Correas Jean-Michel,Anglicheau Dany,Gennisson Jean-Luc,Tanter Mickael
Nephrologie & therapeutique
Renal elastography has become available with the development of noninvasive quantitative techniques (including shear-wave elastography), following the rapidly growing field of diagnosis and quantification of liver fibrosis, which has a demonstrated major clinical impact. Ultrasound or even magnetic resonance techniques are leaving the pure research area to reach the routine clinical use. With the increased incidence of chronic kidney disease and its specific morbidity and mortality, the noninvasive diagnosis of renal fibrosis can be of critical value. However, it is difficult to simply extend the application from one organ to the other due to a large number of anatomical and technical issues. Indeed, the kidney exhibits various features that make stiffness assessment more complex, such as the presence of various tissue types (cortex, medulla), high spatial orientation (anisotropy), local blood flow, fatty sinus with variable volume and echotexture, perirenal space with variable fatty content, and the variable depth of the organ. Furthermore, the stiffness changes of the renal parenchyma are not exclusively related to fibrosis, as renal perfusion or hydronephrosis will impact the local elasticity. Renal elastography might be able to diagnose acute or chronic obstruction, or to renal tumor or pseudotumor characterization. Today, renal elastography appears as a promising application that still requires optimization and validation, which is the contrary for liver stiffness assessment.
US Time-Harmonic Elastography for the Early Detection of Glomerulonephritis.
Grossmann Markus,Tzschätzsch Heiko,Lang Sophia T,Guo Jing,Bruns Anne,Dürr Michael,Hoyer Bimba Franziska,Grittner Ulrike,Lerchbaumer Markus,Nguyen Trong Manh,Schultz Michael,Hamm Bernd,Braun Jürgen,Sack Ingolf,Marticorena Garcia Stephan R
Background Glomerulonephritis refers to renal diseases characterized by glomerular and tubulointerstitial fibrosis. Multifrequency US time-harmonic elastography enables the noninvasive quantification of tissue elasticity. Purpose To assess the diagnostic performance of US time-harmonic elastography for the early detection of glomerulonephritis. Materials and Methods From August 2016 through May 2017, study participants with biopsy-proven glomerulonephritis were prospectively examined with US time-harmonic elastography. Participants were subdivided according to chronic kidney disease (CKD) stage. All participants underwent elastography of both kidneys to generate full-field-of-view maps of renal shear wave speed (SWS). SWS was determined separately for the whole renal parenchyma, cortex, and medulla and was correlated with quantitative B-mode findings such as renal length and parenchymal thickness. Diagnostic performance of renal elastography was assessed with receiver operating characteristic curve analysis. Results Fifty-three participants with glomerulonephritis (mean age ± standard deviation, 49 years ± 14) and 30 healthy volunteers (mean age, 37 years ± 11) were evaluated. Age-adjusted renal SWS was lower in participants with glomerulonephritis than in healthy volunteers in the parenchyma, cortex, and medulla, with mean values of 1.55 m/sec (95% confidence interval [CI]: 1.51 m/sec, 1.59 m/sec) and 1.69 m/sec (95% CI: 1.64 m/sec, 1.74 m/sec; < .001), respectively, in parenchyma, 1.80 m/sec (95% CI: 1.75 m/sec, 1.84 m/sec) and 2.08 m/sec (95% CI: 2.02 m/sec, 2.13 m/sec; < .001) in cortex, and 1.25 m/sec (95% CI: 1.21 m/sec, 1.29 m/sec) and 1.33 (95% CI: 1.27 m/sec, 1.38 m/sec; = .03) in medulla. Age-adjusted renal cortex SWS was lower in participants with glomerulonephritis and stage 1 CKD (preserved renal function) than in healthy volunteers (mean, 1.88 [95% CI: 1.81, 1.96] vs 2.08 [95% CI: 2.02, 2.13]; < .001). In participants with CKD, renal cortex SWS values showed a positive association with estimated glomerular filtration rate ( = 39; = 0.56; < .001). Exploratory diagnostic performance of US time-harmonic elastography (area under the receiver operating characteristic curve [AUC], 0.89; 95% CI: 0.82, 0.97) outperformed that of B-mode parameters such as parenchymal thickness (AUC, 0.64; 95% CI: 0.51, 0.77; < .001) and renal length (AUC, 0.55; 95% CI: 0.40, 0.68; < .001) in identifying glomerulonephritis. Conclusion US time-harmonic elastography depicts abnormal renal stiffness in glomerulonephritis, particularly among patients with early disease and preserved renal function. Advanced chronic kidney disease is associated with further cortical softening. Time-harmonic elastography outperforms B-mode-based size quantification. © RSNA, 2019
Pre-procedural shear wave elastography on prediction of hemorrhage after percutaneous real-time ultrasound-guided renal biopsy.
