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

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.

Renal stiffness measured by shear wave elastography and its relationship with perirenal fat in patients with chronic kidney disease

PURPOSE

This study aimed to utilize shear wave elastography (SWE) to assess changes in renal stiffness and its influencing factors in patients with chronic kidney disease (CKD) across different estimated glomerular filtration rate (eGFR) categories. It also sought to determine the correlation between perirenal fat (PF) and renal stiffness at various stages of CKD.

METHODS

A total of 190 CKD patients and 50 healthy controls were evaluated. Clinical parameters, conventional renal ultrasound measurements, PF, and renal stiffness trends were assessed separately. Factors independently associated with renal stiffness and PF were further analyzed.

RESULTS

Renal parenchymal stiffness was significantly higher in the Albumin-CKD G1-2 (ALB-CKD G1-2) and CKD G3 groups than in the control group (p < 0.05). The parenchymal stiffness of the CKD G3 group was higher than that of the ALB-CKD G1-2 group (p < 0.05). The independent factors of renal parenchymal stiffness varied at different stages of disease development, with eGFR and PF being significant factors in the CKD G3 group. PF was elevated in the ALB-CKD G1-2 and CKD G3 groups compared to the control group, and the independent factors of PF varied across different stages, although waist circumference remained a common factor.

CONCLUSION

Using SWE to detect renal elastic moduli can effectively assess changes in renal stiffness in patients with CKD with varying eGFRs. PF is an independent factor of renal stiffness in patients with CKD G3, providing a foundation for early diagnosis and clinical treatment.

The value of shear wave elasticity and shear wave dispersion imaging to evaluate the viscoelasticity of renal parenchyma in children with glomerular diseases

BACKGROUND

To study the value of shear wave elasticity and shear wave dispersion imaging to evaluate the viscoelasticity of renal parenchyma in children with glomerular diseases.

METHODS

Forty-three children with glomerular diseases were prospectively evaluated by shear wave elasticity (SWE) and shear wave dispersion imaging (SWD); 43 healthy volunteers served as the control group. The shear wave velocities (SWV) and the dispersion slopes were measured at the upper, middle, and lower poles of both kidneys. The analysis of mean SWV and mean dispersion slope in control and patient groups was used to further evaluate the value of SWE and SWD in the viscoelasticity of renal parenchyma in children with glomerular disease.

RESULTS

The mean SWV in children with glomerular disease was higher than that in the healthy control group (1.61 ± 0.09 m/s vs. 1.43 ± 0.07 m/s, p < 0.001). Compared with healthy group, the mean dispersion slope in children with glomerular disease was significantly increased (13.5 ± 1.39 (m/s)/kHz vs. 12.4 ± 1.40 (m/s)/kHz, p < 0.001). Correlation analysis showed absence of correlation between the SWV and dispersion slope of occult blood, serum creatinine, 24-h urine protein, blood albumin, BMI and ROI box depth of children with glomerular disease.

CONCLUSIONS

The present study shows that it is feasible to use SWE and SWD to evaluate the difference of viscoelasticity of the renal parenchyma between healthy children and those with glomerular disease.

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.

Sedative effect with the combination of butorphanol and midazolam on two-dimensional shear wave elastography of pancreas and kidney in healthy dogs

OBJECTIVE

To evaluate the sedative effect of a combination of butorphanol and midazolam on 2-D shear wave elastography (SWE) of the kidneys and pancreas in dogs.

ANIMALS

8 clinically healthy dogs.

PROCEDURES

We conducted a 2-D SWE examination of the bilateral kidneys and the pancreas before and after IV of 0.2 mg/kg butorphanol and 0.1 mg/kg midazolam in each dog. We performed 2-D SWE on the left kidney via a subcostal approach with the dog in right lateral recumbency, on the right kidney via the intercostal approach with the dog in left lateral recumbency, and on the right lobe of the pancreas via the subcostal approach. Subsequently, the pancreas and kidney shear wave velocities (SWV) pre- and postsedation were compared.

RESULTS

On qualitative evaluation using color mapping, the pancreas and kidneys showed a homogeneous blue-to-green color in pre- and post-sedation 2-D SWE. There was no significant difference in SWV pre- and post-sedation in the pancreas and kidneys.

