levels, and the LY294002 application inhibited SPP1 inhibition-mediated anti-apoptotic effect CONCLUSION: Taken together, SPP1 exacerbates renal IRI in vivo and in vitro via promoting programmed cell death by inhibiting PI3K/AKT signaling pathway.

Ultrasound elastography in chronic kidney disease: a systematic review and meta-analysis

Ultrasound elastography (USE) is a noninvasive technique for assessing tissue elasticity, and its application in nephrology has aroused growing interest in recent years. The purpose of this article is to systematically review the clinical application of USE in patients with chronic kidney disease (CKD), including native and transplanted kidneys, and quantitatively investigate differences in elasticity values between healthy individuals and CKD patients. Furthermore, we provide a qualitative analysis of the studies included, discussing the potential interplay between renal stiffness, estimated glomerular filtration rate, and fibrosis. In January 2022, a systematic search was carried out on the MEDLINE (PubMed) database, concerning studies on the application of USE in patients with CKD, including patients with transplanted kidneys. The results of the included studies were extracted by two independent researchers and presented mainly through a formal narrative summary. A meta-analysis of nine study parts from six studies was performed. A total of 647 studies were screened for eligibility and, after applying the exclusion and inclusion criteria, 69 studies were included, for a total of 6728 patients. The studies proved very heterogeneous in terms of design and results. The shear wave velocity difference of - 0.82 m/s (95% CI: - 1.72-0.07) between CKD patients and controls was not significant. This result agrees with the qualitative evaluation of included studies that found controversial results for the relationship between renal stiffness and glomerular filtration rate. On the contrary, a clear relationship seems to emerge between USE values and the degree of fibrosis. At present, due to the heterogeneity of results and technical challenges, large-scale application in the monitoring of CKD patients remains controversial.

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.

ALTERATION IN SHEAR WAVE ELASTOGRAPHY IS ASSOCIATED WITH ACUTE KIDNEY INJURY: A PROSPECTIVE OBSERVATIONAL PILOT STUDY

ABSTRACT

Background: Kidney stiffness could change during kidney disease. We hypothesize that acute kidney injury (AKI) would increase renal stiffness. Therefore, evaluating kidney Young's modulus (YM; a measure of tissue stiffness) using shear wave elastography (SWE) might help to diagnose AKI. Methods: This research was divided into two studies. Study A: Male C57BL/6 mice were used to observe kidney YM changes induced by sepsis-associated AKI, which was established by cecal ligation and puncture (CLP). Study B included 54 consecutive critically ill patients with or without AKI. Changes in renal YM were observed. Results: Study A: CLP mice showed a significantly higher kidney YM compared with the sham group. The YM gradually increased from CLP 0 hours to CLP 24 hours, and presented a fair relationship with the renal tubular injury score ( R2 = 0.71) and serum creatinine ( R2 = 0.73). Study B: YM was easily accessible, and the intraclass correlation coefficient ranged from 0.62 to 0.84. Kidney YM was higher in AKI patients and gradually increased from non-AKI to AKI III patients. Furthermore, the YM in the upper, middle, and lower poles of the renal cortex presented a fair relationship with kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin ( R2 ranging from 0.4 to 0.58), and the areas under the curve of the above five indicators for the diagnosis of AKI were 0.7, 0.73, 0.70, 0.74, and 0.79, respectively. Conclusion: SWE-derived estimates of renal stiffness are higher in AKI patients and sepsis-associated AKI mice. However, it has no advantage over NGAL and KIM-1. Trial Registration: Chinese Clinical Trial Registry No: ChiCTR2200061725. Retrospectively registered July 1, 2022, https://www.chictr.org.cn/showproj.aspx?proj=169359 .

Evaluation of renal parenchyma stiffness in children with nephropathy by shear wave elastography: A systematic review and meta-analysis

BACKGROUND

The role of shear wave elastography (SWE) in assessing renal parenchymal stiffness in children with nephropathy is obscure. This systematic review and meta-analysis investigated this issue.

