Non-invasive assessment of kidney allograft fibrosis with shear wave elastography: A radiological-pathological correlation analysis

Comparison of resistive index and shear-wave elastography in the evaluation of chronic kidney allograft dysfunction

BACKGROUND

Detection of early chronic changes in the kidney allograft is important for timely intervention and long-term survival. Conventional and novel ultrasound-based investigations are being increasingly used for this purpose with variable results.

AIM

To compare the diagnostic performance of resistive index (RI) and shear wave elastography (SWE) in the diagnosis of chronic fibrosing changes of kidney allograft with histopathological results.

METHODS

This is a cross-sectional and comparative study. A total of 154 kidney transplant recipients were included in this study, which was conducted at the Departments of Transplantation and Radiology, Sindh Institute of Urology and Transplan tation, Karachi, Pakistan, from August 2022 to February 2023. All consecutive patients with increased serum creatinine levels and reduced glomerular filtration rate (GFR) after three months of transplantation were enrolled in this study. SWE and RI were performed and the findings of these were evaluated against the kidney allograft biopsy results to determine their diagnostic utility.

RESULTS

The mean age of all patients was 35.32 ± 11.08 years. Among these, 126 (81.8%) were males and 28 (18.2%) were females. The mean serum creatinine in all patients was 2.86 ± 1.68 mg/dL and the mean estimated GFR was 35.38 ± 17.27 mL/min/1.73 m2. Kidney allograft biopsy results showed chronic changes in 55 (37.66%) biopsies. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of SWE for the detection of chronic allograft damage were 93.10%, 96.87%%, 94.73%, and 95.87%, respectively, and the diagnostic accuracy was 95.45%. For RI, the sensitivity, specificity, PPV, and NPV were 76.92%, 83.33%, 70.17%, and 87.62%, respectively, and the diagnostic accuracy was 81.16%.

CONCLUSION

The results from this study show that SWE is more sensitive and specific as compared to RI in the evaluation of chronic allograft damage. It can be of great help during the routine follow-up of kidney transplant recipients for screening and early detection of chronic changes and selecting patients for allograft biopsy.

Evaluation of Robustness of S-Transform Based Phase Velocity Estimation in Viscoelastic Phantoms and Renal Transplants

Ultrasound shear wave elastography (SWE) methods are being used to differentiate healthy versus diseased tissue on the basis of their viscoelastic mechanical properties. Tissue viscoelasticity is often studied by analyzing shear wave phase velocity dispersion curves, which is the variation of phase velocity with frequency or wavelength. Recently, a unique approach using a generalized Stockwell transformation (GST-SFK) was proposed for the calculation of dispersion curves in viscoelastic media over expanded frequency band. In this work, the method's robustness was evaluated on data from five custom-made viscoelastic tissue-mimicking phantoms and sixty in vivo renal transplants. For each phantom, 15 shear wave motion data acquisitions were taken, while 10-13 acquisitions were acquired for renal transplants measured in the renal cortex. For each data-set mean and standard deviation (SD) of estimated phase velocity dispersion curves were studied. In addition, the viscoelastic parameters of the Zener model were examined, which were preceded by a convergence analysis. For viscoelastic phantoms scanned with a research ultrasound scanner, and for the in vivo renal transplants scanned with a clinical scanner, the decisive advantage of the GST-SFK method over the standard two-dimensional Fourier transform (2D-FT) method was shown. The GST-SFK method provided dispersion curve estimates with lower SD over a wider frequency band in comparison to the 2D-FT method. These advantages are relevant to the analysis of the mechanical properties of tissues in clinical practice to discriminate healthy from diseased tissue.

Shear wave elastography parameters adds prognostic value to adverse outcome in kidney transplantation recipients

INTRODUCTION

The tissue stiffness of donor kidneys in transplantation may increase due to pathological changes such as glomerulosclerosis and interstitial fibrosis, and those changes associate worse outcomes in kidney transplantation recipients. Ultrasound elastography is a noninvasive imaging examination with the ability to quantitatively reflect tissue stiffness. Aim of this study was to evaluate the prognostic value of ultrasound elastography for adverse kidney outcome in kidney transplantation recipients.