CLINICAL RELEVANCE

Intravenous administration of a combination of 0.2 mg/kg butorphanol and 0.1 mg/kg midazolam did not change the 2-D SWE of the pancreas and kidneys significantly. The combination of butorphanol and midazolam can be used in healthy dogs for 2-D SWE evaluation of the pancreas and kidneys, especially when the patient is uncooperative during the examination.

Relationship between Novel Elastography Techniques and Renal Fibrosis-Preliminary Experience in Patients with Chronic Glomerulonephritis

INTRODUCTION

A renal biopsy represents the gold standard in the diagnosis, prognosis, and management of patients with glomerulonephritis. So far, non-invasive elastographic techniques have not confirmed their utility in replacing a biopsy; however, the new and improved software from Hologic Supersonic Mach 30 is a promising method for assessing the renal tissue's stiffness and viscosity. We investigated whether this elastography technique could reveal renal tissue fibrosis in patients with chronic glomerulonephritis.

MATERIALS AND METHODS

Two-dimensional-shear wave elastography (SWE) PLUS and viscosity plane-wave ultrasound (Vi PLUS) assessments were performed in 40 patients with chronic glomerulopathies before being referred for a renal biopsy. For each kidney, the mean values of five stiffness and viscosity measures were compared with the demographic, biological, and histopathological parameters of the patients.

RESULTS

In total, 26 men and 14 women with a mean age of 52.35 ± 15.54 years, a mean estimated glomerular filtration rate (eGFR) of 53.8 ± 35.49 mL/min/1.73m², and a mean proteinuria of 6.39 ± 7.42 g/24 h were included after providing their informed consent. Out of 40 kidney biopsies, 2 were uninterpretable with inappropriate material and were divided into four subgroups based on their fibrosis percentage. Even though these elastography techniques were unable to differentiate between separate fibrosis stages, when predicting between the fibrosis and no-fibrosis group, we found a cut-off value of <20.77 kPa with the area under the curve (AUC) of 0.860, a p < 0.001 with 88.89% sensitivity, and a 75% specificity for the 2D SWE PLUS measures and a cut-off value of <2.8 Pa.s with an AUC of 0.792, a p < 0.001 with 94% sensitivity, and a 60% specificity for the Vi PLUS measures. We also found a cut-off value of <19.75 kPa for the 2D SWE PLUS measures (with an AUC of 0.789, p = 0.0001 with 100% sensitivity, and a 74.29% specificity) and a cut-off value of <1.28 Pa.s for the Vi PLUS measures (with an AUC 0.829, p = 0.0019 with 60% sensitivity, and a 94.29% specificity) differentiating between patients with over 40% fibrosis and those with under 40%. We also discovered a positive correlation between the glomerular filtration rate (eGFR) and 2D-SWE PLUS values (r = 0.7065, p < 0.0001) and Vi PLUS values (r = 0.3637, p < 0.0211). C reactive protein (CRP) correlates with the Vi PLUS measures (r = -0.3695, p = 0.0189) but not with the 2D SWE PLUS measures (r = -0.2431, p = 0.1306).

CONCLUSION

Our findings indicate that this novel elastography method can distinguish between individuals with different stages of renal fibrosis, correlate with the renal function and inflammation, and are easy to use and reproducible, but further research is needed for them to be employed routinely in clinical practice.

