Non-invasive evaluation of stable renal allograft function using point shear-wave elastography

Role of Shear Wave Elastography for Assessment of Renal-Allograft Fibrosis and its Correlation With Histopathology

OBJECTIVES

To investigate whether shear wave elastography (SWE) can accurately identify interstitial fibrosis and tubular atrophy (IFTA) in chronic renal allograft injury (CRAI) and whether it can differentiate between different grades of IFTA.

MATERIALS AND METHODS

Prospective observational study on renal transplant recipients who presented with CRAI. Patient selection was done on the basis of clinical presentation, serum creatinine, and eGFR levels. Biopsy and SWE were performed and SWE values were correlated with histopathological findings according to Banff schema. Receiver operating characteristic (ROC) was also analyzed to assess the diagnostic efficacy of SWE.

RESULTS

Sxity-one patients were evaluated. Ten patients had no IFTA, 33 patients had mild IFTA, 16 patients had moderate IFTA, and 2 patients had severe IFTA. Mean parenchymal stiffness values in no IFTA, mild IFTA, moderate IFTA and severe IFTA were 39.86 ± 2.17 kPa (3.64 ± 0.09 m/s), 41.59 ± 3.36 kPa (3.71 ± 0.15 m/s), 47.59 ± 3.34 kPa (3.98 ± 0.14 m/s), and 53.83 ± 1.41 kPa (4.25 ± 0.03 m/s), respectively. SWE values of parenchymal stiffness reached statistical significance to differentiate between mild, moderate, and severe IFTA. ROC analysis revealed cut-off values of 45.09 kPa (3.89 m/s) to differentiate between mild IFTA and moderate IFTA, 52.06 kPa (4.18 m/s) to differentiate between moderate IFTA and severe IFTA with acceptable sensitivity and specificity.

CONCLUSION

SWE is a non-invasive and cost-effective imaging tool to evaluate the disease status of renal allografts affected by CRAI. Thus, it can be of paramount importance if added to the regular follow-up imaging protocol of renal allograft along with grayscale and Doppler imaging.

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.

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.

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.

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.

Quantitative ultrasound for non-invasive evaluation of subclinical rejection in renal transplantation

OBJECTIVES

This study aimed to investigate the predictive efficacy of shear-wave elastography, superb microvascular imaging (SMI), and CEUS for allograft rejection in kidney transplants without graft dysfunction.

METHODS

From January 2021 to November 2021, 72 consecutive patients who underwent both allograft biopsy and ultrasound were evaluated. Blood test results were obtained within a week of the ultrasound examinations, which were performed before the protocol biopsy. Resistive index (RI), tissue viscoelasticity, vascular index, and quantitative CEUS parameters were measured. Patients were divided based on biopsy results into the rejection and non-rejection groups.

RESULTS

Among the 72 patients, 21 patients had pathological characteristics of acute rejection. RI of allograft was significantly higher in the rejection group (p = 0.007), compared to the non-rejection group. There were no significant between-group differences in vascular indices of SMI, mean elasticity, and mean viscosity. Meanwhile, among the parameters obtained by the time-intensity curve on CEUS, the cortical and medullary ratios of average contrast signal intensity, peak enhancement, wash-in area AUC, wash-in perfusion index, wash-out AUC, and wash-in and wash-out AUC were significantly different between the two groups (p < 0.05). In the receiver operating characteristic curve analysis for predicting allograft rejection, the AUC was 0.853 for the combination of six CEUS parameters, RI, and blood urea nitrogen.

CONCLUSIONS

Among non-invasive quantitative ultrasound measurements, CEUS parameters are the most useful for diagnosing subclinical allograft rejection. Furthermore, the combination of CEUS parameters, RI, and blood urea nitrogen may be helpful for the early detection of renal allograft rejection.

KEY POINTS

• Among non-invasive quantitative ultrasound measurements, CEUS parameters are the most useful for the diagnosis of subclinical allograft rejection. • On CEUS, the C/M ratios of MeanLin, PE, WiAUC, WiPI, WoAUC, and WiWoAUC are significantly lower in the rejection group; the combination of these showed reliable predictive performance for rejection. • The combination of CEUS parameters, RI, and BUN has a high predictive capability for subclinical allograft rejection.

Prediction of Renal Function 1 Year After Transplantation Using Machine Learning Methods Based on Ultrasound Radiomics Combined With Clinical and Imaging Features

Kidney transplantation is the most effective treatment for advanced chronic kidney disease (CKD). If the prognosis of transplantation can be predicted early after transplantation, it might improve the long-term survival of patients with transplanted kidneys. Currently, studies on the assessment and prediction of renal function by radiomics are limited. Therefore, the present study aimed to explore the value of ultrasound (US)-based imaging and radiomics features, combined with clinical features to develop and validate the models for predicting transplanted kidney function after 1 year (TKF-1Y) using different machine learning algorithms. A total of 189 patients were included and classified into the abnormal TKF-1Y group, and the normal TKF-1Y group based on their estimated glomerular filtration rate (eGFR) levels 1 year after transplantation. The radiomics features were derived from the US images of each case. Three machine learning methods were employed to establish different models for predicting TKF-1Y using selected clinical and US imaging as well as radiomics features from the training set. Two US imaging, four clinical, and six radiomics features were selected. Then, the clinical (including clinical and US image features), radiomics, and combined models were developed. The area under the curves (AUCs) of the models was 0.62 to 0.82 within the test set. Combined models showed statistically higher AUCs than the radiomics models (all p-values <.05). The prediction performance of different models was not significantly affected by the different machine learning algorithms (all p-values >.05). In conclusion, US imaging features combined with clinical features could predict TKF-1Y and yield an incremental value over radiomics features. A model integrating all available features may further improve the predictive efficacy. Different machine learning algorithms may not have a significant impact on the predictive performance of the model.

