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Metabolic sex differences have recently been shown to be particularly important in tailoring treatment strategies. Sex has a major effect on fat turnover rates and plasma lipid delivery in the body. Differences in kidney structure and transporters between male and female animals have been found. Here we investigated sex-specific renal pyruvate metabolic flux and whole-kidney functional status in age-matched healthy Wistar rats. Blood oxygenation level-dependent and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) were used to assess functional status. Hyperpolarized [1- 13 C]pyruvate was used to assess the metabolic differences between male and female rats. Female rats had a 41% ± 3% and 41% ± 5% lower absolute body and kidney weight, respectively, than age-matched male rats. No difference was seen between age-matched male and female rats in the kidney-to-body weight ratio. A 56% ± 11% lower lactate production per mL/100 mL/min was found in female rats than in age-matched male rats measured by hyperpolarized magnetic resonance and DCE MRI. Female rats had a 33% ± 11% higher glomerular filtration rate than age-matched male rats measured by DCE MRI. A similar renal oxygen tension (T2*) was found between age-matched male and female rats as shown by blood oxygenation level-dependent MRI. The results were largely independent of the pyruvate volume and the difference in body weight. This study shows an existing metabolic difference between kidneys in age-matched male and female rats, which indicates that sex differences need to be considered when performing animal experiments., Competing Interests: Conflict of Interest: None reported., (© 2020 The Authors. Published by Grapho Publications, LLC.)

Purpose: Anesthesia is necessary for most animal studies requiring invasive procedures. It is well documented that various types of anesthesia modulate a wide variety of important metabolic and functional processes in the body, and as such, represent a potential limitation in the study design. In the present study, we aimed to investigate the renal functional and metabolic consequences of 3 typical rodent anesthetics used in preclinical MRI: sevoflurane, inaction, and a mixture of fentanyl, fluanisone, and midazolam (FFM)., Methods: The renal effects of 3 different classes of anesthetics (inactin, servoflurane, and FFM) were investigated using functional and metabolic MRI. The renal glucose metabolism and hemodynamics was characterized with hyperpolarized [1- 13 C]pyruvate MRI and by DCE imaging., Results: Rats receiving sevoflurane or FFM had blood glucose levels that were 1.3-fold to 1.4-fold higher than rats receiving inactin. A 2.9-fold and 4.8-fold increased 13 C-lactate/ 13 C-pyruvate ratio was found in the FFM mixture anesthetized group compared with the sevoflurane and the inactin anesthetized groups. The FFM anesthesia resulted in a 50% lower renal plasma flow compared with the sevoflurane and the inactin anesthetized groups., Conclusion: This study demonstrates different renal metabolic and hemodynamic changes under 3 different anesthetics, using hyperpolarized MR in rats. Inactin and sevoflurane were found to affect the renal hemodynamic and metabolic status to a lesser degree than FFM. Sevoflurane anesthesia is particularly easy to induce and maintain during the whole anesthesia procedure, and as such, represents a good alternative to inaction, although it alters the blood glucose level., (© 2018 International Society for Magnetic Resonance in Medicine.)

Purpose: In the current study, we investigated hyperpolarized urea as a possible imaging biomarker of the renal function by means of the intrarenal osmolality gradient., Methods: Hyperpolarized three-dimensional balanced steady state 13 C MRI experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements was performed on two groups of rats, a streptozotocin type 1 diabetic group and a healthy control group., Results: A significant decline in intrarenal steepness of the urea gradient was found after 4 weeks of untreated insulinopenic diabetes in agreement with an increased urea transport transcription., Conclusion: MRI and hyperpolarized [ 13 C, 15 N]urea can monitor the changes in the corticomedullary urea concentration gradients in diabetic and healthy control rats. Magn Reson Med 77:1650-1655, 2017. © 2016 International Society for Magnetic Resonance in Medicine., (© 2016 International Society for Magnetic Resonance in Medicine.)