MATERIALS AND METHODS

PubMed, Embase, Web of Science, and the Cochrane Library databases were searched for studies evaluating renal parenchyma stiffness in children with nephropathy by SWE from inception to October 2021. The search was not limited by language. Two investigators independently screened the literature and extracted data. Any discrepancies were resolved via discussion with the senior professor. Study quality was assessed by the Newcastle-Ottawa Scale and the standardized mean difference of shear wave velocity (SWV) for the evaluation of renal parenchyma stiffness was determined.

RESULTS

Eight studies involving a total of 496 children with nephropathy and 353 healthy children were selected. Eight studies used SWV as parameters of renal parenchyma stiffness. The SWV was not significantly different in children with renal lesion than in those without renal lesion, with a standardized mean difference of 0.49 (95% confidence level, -0.40 to 1.39, p = 0.28). There was a high heterogeneity between studies.

CONCLUSION

Although there was significant difference in SWE of renal parenchyma between controls and patients in each study we included, statistical differences were not seen after results of all research were amalgamated due to different diseases with different pathomechanisms. SWE could be used to evaluate renal parenchymal stiffness in children with kidney disease after more well-designed and high-quality studies with a large sample size will be performed in the future.

Technical Performance of Acoustic Radiation Force Impulse Imaging for Measuring Renal Parenchymal Stiffness: A Systematic Review and Meta-Analysis

OBJECTIVES

To estimate the technical performance of acoustic radiation force impulse (ARFI) imaging (two-dimensional shear wave elastography [2D-SWE] and point shear wave elastography [p-SWE]) for measuring renal parenchymal stiffness.

METHODS

EMBASE and PubMed databases were searched for studies reporting technical performance of ARFI imaging in terms of technical failure, interobserver agreement, and/or intraobserver agreement. The proportion of technical failure and intraclass correlation coefficients (ICCs) for interobserver and intraobserver agreement was pooled. The pooled estimates of native and transplanted kidneys were obtained separately. Meta-regression and subgroup analyses were conducted to explore heterogeneity.

RESULTS

Twenty-four studies (2993 patients) were included. The pooled proportions of technical failure were 4.3% (95% confidence interval [CI] 2.2-8.5%) and 6.6% (95% CI 4.0-10.7%) in native and transplanted kidneys, respectively. The pooled ICCs of interobserver agreement were 0.70 (95% CI 0.68-0.83) and 0.81 (95% CI 0.68-0.89), indicating moderate and good agreement in native and transplanted kidneys, respectively. The pooled ICC showed good (0.77; 95% CI 0.49-0.91) intraobserver agreement in native kidneys. Regarding interobserver agreement in transplanted kidneys, ROI location (mid pole only versus others) was a significant factor of heterogeneity (P = .04).

CONCLUSIONS

The ARFI-based SWE techniques show good technical performance for measuring renal parenchymal stiffness. The wide range of SWE protocols necessitates development of standardized guidelines on the use of renal ARFI imaging.

Renal Subcapsular Hematoma Formation Due to Hydronephrosis Caused by Recurrent Uterine Cervical Cancer

Most non-traumatic renal subcapsular hematomas are found in the presence of primary or metastatic renal tumors, or in the presence of vascular disease of the renal blood vessels. We managed an asymptomatic renal subcapsular hematoma that formed due to uterine cervical cancer that metastasized to the left common iliac lymph nodes. A 48-year-old woman with stage IB1 cervical cancer underwent neoadjuvant chemotherapy and concurrent chemoradiation following a radical hysterectomy. Six months after the completion of her first treatment, she developed left-sided hydronephrosis, a left subcapsular hematoma and left common iliac lymph nodes enlargement as demonstrated with contrast-enhanced computed tomography. Although a renal subcapsular hematoma is rarely a symptom of cervical cancer recurrence, it should be considered if other neoplastic or vascular diseases are ruled out.