METHODS

Shear wave elastography (SWE) examinations were performed by two independent operators in kidney transplantation recipients. The primary outcome was a composite of kidney graft deterioration, all-cause re-hospitalization, and all-cause mortality. Survival analysis was calculated by Kaplan-Meier curves with the log-rank test and Cox regression analysis.

RESULTS

A total of 161 patients (mean age 46 years, 63.4% men) were followed for a median of 20.1 months. 27 patients (16.77%) reached the primary endpoint. The mean and median tissue stiffness at the medulla (hazard ratio: 1.265 and 1.229, respectively), estimated glomerular filtration rate (eGFR), and serum albumin level were associated with the primary outcome in univariate Cox regression. Adding mean or median medulla SWE to a baseline model containing eGFR and albumin significantly improved its discrimination (C-statistics: 0.736 for the baseline, 0.766 and 0.772 for the model added mean and median medulla SWE, respectively).

CONCLUSION

The medullary tissue stiffness of kidney allograft measured by shear wave elastography may provide incremental prognostic value to adverse outcomes in kidney transplantation recipients. Including SWE parameters in kidney transplantation recipients management could be considered to improve risk stratification.

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.

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.

Shear wave elastography using high-frequency linear probe for transplant kidney monitoring: A methodological study

OBJECTIVES

To investigate the influencing factors of the image quality of shear wave elastography (SWE) performed using a high-frequency probe and its reproducibility for renal allografts.

METHODS

A total of 211 patients with transplanted kidneys who underwent SWE examination performed using high-frequency or low-frequency probes were recruited for the study. The reproducibility of inter- and intraobserver agreements were analysed by using the intraclass correlation coefficient (ICC). According to the colour filling of the area of interest and imaging noise when conducting SWE, the image quality was classified as three grades: "good", "common", and "poor". A logistic regression was used to analyse the independent factors for SWE quality.

RESULTS

In the comparative analysis, high frequency, transection measurement and middle pole were selected as the appropriate measurement methods. Regarding reproducibility, the ICCs) of the intra- and interobserver agreements were 0.85 and 0.77, respectively. Multivariate analysis indicated that only the skin allograft distance and kidney width were independent variables for SWE quality. In the subgroup analysis of the skin-allograft distance, the "good" and "common" rates of images decreased as the distance increased, but the CV (coefficients of variation) showed the opposite trend. The SWE quality of kidney width <5.4 cm was significantly better than that of kidney width ≥5.4 cm.

CONCLUSIONS

High-frequency SWE can be used in the evaluation of transplanted kidneys due to its good repeatability and high successful measurement rate, but we should pay attention to the influence of the skin-allograft distance and kidney width on SWE quality.

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.

Nomogram based on high-frequency shear wave elastography (SWE) to evaluate chronic changes after kidney transplantation

OBJECTIVES

To construct a nomogram with high-frequency shear wave elastography (SWE) as a noninvasive method to accurately assess chronic changes in renal allografts.

METHODS

A total of 191 renal transplantation patients (127 cases in the training group and 64 cases in the verification group) were included in this study. All patients received conventional ultrasound and high-frequency SWE examination, followed directly by biopsy the next day. The chronic changes were divided into mild, moderate, and severe. Multivariate logistic analyses were used to select significant variables, which were used to develop the nomogram. Nomogram models were assessed by receiver operating characteristic (ROC) curves, calibration plots, and decision curve analysis (DCA).

RESULTS

The cutoff value of SWE in mild, moderate, and severe chronic changes was 18.9, 22.5, and 27.6 kPa, respectively. The areas under the curve (AUCs) of SWE in the differential diagnosis of mild and moderate to severe chronic changes and mild to moderate and severe chronic changes were 0.817 and 0.870, respectively. Multivariate analysis showed that time since transplantation, proteinuria, glomerular filtration rate, echogenicity, and SWE were independent diagnostic factors for moderate to severe chronic changes (all p < 0.05); thus, a nomogram was successfully developed. The AUCs of the nomogram in the training and validation groups were 0.905 and 0.938, respectively. The high agreement between the model predictions and the actual observations was confirmed by calibration plot and DCA.

