Anatomically correct assessment of the orientation of the cardiomyocytes using diffusion tensor imaging

Diffusion tensor imaging has been used for assessing the orientation of cardiac myocytes for decades. Striking methodological differences exist between studies when quantifying these orientations. This limits the comparability between studies, and impedes collaboration and the drawing of appropriate physiological conclusions. We have sought to elucidate these differences, permitting us to propose a standardised "tool set" that might better establish consensus in future studies. We fixed hearts from seven 25 kg pigs in formalin, and scanned them using diffusion tensor imaging. Using various angle definitions as found in literature, we assessed the orientations of cardiomyocytes, comparing them in terms of helical and intrusion angles, along with the orientation of their aggregations. The difference between assessment of the helical angle with and without relation to the epicardial curvature was 25.2° (SD: 7.9) at the base, 5.8° (1.9) at the equatorial level, and 28.0° (7.0) at the apex, ANOVA P = 0.001. In comparable fashion, the intrusion angle differed by 25.9° (12.9), 7.6° (0.98) and 17.5° (4.7), P = 0.01, and the angle of the aggregates (E3-angle) differed by 25.0° (13.5) at the base, 9.4° (1.7) at the equator, and 23.1° (6.2) apically, P = 0.003. When assessing 14 definitions used in literature to calculate the orientation of aggregates, only 4 rendered identical results. The findings show that any attempt to use projection of eigenvectors introduces considerable bias. The epicardial curvature of the ventricular cone needs to be taken into account when seeking to provide accurate quantification of the orientation of the aggregated cardiomyocytes, especially in the apical and basal regions. This means that projection of eigenvectors should be avoided prior to quantifying myocyte orientation, especially when assessing radial orientation. Based on our results, we suggest appropriate methods for valid assessment of myocyte orientation using diffusion tensor imaging.

Consensus-based technical recommendations for clinical translation of renal BOLD MRI

Harmonization of acquisition and analysis protocols is an important step in the validation of BOLD MRI as a renal biomarker. This harmonization initiative provides technical recommendations based on a consensus report with the aim to move towards standardized protocols that facilitate clinical translation and comparison of data across sites. We used a recently published systematic review paper, which included a detailed summary of renal BOLD MRI technical parameters and areas of investigation in its supplementary material, as the starting point in developing the survey questionnaires for seeking consensus. Survey data were collected via the Delphi consensus process from 24 researchers on renal BOLD MRI exam preparation, data acquisition, data analysis, and interpretation. Consensus was defined as ≥ 75% unanimity in response. Among 31 survey questions, 14 achieved consensus resolution, 12 showed clear respondent preference (65-74% agreement), and 5 showed equal (50/50%) split in opinion among respondents. Recommendations for subject preparation, data acquisition, processing and reporting are given based on the survey results and review of the literature. These technical recommendations are aimed towards increased inter-site harmonization, a first step towards standardization of renal BOLD MRI protocols across sites. We expect this to be an iterative process updated dynamically based on progress in the field.

Hyperpolarised 13C-MRI metabolic and functional imaging: an emerging renal MR diagnostic modality

Magnetic resonance imaging (MRI) is a well-established modality for assessing renal morphology and function, as well as changes that occur during disease. However, the significant metabolic changes associated with renal disease are more challenging to assess with MRI. Hyperpolarized carbon-13 MRI is an emerging technique which provides an opportunity to probe metabolic alterations at high sensitivity by providing an increase in the signal-to-noise ratio of 20,000-fold or more. This review will highlight the current status of hyperpolarised 13C-MRI and its translation into the clinic and how it compares to metabolic measurements provided by competing technologies such as positron emission tomography (PET).