Purpose: A decline in cortico-medullary osmolality gradient of the kidney may serve as an early indicator of pathological disruption of the tubular reabsorption process. The purpose of this study was to investigate the feasibility of hyperpolarized 13 C, 15 N 2 -urea MRI as a biomarker of renal function in healthy porcine kidneys resembling the human physiology., Methods: Five healthy female Danish domestic pigs (weight 30 kg) were scanned at 3 Tesla (T) using a 13 C 3D balanced steady-state MR pulse sequence following injection of hyperpolarized 13 C, 15 N 2 -urea via a femoral vein catheter. Images were acquired at different time points after urea injection, and following treatment with furosemide., Results: A gradient in cortico-medullary urea was observed with an intramedullary accumulation 75 s after injection of hyperpolarized 13 C, 15 N 2 -urea, whereas images acquired at earlier time points postinjection were dominated by cortical perfusion. Furosemide treatment resulted in an increased urea accumulation in the cortical space, leading to a reduction of the medullary-to-cortical signal ratio of 49%., Conclusion: This study demonstrates that hyperpolarized 13 C, 15 N 2 -urea MRI is capable of identifying the intrarenal accumulation of urea and can differentiate acute renal functional states in multipapillary kidneys, highlighting the potential for human translation. Magn Reson Med 76:1895-1899, 2016. © 2016 International Society for Magnetic Resonance in Medicine., (© 2016 International Society for Magnetic Resonance in Medicine.)

Purpose: Our aim was to assess a novel (13) C radial fast spin echo golden ratio single shot method for interrogating early renal changes in the diabetic kidney, using hyperpolarized (HP) [(13) C,(15) N2 ]urea as a T2 relaxation based contrast bio-probe., Methods: A novel HP (13) C MR contrast experiment was conducted in a group of streptozotocin type-1 diabetic rat model and age matched controls., Results: A significantly different relaxation time (P = 0.004) was found in the diabetic kidney (0.49 ± 0.03 s) compared with the controls (0.64 ± 0.02 s) and secondly, a strong correlation between the blood oxygen saturation level and the relaxation times were observed in the healthy controls., Conclusion: HP [(13) C,(15) N2 ]urea apparent T2 mapping may be a useful for interrogating local renal pO2 status and renal tissue alterations. Magn Reson Med, 2015. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made., (© 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: Our aim was to determine the quantitative reproducibility of metabolic breakdown products in the kidney following intravenous injection of hyperpolarized [1-(13)C]pyruvate and secondly to investigate the metabolic effect on the pyruvate metabolism of oral sucrose load using dissolution dynamic nuclear polarization. By this technique, metabolic alterations in several different metabolic related diseases and their metabolic treatment responses can be accessed., Methods: In four healthy pigs the lactate-to-pyruvate, alanine-to-pyruvate and bicarbonate-to-pyruvate ratio was measured following administration of regular cola and consecutive injections of hyperpolarized [1-(13)C]pyruvate four times within an hour., Results: The overall lactate-to-pyruvate metabolic profile changed significantly over one hour following an acute sucrose load leading to a significant rise in blood glucose., Conclusion: The reproducibility of hyperpolarized magnetic resonance spectroscopy in the healthy pig kidney demonstrated a repeatability of more than 94% for all metabolites and, furthermore, that the pyruvate to lactate conversion and the blood glucose level is elevated following endogastric sucrose administration., (© 2015 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.)

Combretastatin A-4 disodium phosphate (CA4P) is a vascular disrupting agent known to mediate its effects primarily on tumor blood vessels. CA4P has previously been shown to induce a significant increase in mean arterial blood pressure and in hemoglobin concentration in mice. In the present study, we examined whether this is associated with a general leakage of water into certain tissues or with changes in renal water handling. Munich-Wistar rats received either CA4P (30 mg/kg body wt) or saline intraperitoneally as a bolus injection. One hour later, hemoglobin concentration and mean blood pressure increased significantly. MRI showed no significant changes in tissue water content following CA4P administration. However, urine output and salt excretion increased 1 h after CA4P treatment, without changes in urinary and medullary osmolality. Aquaporin 2 (AQP2) mRNA levels in kidney inner medulla did not change 1 h after CA4P treatment, but semiquantitative confocal laser-scanning microscopy analysis demonstrated a decrease in phosphorylated AQP2 (pS256-AQP2) apical distribution within the collecting ducts of CA4P-treated rats compared with the characteristic apical localization in control rats. Furthermore, we demonstrated that CA4P cause disruption of microtubules and a weaker apical labeling of pS256-AQP2 in collecting duct principal cells within 1 h. In conclusion, our data indicate that water escapes from the vascular system after CA4P treatment, and it may take place primarily through a renal mechanism. The CA4P-mediated increase in urine output seems to be a local effect in the collecting ducts due to reduced AQP2 trafficking to the apical plasma membrane.