Çildağ Mehmet Burak,Gök Mustafa,Abdullayev Oguz
La Radiologia medica
PURPOSE:To evaluate the relationship between renal elasticity which was determined with shear wave elastography (SWE) and hemorrhage in patients who undergone percutaneous renal parenchyma biopsy (PRB). MATERIALS AND METHODS:In total, 60 patients who were performed ultrasound-guided PRB after the B-mode ultrasonography and SWE assessment were recruited in this study. All patients' serum creatinine, blood urea nitrogen and coagulation tests before PRB were obtained from medical records. The patients were divided into two groups who did and did not develop hemorrhage after PRB. We investigated whether there was any statistically significant difference between the two groups in terms of laboratory findings, B-mode ultrasonographic measurements and SWE measurements. RESULTS:Of the 60 patients, 23 (38.3%) had post-procedure hemorrhage and 37 (61.7%) had not. Mean hemorrhage size was 17.04 mm (7-50 mm). The mean value of renal cortical shear wave velocity of all patients was 1.91 m/s (0.96-3.57 m/sn). Patients with post-procedure hemorrhage had significantly lower mean shear wave velocity compared with patients with no hemorrhage (p < 0.05). ROC curve analysis suggested that the optimum SWV cutoff point for hemorrhage presence was 1.21 m/sn, with 39.1% sensitivity and 97.3% specificity. There was no other statistically significant demographic, ultrasonographic or laboratory value differences between two groups. CONCLUSION:Although shear wave velocities have low sensitivity for hemorrhage after renal biopsy, high specificity and statistically significant difference in hemorrhage and non-hemorrhage group suggest that patients who have lower renal cortical shear wave velocity have a tendency to hemorrhage after PRB.
Increased renal cortical stiffness obtained by share-wave elastography imaging significantly predicts the contrast-induced nephropathy in patients with preserved renal function.
Sumbul Hilmi Erdem,Koc Ayse Selcan,Demirtas Derya,Koca Hasan,Pekoz Burcak Cakir,Gorgulu Feride Fatma,Donmez Yurdaer,Demirtas Abdullah Orhan,Koc Mevlut,Icen Yahya Kemal
Journal of ultrasound
PURPOSE:We aimed to investigate the relation between renal cortical stiffness (CS) obtained by shear-wave elastography (SWE) and contrast-induced nephropathy (CIN) development in interventional treatment-planned acute coronary syndrome (ACS) patients. METHODS:Our study group consisted of 465 ACS patients. Routine laboratory assessments, B-mode, Doppler, and SWE renal ultrasonography (USG) evaluations were performed. Renal resistive index (RRI), renal pulsatility index (RPI), and acceleration time (AT) and CS were measured. Patients were grouped as with and without CIN. RESULTS:Among the study group, 55 patients (11.8%) had CIN. Age, diabetes mellitus (DM), hypertension (HT), basal creatinine, CK-MB and troponin I levels, contrast volume, contrast volume/weight ratio, SYNTAX score, RRI, RPI, AT, and CS values were significantly higher in patients with CIN. eGFR was lower in patients who developed CIN. Age, contrast volume/weight ratio, and CS were determined as independent predictors of CIN occurrence in logistic regression analysis. In multivariate logistic analysis, increase of age (each year), contrast volume/weight (each 0.2 mL/kg), and CS (each 1 kPa) were found to augment the development of CIN by 7.1, 59.5, and 62.3%, respectively. In the ROC analysis, CS had the highest AUROC value. The cutoff value of CS obtained by the ROC curve analysis was 7 kPa for the CIN development (sensitivity: 74.5%, specificity: 72.5%). CONCLUSION:CS value is a simple, cheap, reproducible, noninvasive, and objective parameter for the detection of CIN development. ACS patients should be directed to renal USG, and routine CS value should be written besides USG measurements in reports.
