Noninvasive In Vivo Assessment of Renal Tissue Elasticity During Graded Renal Ischemia Using MR Elastography

Abstract

Objectives Magnetic Resonance Elastography (MRE) allows noninvasive assessment of tissue stiffness in vivo. Renal arterial stenosis (RAS), a narrowing of the renal artery, promotes irreversible tissue fibrosis that threatens kidney viability and may elevate tissue stiffness. However, kidney stiffness may also be affected by hemodynamic factors. This study tested the hypothesis that renal blood flow (RBF) is an important determinant of renal stiffness as measured by MRE. Material and Methods In six anesthetized pigs MRE studies were performed to determine cortical and medullary elasticity during acute graded decreases in RBF (by 20, 40, 60, 80, and 100% of baseline) achieved by a vascular occluder. Three sham-operated swine served as time control. Additional pigs were studied with MRE six weeks after induction of chronic unilateral RAS (n=6) or control (n=3). Kidney fibrosis was subsequently evaluated histologically by trichrome staining. Results During acute RAS the stenotic cortex stiffness decreased (from 7.4 ± 0.3 to 4.8 ± 0.6 kPa, p=0.02 vs. baseline) as RBF decreased. Furthermore, in pigs with chronic RAS (80±5.4% stenosis) in which RBF was decreased by 60±14% compared to controls, cortical stiffness was not significantly different from normal (7.4 ± 0.3 vs. 7.6 ± 0.3 kPa, p=0.3), despite histological evidence of renal tissue fibrosis. Conclusion Hemodynamic variables modulate kidney stiffness measured by MRE and may mask the presence of fibrosis. These results suggest that kidney turgor should be considered during interpretation of elasticity assessments.

Magnetic resonance elastography in the detection of hepatorenal syndrome in patients with cirrhosis and ascites

“…This led us to postulate whether reduced renal perfusion in HRS would translate to reduced renal stiffness on MRE. This hypothesis is supported by two animal studies that suggest that renal perfusion is an important determinant of renal stiffness [10,15]. Gennisson et al investigated the influence of blood pressure on renal stiffness using ultrasound elastography [15].…”

“…These properties of living tissues, including between physiologic and pathologic states, vary over a wider dynamic range on MRE compared with conventional imaging modalities such as ultrasound, computed tomography or magnetic resonance imaging (MRI). Early studies have suggested that MRE is sensitive to pathophysiologic changes such as renal fibrosis and renal hypoperfusion [9][10][11][12]. To our knowledge, the clinical feasibility of MRE for detecting HRS in patients with cirrhosis has not previously been reported.…”

Renal Relevant Radiology

“…Based on the assumption that excessive extracellular matrix deposition in fibrotic tissues increases their stiffness, MREderived stiffness has been used as an index of fibrosis. The feasibility of using MRE in the kidney has been demonstrated in transplant patients (43) and in swine renal artery stenosis (44,45). Interestingly, studies utilizing graded renal ischemia demonstrated that hemodynamic modulation of renal cortical stiffness hampers discrimination of fibrotic from nonfibrotic kidneys (44).…”

“…The feasibility of using MRE in the kidney has been demonstrated in transplant patients (43) and in swine renal artery stenosis (44,45). Interestingly, studies utilizing graded renal ischemia demonstrated that hemodynamic modulation of renal cortical stiffness hampers discrimination of fibrotic from nonfibrotic kidneys (44). However, MRE is capable of detecting fibrosis in the intrinsically hypoperfused medulla (45), which is less dependent on perfusion pressure.…”

Quantification of Kidney Fibrosis Using Ultrasonic Shear Wave Elastography

“…There have been many studies on the usefulness of ultrasound and magnetic resonance elastography for assessment of hepatic fibrosis in patients with chronic liver disease. 8,[13][14][15][16][17][18] Recent clinical studies used noninvasive diagnostic tools (eg, acoustic radiation force impulse imaging and transient elastography) for transplanted kidney monitoring. [19][20][21] These studies showed the clinical feasibility of ultrasound elastography for kidney evaluation.…”