The present study was designed to evaluate the short-term effects of intravenous administration of furosemide on key functions in the kidney cortex and the outer and inner medulla of rats by using magnetic resonance imaging (MRI). Renal tissue water content, renal tissue oxygenation (in relation to the magnetic resonance spin-spin relaxation rate), the apparent diffusion coefficient (ADC) of water, and volume of renal blood flow were measured. Furosemide administration resulted in an increased water content in all regions of the kidney. In parallel with this, we found a significant reduction in ADC in the cortex (2.7 +/- 0.1 x 10(-3) to 2.3 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01) and in the outer medulla (2.3 +/- 0.1 x 10(-3) to 2.0 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01), indicating that the intra- to extracellular volume fraction of water increased in response to furosemide administration. Furosemide also decreased the blood oxygenation in the cortex (49.1 +/- 2.9 to 40.9 +/- 2.0 s(-1); P < 0.01), outer medulla (41.9 +/- 2.8 to 33.2 +/- 1.6 s(-1); P < 0.01) and in the inner medulla (37.1 +/- 2.9 to 26.7 +/- 1.8 s(-1); P < 0.01), indicating an increased amount of oxygenated Hb in the renal tissue. Moreover, renal blood flow decreased in response to furosemide (6.9 +/- 0.2 to 4.4 +/- 0.2 ml/min; P < 0.001). In conclusion, furosemide administration was associated with increased renal water content, an increase in the intra- to extracellular volume fraction of water, an increased oxygen tension, and a decrease in the renal blood flow. Thus MRI provides an integrated evaluation of changes in renal function, leading to decreased renal water and solute reabsorption in response to furosemide, and, in addition, MRI provides an alternative tool to monitor noninvasively changes at the cellular level.

The incidence of congenital hydronephrosis is approximately 1% and is often associated with renal insufficiency. It is unknown whether early release is essential to prevent deterioration of renal function. Rats were subjected to partial unilateral ureteral obstruction (PUUO) on postnatal day 2. The obstruction was left in place or released after 1 or 4 wk. Renal blood flow (RBF) and kidney size were measured sequentially over 24 wk using MRI. In rats in which the obstruction was left in place, RBF of the obstructed kidney was progressively reduced to 0.92 +/- 0.17 vs. 1.79 +/- 0.12 ml.min(-1).100 g body wt(-1) (P < 0.05) after 24 wk. Similarly, glomerular filtration rate of the obstructed kidney was severely reduced at 24 wk: 172 +/- 36 vs. 306 +/- 42 microl.min(-1).100 g body wt(-1) (P < 0.05). These changes were preceded by development of severe hydronephrosis and obstructive nephropathy with a reduction in total protein content: 45 +/- 3 vs. 58 +/- 4 mg/kidney. Moreover, nonreleased PUUO caused a marked natriuresis (0.32 +/- 0.07 vs. 0.11 +/- 0.02 micromol.min(-1).100 g body wt(-1), P < 0.05) and impaired solute free water reabsorption (0.47 +/- 0.16 vs. 2.71 +/- 0.67 microl.min(-1).100 g body wt(-1), P < 0.05), consistent with a significant downregulation of Na-K-ATPase to 62 +/- 7%, aquaporin-1 to 53 +/- 3%, and aquaporin-3 to 53 +/- 7% of sham levels. Release after 1 wk completely prevented development of hydronephrosis, reduction in RBF and glomerular filtration rate, and downregulation of renal transport proteins, whereas release after 4 wk had no effect. These results suggest that early release of neonatal obstruction provides dramatically better protection of renal function than release of obstruction after the maturation process is completed.