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

Early detection of chronic kidney disease is important to prevent progression of irreversible kidney damage, reducing the need for renal transplantation. Shear wave elastography is ideal as a quantitative imaging modality to detect chronic kidney disease because of its non-invasive nature, low cost and portability, making it highly accessible. However, the complexity of the kidney architecture and its tissue properties give rise to various confounding factors that affect the reliability of shear wave elastography in detecting chronic kidney disease, thus limiting its application to clinical trials. The objective of this review is to highlight the confounding factors presented by the complex properties of the kidney, in addition to outlining potential mitigation strategies, along with the prospect of increasing the versatility and reliability of shear wave elastography in detecting chronic kidney disease.

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.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

The association between renal elasticity evaluated by Real-time tissue elastography and renal fibrosis

BACKGROUND

The progression of chronic kidney disease (CKD) depends on the extent of fibrosis in the kidneys; however, a renal biopsy is necessary to evaluate the severity of renal fibrosis. Real-time tissue elastography (RTE), which measures heartbeat-induced tissue displacement, can assess the elasticity of organs. Here, we aimed to investigate the correlation between renal elasticity and the extent of fibrosis in renal biopsy samples.

METHODS

We investigated 29 consecutive patients who underwent a renal biopsy at Ehime University Hospital from February 2018 to August 2019. Renal fibrosis was categorized into three grades, mild (< 25%), moderate (25-50%), and severe (> 50%), based on the total affected area within the biopsy sample. The association between renal elasticity assessed by RTE and the grade of renal fibrosis was evaluated, and a receiver operating characteristic curve was used to distinguish the severity of renal fibrosis.

RESULTS

The mean age and estimated glomerular filtration rate (eGFR) were 58.8 years and 55.2 mL/min/1.73 m², respectively. The median urine protein-to-creatinine ratio was 1.24 g/gCr. The mean renal elasticity of mild, moderate, and severe renal fibrosis was 3.40, 3.98, and 4.77, respectively. Renal elasticity of native kidneys was significantly positively correlated with the grade of renal fibrosis (ρ = 0.529, P = 0.003). At the cutoff point of 3.81, the area under the curve, sensitivity, and specificity were 0.778, 68.4%, and 81.8%, respectively.

CONCLUSION

Real-time tissue elastography is a promising, non-invasive method for assessing renal fibrosis in patients with CKD.

Ultrasound Shear Wave Elastography and Transient Optical Coherence Elastography: Side-by-Side Comparison of Repeatability and Accuracy

Objective: We compare the repeatability and accuracy of ultrasound shear wave elastography (USE) and transient optical coherence elastography (OCE). Methods: Elastic wave speed in gelatin phantoms and chicken breast was measured with USE and OCE and compared with uniaxial mechanical compression testing. Intra- and Inter-repeatability were analyzed using Bland-Altman plots and intraclass correlation coefficients (ICC). Results: OCE and USE differed from uniaxial testing by a mean absolute percent error of 8.92% and 16.9%, respectively, across eight phantoms of varying stiffness. Upper and lower limits of agreement for intrasample repeatability for USE and OCE were ±0.075 m/s and −0.14 m/s and 0.13 m/s, respectively. OCE and USE both had ICCs of 0.9991. In chicken breast, ICC for USE was 0.9385 and for OCE was 0.9924. Conclusion: OCE and USE can detect small speed changes and give comparable measurements. These measurements correspond well with uniaxial testing.