Application value of shear-wave elastography combined with monochrome superb microvascular imaging in renal allograft chronic rejection

BACKGROUND

Conventional ultrasound (US), which include gray scale US and Doppler US, is the first-line imaging modality for the evaluation of renal allograft; however, conventional US indicators have limitations.

OBJECTIVE

To explore the application value of shear-wave elastography (SWE) combined with monochrome superb microvascular imaging (mSMI) in renal allograft chronic rejection (CR).

METHODS

From November 2021 to February 2022 in the Lanzhou University Second Hospital, the US features of 54 patients with renal allograft were retrospectively analyzed. Patients were categorized into two groups: stable group(n = 44) and CR group(n = 10), with clinical diagnosis as reference standard. The vascular index (VI) on mSMI and parenchymal stiffness were measured in the middle cortex of all renal allografts and receiver operating characteristic (ROC) curves were drawn to evaluate the feasibility of differentiation. Statistically significant US features and biochemical indicators such as creatinine were scored, and the results of the scores were analyzed by ROC curve.

RESULTS

The VI on mSMI of the stable group (49.5±2.0) was significantly greater than that of the CR group (33.8±5.9) (P = 0.028). There was a statistically significant difference in parenchymal stiffness between stable group (16.2kPa±1.2) and CR group (33.9kPa±6.6) (P = 0.027). The sensitivity was 90% and specificity was 81.8% of the scores in the differentiation of stable group from CR group (cut-off value, 2; P = 0.000).

CONCLUSION

SWE combined with mSMI may help differentiate stable renal allograft from renal allograft CR and have the potential application value in the diagnosis of renal allograft CR.

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 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.

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.

Magnetic resonance elastography vs. point shear wave ultrasound elastography for the assessment of renal allograft dysfunction

PURPOSE

To investigate the utility of magnetic resonance elastography (MRE) vs. ultrasound (US) point shear wave elastography (pSWE) for the assessment of chronic renal allograft dysfunction, prediction of outcome and determine the correlation with Banff pathology scores.

METHODS

In this IRB approved prospective study, 27 enrolled patients with functional (n = 15) and chronic dysfunctional (n = 12) renal allografts underwent same day 2D MRE and pSWE. Histogram parameters [including mean, median, standard deviation, kurtosis and skewness] of the magnitude of the complex shear modulus (MRE) and median Young's modulus (pSWE) were measured in the cortex (MRE and pSWE) and combined corticomedullary regions (MRE). Histopathology was available for 16 patients (4 functional, 12 dysfunctional).

RESULTS

MRE and pSWE stiffness were not significantly different between functional and dysfunctional groups (p range 0.139-0.347). The skewness of MRE corticomedullary stiffness was significantly lower (p = 0.04) in patients with chronic dysfunction and correlated significantly with Banff histopathologic scores (range r=-0.518-0.567, p = 0.035-0.040). MRE cortical and corticomedullary mean stiffness showed strong performance in predicting graft loss/relist (AUC 0.958, p = 0.011 for both). Reliable pSWE measurements were obtained in 13 patients (48 %). pSWE stiffness did not correlate with Banff scores and did not predict outcome.

CONCLUSIONS

The skewness of MRE corticomedullary stiffness is sensitive to changes in chronic allograft dysfunction, while mean/median MRE renal stiffness and median US stiffness did not differentiate patients with stable function vs those with chronic renal allograft dysfunction. MRE corticomedullary mean stiffness appears to be a predictor of graft loss/relist. pSWE was not found to be a useful method for assessing renal allografts.

Evaluation of maternal renal cortical elasticity in pregnancies with early- and late-onset preeclampsia