A first-pass upslope approach was used to estimate differential renal blood flow (DRBF) and a Patlak-Rutland approach was used to estimate differential renal function (DRF) using Gd-DTPA-BMA-enhanced MRI. DRBF and DRF were estimated in rat kidneys under three different experimental conditions: 1) transient renal artery occlusion (TRAO); 2) partial unilateral ureteric obstruction (PUO); and 3) sham-operated control rats (SHAM). A bolus of Gd-DTPA-BMA was given intravenously during a dynamic single slice T1-weighted gradient echo sequence, which allowed calculation of concentration from signal intensity values. Calculations based on the raw signal intensity showed that DRBF was decreased in both PUO (44 +/- 1%; P < 0.05) and in TRAO (38 +/- 1%; P < 0.05) compared with SHAM (52 +/- 1%). Converting the signal intensity into a measure of Gd-DTPA-BMA concentration did not substantially alter these findings (PUO: 40 +/- 3%, P < 0.05; TRAO: 35 +/- 2%, P < 0.05; SHAM 49 +/- 1%). Likewise, DRF decreased in both PUO (43 +/- 4%; P < 0.05) and TRAO (39 +/- 3%; P < 0.05) compared with SHAM (48 +/- 2%). Converting the signal intensity into measurements of Gd-DTPA-BMA concentration revealed similar findings (PUO: 41 +/- 5%, P < 0.05; TRAO: 34 +/- 5%, P < 0.05; SHAM: 49 +/- 2%). Our results suggest that renal damage in rats may be demonstrated by an observed reduction of DRBF and DRF as estimated from single-slice Gd-DTPA-BMA enhanced signal intensity using time-activity curves with and without quantitation of Gd-concentration., (Copyright 2004 Wiley-Liss, Inc.)

The objective of this study was to examine the effect of unilateral ureteral obstruction on the apparent diffusion coefficient (ADC) in pig kidney. Changes in ADC is suggested to reflect changes in the ratio of extracellular to intracellular volume. Thirteen pigs were allocated into three groups: 1) pigs subjected to acute unilateral ureteral obstruction (AUO) (n = 3), 2) pigs subjected to chronic partial unilateral obstruction (CPUO) (n = 3), and 3) control pigs (n = 7). The extra- to intracellular volume ratio was indirectly measured in both the ipsilateral obstructed kidney and contralateral non-obstructed kidney by the ADC of the renal tissue using diffusion-weighted echo-planar magnetic resonance imaging. ADC was 2.07 +/- 0.27 x 10(-3) mm2/s in the cortex and 2.10 +/- 0.24 x 10(-3) mm2/s in the medulla of normal control kidneys. In the obstructed kidney from the AUO group the ADC of the medulla was significantly reduced 24 hours after occlusion of the ureter (1.65 +/- 0.05 x 10(-3) mm2/s vs 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05). Similarly ADC decreased slightly in the cortex of the ipsilateral kidney. In contrast, ADC of the ipsilateral kidney of CPUO pigs was increased both in the renal medulla (3.13 +/- 0.21 x 10(-3) mm2/s vs. 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05) and cortex (3.09 +/- 0.14 x 10(-3) mm2/s vs. 2.07 x 10(-3) mm2/s, p < 0.05). In conclusion, the results of the present study suggest that diffusion weighted imaging (ADC) may be a useful parameter to incorporate when identifying whether a ureteric obstruction is acute or chronic.