MR Elastography of the Abdomen: Basic Concepts

Magnetic resonance elastography (MRE) is an emerging imaging modality that maps the elastic properties of tissue such as the shear modulus. It allows for noninvasive assessment of stiffness, which is a surrogate for fibrosis. MRE has been shown to accurately distinguish absent or low stage fibrosis from high stage fibrosis, primarily in the liver. Like other elasticity imaging modalities, it follows the general steps of elastography: (1) apply a known cyclic mechanical vibration to the tissue; (2) measure the internal tissue displacements caused by the mechanical wave using magnetic resonance phase encoding method; and (3) infer the mechanical properties from the measured mechanical response (displacement), by generating a simplified displacement map. The generated map is called an elastogram.While the key interest of MRE has traditionally been in its application to liver, where in humans it is FDA approved and commercially available for clinical use to noninvasively assess degree of fibrosis, this is an area of active research and there are novel upcoming applications in brain, kidney, pancreas, spleen, heart, lungs, and so on. A detailed review of all the efforts is beyond the scope of this chapter, but a few specific examples are provided. Recent application of MRE for noninvasive evaluation of renal fibrosis has great potential for noninvasive assessment in patients with chronic kidney diseases. Development and applications of MRE in preclinical models is necessary primarily to validate the measurement against "gold-standard" invasive methods, to better understand physiology and pathophysiology, and to evaluate novel interventions. Application of MRE acquisitions in preclinical settings involves challenges in terms of available hardware, logistics, and data acquisition. This chapter will introduce the concepts of MRE and provide some illustrative applications.This publication is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by another separate chapter describing the experimental protocol and data analysis.

Ultrasound Shear Wave Elastography and Doppler Sonography to Assess the Effect of Hydration on Human Kidneys: A Preliminary Observation

To assess the feasibility of ultrasound imaging in depicting the changes in kidney size, hemodynamics and cortex viscoelasticity after hydration, we prospectively performed 2-D ultrasound shear wave elastography (SWE) and Doppler sonography of bilateral kidneys in 30 volunteers. Kidney length, cortex shear wave velocity (SWV), shear wave dispersion (SWD), interlobar artery peak systolic velocity (PSV), end-diastolic velocity (EDV) and resistive index (RI) were measured before and 60 min after with and without drinking water (1 L). The differences in kidney length, SWV, PSV, EDV and color pixel intensity before and after hydration were significant (p < 0.001), whereas these differences were not significant without hydration (p > 0.05). SWD and RI did not significantly differ with or without hydration. Inter- and intra-observer reliability in performing SWE and Doppler sonography was good. The use of Doppler sonography and ultrasound SWE to evaluate the effect of hydration on kidney size, hemodynamics and viscoelasticity seem to be feasible.

Pre-procedural shear wave elastography on prediction of hemorrhage after percutaneous real-time ultrasound-guided renal biopsy

PURPOSE

To evaluate the relationship between renal elasticity which was determined with shear wave elastography (SWE) and hemorrhage in patients who undergone percutaneous renal parenchyma biopsy (PRB).

MATERIALS AND METHODS

In total, 60 patients who were performed ultrasound-guided PRB after the B-mode ultrasonography and SWE assessment were recruited in this study. All patients' serum creatinine, blood urea nitrogen and coagulation tests before PRB were obtained from medical records. The patients were divided into two groups who did and did not develop hemorrhage after PRB. We investigated whether there was any statistically significant difference between the two groups in terms of laboratory findings, B-mode ultrasonographic measurements and SWE measurements.

RESULTS

Of the 60 patients, 23 (38.3%) had post-procedure hemorrhage and 37 (61.7%) had not. Mean hemorrhage size was 17.04 mm (7-50 mm). The mean value of renal cortical shear wave velocity of all patients was 1.91 m/s (0.96-3.57 m/sn). Patients with post-procedure hemorrhage had significantly lower mean shear wave velocity compared with patients with no hemorrhage (p < 0.05). ROC curve analysis suggested that the optimum SWV cutoff point for hemorrhage presence was 1.21 m/sn, with 39.1% sensitivity and 97.3% specificity. There was no other statistically significant demographic, ultrasonographic or laboratory value differences between two groups.

CONCLUSION

Although shear wave velocities have low sensitivity for hemorrhage after renal biopsy, high specificity and statistically significant difference in hemorrhage and non-hemorrhage group suggest that patients who have lower renal cortical shear wave velocity have a tendency to hemorrhage after PRB.

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

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

Shear Wave Elastography in the Evaluation of the Kidneys in Pediatric Patients with Unilateral Vesicoureteral Reflux

OBJECTIVES

To evaluate the ability of shear wave elastography (SWE) to detect renal parenchymal scar formation in patients with vesicoureteral reflux.