Comparison of ultrasound shear wave elastography with magnetic resonance elastography and renal microvascular flow in the assessment of chronic renal allograft dysfunction.
Marticorena Garcia Stephan R,Guo Jing,Dürr Michael,Denecke Timm,Hamm Bernd,Sack Ingolf,Fischer Thomas
Acta radiologica (Stockholm, Sweden : 1987)
Background Monitoring of renal allograft function is essential for early identification of dysfunction and improvement of kidney transplant (KTX) outcome. Purpose To non-invasively assess renal stiffness in KTX recipients using ultrasound shear wave elastography (USE) in correlation with multifrequency magnetic resonance elastography (MRE), renal allograft function, and renal microvascular flow determined using a novel ultrasound microvascular imaging technique. Material and Methods This prospective study investigated 25 KTXs (functional KTX [FCT], n = 14; chronic KTX insufficiency [DYS], n = 11) in 20 KTX recipients (mean age = 43 ± 14 years). USE was performed using a high-frequency broadband linear transducer and compared with MRE. Shear wave velocity (SWV) was correlated with the estimated glomerular filtration rate (eGFR). Qualitative differences in renal microvascular flow were obtained using SMI. Results FCT had higher SWV than DYS in both cortex and pyramids (cortex, FCT: 3.75 ± 0.82 m/s vs. DYS: 2.79 ± 0.73 m/s, P = 0.0002; pyramid, FCT: 2.89 ± 0.46 m/s vs. DYS: 2.39 ± 0.34 m/s, P = 0.044). Cutoff values of 3.265 m/s for cortex, 2.535 m/s for pyramids, and 2.985 m/s for combined non-hilar parenchyma provided sensitivities of 72.7%, 77.8%, and 90.9% and specificities of 71.4%, 78.6%, and 85.7% for detecting renal allograft dysfunction with area under the receiver operating characteristic curve (AUC) values of 0.831, 0.841, 0.925 (95% confidence interval [CI] = 0.67-0.99, 0.66-1.02, 0.83-1.03). USE correlated positively with eGFR ( r = 0.741, P = 0.0004) and with MRE-derived SWV ( r = 0.562, P = 0.004). Renal microvascular flow was decreased in DYS. Conclusion USE is sensitive to renal allograft dysfunction, which is characterized by reduced SWV and renal perfusion. USE has higher image resolution than MRE, while MRE has slightly better diagnostic accuracy.
Magnetic resonance elastography vs. point shear wave ultrasound elastography for the assessment of renal allograft dysfunction.
Kennedy Paul,Bane Octavia,Hectors Stefanie J,Gordic Sonja,Berger Mark,Delaney Veronica,Salem Fadi,Lewis Sara,Menon Madhav,Taouli Bachir
European journal of radiology
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.
Association of Renal Elasticity and Renal Function Progression in Patients with Chronic Kidney Disease Evaluated by Real-Time Ultrasound Elastography.