Non-Invasive Evaluation of Kidney Elasticity and Viscosity in a Healthy Cohort

Introduction: There is currently a lack of published data on kidney elasticity and viscosity. Non-invasive techniques, such as two-dimensional shear-wave elastography (2D-SWE PLUS) and viscosity plane-wave ultrasound (Vi PLUS), have surfaced as new detection methods, which, thanks to efficient processing software, are expected to improve renal stiffness and viscosity measurements. This study aims to be the first one to assess the normal range values in normal renal function subjects and to investigate the factors that impact them. Methods: We conducted a cross-sectional study employing 50 participants (29 women and 21 men) with a mean age of 42.22 ± 13.17, a mean estimated glomerular filtration rate (eGFR) of 97.12 ± 11 mL/min/1.73 m2, a mean kidney length of 10.16 ± 0.66 cm, and a mean body mass index (BMI) of 24.24 ± 3.98. With a C6-1X convex transducer and the Ultra-FastTM software available on the Hologic Aixplorer Mach 30 ultrasound system, we acquired five measurements of renal cortical stiffness and viscosity (achieved from five distinct images in the middle part of the subcapsular cortex) from each kidney. The ten measurements’ median values correlated with the participant’s demographical, biological, and clinical parameters. Results: The mean kidney elasticity was 31.88 ± 2.89 kiloPascal (kPa), and the mean viscosity was 2.44 ± 0.57 Pascal.second (Pa.s) for a mean measurement depth 4.58 ± 1.02 cm. Renal stiffness seemed to be influenced by age (r = −0.7047, p < 0.0001), the measurement depth (r = −0.3776, p = 0.0075), and eGFR (r = 0.6101, p < 0.0001) but not by BMI (r = −0.2150, p = 0.1338), while viscosity appeared to be impacted by age (r = −0.4251, p = 0.0021), eGFR (r = 0.4057, p = 0.0038), the measurement depth (r = −0.4642, p = 0.0008), and BMI (r = −0.3676, p = 0.0086). The results of the one-way ANOVA used to test the differences in the variables among the three age sub-groups are statistically significant for both 2D-SWE PLUS (p < 0.001) and Vi PLUS (p = 0.015). The method found good intra-operator reproducibility for the 2D-SWE PLUS measurements, with an ICC of 0.8365 and a 95% CI of 0.7512 to 0.8990, and for the Vi PLUS measurements, with an ICC of 0.9 and a 95% CI of 0.8515 to 0.9397. Conclusions: Renal stiffness and viscosity screening may become an efficacious, low-cost way to gather supplemental diagnostic data from patients with chronic kidney disease (CKD). The findings demonstrate that these non-invasive methods are highly feasible and not influenced by gender and that their values correlate with renal function and decrease with age progression. Nevertheless, more research is required to ascertain their place in clinical practice.

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.

Assessment of Renal Allograft Stiffness and Viscosity Using 2D SWE PLUS and Vi PLUS Measures-A Pilot Study

Elastography is a useful noninvasive tool for the assessment of renal transplant recipients. 2D-shear wave elastography (SWE) PLUS and viscosity plane-wave ultrasound (Vi PLUS) have emerged as novel techniques that promise to offer improved renal stiffness and viscosity measures due to improved processing algorithms. Methods: We performed a cross-sectional study of 50 kidney transplanted patients (16 women, 34 men; mean age of 47.5 ± 12.5; mean estimated glomerular filtration rate (eGFR) estimated by Chronic Kidney Disease Epidemiology Collaboration formula: 52.19 ± 22.6 mL/min/1.73 m2; and a mean duration after transplant of 10.09 ± 5 years). For every patient, we obtained five valid measurements of renal stiffness (obtained from five different frames in the cortex of the renal graft), and also tissue viscosity, with a C6-1X convex transducer using the Ultra-Fast™ software available on the Aixplorer Mach 30 ultrasound system (Supersonic Imagine, Aix-en-Provence, France). The median values of elastographic and viscosity measures have been correlated with the patients’ demographic, biological, and clinical parameters. Results: We obtained a cut-off value of renal cortical stiffness of <27.3 kiloPascal(kPa) for detection of eGFR < 60 mL/min/1.73 m2 with 80% sensitivity and 85% specificity (AUC = 0.811, p < 0.0001), a cut-off value of <26.9 kPa for detection of eGFR < 45 mL/min/1.73 m2 with 82.6% sensitivity and 74% specificity (AUC = 0.789, p < 0.0001), and a cut-off value of <23 kPa for detection of eGFR < 30 mL/min/1.73 m2 with 88.8% sensitivity and 75.6% specificity (AUC = 0.852, p < 0.0001). We found a positive correlation coefficient between eGFR and the median measure of renal cortical stiffness (r = 0.5699, p < 0.0001), between eGFR the median measure of viscosity (r = 0.3335, p = 0.0180), between median depth of measures and renal cortical stiffness (r = −0.2795, p = 0.0493), and between median depth of measures and body mass index (BMI) (r = 0.6574, p < 0.0001). Our study showed good intra-operator agreement for both 2D SWE PLUS measures—with an intraclass correlation coefficient (ICC) of 0.9548 and a 95% CI of 0.9315 to 0.9719—and Vi PLUS, with an ICC of 0.8323 and a 95% CI of 0.7457 to 0.8959. The multivariate regression model showed that 2D SWE PLUS values were associated with eGFR, Vi PLUS, and depth of measures. Conclusions: Assessment of renal allograft stiffness and viscosity may prove to be an effective method for identifying patients with chronic allograft injury and could prove to be a low-cost approach to provide additional diagnostic information of kidney transplanted patients.

