Scientific Papers

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

To our knowledge, this is the first study to evaluate the viscoelasticity of renal parenchyma in children with glomerular disease using SWE combined with dispersion imaging. Shear wave elastography combined with dispersion imaging showed higher SWV and dispersion slope in the patient group than in the control group when evaluating the viscoelasticity of renal parenchyma. ROC analysis showed that SWV and dispersion slope could distinguish between the patient and control groups, and SWV had higher efficiency. When the AUC was 0.95, the sensitivity, specificity, and cut-off values were 83.7%, 90.7%, and 15.1 m/s, respectively.

Glomerular disease is a common type of diffuse kidney disease in children. During the development of glomerular disease, pathological changes such as glomerulosclerosis, vascular collapse, and atrophy, interstitial fibrosis, and inflammation occur [13], which may lead to changes in the tissue viscoelasticity. Because of conventional ultrasonography is not very sensitive for the detection of early kidney damage, and positive results can only be obtained when the kidneys are significantly damaged, so that the kidneys have progressed to significant parenchymal damage or even insufficiency pathologically [14]. In recent years, the development of new ultrasound technology has provided new ideas for the diagnosis of chronic kidney disease, e.g., SWE has been used to assess SWV in renal interstitial fibrosis in chronic kidney disease [15,16,17]. The results of this study showed that bilateral renal SWV measurements in the patient group were significantly higher than those in the control group. [16] Previous study [18] showed that the SWV was higher in the glomerular disease group than in the healthy control group, which was consistent with our findings, but only the elasticity of the kidney was examined and its viscosity was not evaluated.

To the best of our knowledge, SWD technology is mostly used in the field of liver [19, 20], and relevant studies had pointed out that there were differences in SWV and dispersion coefficient measured by different inflammatory stages and concluded that SWV was mainly related to liver fibrosis grade, and dispersion slope was mainly related to inflammation and necrosis grade [10]. But this is the first time the technique has been applied in kidney research. In our study, we found that the dispersion slope of children with glomerular disease was higher than those of healthy children (p < 0.001). It is well known that dispersion is related to the slow wave velocity and frequency of slow wave attenuation in the viscous component [11], and the analysis of the dispersion characteristics of shear waves can be used as an indirect method to measure viscosity. Therefore, we believe that the promising results of SWD in glomerular disease may be of value in diagnosis as well as later quantitative monitoring, considering the application of SWD in the assessment of liver disease and its non-invasive nature and ease of access.

ROC curves were used to determine the best SWV and dispersion slope for the diagnosis of glomerular diseases in children. The critical value of SWE for predicting glomerular disease in children was 1.51 m/s, with a sensitivity of 83.7% and specificity of 90.7%, which was close to the critical value of Xu et al.‘s study, but our sensitivity and specificity were better than theirs [18]. This also indicates that SWE has a good diagnostic ability in glomerular diseases in children. The sensitivity and specificity of the cut-off value of SWD suggested by the ROC curve are not strong, which may also be related to the differences in the mechanism, time, and severity of the inflammatory process of kidney diseases. However, it is still necessary to further expand the sample size to conduct controlled studies according to disease severity.

The pathological results of children in the disease group showed that very few children had fibrosis in kidney tissue, which may be related to the age and severity of the disease. This finding shows that changes in kidney stiffness are related to other factors in addition to renal fibrosis. And the study by Gennisson et al. [21] showed that the elasticity of the kidney is related to urine pressure and increases with increased urine pressure. In addition, in studies of glomerular diseases in adults, it has been found that age has an effect on kidney stiffness, since degeneration is a physiological phenomenon of cell and organ aging and is therefore associated with structural changes in the kidneys [22]. Due to these changes, renal blood flow decreases with age, which has an impact on SWV values [23, 24].

To control the quality of the measured SWV, Maralescu et al. [25] found that renal stiffness was influenced by the measurement depth (r=-0.3776, p = 0.0075). Our results showed that the measurement depth of the patient group and the control group was not statistically significant (p = 0.80), which also indicated that the measurement depth did not affect the measurement of SWV and dispersion slope. Further, Barr et al. proposed that interquartile range (IQR) should be used to assess the quality of the data. IQR is a measure of statistical dispersion equal to the difference between the upper and lower quartiles. The IQR/median was < 0.30 for kPa measurements and < 0.15 for m/s measurements, indicating that the dataset is likely to be acceptable [26]. As there are no guidelines in the current literature to ensure appropriate SWD measurements, and dispersal slope measurements also require appropriate SW velocity measurements, the recommended 2D-SWE method should be used [26]. This quality standard was also followed in the SWV measurements in our study.

The current study has some limitations. First, we studied relatively small sample sizes and did not group the included samples by age. Therefore, we need to further expand the sample size and group children of different ages to better compare the SWV and dispersal slope range of the normal renal cortex in children of different ages with the results measured in children of corresponding age with disease. Second, the number of diseases included in the study is small, which will be one of the key points of our next research. In addition, no pathological grading was performed on the included disease groups during the study period; hence, there was no conclusion on whether there were significant statistical differences in SWV and dispersion slope measurements between different pathological grades.

This study suggests that SWE and SWD imaging are likely useful in distinguishing healthy from glomerular disease renal parenchyma based on differences in tissue viscoelastic behavior. Although our findings are preliminary, it suggests that the method has considerable clinical potential.

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