Lin Hugo You-Hsien,Lee Yu-Li,Lin Kun-Der,Chiu Yi-Wen,Shin Shyi-Jang,Hwang Shang-Jyh,Chen Hung-Chun,Hung Chi-Chih
Glomerulosclerosis and tubulointerstitial fibrosis are associated with lower renal parenchymal elasticity. This study was designed to evaluate the predictive ability of renal elasticity in patients with chronic kidney disease (CKD). 148 non-CKD patients and 227 patients with CKD were recruited. 145 (38.7%) were female, 166 (73.1%) had diabetes, the mean estimated glomerular filtration rate (eGFR) was 33.9 ± 15.8 ml/min/1.73 m and the median urinary protein-to-creatinine ratio (UPCR) 502 (122-1491) mg/g. Patients with later stages of CKD had lower renal elasticity values, indicating stiffer kidneys (p < 0.001), and smaller kidney (p < 0.001). Renal elasticity correlated with log-transformed UPCR (β = -7.544, P < 0.001). Renal length correlated with age (β = -0.231, P < 0.001), sex (β = -3.730, P < 0.001), serum albumin level (β = -3.024, P = 0.001), body mass index (β = 0.390, P = 0.009) and eGFR (β = 0.146, P < 0.001). In fully-adjusted logistic regression model, the odds ratio (OR) per 10 unit change in renal elasticity for rapid renal deterioration was 0.928 (95% CI, 0.864-0.997; P = 0.042). The OR per 1 mm change in renal length for rapid renal deterioration was 1.022 (95% CI, 0.994-1.050; P = 0.125). Renal elasticity is associated with proteinuria and rapid renal deterioration in patients with CKD.
Interstitial fibrosis scored on whole-slide digital imaging of kidney biopsies is a predictor of outcome in proteinuric glomerulopathies.
Mariani Laura H,Martini Sebastian,Barisoni Laura,Canetta Pietro A,Troost Jonathan P,Hodgin Jeffrey B,Palmer Matthew,Rosenberg Avi Z,Lemley Kevin V,Chien Hui-Ping,Zee Jarcy,Smith Abigail,Appel Gerald B,Trachtman Howard,Hewitt Stephen M,Kretzler Matthias,Bagnasco Serena M
Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association
Background:Interstitial fibrosis (IF), tubular atrophy (TA) and interstitial inflammation (II) are known determinants of progression of renal disease. Standardized quantification of these features could add value to current classification of glomerulopathies. Methods:We studied 315 participants in the Nephrotic Syndrome Study Network (NEPTUNE) study, including biopsy-proven minimal change disease (MCD = 98), focal segmental glomerulosclerosis (FSGS = 121), membranous nephropathy (MN = 59) and IgA nephropathy (IgAN = 37). Cortical IF, TA and II were quantified (%) on digitized whole-slide biopsy images, by five pathologists with high inter-reader agreement (intra-class correlation coefficient >0.8). Tubulointerstitial messenger RNA expression was measured in a subset of patients. Multivariable Cox proportional hazards models were fit to assess association of IF with the composite of 40% decline in estimated glomerular filtration rate (eGFR) and end-stage renal disease (ESRD) and separately as well, and with complete remission (CR) of proteinuria. Results:IF was highly correlated with TA (P < 0.001) and II (P < 0.001). Median IF varied by diagnosis: FSGS 17, IgAN 21, MN 7, MCD 1 (P < 0.001). IF was strongly correlated with baseline eGFR (P < 0.001) and proteinuria (P = 0.002). After adjusting for clinical pathologic diagnosis, age, race, global glomerulosclerosis, baseline proteinuria, eGFR and medications, each 10% increase in IF was associated with a hazard ratio of 1.29 (P < 0.03) for ESRD/40% eGFR decline, but was not significantly associated with CR. A total of 981 genes were significantly correlated with IF (|r| > 0.4, false discovery rate (FDR) < 0.01), including upstream regulators such as tumor necrosis factor, interferon gamma (IFN-gamma), and transforming growth factor beta 1 (TGF-B1), and signaling pathways for antigen presentation and hepatic fibrosis. Conclusions:The degree of IF is associated with risk of eGFR decline across different types of proteinuric glomerulopathy, correlates with inflammatory and fibrotic gene expression, and may have predictive value in assessing risk of progression.
Automated quantification of renal interstitial fibrosis for computer-aided diagnosis: A comprehensive tissue structure segmentation method.
