# Renal Acoustic Radiation Force Impulse Elastography in Hypertensive Nephroangiosclerosis Patients
## 1 Introduction  
Hypertensive nephroangiosclerosis (HN) represents the renal involvement secondary to the long-term evolution of arterial hypertension, being the second or third most common cause of renal replacement therapy in Europe, USA, respective in Japan [1; 2; 3]. The epidemiological data revealed that the HN incidence had increased both in Europe and in United States of America in the last 20 years. About 15% in Europe, respective 28% in United States of America of new cases with end-stage renal disease had HN as an etiology [4; 5].  
[PERSON] et al. demonstrated an existence of a strong relationship between high blood pressure, renal involvement and cardiovascular disease [6]. On the other side, microalbuminuria and macroalbuminuria represent the important risk factors for cardiovascular events [7], and for the progression of renal involvement to chronic kidney disease [8].  
In current medical practice, the diagnosis of HN is established on a clinical examination and laboratory tests, only a small proportion of patients benefit from histopathologicalexamination. Therefore, epidemiological data vary widely between different medical centers (in Europe, between 5 and 33% of ESRD cases have as etiology HN) [5].  
Hypertension-induced kidney damage involves vasculature, glomeruli, and tubulotintersitium. Intrarenal arteries show progressive intimal thickening and fibrosis, caused by collagen deposition, and, media thickening, attributable to smooth muscle cell hyperplasia. Afferent arterioles present a process of hyalinization. Glomerular involvement is heterogeneous: normal morphology, ischemic, obliterated glomeruli, with collapsed capillaries, or others hypertrophied. Another hallmark of hypertensive kidney injury is tubular atrophy, associated with interstitial fibrosis. These histological changes have a progressive evolution, from asymptomatic organ damage to symptomatic organ damage, with chronic kidney disease appearance. But this evolution may be slowed, if the kidney involvement is diagnosed early and the patients receive an appropriate treatment [4; 9].  
These renal morphological changes have an impact on renal function. Increased albuminuria and reduced glomerular filtration rate are the first changes that define the incipient kidney damage in HN [9]. But besides serum and urinary biomarkers, ultrasonographic investigations (B-mode and Doppler) play an important role in the diagnosis of HN. B-mode ultrasound evaluates the kidney position and the morphology (kidney length, parenchyma thickness and echogenicity). But, unfortunately, ultrasonographic changes appear late in the disease evolution [4; 9; 10]. Through colour duplex Doppler and power Doppler ultrasound, the renal and intrarenal vascularization (arterial and venous) are estimated, providing information about the kidney function [11; 12].  
All the morphological abnormalities of the kidneys listed above can cause elastic compliance changes, determined by a new ultrasonographic method, known as Acoustic Radiation Force Impulse Elastography (ARFI), as shear wave velocity (SWV). In ARFI, the acoustic pulses emitted by the transducer generate micrometric displacements (1-20 \(\upmu\)m) in the examined tissue. The square region of interest (ROI) is used to measure micrometric displacements. The displacement generates the shear waves, which propagate away from the ROI and are captured by the same transducer, displaying them as m/s. ARFI technique has many advantages over other elastographic methods. First, it is not operator-dependent. Another advantage of the ARFI technique is that it is not based on transducer compression. By using ARFI, the deep organs, like kidneys, can be successfully examined [13; 14; 15].  
The aim of this study is to investigate the kidney SWV in patients with HN, and to establish the correlations between SWV and UACR, eGFR, and RRI.