Non-invasive assessment of renal allograft fibrosis by dynamic sonographic tissue perfusion measurement

From inflammation to renal fibrosis: A one-way road in autoimmunity?

Renal fibrosis is now recognized as a main determinant of renal pathology to include chronic kidney disease. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space, and around arterioles predicts and contributes to the functional demise of the nephron and its surrounding vasculature. The recent identification of the major cell populations of fibroblast precursors in the kidney interstitium such as pericytes and tissue-resident mesenchymal stem cells, or bone-marrow-derived macrophages, and in the glomerulus such as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process thought the lens of involved immunological pathways. Besides, a growing body of evidence is supporting the role of the lymphatic system in modulating the immunological response potentially leading to inflammation and ultimately renal damage. These notions have moved our understanding of renal fibrosis to be recognized as a clinical entity and new main player in autoimmunity, impacting directly the management of patients.

Diagnostic performance of renal cortical elasticity by supersonic shear wave imaging in pediatric glomerular disease

PURPOSE

To explore the diagnostic performance of renal cortical elasticity expressed by Young's modulus (YM) using the supersonic shear wave imaging (SSI) technique in pediatric glomerular disease.

MATERIALS AND METHODS

Seventy-one children with glomerular disease confirmed by renal biopsy and sixty healthy volunteers were enrolled in this study. Conventional and SSI ultrasound examinations were performed in all individuals for both kidneys. We measured renal length, renal width, renal thickness, parenchyma thickness, interlobar arterial resistive index (RI) and the YM of the middle and lower pole.

RESULTS

Regardless of which pole and which side of the kidney, the YM in the disease group was significantly higher than that in the control group (P < 0.001). The YM of the middle pole in the left kidney demonstrated the largest AUC (0.936, P < 0.001), and the corresponding cut-off value was 15.48 kPa with a sensitivity of 87.3% and a specificity of 86.7%. There was no significant difference in the YM among different pathological types of pediatric glomerular disease in the disease group, and the same in different grades of patients with Immunoglobulin A (IgA) nephropathy by Lee classification and the Oxford Classification as well as Henoch-Schonlein purpura nephritis (HSPN) by International Study of Kidney Disease in Children (ISKDC) classification (P > 0.05). We found positive but weak correlations between the YM and renal length (r = 0.299, P = 0.001), renal width (r = 0.408, P < 0.001), renal thickness (r = 0.299, P = 0.001), and parenchyma thickness (r = 0.212, P = 0.015), whereas the YM had no significant correlations with age, sex, BMI, interlobar arterial RI, and laboratory findings (P > 0.05).

CONCLUSIONS

SSI technology is a non-invasive and feasible method for the diagnosis of pediatric glomerular disease. However, SSI did not show good performance in distinguishing different pathological types and disease grades in our study.

Diagnostic accuracy of ultrasound-based multimodal radiomics modeling for fibrosis detection in chronic kidney disease

OBJECTIVES

To predict kidney fibrosis in patients with chronic kidney disease using radiomics of two-dimensional ultrasound (B-mode) and Sound Touch Elastography (STE) images in combination with clinical features.

METHODS

The Mindray Resona 7 ultrasonic diagnostic apparatus with SC5-1U convex array probe (bandwidth frequency of 1-5 MHz) was used to perform two-dimensional ultrasound and STE software. The severity of cortical tubulointerstitial fibrosis was divided into three grades: mild interstitial fibrosis and tubular atrophy (IFTA), fibrotic area < 25%; moderate IFTA, fibrotic area 26-50%; and severe IFTA, fibrotic area > 50%. After extracting radiomics from B-mode and STE images in these patients, we analyzed two classification schemes: mild versus moderate-to-severe IFTA, and mild-to-moderate versus severe IFTA. A nomogram was constructed based on multiple logistic regression analyses, combining clinical and radiomics. The performance of the nomogram for differentiation was evaluated using receiver operating characteristic (ROC), calibration, and decision curves.