Tey Wei Keat,Kuang Ye Chow,Ooi Melanie Po-Leen,Khoo Joon Joon
Computer methods and programs in biomedicine
Interstitial fibrosis in renal biopsy samples is a scarring tissue structure that may be visually quantified by pathologists as an indicator to the presence and extent of chronic kidney disease. The standard method of quantification by visual evaluation presents reproducibility issues in the diagnoses. This study proposes an automated quantification system for measuring the amount of interstitial fibrosis in renal biopsy images as a consistent basis of comparison among pathologists. The system extracts and segments the renal tissue structures based on colour information and structural assumptions of the tissue structures. The regions in the biopsy representing the interstitial fibrosis are deduced through the elimination of non-interstitial fibrosis structures from the biopsy area and quantified as a percentage of the total area of the biopsy sample. A ground truth image dataset has been manually prepared by consulting an experienced pathologist for the validation of the segmentation algorithms. The results from experiments involving experienced pathologists have demonstrated a good correlation in quantification result between the automated system and the pathologists' visual evaluation. Experiments investigating the variability in pathologists also proved the automated quantification error rate to be on par with the average intra-observer variability in pathologists' quantification. BACKGROUND AND OBJECTIVE:Interstitial fibrosis in renal biopsy samples is a scarring tissue structure that may be visually quantified by pathologists as an indicator to the presence and extent of chronic kidney disease. The standard method of quantification by visual evaluation presents reproducibility issues in the diagnoses due to the uncertainties in human judgement. METHODS:An automated quantification system for accurately measuring the amount of interstitial fibrosis in renal biopsy images is presented as a consistent basis of comparison among pathologists. The system identifies the renal tissue structures through knowledge-based rules employing colour space transformations and structural features extraction from the images. In particular, the renal glomerulus identification is based on a multiscale textural feature analysis and a support vector machine. The regions in the biopsy representing interstitial fibrosis are deduced through the elimination of non-interstitial fibrosis structures from the biopsy area. The experiments conducted evaluate the system in terms of quantification accuracy, intra- and inter-observer variability in visual quantification by pathologists, and the effect introduced by the automated quantification system on the pathologists' diagnosis. RESULTS:A 40-image ground truth dataset has been manually prepared by consulting an experienced pathologist for the validation of the segmentation algorithms. The results from experiments involving experienced pathologists have demonstrated an average error of 9 percentage points in quantification result between the automated system and the pathologists' visual evaluation. Experiments investigating the variability in pathologists involving samples from 70 kidney patients also proved the automated quantification error rate to be on par with the average intra-observer variability in pathologists' quantification. CONCLUSIONS:The accuracy of the proposed quantification system has been validated with the ground truth dataset and compared against the pathologists' quantification results. It has been shown that the correlation between different pathologists' estimation of interstitial fibrosis area has significantly improved, demonstrating the effectiveness of the quantification system as a diagnostic aide.
Combination of Functional Magnetic Resonance Imaging and Histopathologic Analysis to Evaluate Interstitial Fibrosis in Kidney Allografts.
Wang Wei,Yu Yuanmeng,Wen Jiqiu,Zhang Mingchao,Chen Jinsong,Cheng Dongrui,Zhang Longjiang,Liu Zhihong
Clinical journal of the American Society of Nephrology : CJASN