Shear wave elastography in early diabetic kidney disease

OBJECTIVE:

This study aimed to analyze the kidneys among the subjects with early stages of type 2 diabetic kidney disease by shear wave elastography quantitatively.

METHODS:

A total of 108 patients with type 2 diabetic kidney disease and 17 control subjects were enrolled. According to the estimated glomerular filtration rate and urinary albumin-to-urinary creatinine ratio, patients were classified into stages 1 to 3 diabetic kidney disease. Grayscale ultrasound andshear wave elastography were performed. The sizes, depths, and shear wave elastography values were recorded. These parameters were compared between the diabetic kidney disease and the control subjects.

RESULTS:

The mean shear wave elastography values were significantly higher in the diabetic kidney disease group (10.156±1.75 kPa vs. 8.241±1.4 kPa; p<0.001). We obtained statistically significantly higher shear wave elastography values in stages 2 and 3 diabetic kidney disease subjects than control subjects and in patients with stage 3 diabetic kidney disease compared to those with stage 1 diabetic kidney disease (p<0.05 for all). We obtained a cutoff value of 9.23 kPa for predicting diabetic kidney disease in early stages, with a sensitivity of 67% and a specificity of 82%.

CONCLUSION:

Shear wave elastography may be used as a noninvasive, simple, and quantitative method to provide diagnostic information as a part of routine management of patients with type 2 diabetes mellitus, especially in the early stages of diabetic kidney disease.

Are the Currently Available Elastography Methods Useful in the Assessment of Chronic Kidney Disease? A Systematic Review and a Meta-Analysis

Background: We require an quantitative imaging technique for the diagnosis and assessment of chronic kidney disease (CKD). Renal elastography has been widely used in recent years in different studies; however, the results across them are not consistent and, as a result, we conducted a meta-analysis of the published literature on this topic. Methods: The databases of PubMed, Medscape, Medline were searched for all studies published in English from 2010 until November 2021 that evaluated kidney shear wave speed (SWS) by elastography in patients with CKD. Trial design, methodological information, patient characteristics, interventions, results, and outcome data were all collected from each study according to a set protocol. Results: We found 37 publications, yet only 18 studies that utilized point shear wave elastography (Virtual Touch Quantification—VTQ system) were compared because the values achieved using different types of elastography are not evaluable. Finally, 1995 attendees (1241 patients with CKD versus 781 healthy subjects as the control group) were included. When comparing mean values of kidney SWS between studies we found increased heterogeneity Q = 513.133; DF = 10; p < 0001, I2 (inconsistency) = 98.12% (95% CI for I2 97.52–98.57%). With a standardized mean difference of −0.216, patients with CKD have a lower kidney SWS than healthy controls. A positive association between kidney SWS and eGFR was also discovered across the presented studies, with a pooled correlation coefficient of 0.38 (Z = 10.3, p < 0.001), Q = 73.3, DF = 5, p < 000.1, I2 = 93.18% (95% CI for I2 87.86 to 96.18). The pooled area under the ROC curve for kidney SWS to predict chronic kidney disease was 0.831 (95% CI, p < 0.001), Q = 28.32, DF = 6, p = 0.0001, I2 = 78.8% (95% CI for I2 56.37 to 89.72). In the four articles that used the Elast-PQ method, the data presented were insufficient for statistical analysis: area under the curve (AUC) values are used to compare distinct characteristics (differentiating kidney SWS between mildly and moderately impaired kidneys, between non-diabetic/prediabetic/diabetic patients, or kidney SWS between the CKD and control group), therefore not being suitable for further evaluation. Conclusions: The results show that patients with CKD have a lower kidney SWS than healthy controls. However, the number of studies involving renal elastography that have been published is limited and show an increased heterogeneity. Further research is needed to determine which factors actually influence kidney SWS in CKD patients and, as a result, to specify the role and indication of renal elastography in clinical practice.

