High Temporal Resolution Parametric MRI Monitoring of the Initial Ischemia/Reperfusion Phase in Experimental Acute Kidney Injury

Abstract

Ischemia/reperfusion (I/R) injury, a consequence of kidney hypoperfusion or temporary interruption of blood flow is a common cause of acute kidney injury (AKI). There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI. Non-invasive in vivo parametric magnetic resonance imaging (MRI) may elucidate spatio-temporal pathophysiological changes in the kidney by monitoring the MR relaxation parameters T2* and T2, which are known to be sensitive to blood oxygenation. The aim of our study was to establish the technical feasibility of fast continuous T2*/T2 mapping throughout renal I/R. MRI was combined with a remotely controlled I/R model and a segmentation model based semi-automated quantitative analysis. This technique enabled the detailed assessment of in vivo changes in all kidney regions during ischemia and early reperfusion. Significant changes in T2* and T2 were observed shortly after induction of renal ischemia and during the initial reperfusion phase. Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats. This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

Renal Oxygenation and Hemodynamics in Kidney Injury

“…Similarly, in pigs with 45 minutes of aortic cross-clamping, reduced oxygenation and persistent hypoxia at 4 hours of reperfusion was observed [23]. Using MRI in rats before and after 45 minutes of ischemia followed by reperfusion for approximately 100 minutes, global reduction in tissue oxygenation during ischemia was observed [24]. Cortical oxygenation was at baseline after reperfusion, but outer medullary oxygenation remained persistently low.…”

Detailing the Relation Between Renal T2* and Renal Tissue pO2 Using an Integrated Approach of Parametric Magnetic Resonance Imaging and Invasive Physiological Measurements

“…For this purpose, the layers (cortex (C), outer medulla (OM), inner medulla (IM)) were identified and measured in a series of freshly extracted rat kidneys [18]. The layers' dimensions were related to the individual kidney's length and width in the coronal view.…”

“…From these measurements, a standardized model was derived that comprises a rectangular frame that tightly encloses the kidney and predefined distance from the borders between these kidney layers to avoid any 'contamination' from the neighboring layers (partial segment effects) and to allow for inter-individual variations in morphology without the need to change the ROI position. The earlier described kidney segmentation model [18] was adapted for the current study to avoid overlap of the ROIs with the locations of the pO 2 /Laser-flux probes (Fig. 2).…”

T1-mapping for assessment of ischemia-induced acute kidney injury and prediction of chronic kidney disease in mice

“…However, these parameters are insensitive, influenced by many factors other than renal function [9,10], and are insufficient to estimate the severity and prognosis of AKI. Functional magnetic resonance imaging (MRI) provides promising new techniques such as arterial spin labelling [11], blood oxygen level dependency imaging [12,13], and diffusion weighted imaging [14][15][16] to examine noninvasively renal function and pathology.…”