We assessed the longitudinal changes in renal vein blood flow (RVBF) and kidney volume in response to neonatally induced partial unilateral ureteral obstruction (PUUO) in rats with a magnetic resonance imaging (MRI) technique. During anesthesia, either the upper third or two thirds of the left ureter was embedded into the psoas muscle in newborn rats, creating either a mild (n=20) or a severe (n=9) partial obstruction. Control groups consisted of sham-operated (n=12) and non-operated (n=15) rats. During the following 24 weeks, RVBF and kidney volume were measured sequentially every 2-6 weeks with MRI, beginning 9 days after the operation. Both mild and severe obstruction caused a time-dependent decrease in RVBF. At week 24, the mean RVBF had decreased to 79% of the controls in the mildly obstructed kidneys (mean+/-SE: 1.45+/-0.14 vs 1.84+/-0.08 ml/min/100 g body weight, P<0.05) and to 57% of controls in the severely obstructed kidneys (1.05+/-0.10 vs 1.84+/-0.08 ml/min/100 g body weight, P<0.05). The renal pelvis volume increased and the renal parenchymal volume decreased significantly in the severely obstructed kidneys compared to the mildly obstructed kidneys. A good correlation was found between kidney volume measured in vivo using MRI and that measured in vitro (r>0.8, P<0.05), and between RVBF and renal parenchymal volume (r=0.758, P<0.01). In conclusion, the degree of reduction in RVBF depends on the severity and the duration of the PUUO. MRI can safely and reliably be used to monitor the longitudinal changes in RVBF and kidney volume in rats from early life.

Metabolic sex differences have recently been shown to be particularly important in tailoring treatment strategies. Sex has a major effect on fat turnover rates and plasma lipid delivery in the body. Differences in kidney structure and transporters between male and female animals have been found. Here we investigated sexspecific renal pyruvate metabolic flux and whole-kidney functional status in age-matched healthy Wistar rats. Blood oxygenation level-dependent and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) were used to assess functional status. Hyperpolarized [1-13C]pyruvate was used to assess the metabolic differences between male and female rats. Female rats had a 41% 6 3% and 41% 6 5% lower absolute body and kidney weight, respectively, than age-matched male rats. No difference was seen between agematched male and female rats in the kidney-to-body weight ratio. A 56% 6 11% lower lactate production per mL/100 mL/min was found in female rats than in age-matched male rats measured by hyperpolarized magnetic resonance and DCE MRI. Female rats had a 33% 6 11% higher glomerular filtration rate than age-matched male rats measured by DCE MRI. A similar renal oxygen tension (T2*) was found between agematched male and female rats as shown by blood oxygenation level-dependent MRI. The results were largely independent of the pyruvate volume and the difference in body weight. This study shows an existing metabolic difference between kidneys in age-matched male and female rats, which indicates that sex differences need to be considered when performing animal experiments. [ABSTRACT FROM AUTHOR]

Purpose In the current study, we investigated hyperpolarized urea as a possible imaging biomarker of the renal function by means of the intrarenal osmolality gradient. Methods Hyperpolarized three-dimensional balanced steady state 13C MRI experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements was performed on two groups of rats, a streptozotocin type 1 diabetic group and a healthy control group. Results A significant decline in intrarenal steepness of the urea gradient was found after 4 weeks of untreated insulinopenic diabetes in agreement with an increased urea transport transcription. Conclusion MRI and hyperpolarized [13C,15N]urea can monitor the changes in the corticomedullary urea concentration gradients in diabetic and healthy control rats. Magn Reson Med 77:1650-1655, 2017. © 2016 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Renal ischemia-reperfusion injury is the state of which a tissue experiences injury after a phase of restrictive blood supply and recirculation. Ischemia-reperfusion injury (I/R-I) is a leading cause of acute kidney injury (AKI) in several disease states, including kidney transplantation, sepsis, and hypovolemic shock. The most common methods to evaluate AKI are creatinine clearance, plasma creatinine, blood urea nitrogen, or renal histology. However, currently, there are no precise methods to directly assess renal injury state noninvasively. Hyperpolarized 13C-pyruvate MRI enables noninvasive accurate quantification of the in vivo conversion of pyruvate to lactate, alanine, and bicarbonate. In the present study, we investigated the in situ alterations of metabolic conversion of pyruvate to lactate, alanine, and bicarbonate in a unilateral I/R-I rat model with 30 min and 60 min of ischemia followed by 24 h of reperfusion. The pyruvate conversion was unaltered compared with sham in the 30 min I/R-I group, while a significant reduced metabolic conversion was found in the postischemic kidney after 60 min of ischemia. This indicates that after 30 min of ischemia, the kidney maintains normal metabolic function in spite of decreased kidney function, whereas the postischemic kidney after 60 min of ischemia show a generally reduced metabolic enzyme activity concomitant with a reduced kidney function. We have confidence that these findings can have a high prognostic value in prediction of kidney injury and the outcome of renal injury. [ABSTRACT FROM AUTHOR]