RESULTS

A total of 150 patients undergoing kidney biopsy were enrolled (mild IFTA: n = 74; moderate IFTA: n = 33; severe IFTA: n = 43) and randomized into training (n = 105) and validation cohorts (n = 45). To differentiate between mild and moderate-to-severe IFTA, a nomogram incorporating STE radiomics, albumin, and estimated glomerular filtration (eGFR) rate achieved an area under the ROC curve (AUC) of 0.91 (95% confidence interval [CI]: 0.85-0.97) and 0.85 (95% CI: 0.77-0.98) in the training and validation cohorts, respectively. Between mild-to-moderate and severe IFTA, the nomogram incorporating B-mode and STE radiomics features, age, and eGFR achieved an AUC of 0.93 (95% CI: 0.89-0.98) and 0.83 (95% CI: 0.70-0.95) in the training and validation cohorts, respectively. Finally, we performed a decision curve analysis and found that the nomogram using both radiomics and clinical features exhibited better predictability than any other model (DeLong test, p < 0.05 for the training and validation cohorts).

CONCLUSION

A nomogram based on two-dimensional ultrasound and STE radiomics and clinical features served as a non-invasive tool capable of differentiating kidney fibrosis of different severities.

KEY POINTS

• Radiomics calculated based on the ultrasound imaging may be used to predict the severities of kidney fibrosis. • Radiomics may be used to identify clinical features associated with the progression of tubulointerstitial fibrosis in patients with CKD. • Non-invasive ultrasound imaging-based radiomics method with accuracy aids in detecting renal fibrosis with different IFTA severities.

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.

Quantitative parameters of contrast-enhanced ultrasonography for assessment of renal pathology: A preliminary study in chronic kidney disease

OBJECTIVE

To assess the severity of renal pathology in patients with chronic kidney disease (CKD) using contrast-enhanced ultrasonography (US).

METHODS

275 patients with CKD who were proven by renal biopsy and 30 healthy adults were examined using conventional US and contrast-enhanced US. Ultrasonic parameters included renal length, cortical thickness, rise time (RT), peak intensity (PI), area under the time-intensity curve (AUC), wash-in slope (WIS) and time to peak (TTP). Based on pathological scores, CKD patients were classified into mild, and moderate to severe CKD groups. The logistic regression analysis and receiver operating characteristic (ROC) curves were used.

RESULTS

PI and AUC differed significantly among the controls, mild and moderate to severe CKD groups (P < 0.05). There was significant difference in PI among the different pathology types (P < 0.05). The multivariate logistic regression analysis showed that PI was associated independently with the severity of renal pathology in patients with CKD (P < 0.05). PI less than 13.87 dB had a certain diagnostic ability, and the sensitivity and specificity were 72.5% and 64.0%, respectively.

CONCLUSIONS

Contrast-enhanced US may be useful for noninvasive assessment of the severity of renal pathology. PI may be potentially valuable for guiding therapy and follow-up in patients with CKD.

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

Background

To evaluate the effect of perfusion status on elasticity measurements of different compartments in the kidney using shear wave elastography (SWE) both in vivo and ex vivo.

Methods

Thirty-two rabbit kidneys were used to observe the elasticity variation caused by renal artery stenosis and vein ligation in vivo, and six beagle kidneys were studied ex vivo to explore the effect of renal perfusion on elasticity. Supersonic SWE was applied to quantify the elasticity values of different renal compartments (cortex, medulla and sinus). Additionally, histopathological examination was performed to explore the possible mechanisms.

