Detection of acute renal ischemia in swine using blood oxygen level‐dependent magnetic resonance imaging
ABSTRACT PurposeTo 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 MethodsBOLD 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.ResultsMean R2* measurements increased from baseline during renal artery occlusion in the cortex (axial, 13.8–24.6 second−1; coronal, 14.4–24.7 second−1) and medulla (axial, 19.3–32.2 second−1; coronal, 20.1–30.7 second−1). These differences were significant for both the cortex (axial, P < 0.04; coronal, P < 0.005) and medulla (axial, P < 0.02; coronal, P < 0.0005). No significant change was observed in the contralateral kidney.ConclusionR2* 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. J. Magn. Reson. Imaging 2005. © 2005 Wiley-Liss, Inc.
- SourceAvailable from: Matthias Stuber
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- "Since 1996, BOLD-MRI has been used in humans to evaluate, amongst others, the effect of water diuresis on renal medulla and cortex in healthy volunteers [34, 35] and diabetic patients  and to monitor changes in renal oxygenation after administration of different drugs [36, 37] and after acute renal ischemia [38, 39]. "
ABSTRACT: Animal studies suggest that renal tissue hypoxia plays an important role in the development of renal damage in hypertension and renal diseases, yet human data were scarce due to the lack of noninvasive methods. Over the last decade, blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI), detecting deoxyhemoglobin in hypoxic renal tissue, has become a powerful tool to assess kidney oxygenation noninvasively in humans. This paper provides an overview of BOLD-MRI studies performed in patients suffering from essential hypertension or chronic kidney disease (CKD). In line with animal studies, acute changes in cortical and medullary oxygenation have been observed after the administration of medication (furosemide, blockers of the renin-angiotensin system) or alterations in sodium intake in these patient groups, underlining the important role of renal sodium handling in kidney oxygenation. In contrast, no BOLD-MRI studies have convincingly demonstrated that renal oxygenation is chronically reduced in essential hypertension or in CKD or chronically altered after long-term medication intake. More studies are required to clarify this discrepancy and to further unravel the role of renal oxygenation in the development and progression of essential hypertension and CKD in humans.International Journal of Hypertension 02/2013; 2013:696598. DOI:10.1155/2013/696598
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- "Various stimuli were used to study the regulation of renal perfusion and oxygenation in animals under physiological conditions. For this purpose, vasoactive agents like nitric oxide (Li et al. 2003, 2009), prostaglandins (Prasad et al. 2001), reductions in RPP (Juillard et al. 2004, Alford et al. 2005), water diuresis (Prasad & Epstein 1999, Epstein et al. 2002, Haque et al. 2011) and changes in inspiratory oxygen fraction (Pedersen et al. 2005) were used to modify renal perfusion and oxygen delivery. To lower renal oxygen consumption, diuretics that reduce tubular reabsorption were applied (Li et al. 2004, Gomez et al. 2009, Warner et al. 2011). "
ABSTRACT: Acute kidney injury of various origins share a common link in the pathophysiological chain of events: imbalance between renal medullary oxygen delivery and oxygen demand. For in vivo assessment of kidney haemodynamics and oxygenation in animals quantitative but invasive physiological methods are established. A very limited number of studies attempted to link these invasive methods with parametric Magnetic Resonance Imaging (MRI) of the kidney. Moreover, the validity of parametric MRI (pMRI) as a surrogate marker for renal tissue perfusion and renal oxygenation has not been systematically examined yet. For this reason we set out to combine invasive techniques and non-invasive MRI in a integrated hybrid setup (MR-PHYSIOL) with the ultimate goal to calibrate, monitor and interpret parametric MR and physiological parameters by means of standardized interventions. Here we present a first report on the current status of this multi-modality approach. For this purpose we first highlight key characteristics of renal perfusion and oxygenation. Secondly, concepts for in vivo characterization of renal perfusion and oxygenation are surveyed together with the capabilities of MRI for probing blood oxygenation dependent tissue stages. Practical concerns evoked by the use of strong magnetic fields in MRI and interferences between MRI and invasive physiological probes are discussed. Technical solutions that balance the needs of in vivo physiological measurements together with the constraints dictated by small bore MR scanners are presented. An early implementation of the integrated MR-PHYSIOL approach is demonstrated including brief interventions of hypoxia and hyperoxia. Acta Physiologica © 2013 Scandinavian Physiological Society.Acta Physiologica 01/2013; 207(4). DOI:10.1111/apha.12065 · 4.38 Impact Factor
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ABSTRACT: Presence of renal hypoxia and its consequences to renal pathophysiology is well accepted now. Most data on renal oxygenation available today are based on animal models, and an ability to translate the findings to humans was highly desired. Although, several novel methodologies are being pursued, to date blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) is the only known technique available to evaluate renal oxygenation in humans. The technique is noninvasive, based on an endogenous contrast mechanism, and can be applied to both animal models and humans. The ability to evaluate relative renal oxygenation status in both health and disease could be useful in better understanding the pathophysiology and allowing for monitoring of potential novel interventions. In this chapter, we provide an overview of the principles involved and the implementation and various applications that investigators around the world have pursued to date.