BACKGROUND AND OBJECTIVES:Recent developments indicated that functional magnetic resonance imaging (MRI) could potentially provide noninvasive assessment of kidney interstitial fibrosis in patients with kidney diseases, but direct evidence from histopathology is scarce. We aimed to explore the diagnostic utilities of functional MRI for the evaluation of kidney allograft interstitial fibrosis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS:We prospectively examined 103 kidney transplant recipients who underwent for-cause biopsies and 20 biopsy-proven normal subjects with functional MRI. Histomorphometric analyses of interstitial fibrosis and peritubular capillary densities were performed on digitally scanned Masson's trichrome- and CD34-stained slides, respectively. The performances of functional MRI to discriminate interstitial fibrosis were assessed by calculating the area under the curve using receiver-operating characteristic curve. RESULTS:Main pathologic findings in this single-center cohort were representative of common diagnostic entities in the kidney allografts, with rejection (32%) and glomerulonephritides (31%) accounting for the majority of diagnoses. Apparent diffusion coefficient from diffusion-weighted imaging correlated with interstitial fibrosis (ρ=-0.77; <0.001). Additionally, decreased arterial spin labelings were accompanied by peritubular capillary density reductions (=0.77; <0.001). Blood oxygen level-dependent (BOLD) imaging demonstrated cortical hypoxia with increasing interstitial fibrosis (ρ=0.61; <0.001). The area under the curve for the discrimination of ≤25% versus >25% interstitial fibrosis and ≤50% versus >50% interstitial fibrosis were 0.87 (95% confidence interval [95% CI], 0.79 to 0.93) and 0.88 (95% CI, 0.80 to 0.93) by apparent diffusion coefficient, 0.92 (95% CI, 0.85 to 0.97) and 0.94 (95% CI, 0.87 to 0.98) by arterial spin labeling, 0.81 (95% CI, 0.72 to 0.88) and 0.86 (95% CI, 0.78 to 0.92) by perfusion fraction, 0.79 (95% CI, 0.69 to 0.87) and 0.85 (95% CI, 0.76 to 0.92) by BOLD imaging, respectively. CONCLUSIONS:Functional MRI measurements were strongly correlated with kidney allograft interstitial fibrosis. The performances of functional MRI for discriminating ≤50% versus >50% interstitial fibrosis were good to excellent.
Contrast-enhanced ultrasonography for assessment of tubular atrophy/interstitial fibrosis in immunoglobulin A nephropathy: a preliminary clinical study.
Yang Wenqi,Mou Shan,Xu Yao,Du Jing,Xu Li,Li Fenghua,Li Hongli
Abdominal radiology (New York)
PURPOSE:To investigate the potential of contrast-enhanced ultrasonography (CEUS) for evaluating the severity of tubular atrophy/interstitial fibrosis (TA/IF) in immunoglobulin A nephropathy (IgAN) patients. MATERIALS AND METHODS:A total of 80 patients with IgAN and 33 healthy adults were investigated. Patients were divided into three groups according to the TA/IF (T) grade of the Oxford classification: T0 (n = 28), T1 (n = 35), and T2 (n = 17). Patients and control subjects underwent conventional ultrasound (US) and CEUS. Time-intensity curves of CEUS were drawn for regions of interest located in the renal cortex and medulla using QLab software. Conventional US and CEUS quantitative parameters were analyzed. One-way analysis of variance (ANOVA), binary logistic regression, and receiver operating characteristic (ROC) curves were used. RESULTS:There were no significant differences in renal size, cortical thickness, and medullary perfusion parameters (P > 0.05), whereas the differences in peak intensity (PI), area under the time-intensity curve (AUC) and wash-in slope (WIS) of cortical perfusion parameters between the control subjects and patients were significant (P < 0.05). PI was significantly lower with the increasing degree of T (P < 0.05). PI was associated independently with the degree of T in IgAN patients (P < 0.05). ROC analysis revealed that using the optimal cutoff values of 15.38 dB for diagnosis of T0-T1 (sensitivity 83.30% and specificity 63.00%) and 14.69 dB for diagnosis of T2 (sensitivity 100.00% and specificity 66.70%), the corresponding areas under the ROC curve were found to be 0.782 and 0.952, respectively. CONCLUSIONS:CEUS can potentially be used as a noninvasive imaging marker to evaluate the severity of TA/IF in IgAN patients.
Renal transplant elasticity ultrasound imaging: correlation between normalized strain and renal cortical fibrosis.