CONCLUSIONS

Based on SWE, the nomogram provided an insightful and applicable tool to evaluate chronic changes in renal allografts.

KEY POINTS

• In kidney transplantation, compared with acute changes, chronic changes are significantly correlated with cortical stiffness. • SWE shows good performance in identifying mild to moderate and severe chronic changes, with an AUC of 0.870. • Time since transplantation, proteinuria, glomerular filtration rate, echogenicity, and SWE are independent diagnostic factors for moderate to severe chronic changes in renal allografts.

Factors affecting the shear wave elastic quantitative measurement of penile tissue in rats

Background

As a new ultrasound technology, 2-dimensional shear wave elastography (2D-SWE) can evaluate the elastic characteristics of penile tissue. However, no studies have reported the main factors affecting the shear wave elastic quantitative measurement (SWQ) in penile tissue.

Objectives

To analyze the main factors affecting the SWQ reflecting the elastic characteristics of penile tissue by 2D-SWE.

Methods

Twenty healthy male Sprague-Dawley rats (5-60 weeks old) were selected for this study. We performed the 2D-SWE examination on the penis using the Aixplorer ultrasound system, with SWQ as the measurement index. We performed penile immunohistochemistry analysis with the positive area proportion (PAP) of alpha-smooth muscle actin (PAPS) and type III collagen fiber (PAPC) as the outcomes. Then, we conducted multiple linear regression analysis to explore the correlation of SWQ with PAPS and PAPC and established the regression equation.

Results

The multiple linear regression analysis showed that the linear regression equation (SWQ = 10.376 - 0.05 PAPS - 0.07 PAPC) was statistically significant (F = 21.153, P < 0.001). The content of smooth muscle cells (SMCs) and collagen fibers was negatively correlated with SWQ, affecting 42.6% of the total variation in SWQ (R2 = 0.426).

Conclusions

SMCs and collagen fibers are the main factors affecting the SWQ value of penile tissue and the primary tissue components determining the SWQ when using 2D-SWE to quantitatively evaluate the elastic characteristics of penile tissue.

Magnetic Resonance Elastography as Surrogate Marker of Interstitial Fibrosis in Kidney Transplantation: A Prospective Study

Background

Fibrosis progression is a major prognosis factor in kidney transplantation. Its assessment requires an allograft biopsy, which remains an invasive procedure at risk of complications.

Methods

We assessed renal stiffness by magnetic resonance elastography (MRE) as a surrogate marker of fibrosis in a prospective cohort of kidney transplant recipients compared with the histologic gold standard. Interstitial fibrosis was evaluated by three methods: the semi-quantitative Banff ci score, a visual quantitative evaluation by a pathologist, and a computer-assisted quantitative evaluation. MRE-derived stiffness was assessed at the superior, median, and inferior poles of the allograft.

Results

We initially enrolled 73 patients, but only 55 had measurements of their allograft stiffness by MRE before an allograft biopsy. There was no significant correlation between MRE-derived stiffness at the biopsy site and the ci score (ρ=-0.25, P=0.06) or with the two quantitative assessments (pathologist: ρ=-0.25, P=0.07; computer assisted: ρ=-0.21, P=0.12). We observed negative correlations between the stiffness of both the biopsy site and the whole allograft, with either the glomerulosclerosis percentage (ρ=-0.32, P=0.02 and ρ=-0.31, P=0.02, respectively) and the overall nephron fibrosis percentage, defined as the mean of the percentages of glomerulosclerosis and interstitial fibrosis (ρ=-0.30, P=0.02 and ρ=-0.28, P=0.04, respectively). At patient level, mean MRE-derived stiffness was similar across the three poles of the allograft (±0.25 kPa). However, a high variability of mean stiffness was found between patients, suggesting a strong influence of confounding factors. Finally, no significant correlation was found between mean MRE-derived stiffness and the slope of eGFR (P=0.08).

Conclusions

MRE-derived stiffness does not directly reflect the extent of fibrosis in kidney transplantation.

