# Renal Ultrasound Elastography: A Review of the Previous Reports on Chronic Kidney Diseases
## 6 Ultrasound Elastography in Chronic Kidney Disease  
CKD is a major public health concern. The prevalence of CKD and the number of patients requiring renal replacement therapy are increasing worldwide. As CKD leads to an increased risk of cardiovascular disease and end-stage renal disease, the early detection of kidney dysfunction and the prevention of CKD progression are crucial. Regardless of the etiology of kidney disease, glomerular sclerosis, tubular atrophy, and interstitial fibrosis dominate the progression of renal dysfunction. Therefore, the early detection of the pathological alterations would be an early marker of a decline in renal function. Conventional methods for the assessment of kidney disease mostly depend on the functional assessment of serum or urinary biomarkers and a morphological assessment by ultrasound, computed tomography, and magnetic resonance imaging. However, there are no established modalities for the detection or assessment of pathological changes except for a renal biopsy. Ultrasound elastography is an alternative modality for the non-invasive assessment of pathological changes. Several reports have investigated the feasibility of ultrasound elastography in patients with kidney disease. SWE has been used in most previous investigations in the field of CKD (Table 2). However, previous studies that investigated the relationship between the SWV and renal function or the CKD stage are not consistent with each other. [PERSON] et al. performed ARFI elastography in 64 patients with CKD and 327 healthy subjects and investigated the differences in the SWVs. They found that the SWVs in patients with CKD were significantly lower than those in healthy subjects [46]. Similarly, in 148 non-CKD and 227 CKD patients, renal elasticity tended to decrease in patients with advanced-stage kidney disease [47]. Although the etiology of CKD was not shown in their report, the decreasing trend of the SWV with the progression of renal dysfunction was also shown in other reports. In another study with 163 CKD patients, most of whom were diagnosed with glomerulonephritis, the SWV correlated positively with the glomerular filtration rate (GFR) [48]. Similarly, positive correlations between the SWV and renal function have been observed in patients with diabetic nephropathy and nephrosclerosis [49; 50]. As interstitial fibrosis is often observed in patients with advanced kidney disease, these positive correlations between the SWV and renal function are the opposite of those observed in other organs such as the liver, with high SWVs in the advanced stage of fibrosis. In contrast with these observations, negative correlations between the SWV and GFR were observed in CKD patients with diabetic nephropathy and glomerulonephritis [51; 52]. In a study including patients with stage 3 to 4 CKD with diabetes mellitus, [PERSON] et al. reported an increased renal cortical stiffness in patients with kidney disease. In addition, the cortical stiffness correlated negatively with the estimated GFR [51]. [PERSON] et al. investigated the association between renal elasticity and patient characteristics in those who underwent renal biopsies; renal stiffness correlated inversely with renal function [52]. Another study in 25 patients with CKD showed that the SWE values were higher in patients with CKD than in healthy subjects [53]. The SWV in patients undergoing hemodialysis was previously investigated. There were no significant differences in the SWVs between patients without kidney disease and those with end-stage renal disease [28]. Thus far, there is no consensus regarding the changes in renal elasticity according to the decline in renal function. Among several factors that influence the results of SWE, one explanation for this discrepancy is the heterogeneity of the patient cohort. The patient age influences the SWV; the SWV tends to be higher in elderly subjects [46; 52].