Shear wave elastography and Doppler ultrasound in kidney transplant recipients

Role of multi-parametric ultrasonography for the assessment and monitoring of functional status of renal allografts with histopathological correlation

BACKGROUND

The study focuses on the use of multi-parametric ultrasound [gray scale, color Doppler and shear wave elastography (SWE)] to differentiate stable renal allografts from acute graft dysfunction and to assess time-dependent changes in parenchymal stiffness, thereby assessing its use as an efficient monitoring tool for ongoing graft dysfunction. To date, biopsy is the gold standard for evaluation of acute graft dysfunction. However, because it is invasive, it carries certain risks and cannot be used for follow-up monitoring. SWE is a non-invasive imaging modality that identifies higher parenchymal stiffness values in cases of acute graft dysfunction compared to stable grafts.

AIM

To assess renal allograft parenchymal stiffness by SWE and to correlate its findings with functional status of the graft kidney.

METHODS

This prospective observational study included 71 renal allograft recipients. Multi-parametric ultrasound was performed on all patients, and biopsies were performed in cases of acute graft dysfunction. The study was performed for a period of 2 years at Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, a tertiary care center in north India. Independent samples t-test was used to compare the means between two independent groups. Paired-samples t-test was used to test the change in mean value between baseline and follow-up observations.

RESULTS

Thirty-one patients had experienced acute graft dysfunction at least once, followed by recovery, but none of them had a history of chronic renal allograft injury. Mean baseline parenchymal stiffness in stable grafts and acute graft dysfunction were 30.21 + 2.03 kPa (3.17 + 0.11 m/s) and 31.07 + 2.88 kPa (3.22 + 0.15 m/s), respectively; however, these differences were not statistically significant (P = 0.305 and 0.252, respectively). There was a gradual decrease in SWE values during the first 3 postoperative months, followed by an increase in SWE values up to one-year post-transplantation. Patients with biopsy-confirmed graft dysfunction showed higher SWE values compared to those with a negative biopsy. However, receiver operating characteristic analysis failed to show statistically significant cut-off values to differentiate between the stable graft and acute graft dysfunction.

CONCLUSION

Acute graft dysfunction displays higher parenchymal stiffness values compared to stable grafts. Therefore, SWE may be useful in monitoring the functional status of allografts to predict any ongoing dysfunction.

Predictive Model for Post-Transplant Renal Fibrosis Using Ultrasound Shear Wave Elastography

BACKGROUND The aim of this study was to investigate the clinical utility of ultrasound shear wave elastography (SWE) for assessment of renal fibrosis in post-renal transplant patients. MATERIAL AND METHODS We selected 183 patients who underwent renal transplantation. The complete dataset was randomly partitioned into a training cohort (128 cases) and a validation cohort (55 cases). All patients were subjected to SWE and renal allograft biopsy. The baseline data was compared using t-test, Z-test, or chi-square test. Through univariate and multivariate analyses, we identified independent risk factors influencing renal fibrosis after transplantation, a predictive model for post-transplant renal fibrosis was developed, and calibration curves, decision curve analyses, and ROC curves were generated. RESULTS Age, TST, Scr, GFR, and Emean showed significant differences (P<0.05). The C-index of the nomogram was 0.85, and the calibration curve and Hosmer-Lemeshow test demonstrated accurate diagnosis of fibrosis in both the training and validation sets (P>0.05). DCA showed that the prediction model effectively improved the diagnostic accuracy of fibrosis. The highest AUC of the nomogram for combined prediction of renal fibrosis in transplant patients was 0.902 in the training group and 0.871 in the validation group. These values were significantly higher compared to the AUCs of individual predictors (P<0.05). CONCLUSIONS Ultrasound SWE allows for early evaluation of renal fibrosis following transplantation. The prediction model, constructed by amalgamating other indicators, augments the accuracy and reliability of the prediction, providing more precise and accurate diagnostic and therapeutic recommendations for clinical practitioners.

Investigating the role of ultrasound-based shear wave elastography in kidney transplanted patients: correlation between non-invasive fibrosis detection, kidney dysfunction and biopsy results-a systematic review and meta-analysis

INTRODUCTION

Interstitial fibrosis and tubular atrophy are leading causes of renal allograft failure. Shear wave elastography could be a promising noninvasive method for providing information on the state of the kidney, with specific regard to fibrosis but currently available data in the literature are controversial. Our study aimed to analyze the correlation between shear wave elastography and various kidney dysfunction measures.

METHODS

This review was registered on PROSPERO (CRD42021283152). We systematically searched three major databases (MEDLINE, Embase, and CENTRAL) for articles concerning renal transplant recipients, shear wave elastography, fibrosis, and kidney dysfunction. Meta-analytical calculations for pooled Pearson and Spearman correlation coefficients (r) were interpreted with 95% confidence intervals (CIs). Heterogeneity was tested with Cochran's Q test. I2 statistic and 95% CI were reported as a measurement of between-study heterogeneity. Study quality was assessed with the QUADAS2 tool.