METHODS

We prospectively evaluated 49 patients with unilateral grade 2 or higher-degree VUR. All patients underwent dimercaptosuccinic acid (DMSA) scintigraphy for evaluation of the renal parenchymal scar. After the DMSA scan, 2 radiologists, who were blinded to clinical data and each other's measurements, evaluated the kidneys of the patients using SWE. The kidneys were divided into 3 parts: upper pole, middle region, and lower pole, and 3 regions of interest were placed to each part. Shear wave velocity (SWV) values were calculated using meters per second as a unit and recorded for each region. Afterward, SWV values were compared to DMSA results.

RESULTS

There was no significant difference between the observers' mean SWV values of kidneys with VUR without scar formation (mean ± SD, 2.11 ± 0.06 and 2.09 ± 0.05 m/s) and the contralateral normal kidney SVW values (2.11 ± 0.06 and 2.10 ± 0.05 m/s; P = .936 and .724, respectively). We observed a significant difference between the mean SWV values of the kidneys with VUR accompanied by scar formation (2.28 ± 0.10 and 2.27 ± 0.11 m/s) and the mean SWV values of the contralateral normal kidneys (2.09 ± 0.05 and 2.10 ± 0.04 m/s; P < .001 for both observers).

CONCLUSIONS

Shear wave elastography could detect scar tissue in kidneys; however, the variability of the stiffness due to the kidney's complex structure, and variations in blood perfusion and the glomerular filtration rate of the kidney might limit the use of SWE in current clinical diagnostic algorithms for VUR.

Renal Tubular- and Vascular Basement Membranes and their Mimicry in Engineering Vascularized Kidney Tubules

The high prevalence of chronic kidney disease leads to an increased need for renal replacement therapies. While there are simply not enough donor organs available for transplantation, there is a need to seek other therapeutic avenues as current dialysis modalities are insufficient. The field of regenerative medicine and whole organ engineering is emerging, and researchers are looking for innovative ways to create (part of) a functional new organ. To biofabricate a kidney or its functional units, it is necessary to understand and learn from physiology to be able to mimic the specific tissue properties. Herein is provided an overview of the knowledge on tubular and vascular basement membranes' biochemical components and biophysical properties, and the major differences between the two basement membranes are highlighted. Furthermore, an overview of current trends in membrane technology for developing renal replacement therapies and to stimulate kidney regeneration is provided.

Is Kidney Stiffness Measured Using Elastography Influenced Mainly by Vascular Factors in Patients with Diabetic Kidney Disease?

Studies published so far using ultrasound-based elastography in the kidneys, lack to prove a clear relationship between kidney shear wave speed (KSWS) and renal disease progression. Taking into account that the kidney is a highly vascularized organ, the present study aims to find a relationship between KSWS and vascular factors (blood pressure [BP], arterial stiffness). Our study included 38 diabetic kidney disease patients (mean age 56.52 ± 16.12 years, 19 female, 19 male). KSWS, an indicator of renal stiffness, was measured using point Shear Wave Elastography (pSWE; Siemens Acuson S2000). In every patient, we recorded BP, and we measured aortic augmentation index (AAI) and brachial pulse wave velocity (PWV), using oscillometry. We found statistically significant indirect correlations of KSWS with indicators of arterial stiffness, such as PWV ( r = -.41, p = .036), and AAI ( r = -.37, p = .031). We found also an indirect correlation of KSWS with diastolic BP ( r = -.65, p = .02) and systolic BP ( r = -.54, p = .008). We found no correlation of KSWS with estimated glomerular filtration rate (eGFR), urinary albumin/creatinine ratio, stage of diabetic retinopathy, or glycated hemoglobin. Our study shows that high BP and the progression of arteriosclerosis (high PWV and AAI), leads to a decrease of renal stiffness. Thus, it seems that KSWS is influenced by renal blood flow, rather than other factors, such as albuminuria or chronic kidney disease stage.