Purpose A decline in cortico-medullary osmolality gradient of the kidney may serve as an early indicator of pathological disruption of the tubular reabsorption process. The purpose of this study was to investigate the feasibility of hyperpolarized 13C,15N2-urea MRI as a biomarker of renal function in healthy porcine kidneys resembling the human physiology. Methods Five healthy female Danish domestic pigs (weight 30 kg) were scanned at 3 Tesla (T) using a 13C 3D balanced steady-state MR pulse sequence following injection of hyperpolarized 13C,15N2-urea via a femoral vein catheter. Images were acquired at different time points after urea injection, and following treatment with furosemide. Results A gradient in cortico-medullary urea was observed with an intramedullary accumulation 75 s after injection of hyperpolarized 13C,15N2-urea, whereas images acquired at earlier time points postinjection were dominated by cortical perfusion. Furosemide treatment resulted in an increased urea accumulation in the cortical space, leading to a reduction of the medullary-to-cortical signal ratio of 49%. Conclusion This study demonstrates that hyperpolarized 13C,15N2-urea MRI is capable of identifying the intrarenal accumulation of urea and can differentiate acute renal functional states in multipapillary kidneys, highlighting the potential for human translation. Magn Reson Med 76:1895-1899, 2016. © 2016 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose The aim of this work was to investigate whether hyperpolarized 13C,15N2-urea can be used as an imaging marker of renal injury in renal unilateral ischemic reperfusion injury (IRI), given that urea is correlated with the renal osmotic gradient, which describes the renal function. Methods Hyperpolarized three-dimensional balanced steady-state 13C magnetic resonance imaging (MRI) experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements were performed in rats subjected to unilateral renal ischemia for 60-minute and 24-hour reperfusion. Results We revealed a significant reduction in the intrarenal gradient in the ischemic kidney in agreement with cortical injury markers neutrophil gelatinase-associated lipocalin and kidney injury molecule 1, as well as functional kidney parameters. Conclusion Hyperpolarized functional 13C,15N2 urea MRI can be used to successfully detect changes in the intrarenal urea gradient post-IRI, thereby enabling in vivo monitoring of the intrarenal functional status in the rat kidney. Magn Reson Med 76:1524-1530, 2016. © 2016 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Early diabetic nephropathy is largely undetectable before substantial functional changes have occurred. In the present study, we investigated the distribution of electrolytes and urea in the early diabetic kidney in order to explore whether pathophysiological and metabolic changes appear concomitantly with a decreased sodium and urea gradient. By using hyperpolarized 13C urea it was possible to measure the essential intrarenal electrolyte gradients and the acute changes following furosemide treatment. No differences in either intrarenal urea or sodium gradients were observed in early diabetes compared to healthy controls. These results indicate that the early metabolic and hypertrophic changes occurring in the diabetic kidney prelude the later functional alterations in diabetic kidney function, thus driving the increased metabolic demand commonly occurring in the diabetic kidney. [ABSTRACT FROM AUTHOR]

Purpose Our aim was to assess a novel 13C radial fast spin echo golden ratio single shot method for interrogating early renal changes in the diabetic kidney, using hyperpolarized (HP) [13C,15N2]urea as a T2 relaxation based contrast bio-probe. Methods A novel HP 13C MR contrast experiment was conducted in a group of streptozotocin type-1 diabetic rat model and age matched controls. Results A significantly different relaxation time ( P = 0.004) was found in the diabetic kidney (0.49 ± 0.03 s) compared with the controls (0.64 ± 0.02 s) and secondly, a strong correlation between the blood oxygen saturation level and the relaxation times were observed in the healthy controls. Conclusion HP [13C,15N2]urea apparent T2 mapping may be a useful for interrogating local renal pO2 status and renal tissue alterations. Magn Reson Med, 2015. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Magn Reson Med 75:515-518, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]