Glycated Hemoglobin and Risk of Arterial Stiffness in a Chinese Han Population: A Longitudinal Study

BACKGROUND AND AIMS

Glycated hemoglobin (HbA1c) associates with the risk of arterial stiffness, and such association can be found between fasting blood glucose (FBG), postprandial blood glucose (PBG), triglyceride-glucose index (TyG index), and arterial stiffness. However, the results were inconsistent, longitudinal studies were sparse, and comparison of these glycemic parameters was less conducted. We aimed to explore the longitudinal relationship between HbA1c and arterial stiffness and compare the effect of the parameters.

METHODS

Data were collected from 2011 to 2019 in Beijing Health Management Cohort (BHMC) study. Cox proportional hazard models were fitted to investigate the association between the parameters and arterial stiffness. A generalized estimation equation (GEE) analysis was conducted to investigate the effect of repeated measurements of glycemic parameters. A receiver operating characteristic (ROC) analysis was performed to compare the predictive value of glycemic parameters for arterial stiffness.

RESULTS

Among 3,048 subjects, 591 were diagnosed as arterial stiffness during the follow-up. The adjusted hazard ratio (HR) [95% confidence interval (CI)] for arterial stiffness of the highest quartile group of HbA1c was 1.63 (1.22-2.18), which was higher than those of FBG, PBG, and TyG index. The nonlinear association of arterial stiffness with HbA1c and PBG was proved. The robust results of the sensitivity analysis were obtained.

CONCLUSIONS

HbA1c is an important risk factor of arterial stiffness compared with PBG, FBG, and TyG index, and has a strong predictive ability for arterial stiffness among non-diabetics and the general population.

Elastography ultrasound with machine learning improves the diagnostic performance of traditional ultrasound in predicting kidney fibrosis

BACKGROUND

Noninvasively predicting kidney tubulointerstitial fibrosis is important because it's closely correlated with the development and prognosis of chronic kidney disease (CKD). Most studies of shear wave elastography (SWE) in CKD were limited to non-linear statistical dependencies and didn't fully consider variables' interactions. Therefore, support vector machine (SVM) of machine learning was used to assess the prediction value of SWE and traditional ultrasound techniques in kidney fibrosis.

METHODS

We consecutively recruited 117 CKD patients with kidney biopsy. SWE, B-mode, color Doppler flow imaging ultrasound and hematological exams were performed on the day of kidney biopsy. Kidney tubulointerstitial fibrosis was graded by semi-quantification of Masson staining. The diagnostic performances were accessed by ROC analysis.

RESULTS

Tubulointerstitial fibrosis area was significantly correlated with eGFR among CKD patients (R = 0.450, P < 0.001). AUC of SWE, combined with B-mode and blood flow ultrasound by SVM, was 0.8303 (sensitivity, 77.19%; specificity, 71.67%) for diagnosing tubulointerstitial fibrosis (>10%), higher than either traditional ultrasound, or SWE (AUC, 0.6735 [sensitivity, 67.74%; specificity, 65.45%]; 0.5391 [sensitivity, 55.56%; specificity, 53.33%] respectively. Delong test, p < 0.05); For diagnosing different grades of tubulointerstitial fibrosis, SWE combined with traditional ultrasound by SVM, had AUCs of 0.6429 for mild tubulointerstitial fibrosis (11%-25%), and 0.9431 for moderate to severe tubulointerstitial fibrosis (>50%), higher than other methods (Delong test, p < 0.05).

CONCLUSION

SWE with SVM modeling could improve the diagnostic performance of traditional kidney ultrasound in predicting different kidney tubulointerstitial fibrosis grades among CKD patients.

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.

Shear wave elastography accurately detects chronic changes in renal histopathology

AIM

Renal biopsy is the gold standard for the histological characterization of chronic kidney disease (CKD), of which renal fibrosis is a dominant component, affecting its stiffness. The aim of this study was to investigate the correlation between kidney stiffness obtained by shear wave elastography (SWE) and renal histological fibrosis.

METHODS

Shear wave elastography assessments were performed in 75 CKD patients who underwent renal biopsy. The SWE-derived estimates of the tissue Young's modulus (YM), given as kilopascals (kPa), were measured. YM was correlated to patients' renal histological scores, broadly categorized into glomerular, tubulointerstitial and vascular scores.