RESULTS

In total, 16 studies were included in our meta-analysis. Results showed a moderate correlation between kidney stiffness and interstitial fibrosis and tubular atrophy, graded according to BANFF classification, on biopsy findings for pooled Pearson (r = 0.48; CI: 0.20, 0.69; I2 = 84%) and Spearman correlations (r = 0.57; CI: 0.35, 0.72; I2 = 74%). When compared to kidney dysfunction parameters, we found a moderate correlation between shear wave elastography and resistive index (r = 0.34 CI: 0.13, 0.51; I2 = 67%) and between shear wave elastography and estimated Glomerular Filtration Rate (eGFR) (r = -0.65; CI: - 0.81, - 0.40; I2 = 73%). All our outcomes had marked heterogeneity.

CONCLUSION

Our results showed a moderate correlation between kidney stiffness measured by shear wave elastography and biopsy results. While noninvasive assessment of kidney fibrosis after transplantation is an important clinical goal, there is insufficient evidence to support the use of elastography over the performance of a kidney biopsy.

Shear wave elastography in chronic kidney disease - the physics and clinical application

Chronic kidney disease is a leading public health problem worldwide. The global prevalence of chronic kidney disease is nearly five hundred million people, with almost one million deaths worldwide. Estimated glomerular filtration rate, imaging such as conventional ultrasound, and histopathological findings are necessary as each technique provides specific information which, when taken together, may help to detect and arrest the development of chronic kidney disease, besides managing its adverse outcomes. However, estimated glomerular filtration rate measurements are hampered by substantial error margins while conventional ultrasound involves subjective assessment. Although histopathological assessment is the best tool for evaluating the severity of the renal pathology, it may lead to renal insufficiency and haemorrhage if complications occurred. Ultrasound shear wave elastography, an emerging imaging that quantifies tissue stiffness non-invasively has gained interest recently. This method applies acoustic force pulses to generate shear wave within the tissue that propagate perpendicular to the main ultrasound beam. By measuring the speed of shear wave propagation, the tissue stiffness is estimated. This paper reviews the literature and presents our combined experience and knowledge in renal shear wave elastography research. It discusses and highlights the confounding factors on shear wave elastography, current and future possibilities in ultrasound renal imaging and is not limited to new sophisticated techniques.

The application of shear wave quantitative ultrasound elastography in chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a major public health problem, so it is particularly important to quantitatively assess and intervene in the degree of early renal damage in CKD.

OBJECTIVE

The objective of the research is to establish reference values for kidney elasticity by using real-time shear wave elastography (RT-SWE) technology to quantify Young's modulus values in the renal cortex of normal adults. The intention is to provide a foundation for evaluating renal function and structural changes in patients with CKD. Furthermore, this research investigates the role of RT-SWE in the early detection of renal fibrosis in CKD, providing insights into its diagnostic value for detecting pathological changes at an early stage.

METHODS

Between August 2019 and December 2021, we collected a sample of 100 healthy people (55 men with an average age of 43.5 ± 15.2 years and 45 women with an average age of 41.6 ± 19.8 years) for medical evaluations at our hospital's Department of Ultrasound Medicine. In addition, 97 individuals with CKD1-3 stage were considered. Following the removal of contraindications and relevant confounding variables, we included a final cohort of 80 individuals in the research (45 men and 35 females, with an average age of 39.1 ± 19.2 years). The RENAL mode was selected and a convex array probe S6-1 operating at a frequency of 3.5-5.5 MHz was used in the research, which made use of the French Supersonic AixPlorer ultrasonic diagnostic instrument. Renal RT-SWE elastography was performed after conventional two-dimensional and color Doppler ultrasonography. The study used RT-SWE technology to assess the mean Young's modulus of the cortex in healthy individuals (Emean), with data analysis and comparisons based on age and gender. Furthermore, the Emean values of CKD stage 1-3 patients were determined, and analyses were performed about 24-hour urine protein quantitative (24hUTP), serum creatinine concentration (SCr), and renal biopsy pathology, specifically the degree of interstitial fibrosis.

RESULTS

Healthy group: a) The average kPa values of the left kidney (4.2 ± 2.3), right kidney (4.3 + 2.5) kPa, both kidneys' average kPa values (4.3 ± 2.4) kPa, and the average kPa values of the left and right kidneys do not differ statistically (p= 0.986). b) There was no difference in the kPa values of healthy male and female kidneys (4.4 + 2.1 and 4.2 + 2.6, respectively. c) There was no difference in the renal kPa values of healthy adults aged 50 (4.4 ± 2.8) kPa and renal kPa of the 50-year-old population (4.2 + 2.1) kPa (p= 0.041). Case group: a) the group of patients with CKD1-3 stage and the group did not vary in their Emean values (both p< 0.05); b) There is a difference between CKD stages 1, 2, and 3 (p< 0.05), however, there is still no difference in the pyEmean value corrected for patient age between patients in stages 1 and 2 (p> 0.05).

CONCLUSION

The study reveals no significant differences in the Emean value of bilateral kidneys in normal people and no differences in the elasticity value of kidneys and gender. However, age-based differences were statistically significant. pyEmean may be useful for comparing CKD stage 1, 2, and 3 patients, and RT-SWE can assess early renal damage.