Division of Nephrology and Hypertension, Department of Medicine, Mayo Clinic, Rochester, MN, USA.
Invest Radiol. 2011 Aug;46(8):509-14. doi: 10.1097/RLI.0b013e3182183a95.
: 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.
: In 6 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 6 weeks after induction of chronic unilateral RAS (n = 6) or control (n = 3). Kidney fibrosis was subsequently evaluated histologically by trichrome staining.
: 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 with controls, cortical stiffness was not significantly different from normal (7.4 ± 0.3 vs. 7.6 ± 0.3 kPa, P = 0.3), despite histologic evidence of renal tissue fibrosis.
: 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.
磁共振弹性成像（MRE）允许对体内组织硬度进行非侵入性评估。肾动脉狭窄（RAS）是肾动脉狭窄，可促进威胁肾脏存活的不可逆组织纤维化，并可能增加组织硬度。然而，肾脏硬度也可能受到血流动力学因素的影响。本研究检验了肾脏血流（RBF）是通过 MRE 测量的肾脏硬度的重要决定因素的假设。
在 6 头麻醉猪中，通过血管夹进行急性分级 RBF 降低（基线的 20%、40%、60%、80%和 100%），进行 MRE 研究以确定皮质和髓质弹性。三只假手术猪作为时间对照。另外，用 MRE 研究了 6 周后诱导的慢性单侧 RAS（n = 6）或对照（n = 3）的猪。随后通过三染色法评估组织纤维化。
在急性 RAS 中，随着 RBF 的降低，狭窄皮质的硬度降低（从 7.4 ± 0.3 至 4.8 ± 0.6 kPa，P = 0.02 与基线相比）。此外，在慢性 RAS （80% ± 5.4%狭窄）的猪中，与对照组相比，RBF 降低了 60% ± 14%，皮质硬度与正常猪无显著差异（7.4 ± 0.3 与 7.6 ± 0.3 kPa，P = 0.3），尽管有肾脏组织纤维化的组织学证据。
血流动力学变量调节 MRE 测量的肾脏硬度，并可能掩盖纤维化的存在。这些结果表明，在解释弹性评估时应考虑肾脏充盈。