Soft, Dynamic Hydrogel Confinement Improves Kidney Organoid Lumen Morphology and Reduces Epithelial-Mesenchymal Transition in Culture

Pluripotent stem cell-derived kidney organoids offer a promising solution to renal failure, yet current organoid protocols often lead to off-target cells and phenotypic alterations, preventing maturity. Here, various dynamic hydrogel architectures are created, conferring a controlled and biomimetic environment for organoid encapsulation. How hydrogel stiffness and stress relaxation affect renal phenotype and undesired fibrotic markers are investigated. The authors observe that stiff hydrogel encapsulation leads to an absence of certain renal cell types and signs of an epithelial-mesenchymal transition (EMT), whereas encapsulation in soft, stress-relaxing hydrogels leads to all major renal segments, fewer fibrosis or EMT associated proteins, apical proximal tubule polarization, and primary cilia formation, representing a significant improvement over current approaches to culture kidney organoids. The findings show that engineering hydrogel mechanics and dynamics have a decided benefit for organoid culture. These structure-property-function relationships can enable the rational design of materials, bringing us closer to functional engraftments and disease-modeling applications.

Usefulness of transperineal shear wave elastography of levator ani muscle in women with stress urinary incontinence

This study aimed to quantitatively assess the quality of levator ani muscle (LAM) using shear wave elastography (SWE) and to evaluate the association between the elasticity of LAM and stress urinary incontinence (SUI). The study population included 32 women with SUI and 34 women with normal pelvic support. The thickness of LAM, bladder neck descent (BND), and urethral funneling (UF) were assessed by transperineal ultrasound. LAM elasticity was measured by SWE at rest and during the maximal Valsalva maneuver. Age, menopause, BND, and UF showed a positive correlation with SUI. There was no significant between-group difference in the elastic modulus values of LAM at rest. The thickness of LAM in women with SUI was greater than that in control group at rest and during the maximal Valsalva maneuver (P < 0.001). The elastic modulus values of E_max and E_mean were significantly increased from rest to the maximal Valsalva maneuver in all participants (56.24 vs 82.43 kPa and 47.92 vs 72.37 kPa, P < 0.001). The change of these variables from rest to the maximal Valsalva maneuver in the control group was more obvious than that in the SUI group (34.09 vs 17.87 kPa and 31.55 vs 16.82 kPa, P < 0.05). The elasticity of LAM, as quantified by SWE, may potentially be used as an index for predicting SUI.

Shear wave elastography and Doppler ultrasound in kidney transplant recipients

Objective

To evaluate the association between shear wave elastography parameters and arterial resistance in kidney transplant recipients.

Materials and Methods

This was a prospective cross-sectional study involving consecutive adult kidney transplant recipients. All patients underwent color Doppler to evaluate the resistive index (RI) and ultrasound shear wave elastography for the quantification of renal allograft stiffness.

Results

We evaluated 55 patients, of whom 9 (16.4%) had an RI defined as abnormal (≥ 0.79) and 46 (83.6%) had an RI defined as normal (< 0.79). The mean age was higher in the abnormal RI group than in the normal RI group (68.0 ± 8.6 years vs. 42.6 ± 14.1 years; p < 0.001), as was the mean shear wave velocity (2.6 ± 0.4 m/s vs. 2.2 ± 0.4 m/s; p = 0.013). Multivariate analysis identified two independent predictors of arterial resistance: age (OR = 1.169; 95% CI: 1.056 to 1.294; p = 0.003) and shear wave velocity (OR = 17.1; 95% CI: 1.137 to 257.83; p = 0.040).

Conclusion

We observed an association between rigidity in the cortex of the transplanted kidney, as evaluated by shear wave elastography, and arterial resistance, as evaluated by color Doppler, in kidney transplant recipients.