Consensus-based technical recommendations for clinical translation of renal T1 and T2 mapping MRI

To develop technical recommendations on the acquisition and post-processing of renal longitudinal (T1) and transverse (T2) relaxation time mapping. A multidisciplinary panel consisting of 18 experts in the field of renal T1 and T2 mapping participated in a consensus project, which was initiated by the European Cooperation in Science and Technology Action PARENCHIMA CA16103. Consensus recommendations were formulated using a two-step modified Delphi method. The first survey consisted of 56 items on T1 mapping, of which 4 reached the pre-defined consensus threshold of 75% or higher. The second survey was expanded to include both T1 and T2 mapping, and consisted of 54 items of which 32 reached consensus. Recommendations based were formulated on hardware, patient preparation, acquisition, analysis and reporting. Consensus-based technical recommendations for renal T1 and T2 mapping were formulated. However, there was considerable lack of consensus for renal T1 and particularly renal T2 mapping, to some extent surprising considering the long history of relaxometry in MRI, highlighting key knowledge gaps that require further work. This paper should be regarded as a first step in a long-term evidence-based iterative process towards ever increasing harmonization of scan protocols across sites, to ultimately facilitate clinical implementation.

High Intrarenal Lactate Production Inhibits the Renal Pseudohypoxic Response to Acutely Induced Hypoxia in Diabetes

Intrarenal hypoxia develops within a few days after the onset of insulinopenic diabetes in an experimental animal model (ie, a model of type-1 diabetes). Although diabetes-induced hypoxia results in increased renal lactate formation, mitochondrial function is well maintained, a condition commonly referred to as pseudohypoxia. However, the metabolic effects of significantly elevated lactate levels remain unclear. We therefore investigated in diabetic animals the response to acute intrarenal hypoxia in the presence of high renal lactate formation to delineate mechanistic pathways and compare these findings to healthy control animals. Hyperpolarized ¹³C-MRI and blood oxygenation level–dependent ¹H-MRI was used to investigate the renal metabolism of [1-¹³C]pyruvate and oxygenation following acutely altered oxygen content in the breathing gas in a streptozotocin rat model of type-1 diabetes with and without insulin treatment and compared with healthy control rats. The lactate signal in the diabetic kidney was reduced by 12%–16% during hypoxia in diabetic rats irrespective of insulin supplementation. In contrast, healthy controls displayed the well-known Pasteur effect manifested as a 10% increased lactate signal following reduction of oxygen in the inspired air. Reduced expression of the monocarboxyl transporter-4 may account for altered response to hypoxia in diabetes with a high intrarenal pyruvate-to-lactate conversion. Reduced intrarenal lactate formation in response to hypoxia in diabetes shows the existence of a different metabolic phenotype, which is independent of insulin, as insulin supplementation was unable to affect the pyruvate-to-lactate conversion in the diabetic kidney.

Glucose metabolism in brown adipose tissue determined by deuterium metabolic imaging in rats

BACKGROUND/OBJECTIVES

Brown adipose tissue (BAT) has gained growing interest as a potential target for treatment of obesity. Currently, the most widely used technique/method for in vivo measurements of BAT activity in humans is ¹⁸FDG PET/CT. To supplement these investigations novel radiation-free methods are warranted. Deuterium metabolic imaging (DMI) is a novel modality that combines magnetic resonance spectroscopic (MRS) imaging with deuterium-labelled glucose (²H-glucose). This allows for spatio-temporal and metabolic imaging beyond glucose uptake. We aimed to evaluate if DMI could discriminate glucose metabolism in BAT of cold-acclimatised and thermoneutral rats.

SUBJECTS/METHODS

Male Sprague-Dawley rats were housed in a cold environment (9 °C, n = 10) or at thermoneutrality (30 °C, n = 11) for 1 week. For imaging rats were anaesthetized, received a ²H-glucose (1 M, 1.95 g/kg) bolus and DMI was acquired at baseline followed by 20 min time intervals up to 2 h. Furthermore, Dixon MRI was performed for anatomical determination of the interscapular BAT (iBAT) depot along with dynamic contrast enhanced (DCE) MRI to evaluate perfusion.

RESULTS

²H-glucose signal was higher in cold-acclimatised rats compared with thermoneutral rats (p ≤ 0.001) indicating an overall increase in glucose uptake and metabolism. This was in line with a lower fat/water threshold, higher perfusion and increased UCP1 mRNA expression in iBAT (ninefold increment) of cold-acclimatised rats compared with thermoneutral rats.