Results

The elasticity of the cortex was higher than that of the medulla, and the elasticity of the sinus was lowest among the compartments in native kidneys. The Young’s modulus (YM) of the cortex, medulla and sinus increased gradually as the duration of renal vein ligation increased, from 16.34 ± 1.01 kPa to 55.06 ± 5.61 kPa, 13.71 ± 1.16 kPa to 39.63 ± 2.91 kPa, and 12.61 ± 0.84 kPa to 29.30 ± 2.04 kPa, respectively. In contrast, the YM of the three compartments respectively decreased with progressive artery stenosis, from 16.34 ± 1.83 kPa to 11.21 ± 1.79 kPa, 13.31 ± 1.67 kPa to 8.07 ± 1.37 kPa, and 12.78 ± 2.66 kPa to 6.72 ± 0.95 kPa. Artery perfusion was the main factor influencing elasticity in ex vivo. The cortical elasticity was more prone to change with renal perfusion both in vivo and ex vivo. Histopathological examination showed progressive changes in the structure and content of the three compartments, consistent with the elasticity variation.

Conclusions

Both the complex structure/anisotropy and the perfusion of the kidney obviously influence the evaluation of renal elasticity. The measurement of SWE should be performed at a specific location along a certain angle or direction, and renal perfusion status should also be taken into account to ensure reproducible detection.

Research on pediatric glomerular disease and normal kidney with shear wave based elastography point quantification

PURPOSE

To evaluate the renal cortex stiffness in children with glomerular disease by shear wave based elastography point quantification (ElastPQ), and to investigate the association between shear wave velocity (SWV) in the renal cortex and age in normal children, and the inter-gender differences.

MATERIALS AND METHODS

One hundred and five children who were pathologically confirmed with glomerular diseases were selected as the disease group. Meanwhile, 120 healthy children were selected as the control group. Effective values were measured 5 times at the same kidney sites on each side.

RESULTS

Comparisons of SWV measurements between left and right kidneys in the disease and control groups all showed significant differences (left kidney t = 6.896, P = 0.004; right kidney t = 7.415, P = 0.001). In the control group, left and right kidney SWV measurements were all positively correlated with age (left kidney r = 0.792, P = 0.003; right kidney r = 0.794, P = 0.004). Moreover, inter-gender difference was present in the right kidney measurements.

CONCLUSIONS

ElastPQ technology has certain advantages in predicting pediatric glomerular disease compared to conventional ultrasound. ElastPQ technology contributes to the early diagnosis of the disease.

Use of Contrast-Enhanced Ultrasonography to Evaluate Chronic Allograft Nephropathy in Rats and Correlations between Time-Intensity Curve Parameters and Allograft Fibrosis

This study quantitatively analyzed changes in the hemodynamic characteristics of renal allografts at different stages in a rat chronic allograft nephropathy (CAN) model as well as the relationship between hemodynamic parameters and renal allograft fibrosis using contrast-enhanced ultrasonography (CEUS). The experimental group used a CAN rat model (n = 30), and the control group used an orthotopic syngeneic renal transplant model (n = 30). After surgery, creatinine clearance rates were regularly monitored every 2 wk. The checking times were set at 4, 12 and 24 wk after surgery, which represent early, middle and late stage of CAN, respectively. At different stages of CAN, eight rats from each group were randomly selected for CEUS examination. Time-intensity curve (TIC) parameters, including rise time, peak intensity, mean transit time, area under the curve, wash-in slope, time-to-peak and α-smooth muscle actin (α-SMA) expression; Vimentin expression; and chronic allograft damage index scores were evaluated by linear correlation analysis. Before the creatinine clearance rate showed significant abnormalities, the renal allografts in the experimental group had already presented pathologic changes associated with CAN. In the early stage after surgery, compared to the TIC curve of the control group, the experimental group showed increased rise time, mean transit time, area under the curve and time-to-peak, and decreased wash-in slope (p < 0.05). Chronic allograft damage index scores and the expression levels of α-SMA and Vimentin proteins in renal allografts were correlated with TIC parameters (p < 0.05). Compared to creatinine clearance rate, CEUS can detect CAN at earlier stages. The correlations between TIC-related parameters and the expression levels of α-SMA and Vimentin in renal allografts indicate that CEUS is a feasible way to assess the degree of renal allograft fibrosis quantitatively.