RESULTS

Young's modulus correlates significantly with tubulointerstitial score (ρ = 0.442, P < .001) and glomerular score (ρ = 0.375, P = .001). Patients with no glomerular sclerosis showed lower mean YM measurements compared to those with glomerular sclerosis. The mean YM increased as the percentage of interstitial fibrosis and tubular atrophy increased. The area under the receiver operating characteristic curve (ROC) for SWE in differentiating between mildly and moderately impaired kidneys was 0.702.

CONCLUSION

Shear wave elastography accurately detects chronic renal damage resulting from glomerular sclerosis, interstitial fibrosis and tubular atrophy, using the optimal cut-off YM value of ≥5.81 kPa.

Two-Dimensional Shear Wave Elastography of Normal Soft Tissue Organs in Adult Beagle Dogs; Interobserver Agreement and Sources of Variability

Shear wave elastography (SWE) induces lateral shear wave through acoustic pulses of the transducer and evaluates tissue stiffness quantitatively. This study was performed to evaluate feasibility and reproducibility of two-dimensional shear wave elastography (2D SWE) for evaluation of tissue stiffness and to examine technical factors that affect shear wave speed (SWS) measurements in adult dogs. Nine healthy, 2 year-old, adult beagles with the median weight of 9.8 kg were included. In this prospective, experimental, exploratory study, 2D SWE (Aplio 600) from the liver, spleen, kidneys, pancreas, prostate, lymph nodes (submandibular, retropharyngeal, axillary, medial iliac, and inguinal), submandibular salivary gland, and thyroid was performed in anesthetized beagles. Color map was drawn and SWS of each SWE were measured as Young’s modulus (kPa) and shear wave velocity (m/s). The effect of measuring site, scan approach, depth, and anesthesia on SWE was assessed in abdominal organs by two observers independently. A total of 27 SWE examinations were performed in 12 organs by each observer. All SWS measurements were preformed successfully; however, SWE in the renal medulla could not be successfully conducted, and it was excluded from further analysis. Interobserver agreement of SWE was moderate to excellent in all organs, except for the left liver lobe at 10–15 mm depth with the intercostal scan. In the liver, there was no significant effect of the measuring site and scan approach on SWE. SWS of the liver and spleen tended to be higher with increasing the depth, but no significant difference. However, anesthesia significantly increased tissue stiffness in the spleen compared to awake dog regardless of the depth (P < 0.05). There was a significant difference in SWS according to the measuring site in the kidneys and pancreas (P < 0.001). 2D SWE was feasible and highly reproducible for the estimation of tissue stiffness in dogs. Measuring site and anesthesia are sources of variability affecting SWE in abdominal organs. Therefore, these factors should be considered during SWS measurement in 2D SWE. This study provides basic data for further studies on 2D SWE on pathological conditions that may increase tissue stiffness in dogs.

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.

Comparison of Shear Wave Elastography and Conventional Ultrasound in Assessing Kidney Function as Measured Using 51Cr-ethylenediaminetetraacetic Acid and 99Tc-Dimercaptosuccinic Acid

The purpose of this study was to assess the potential of shear wave elastography (SWE) as an indicator of abnormal kidney function defined by radiolabeled glomerular filtration rate (GFR). Fifty-seven patients referred for ⁵¹Cr-ethylenediaminetetraacetic acid GFR and ^99mTc-dimercaptosuccinic acid renal scintigraphy were included. Young's modulus (YM) measured with SWE and kidney length, volume, cortical thickness and parenchymal echogenicity measured with conventional ultrasound were correlated with patients' GFR and renal scintigraphy results. Spearman correlation coefficients between SWE and GFR were negative for the right (r = -0.635, p < 0.0001) and left (r = -0.817, p < 0.0001) kidneys. Positive correlations between left renal cortical thickness (r = 0.381, p = 0.04) and left kidney volume (r = 0.356, p = 0.019) with GFR were reported. SWE correctly predicted the dominant functioning kidney in 94.7% of cases. The area under the receiver operating characteristic curve for SWE (0.800) was superior to that for conventional ultrasound (0.252-0.415). The cutoff value of ≥5.52 kPa suggested a kidney function ≤60 mL/min/1.73 m² (82.4% sensitivity and 76.2% specificity). SWE has advantages over conventional ultrasound in assessing kidney function and distinguishing the dominant functioning kidney.