Noninvasive Assessment of Interstitial Fibrosis and Tubular Atrophy in Renal Transplant by Combining Point-Shear Wave Elastography and Estimated Glomerular Filtration Rate

The purpose of this study was to evaluate the feasibility of the combination of point-shear wave elastography (p-SWE) and estimated glomerular filtration rate (eGFR) for assessing different stages of interstitial fibrosis and tubular atrophy (IF/TA) in patients with chronic renal allograft dysfunction (CAD). From September 2020 to August 2021, 47 patients who underwent renal biopsy and p-SWE examinations were consecutively enrolled in this study. The areas under the receiver operating characteristic curves (AUCs) were calculated to evaluate overall accuracy and to identify the optimal cutoff values for different IF/TA stages. A total of 43 patients were enrolled in this study. The renal cortical stiffness and eGFR showed a significant difference between IF/TA Grade 0–1 and Grade 2–3 (p < 0.001). Additionally, renal stiffness and eGFR were independent predictors for moderate-to-severe IF/TA (Grade ≥ 2) according to multiple logistic regression analysis. The combination of p-SWE and eGFR, with an optimal cutoff value of −1.63, was superior to eGFR alone in assessing moderate-to-severe interstitial fibrosis (AUC, 0.86 vs. 0.72, p = 0.02) or tubular atrophy (AUC, 0.88 vs. 0.74, p = 0.02). There was no difference between p-SWE and eGFR in assessing moderate-to-severe IF/TA (AUC, 0.85 vs. 0.79, p = 0.61). Therefore, combining p-SWE and eGFR is worthy of clinical popularization and application.

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.

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.

Imaging of renal fibrosis

PURPOSE OF REVIEW

Fibrosis is an important biomarker of chronic kidney injury, and a powerful predictor of renal outcome. Currently, the only method for measuring fibrotic burden is histologic analysis, which requires a kidney biopsy in humans, or kidney removal in animal models. These requirements have not only hindered our ability to manage patients effectively, but have also prevented a full understanding of renal fibrosis pathogenesis, and slowed the translation of new antifibrotic agents. The development of noninvasive fibrosis imaging tools could thus transform both clinical care and renal fibrosis research.

RECENT FINDINGS

Conventional imaging modalities have historically failed to image fibrosis successfully. However, recent exciting technological advances have greatly enhanced their capabilities. New techniques, for example, may allow imaging of the physical consequences of scarring, as surrogate measures of renal fibrosis. Similarly, other groups have developed ways to directly image extracellular matrix, either with the use of contrast-enhanced probes, or using matrix components as endogenous contrast agents.

SUMMARY

New developments in imaging technology have the potential to transform our ability to visualize renal fibrosis and to monitor its progression. In doing so, these advances could have major implications for kidney disease care, the development of new antiscarring agents, and our understanding of renal fibrosis in general.

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.

Advances of Contrast-Enhanced Ultrasonography and Elastography in Kidney Transplantation: From Microscopic to Microcosmic

Kidney transplantation is the best choice for patients with end-stage renal disease. To date, allograft biopsy remains the gold standard for revealing pathologic changes and predicting long-term outcomes. However, the invasive nature of transplant biopsy greatly limits its application. Ultrasound has been a first-line examination for evaluating kidney allografts for a long time. Advances in ultrasound in recent years, especially the growing number of studies in elastography and contrast-enhanced ultrasonography (CEUS), have shed new light on its application in kidney transplantation. Elastography, including strain elastography and shear wave elastography, is used mainly to assess allograft stiffness and, thus, predict renal fibrosis. CEUS has been used extensively in evaluating blood microperfusion, assessing acute kidney injury and detecting different complications after transplantation. Requiring the use of microbubbles also makes CEUS a novel method of gene transfer and drug delivery, enabling promising targeted diagnosis and therapy. In this review, we summarize the advances of elastography and CEUS in kidney transplantation and evaluate their potential efficiency in becoming a better complement to or even substitute for transplant biopsy in the future.