Umbilical vein vasomotion detected in vivo by serial three-dimensional pixelwise spatially angle-corrected volume flow measurements

OBJECTIVE

To explore changes in volume flow in the umbilical vein in healthy second-trimester fetuses.

METHODS

This was a prospective observational pilot study performed at Stavanger University Hospital, Norway, between May and October 2013. Serial three-dimensional ultrasound recordings from the umbilical vein were acquired every 30 s in a 5-min period in 43 fetuses at 17-20 weeks' gestation. The recordings were analyzed with pixelwise spatially angle-corrected volume flow measurements.

RESULTS

We observed variation in the umbilical vein volume flow in all fetuses, ranging from a mean minimum of 1.01 mL/s to a mean maximum of 2.60 mL/s. The minimum of all measurements was 57% compared with the mean value and the maximum was 148% of the mean value. The individual flow volume measurements ranged between 0.11 and 4.14 mL/s (mean, 1.76 mL/s). Within this range, an undulating course of all perfusion parameters was observed, with a full period of 4-5 min duration.

CONCLUSION

Healthy second-trimester fetuses show cyclical variation in blood flow in the umbilical vein. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Color-Doppler sonographic tissue perfusion measurements reveal significantly diminished renal cortical perfusion in kidneys with vesicoureteral reflux

Vesicoureteral reflux (VUR) and its sequelae may lead to reduced renal perfusion and loss of renal function. Methods to describe and monitor tissue perfusion are needed. We investigated dynamic tissue perfusion measurement (DTPM) with the PixelFlux-software to measure microvascular changes in the renal cortex in 35 children with VUR and 28 healthy children. DTPM of defined horizontal slices of the renal cortex was carried out. A kidney was assigned to the “low grade reflux”-group if the reflux grade of the voiding cystourethrogram was 1 to 3 and to the “high grade reflux”-group if the reflux grade was 4 to 5. Kidneys with VUR showed a significantly reduced cortical perfusion. Compared to healthy kidneys, this decline reached in low and high grade refluxes within the proximal 50% of the cortex: 3% and 12 %, in the distal 50% of the cortex: 21% and 44 % and in the most distal 20 % of the cortex 41% and 44%. DTPM reveals a perfusion loss in kidneys depending on the degree of VUR, which is most pronounced in the peripheral cortex. Thus, DTPM offers the tool to evaluate microvascular perfusion, to help planning treatment decisions in children with VUR.

Assessment of renal tissue elasticity by acoustic radiation force impulse quantification with histopathological correlation: preliminary experience in chronic kidney disease

OBJECTIVES

Chronic kidney disease (CKD), a progressive and irreversible pathological syndrome, is the major cause of renal failure. Renal fibrosis is the principal process underlying the progression of CKD. Acoustic radiation force impulse (ARFI) quantification is a promising noninvasive method for assessing tissue stiffness. We evaluated whether the technique could reveal renal tissue fibrosis in CKD patients.

METHODS

ARFI assessments were performed in 45 patients with CKD referred for renal biopsies to measure cortical shear wave velocity (SWV). During measurement, a standardized method was employed, which aimed to minimize the potential impact of variation of transducer force, sampling error of non-cortical tissue and structural anisotropy of the kidney. Then SWV was compared to patients' CKD stage and pathological fibrosis indicators.

RESULTS

ARFI could not predict the different stages of CKD. Spearman correlation analysis showed that SWV did not correlate with any pathological indicators of fibrosis.

CONCLUSION

ARFI assesses tissue stiffness of CKD kidneys by measuring cortical SWV. However, SWV did not show significant correlations with CKD stage and fibrosis indicators despite using standardized measurement methods. We therefore suggest that it would be necessary to evaluate the effect of pathological complexity and tissue perfusion of the kidney on stiffness assessment in future studies.

