Correlation of Point Shear Wave Velocity and Kidney Function in Chronic Kidney Disease

Quantitative studies on B-mode ultrasound and point shear wave elastography of kidneys in nonazotemic dogs

Renal diseases in dogs can be diagnosed effectively using B-mode ultrasound. Point shear wave elastography (pSWE) has demonstrated usefulness in diagnosing renal diseases in human medicine. However, its application in veterinary medicine is in its nascent stage. It was hypothesized that establishing pSWE reference values in nonazotemic dogs would prove valuable in differentiating renal diseases. In light of this, a single-center, quantitative study with an objective to normalize B-mode ultrasound parameters and pSWE values of the kidney in nonazotemic dogs was conducted. A total of 198 animals presented with clinical signs of anorexia, vomiting, weight loss, and dehydration were enrolled in the study spanning 2 years. Among them, 52 nonazotemic dogs were included as subjects for the study. B-mode ultrasound quantitative parameters, including length (L), breadth (B), height (H), cortical thickness (RCT), and medulla thickness (RMT) of the kidneys, as well as the diameter of the aorta (Ao), were normalized. Additionally, calculated parameters such as L:Ao, B:Ao, H:Ao, RCT:Ao, and corticomedullary ratios were worked out. Point shear wave elastography values were obtained from the cranial and caudal poles of renal cortices using ElastPQ stiffness software. The pSWE values of kidneys in nonazotemic dogs were normalized. The mean ± standard error values were 1.04 ± 0.08 m/s (95% confidence interval: 0.88-1.19 m/s) and 4.18 ± 0.62 kPa (95% confidence interval: 2.93-5.42 kPa). In conclusion, B-mode ultrasound quantitative parameters, ratios, and pSWE values were normalized in nonazotemic dogs, which may prove valuable in differentiating renal pathologies in canine patients.

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.

Comparison of sound touch elastography and quantification for assessing the renal pathologic changes in patients with proteinuria

OBJECTIVE

Sound touch elastography (STE) and sound touch quantification (STQ) are novel imaging methods to evaluate tissue stiffness. This study aims to investigate renal stiffness in patients with chronic kidney disease (CKD) by STE and STQ, using renal biopsy as 'gold standard'.

METHODS

Between 2019 January and 2022 June, 60 patients who underwent renal biopsy for proteinuria (cases) and 45 healthy volunteers (controls) at our hospital were included in this study. The maximum and mean elastic modulus (Emax, Emean) of region of interest in right kidney were measured by STE and STQ techniques. Biochemical profiles and renal biopsy findings were recorded.

RESULTS

Both Emax and Emean measured by STE were significantly different between cases and controls. ROC analysis of STE measurements revealed using a cutoff of 13.53 kPa for Emax and 10.16 kPa for Emean, the area under the curve (AUC) to distinguish nephropathy from healthy was 0.718 and 0.744. Analysis of ROC for STQ measurements showed that using a cutoff value of 15.87 kPa for Emax and 9.95 kPa for Emean, the AUC for the nephropathy was 0.612 and 0.569. Emax and Emean values were significantly different among CKD patients with mild, moderate and severe pathological stage. The Emax value for STE was positively related to Scr, β2-MG (r = 0.257, 0.292, p < 0.05).

CONCLUSION

Both STE and STQ are non-invasive, feasible methods to quantitatively evaluate renal stiffness. STE is more effective than STQ in the diagnosis of CKD patients with proteinuria.

CRITICAL RELEVANCE STATEMENT

Sound touch elastography is more effective than sound touch quantification in the diagnosis of chronic kidney disease patients with proteinuria.

KEY POINTS

• Emax and Emean measured by STE were different between cases and controls. • Emax and Emean were different among CKD patients with different pathological stages. • The Emax value for STE was positively related to serum creatinine, β2-microglobulin.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

KEY POINTS

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

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.

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.

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.

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.

Two-dimensional (2D) dynamic vibration optical coherence elastography (DV-OCE) for evaluating mechanical properties: a potential application in tissue engineering

Mechanical properties in tissues are an important indicator because they are associated with disease states. One of the well-known excitation sources in optical coherence elastography (OCE) to determine mechanical properties is acoustic radiation force (ARF); however, a complicated focusing alignment cannot be avoided. Another excitation source is a piezoelectric (PZT) stack to obtain strain images via compression, which can affect the intrinsic mechanical properties of tissues in tissue engineering. In this study, we report a new technique called two-dimensional (2D) dynamic vibration OCE (DV-OCE) to evaluate 2D wave velocities without tedious focusing alignment procedures and is a non-contact method with respect to the samples. The three-dimensional (3D) Fourier transform was utilized to transfer the traveling waves (x, y, t) into 3D k-space (k_x, k_y, f). A spatial 2D wavenumber filter and multi-angle directional filter were employed to decompose the waves with omni-directional components into four individual traveling directions. The 2D local wave velocity algorithm was used to calculate a 2D wave velocity map. Six materials, two homogeneous phantoms with 10 mm thickness, two homogeneous phantoms with 2 mm thickness, one heterogeneous phantom with 2 mm diameter inclusion and an ex vivo porcine kidney, were examined in this study. In addition, the ARF-OCE was used to evaluate wave velocities for comparison. Numerical simulations were performed to validate the proposed 2D dynamic vibration OCE technique. We demonstrate that the experimental results were in a good agreement with the results from ARF-OCE (transient OCE) and numerical simulations. Our proposed 2D dynamic vibration OCE could potentially pave the way for mechanical evaluation in tissue engineering and for laboratory translation with easy-to-setup and contactless advantages.

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.