# Renal Ultrasound Elastography: A Review of the Previous Reports on Chronic Kidney Diseases
## 6 Ultrasound Elastography in Chronic Kidney Disease
However, it has been demonstrated that age-adjusted SWVs in patients undergoing hemodialysis were not significantly different from those in patients without kidney disease [28]. Renal blood flow is another factor that influences the SWV. In a relatively large cohort of 319 patients with CKD, [PERSON] et al. showed a significant correlation between the SWV and GFR when the effect of cardiac pulsation was minimized by performing the SWV measurement in synchrony with the cardiac cycle [50]. This positive correlation was observed in both the renal cortex and medulla. This observation was further confirmed by the negative correlation between the SWV and the brachial ankle pulse wave velocity. They further divided the patients according to their etiologies and investigated the positive correlations between the SWV and renal function. As a result, positive correlations between the SWV and estimated GFR were still observed in patients with diabetic nephropathy, nephrosclerosis, and glomerulonephritis. Another study investigated the SWVs in patients with atherosclerosis [54]. Patients with coronary artery disease (whose renal blood flow is supposed to be reduced) showed significantly lower SWVs compared to healthy subjects [54]. In addition, hypertension was an influencing factor for a high renal elasticity in patients with glomerulonephritis [52]. Considering these investigations, renal elasticity is--in part--influenced by renal hemodynamics. Although there have been no reports showing the exact correlations, SWE might be a suitable modality to distinguish hemodynamic-associated renal dysfunction such as nephrosclerosis or renal arterial infarction. Various diseases can lead to renal dysfunction. However, the histological alterations observed in advanced kidney disease are quite similar regardless of the etiology of kidney disease. Therefore, a renal injury, particularly histological alterations, is one of the targets of renal elastography. Among the major histological changes often observed in advanced kidney disease including interstitial fibrosis, glomerular sclerosis, and tubular atrophy, correlations of the renal elasticity with interstitial fibrosis have been extensively investigated. [PERSON] et al. showed that SWE values were significantly higher in patients with CKD who manifested mild or moderate fibrosis [55]. Similarly, [PERSON] et al. reported positive correlations between the grades of fibrosis and the renal elasticity in patients who underwent a renal biopsy [52]. Based on the principle of the ultrasound elastography technique and the fact that the elasticity values increase with the degree of fibrosis in the liver [9; 22], these positive correlations of the tissue elasticity and the degree of fibrosis observed in the kidney were as expected. However, other reports on renal elasticity have shown contradictory results. [PERSON] et al. investigated the relationship between the SWV and the degree of fibrosis in patients with CKD mostly caused by glomerul nephritis. They found no significant correlation between the degree of interstitial fibrosis and the SWV [56]. They also reported no significant correlation between glomerulosclerosis and the SWV. Another report in patients who underwent a renal biopsy also showed that there was no correlation between the SWV and the degree of fibrosis or the degree of glomerulosclerosis [57]. As observed in transplanted kidneys, the variation in the histological alterations in patients with CKD affects the renal elasticity. A substantial degree of interstitial fibrosis is observed in patients with advanced kidney disease. Therefore, other microstructural changes occurring in the damaged kidney are likely to affect the renal elasticity. In patients who underwent a renal biopsy, the association between the SWV and nephron hypertrophic changes was investigated [57]. Nephron hypertrophy was assessed by measuring the glomerular density, glomerular volume, and tubular tuft area.