KEY POINTS

• Acoustic radiation force impulse (ARFI) can quantify tissue elasticity of CKD kidney. • Despite standardized measurement, ARFI-estimated elasticity did not correlate with renal fibrosis. • Effects of pathological complexity and tissue perfusion on renal stiffness warrant further study.

Impact of cardiovascular organ damage on cortical renal perfusion in patients with chronic renal failure

Introduction. Properly preserved renal perfusion is the basic determinant of oxygenation, vitality, nutrition, and organ function and its structure. Perfusion disorders are functional changes and are ahead of the appearance of biochemical markers of organ damage. The aim of this study was to evaluate a relationship between the renal cortex perfusion and markers of cardiovascular organ damage in patients with stable chronic renal failure (CKD). Methods. Seventeen patients (2 F; 15 M; age 47 ± 16) with stable CKD at 2–4 stages and hypertension or signs of heart failure were enrolled in this study. Blood tests with an estimation of renal and cardiac functions, echocardiographic parameters, intima-media thickness (IMT), renal resistance index (RRI), and total (TPI), proximal (PPI), and distal (DPI) renal cortical perfusion intensity measurements were collected. Results. DPI was significantly lower than PPI. TPI significantly correlated with age, Cys, CKD-EPI (cystatin), and IMT, whereas DPI significantly depended on Cystain, CKD-EPI (cystatin; cystatin-creatinine), IMT, NT-proBNP, and troponin I. In multiple stepwise regression analysis model only CKD-EPI (cystatin) independently influenced DPI. Conclusions. Cardiovascular and kidney damage significantly influences renal cortical perfusion. Ultrasound measurement of renal perfusion could be a sensitive method for early investigation of cardiovascular and renal injuries.

Renal ultrasound elastography

Chronic kidney disease (CKD) incidence and prevalence are increasing in Western countries, due particularly to diabetes mellitus and hypertension-related nephropathies. CKD may lead to end-stage renal failure, with extensive morbidity, mortality and increasing health costs. Primary and secondary prevention requires a better knowledge of mechanisms underlying renal scarring, the development of specific therapies to slow down the progression of the disease and the development of non-invasive diagnostic tools to characterize the process. Ultrasound elastography is a new imaging technique under development that provides information about renal stiffness. Kidney elasticity measurements with ultrasound should be performed with a quantitative technique, such as Shearwave techniques. However kidney stiffness is not only related to fibrosis, as it also sensitive to mechanical and functional parameters such as anisotropy, vascularization, hydronephrosis and external pressure. This paper reviews the existing ultrasound elastography techniques. Elastography is a new tool under development for renal tissue characterization and needs further validation in clinical practice.

Interobserver variability of ultrasound elastography in transplant kidneys: correlations with clinical-Doppler parameters

Real-time sonoelastography (RSE) is a relatively new imaging technique that visualizes relative difference in tissue hardness by evaluating changes in local strain in response to external stress. Our aim was to evaluate the ability of investigators to use sonoelastography to detect differences in renal cortical stiffness and assess the relationship between stiffness and clinical-Doppler parameters. In 42 adult renal transplant recipients, sonoelastography of kidney was performed to calculate the strain ratio (SR) of the central echo complex to the renal parenchyma. Resistive index (RI) and pulsatility index (PI) were also measured. Estimated glomerular filtration rate (eGFR) was calculated. Parenchymal stiffness showed significant positive correlation with RI and PI (r: 0.41 p = 0.007 and r: 0.48 p = 0.001, respectively). Parenchymal stiffness and eGFR did not have a significant correlation (p = 0.42). Interobserver agreement, expressed as intraclass correlation coeffiicient was 0.47 (95% CI: 0.05-0.70). Parenchymal stiffness (SR) showed significant positive correlation with RI and PI but sonoelastography has also wide range intra- and low interobserver agreement in renal transplants. Further studies are warranted in larger patient groups to determine the reliability of sonoelastography in renal transplants.