Gao Jing,Weitzel William,Rubin Jonathan M,Hamilton James,Lee Jun,Dadhania Darshana,Min Robert
Ultrasound in medicine & biology
After transplantation, over a widely variable time course, the cortex of the transplanted kidney becomes stiffer as interstitial fibrosis develops and renal function declines. Elasticity ultrasound imaging (EUI) has been used to assess biomechanical properties of tissue that change in hardness as a result of pathologic damage. We prospectively assessed the hardness of the renal cortex in renal transplant allograft patients using a normalized ultrasound strain procedure measuring quasi-static deformation, which was correlated with the grade of renal cortical fibrosis. To determine cortical strain, we used 2-D speckle-tracking software (EchoInsight, Epsilon Imaging, Ann Arbor, MI, USA) to perform offline analysis of stored ultrasound loops capturing deformation of renal cortex and its adjacent soft tissue produced by pressure applied using the scanning transducer. Normalized strain is defined as the mean developed strain in the renal cortex divided by the overall mean strain measured in the soft tissues from the abdominal wall to pelvic muscles. Using the Banff scoring criteria for renal cortical fibrosis as the gold standard, we classified 20 renal transplant allograft biopsy tissue samples into two groups: group 1 (n = 10) with mild (<25%) renal cortical fibrosis and group 2 (n = 10) with moderate (26%-50%) renal cortical fibrosis. An unpaired two-tailed t-test was used to determine the statistical difference in strains between patients with mild and those with moderate renal cortical fibrosis. Receiver operating characteristic curve analysis was performed to assess the accuracy of developed strain and normalized strain in predicting moderate renal cortical fibrosis. The reference strain did not significantly differ between the two groups (p = 0.10). However, the developed renal cortical strain in group 1 with mild fibrosis was higher than that in group 2 with moderate fibrosis (p = 0.025). The normalized strain in group 1 was also higher than that in group 2 (p = 0.0014). The areas under receiver operating characteristic curves for developed strain and normalized strain were 0.78 and 0.95, respectively. The optimal cutoff for distinguishing moderate renal cortical fibrosis was -0.08 for developed strain (sensitivity = 0.50, specificity = 1.0) and 2.5 for normalized strain (sensitivity = 0.80, specificity = 1.0). In summary, renal cortex strain is strongly correlated with grade of renal cortical fibrosis. Normalized strain is superior to developed strain in distinguishing moderate from mild renal cortical fibrosis. We conclude that free-hand real-time strain EUI may be useful in assessing the progression of cortical fibrosis in renal transplant allografts. Further prospective study using this method is warranted.
Comparison of Ultrasound Corticomedullary Strain with Doppler Parameters in Assessment of Renal Allograft Interstitial Fibrosis/Tubular Atrophy.
Gao Jing,Rubin Jonathan M,Weitzel William,Lee Jun,Dadhania Darshana,Kapur Sandip,Min Robert
Ultrasound in medicine & biology
To compare the capability of ultrasound strain and Doppler parameters in the assessment of renal allograft interstitial fibrosis/tubular atrophy (IF/TA), we prospectively measured ultrasound corticomedullary strain (strain) and intra-renal artery Doppler end-diastolic velocity (EDV), peak systolic velocity (PSV) and resistive index (RI) in 45 renal transplant recipients before their kidney biopsies. We used 2-D speckle tracking to estimate strain, the deformation ratio of renal cortex to medulla produced by external compression using the ultrasound transducer. We also measured Doppler EDV, PSV and RI at the renal allograft inter-lobar artery. Using the Banff scoring system for renal allograft IF/TA, 45 patients were divided into the following groups: group 1 with ≤5% (n = 12) cortical IF/TA; group 2 with 6%-25% (n = 12); group 3 with 26%-50% (n = 11); and group 4 with >50% (n = 10). We performed receiver operating characteristic curve analysis to test the accuracy of these ultrasound parameters and duration of transplantation in determining >26% cortical IF/TA. In our results, strain was statistically significant in all paired groups (all p < 0.005) and inversely correlated with the grade of cortical IF/TA (p < 0.001). However, the difference in PSV and EDV was significant only between high-grade (>26%, including 26%-50% and >50%) and low-grade (≤25%, including <5% and 6%-25%) cortical IF/TA (p < 0.001). RI did not significantly differ in any paired group (all p > 0.05). The areas under the receiver operating characteristic curve for strain, EDV, PSV, RI and duration of transplantation in determining >26% cortical IF/TA were 0.99, 0.94, 0.88, 0.52 and 0.92, respectively. Our results suggest that corticomedullary strain seems to be superior to Doppler parameters and duration of transplantation in assessment of renal allograft cortical IF/TA.