Recent advances in medical image processing for the evaluation of chronic kidney disease

Assessment of renal function and structure accurately remains essential in the diagnosis and prognosis of Chronic Kidney Disease (CKD). Advanced imaging, including Magnetic Resonance Imaging (MRI), Ultrasound Elastography (UE), Computed Tomography (CT) and scintigraphy (PET, SPECT) offers the opportunity to non-invasively retrieve structural, functional and molecular information that could detect changes in renal tissue properties and functionality. Currently, the ability of artificial intelligence to turn conventional medical imaging into a full-automated diagnostic tool is widely investigated. In addition to the qualitative analysis performed on renal medical imaging, texture analysis was integrated with machine learning techniques as a quantification of renal tissue heterogeneity, providing a promising complementary tool in renal function decline prediction. Interestingly, deep learning holds the ability to be a novel approach of renal function diagnosis. This paper proposes a survey that covers both qualitative and quantitative analysis applied to novel medical imaging techniques to monitor the decline of renal function. First, we summarize the use of different medical imaging modalities to monitor CKD and then, we show the ability of Artificial Intelligence (AI) to guide renal function evaluation from segmentation to disease prediction, discussing how texture analysis and machine learning techniques have emerged in recent clinical researches in order to improve renal dysfunction monitoring and prediction. The paper gives a summary about the role of AI in renal segmentation.

USEFULNESS OF TRANSPERINEAL VIRTUAL TOUCH QUANTIFICATION IN THE CERVIX FOR PREDICTING OUTCOME OF LABOR INDUCTION

This study aimed to explore the feasibility of transperineal virtual touch tissue quantification (VTQ) for predicting the outcome of labor induction. A total of 80 nulliparous pregnant women were included. Before labor induction, cervical length was measured by B-mode sonography, cervical stiffness was measured by VTQ, and Bishop score was assessed by vaginal examination. Subsequently, labor was induced using standard oxytocin infusion in all patients. Delivery within 24 hours after labor induction was classified as spontaneous delivery; otherwise, cesarean delivery was performed. Out of 80 participants, 48 (60%) delivered vaginally and 32 (40%) underwent cesarean delivery. The cervical length was significantly longer and the shear wave velocity (SWV) was greater in the cesarean delivery group than in the vaginal delivery group (p = 0.004 and p < 0.000, respectively). Logistic regression analysis indicated that only the mean SWV had independent predictive value for the outcome of labor induction (p = 0.011). The best diagnostic cut-off point of the mean SWV was 1.23 m/s, with a sensitivity of 93.8% and a specificity of 89.6%. Transperineal VTQ technique could predict the outcome of labor induction using oxytocin.

Comparison of Supersonic Shear Wave Imaging-Derived Renal Parenchyma Stiffness Between Diabetes Mellitus Patients With and Without Diabetic Kidney Disease

This study aims to evaluate the difference in renal parenchyma stiffness assessed by measuring Young's modulus (YM) using a supersonic shear wave imaging (SSI) technique among healthy patients and patients with type 2 diabetes mellitus (DM) with and without diabetic kidney disease (DKD). We analyzed the correlations of YM with clinical information and conventional ultrasound parameters. All patients (N = 124) were divided into three groups: (i) healthy patients (patients without kidney disease or type 2 DM, N = 31); (ii) patients with type 2 DM without kidney disease (N = 38); and (iii) patients with DKD (N = 55). Conventional and SSI ultrasound examinations were performed in all individuals for both kidneys. Then, we recorded renal length, width, parenchyma thickness, interlobar arterial resistive index (RI) and values of mean, mininum and maximum YM. The mean values of these parameters for the left and right kidneys were calculated for statistical analysis. Statistical significance was considered at p < 0.05. Among all ultrasound parameters, the mean YM demonstrated the largest area under the receiver operating characteristic (ROC) curve (0.860). The areas under the ROC curve (AUCs) for renal length, width, parenchyma thickness, interlobar arterial RI, minimum YM and maximum YM were 0.493, 0.616, 0.507, 0.733, 0.848 and 0.794, respectively. The corresponding cutoff value of mean YM was 31.73 kPa, with a sensitivity of 85.5% and a specificity of 71.0%. The mean YM in patients with type 2 DM without kidney disease (31.44 ± 3.83 kPa) was significantly higher than that in the healthy group (26.45 ± 4.32 kPa) and lower than that in the DKD group (37.60 ± 6.56 kPa). Patients with type 2 DM without kidney disease were considered as stage 0 of DKD. Thus, the mean YM in the control group was significantly lower than that in the stage 0, 2, 3, 4 and 5 subgroups. The mean YM in the stage 0-2 subgroups was lower than that in the stage 5 group, and the mean YM in the stage 0 group was lower than that in the stage 4 group. In the DKD group, the mean YM had a positive correlation with cystine-c (r = 0.634), urea (r = 0.596), creatine (r = 0.690), uric acid (r = 0.263), albumin/creatinine ratio (r = 0.428) and the presence or absence of diabetic retinopathy (r = 0.354). The mean YM also had a negative correlation with the estimated glomerular filtration rate (r = -0.657). SSI is a non-invasive method with which to diagnose DKD and has a performance superior to that of conventional ultrasound. In addition, SSI may provide a secondary index for the staging of DKD and the monitoring of renal damage in type 2 DM patients.