Objective: The current study aimed to investigate renal cortical elasticity (RCE) in early- and late-onset preeclampsia patients and compare the results with healthy controls.Materials and methods: The study consisted of 136 pregnant women. Three groups were identified as; the late-onset preeclampsia (LOP) group (n = 40), the early-onset preeclampsia (EOP) group (n = 32) and the control group (n = 64). RCE values were measured by point shear wave elastography (pSWE). Nine measurements were taken for each kidney and the mean of nine measurements was accepted as the mean RCE value for each kidney. The arithmetic mean of left and right RCE values was accepted as the overall RCE value of a subject. Groups were compared in terms of clinical and biochemical parameters, ultrasonography findings and pSWE values.Results: There was a statistically significant difference between groups in terms of overall RCE values (F[2,133] = 17.96, p < .001). Post hoc comparisons indicated that both preeclampsia groups exhibited significantly higher RCE values than the control group. However, overall RCE values were not significantly different between the EOP and LOP groups. Overall RCE values were significantly and positively correlated with systolic blood pressure (r = 0.363, p < .001), diastolic blood pressure (r = 0.347, p < .001), proteinuria (r = 0.343, p < .001), serum creatinine level (r = 0.181, p = .035), serum uric acid level (r = 0.243, p = .004) and blood urea nitrogen (r = 0.27, p = .001).Conclusion: Our study demonstrated that maternal renal cortical stiffness increased in women with preeclampsia. The increased RCE values may be indicative for the severity of preeclampsia due to positive correlations between renal cortical stiffness and systolic - diastolic blood pressure and serum creatinine level.

Ultrasound elastography correlations between anthropometrical parameters in kidney transplant recipients

Ultrasound elastography (USE) is a method to assess the stiffness of parenchymatous organs. Shear wave elastography (SWE) is considered to be the most suitable elastography method for the non-invasive kidney transplant (KTx) elasticity assessment. The aim of this study was to assess the implementability of SWE for the evaluation of kidney transplant elasticity measurement depending on the depth of an allograft, body mass index (BMI) and donor age. Secondly, to investigate the associations between SWE stiffness measurements and the clinical parameters. This cross-sectional prospective study involved consecutive 100 KTx patients were grouped according to time from transplantation and their BMI (in BMI<25 group the mean was 22.1±2.4, n=42 and in BMI≥25 group the mean BMI was 29.9±3.3, n=58). Mean estimated glomerular filtration rate was almost similar in both groups: <25 group 54.3 and ≥25 group 53.4 mL/min. Mean elastography results were found statistically different (p=0.006) BMI<25 (8.95±5.84 kPa) and BMI≥25 (5.95±3.16 kPa) groups. Significant correlation was found between SWE and the depth of the measurement (r=-0.4, p<0.05). The variations in USE stiffness values were smallest in patients group with lower BMI. In conclusion, we demonstrated that the non-invasive USE measurement stiffness result depends on a patient's BMI, the depth of renal allograft and donor age.

Renal Allograft Rejection: Noninvasive Ultrasound- and MRI-Based Diagnostics

To date, allogeneic kidney transplantation remains the best available therapeutic option for patients with end-stage renal disease regarding overall survival and quality of life. Despite the advancements in immunosuppressive drugs and protocols, episodes of acute allograft rejection, a sterile inflammatory process, continue to endanger allograft survival. Since effective treatment for acute rejection episodes is available, instant diagnosis of this potentially reversible graft injury is imperative. Although histological examination by invasive core needle biopsy of the graft remains the gold standard for the diagnosis of ongoing rejection, it is always associated with the risk of causing substantial graft injury as a result of the biopsy procedure itself. At the same time, biopsies are not immediately feasible for a considerable number of patients taking anticoagulants due to the high risk of complications such as bleeding and uneven distribution of pathological changes within the graft. This can result in the wrong diagnosis due to the small size of the tissue sample taken. Therefore, there is a need for a tool that overcomes these problems by being noninvasive and capable of assessing the whole organ at the same time for specific and fast detection of acute allograft rejection. In this article, we review current state-of-the-art approaches for noninvasive diagnostics of acute renal transplant inflammation, i.e., rejection. We especially focus on nonradiation-based methods using magnetic resonance imaging (MRI) and ultrasound.

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.

Shear wave elastography in the evaluation of renal parenchymal stiffness in patients with chronic kidney disease

OBJECTIVE

To investigate the use of shear wave elastography (SWE)-derived estimates of Young's modulus (YM) as an indicator to detect abnormal renal tissue diagnosed by estimated glomerular filtration rate (eGFR).

METHODS

The study comprised 106 chronic kidney disease (CKD) patients and 203 control subjects. Conventional ultrasound was performed to measure the kidney length and cortical thickness. SWE imaging was performed to measure renal parenchymal stiffness. Diagnostic performance of SWE and conventional ultrasound were correlated with serum creatinine, urea levels and eGFR.

RESULTS

Pearson's correlation coefficient revealed a negative correlation between YM measurements and eGFR (r = -0.576, p < 0.0001). Positive correlations between YM measurements and age (r = 0.321, p < 0.05), serum creatinine (r = 0.375, p < 0.0001) and urea (r = 0.287, p < 0.0001) were also observed. The area under the receiver operating characteristic curve for SWE (0.87) was superior to conventional ultrasound alone (0.35-0.37). The cut-off value of less or equal to 4.31 kPa suggested a non-diseased kidney (80.3% sensitivity, 79.5% specificity).

CONCLUSION

SWE was superior to renal length and cortical thickness in detecting CKD. A value of 4.31 kPa or less showed good accuracy in determining whether a kidney was diseased or not. Advances in knowledge: On SWE, CKD patients show greater renal parenchymal stiffness than non-CKD patients. Determining a cut-off value between normal and diseased renal parenchyma may help in early non-invasive detection and management of CKD.