Detection of acute renal ischemia in swine using blood oxygen level‐dependent magnetic resonance imaging

Abstract

Purpose:To determine the feasibility and sensitivity of blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) to detect acute renal ischemia, using a swine model, and to present the causes of variability and assess techniques that minimize variability introduced during data analysis. Materials and Methods:BOLD MRI was performed in axial and coronal planes of the kidneys of five swine. Color R2* maps were calculated and mean R2* values and 95% confidence intervals (CIs) for the cortex and medulla were determined for baseline, renal artery occlusion and reperfusion conditions. Paired Student's t-tests were used to determine significance.Results: Mean R2* measurements increased from baseline during renal artery occlusion in the cortex (axial, 13.8-24.6 second ). These differences were significant for both the cortex (axial, P Ͻ 0.04; coronal, P Ͻ 0.005) and medulla (axial, P Ͻ 0.02; coronal, P Ͻ 0.0005). No significant change was observed in the contralateral kidney.Conclusion: R2* values were significantly higher than baseline for medulla and cortex during renal artery occlusion. More variability exists in R2* measurements in the medulla than the cortex and in the axial than the coronal plane.

Effect of Sodium Loading/Depletion on Renal Oxygenation in Young Normotensive and Hypertensive Men

“…This is in line with other BOLD-MRI studies, showing little changes in cortical oxygenation in different situations 17,23 ; only extreme conditions, such as acute iatrogenic arterial obstruction in animal models, have been shown to significantly alter cortical R2*. 29 This is explained by the technical limitation of BOLD-MRI for renal cortex analyses. BOLD-MRI is less sensitive to changes in cortical PO 2 , because cortical blood PO 2 lies on the shoulder of the hemoglobin oxygenation curve, in contrast to medullary PO 2 , which lies on the linear part of the curve, and is more sensitive to small changes in oxygen tension.…”

“…Above a urinary sodium excretion of Ϸ300 mmol/d, medullary R2* appears to reach a plateau ( Figure 3A). In addition, at each level of sodium excretion, medullary R2* levels were lower in HT than NT individuals (mean: 29 Figure 3B). When analyzing blood pressure as a continuous variable rather than a dichotomous separator of groups, and independently of salt intake, an inverse correlation between the mean arterial blood pressure, as measured on the days of clearance and MR studies, and medullary R2* values was found (rϭϪ0.37; Pϭ0.026).…”

The significance of BOLD MRI in differentiation between renal transplant rejection and acute tubular necrosis

“…BOLD MRI has been used to investigate intra-renal oxygen bioavailability in the patients and experimental models of kidney diseases, such as water diuresis [5][6][7], diabetes [6], acute ischaemic renal dysfunction [8,9] and unilateral ureteral obstruction [10]. These studies provided evidence that BOLD MRI could effectively detect changes of intrarenal oxygen bioavailability in these diseases.…”

Blood oxygenation level-dependent MRI for assessment of renal oxygenation

“…11,24,25 However, causation is more complex, since renal tissue hypoxia has been dissociated from hyperfiltration in experimental models of diabetes mellitus. 51 Experimental diabetes mellitus is also associated with mitochondrial dysfunction and reduced efficiency of oxygen utilization due to enhanced generation of reactive oxygen species, increased angiotensin II levels, and reduced nitric oxide availability.…”