Shear-Wave Elastography Variability Analysis and Relation with Kidney Allograft Dysfunction: A Single-Center Study

Shear-wave elastography (SWE) showed the absence or presence of significant differences among stable kidney allograft function and allograft dysfunction. We evaluated the variability of kidney allograft stiffness in relation to allograft dysfunction, respectively, in terms of a correlation of stiffness with patients' characteristics. A single-center prospective study on patients who had undergone renal transplantation was conducted between October 2017 and November 2018. Patients were clinically classified as having a stable allograft function or allograft dysfunction. SWE examinations performed by the same radiologist with a LOGIQ E9 were evaluated. Ten measurements were done for Young's modulus (kPa) at the level of allograft cortex and another ten at the level of medulla. Eighty-three SWE examinations from 63 patients, 69 stable allografts, and 14 allografts with dysfunction were included in the analysis. The intra-examinations stiffness showed high variability, with the quantile covariation coefficient ranging from 2.21% to 45.04%. The inter-examinations stiffness showed heterogeneity (from 28.66% to 42.38%). The kidney allograft cortex stiffness showed significantly higher values in cases with dysfunction (median = 28.70 kPa, interquartile range (IQR) = (25.68-31.98) kPa) as compared to those with stable function (median = 20.99 kPa, interquartile range = (16.08-27.68) kPa; p-value = 0.0142). Allograft tissue stiffness (both cortex and medulla) was significantly negatively correlated with body mass index (-0.44, p-value < 0.0001 for allograft cortex and -0.42, p-value = 0.0001 for allograft medulla), and positively correlated with Proteinuria/Creatinuria ratio (0.33, p-value = 0.0021 for allograft cortex and 0.28, p-value = 0.0105 for allograft medulla) but remained statistically significant only in cases with stable function. The cortical tissue stiffness proved significantly higher values for patients with allograft dysfunction as compared to patients with stable function, but to evolve as an additional tool for the evaluation of patients with a kidney transplant and to change the clinical practice, more extensive studies are needed.

Serum N-glycan profiling can predict biopsy-proven graft rejection after living kidney transplantation

BACKGROUND

To evaluate whether serum N-glycan profile can be used as a diagnostic marker of graft rejection after living-donor kidney transplants (KT).

METHODS

We retrospectively examined 174 KT recipients at five medical centers. N-Glycan levels were analyzed in postoperative serum samples using glycoblotting combined with mass spectrometry. We developed an integrated score to predict graft rejection based on a combination of age, gender, immunological risk factors, and serum N-glycan levels at post-KT day D1 and D7. Rejection-free survival rates stratified by the sum of integrated scores (D1 + D7) were evaluated using Kaplan-Meier curves.

RESULTS

Of 174, 52 showed graft rejection (Rejection-pos. group) and 122 recipients did not show graft rejection (Rejection-neg. group). The integrated scores were significantly higher in the Rejection-pos. group than those of the Rejection-neg. group. Area-under-curve (AUC) value of integrated scores at post-KT D1, and D7 were 0.84 and 0.84, respectively. The sum of integrated scores (D1 + D7) ≥ 0.50 identified graft rejection with 81% sensitivity and 80% specificity; with an AUC value of 0.87. Recipients with higher sum of integrated scores (D1 + D7 ≥ 0.5) had significantly shorter rejection-free survival than those with lower scores.

CONCLUSION

Evaluation of serum N-glycosylation profiles can identify recipients who are prone to rejection.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T₁/T₂ mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.