Strain wave elastography for evaluation of renal parenchyma in chronic kidney disease

Abstract

Objective: Chronic kidney disease (CKD) is an important and costly health problem in developed countries and has a tendency to progress to end-stage renal disease regardless of the aetiology. This progress ends in interstitial fibrosis, which decreases the elasticity of tissue. Elastography is a developing technique to assess tissue elasticity. The aim of this study was to determine the difference of strain index (SI) value of renal parenchyma between patients with CKD and healthy individuals. In addition, SI differences of inter-stages were studied.

Methods: Toshiba (Toshiba Medical Systems Corporation, Otawara, Japan) Aplio™ 500 ultrasound device and 3.5- to 5.0-MHz convex probe were used for the elastography examinations.

Results: A total of 58 patients with CKD from nephrology and endocrinology clinics (30 males and 28 females; mean age, 56.14 ± 11.60 years) and 40 normal healthy individuals (19 males and 21 females; mean age, 51.70 ± 11.71 years) were included in this prospective study. The mean SI of normal healthy individuals and patients with CKD (regardless of stages) was 0.42 ± 0.30 and 1.81 ± 0.88, respectively (p < 0.001). SI values were not statistically significant among the CKD stages (except CKD Stages 1 and 3). The area under the receiver operating characteristic curve was 0.956 for SI. The optimal cut-off value for the prediction of CKD was 0.935 (sensitivity, 88% and specificity, 95%).

Conclusion: SI value of sonoelastography can be used to differentiate patients with CKD and healthy individuals. Sonoelastography is an acceptable technique to approach patients with CKD, but we have not shown that it can reliably differentiate different stages.

Advances in knowledge: Determining a cut-off SI value between normal and diseased renal parenchyma can help in the diagnosis of CKD.

Figure 1.

The elastography–ultrasonography image of the kidney. The monitor is divided into three windows. The right window is greyscale ultrasonography image, left window is colour-coded ultrasonography–elastography image and the bottom window is sinusoidal wave of compression and decompression. The circles indicate the region of interests (ROIs). The upper ROI is on the parenchyma and the lower ROI is on the sinus echogeneity. The vertical white line on the sinusoidal wave indicates the point of measurement.

Figure 2.

Clustered box plot chart of the strain index values according to chronic kidney disease (CKD) stages. The top and bottom of the boxes indicate 75 and 25 percentiles, respectively. The line through the middle of each box represents the mean. The error bars show the minimum and maximum values (range). The circles indicate the extreme values. In the x-axis, “0” indicates normal individual healthy volunteers.

Figure 3.

Receiver operating characteristic (ROC) curve estimates the diagnostic performance of strain elastography: for a cut-off value of 0.835, the area under curve was 0.958 (95% confidence interval, 0.901–1.000) and standard error was 0.029. For this cut-off value, the sensitivity was 93.5% and the specificity was 88.2%. A total of 43 of 46 patients (93.5%) and 2 of 17 healthy individuals (11.8%) exceeded this cut-off point.