CONCLUSIONS

We find that DMI can discriminate cold-acclimatised and thermoneutral BAT in rats. This is the first study to evaluate BAT activity by DMI, which may open up for the use of the non-radioactive DMI method for BAT measurements in humans.

Detection of acute kidney injury with hyperpolarized [13 C, 15 N]Urea and multiexponential relaxation modeling

PURPOSE

To assess the utility of Laplacian fitting to describe the differences in hyperpolarized [¹³ C, ¹⁵ N]urea T₂ relaxation in ischemic and healthy rodent kidneys.

METHODS

Six rats with unilateral renal ischemia were investigated. [¹³ C, ¹⁵ N]Urea T₂ mapping was undertaken with a radial fast spin echo method, with subsequent postprocessing performed with regularized Laplacian fitting.

RESULTS

Simulations showed that Laplacian fitting was stable down to a signal-to-noise ratio of 20. In vivo results showed a significant increase in the mono- and decrease in biexponential pools in ischemia reperfusion injury kidneys, in comparison to healthy (14 ± 10% versus 4 ± 2%, 85 ± 10% versus 95 ± 3%; P < .05).

CONCLUSION

We demonstrate, for the first time, the differences in multiexponential behavior of [¹³ C, ¹⁵ N]urea between the healthy and ischemic rodent kidney. The distribution of relaxation pools were found to be both visually and numerically significantly different. The ability to improve the information level in hyperpolarized MR, by using the relaxation contrast mechanisms is an appealing option, that can easily be adopted in large animals and even in clinical studies in the near future.

Consensus-based technical recommendations for clinical translation of renal ASL MRI

OBJECTIVES

This study aimed at developing technical recommendations for the acquisition, processing and analysis of renal ASL data in the human kidney at 1.5 T and 3 T field strengths that can promote standardization of renal perfusion measurements and facilitate the comparability of results across scanners and in multi-centre clinical studies.

METHODS

An international panel of 23 renal ASL experts followed a modified Delphi process, including on-line surveys and two in-person meetings, to formulate a series of consensus statements regarding patient preparation, hardware, acquisition protocol, analysis steps and data reporting.

RESULTS

Fifty-nine statements achieved consensus, while agreement could not be reached on two statements related to patient preparation. As a default protocol, the panel recommends pseudo-continuous (PCASL) or flow-sensitive alternating inversion recovery (FAIR) labelling with a single-slice spin-echo EPI readout with background suppression and a simple but robust quantification model.

DISCUSSION

This approach is considered robust and reproducible and can provide renal perfusion images of adequate quality and SNR for most applications. If extended kidney coverage is desirable, a 2D multislice readout is recommended. These recommendations are based on current available evidence and expert opinion. Nonetheless they are expected to be updated as more data become available, since the renal ASL literature is rapidly expanding.

Consensus-based technical recommendations for clinical translation of renal ASL MRI

Objectives

This study aimed at developing technical recommendations for the acquisition, processing and analysis of renal ASL data in the human kidney at 1.5 T and 3 T field strengths that can promote standardization of renal perfusion measurements and facilitate the comparability of results across scanners and in multi-centre clinical studies.

Methods

An international panel of 23 renal ASL experts followed a modified Delphi process, including on-line surveys and two in-person meetings, to formulate a series of consensus statements regarding patient preparation, hardware, acquisition protocol, analysis steps and data reporting.

Results

Fifty-nine statements achieved consensus, while agreement could not be reached on two statements related to patient preparation. As a default protocol, the panel recommends pseudo-continuous (PCASL) or flow-sensitive alternating inversion recovery (FAIR) labelling with a single-slice spin-echo EPI readout with background suppression and a simple but robust quantification model.

Discussion

This approach is considered robust and reproducible and can provide renal perfusion images of adequate quality and SNR for most applications. If extended kidney coverage is desirable, a 2D multislice readout is recommended. These recommendations are based on current available evidence and expert opinion. Nonetheless they are expected to be updated as more data become available, since the renal ASL literature is rapidly expanding.

Electronic supplementary material

The online version of this article (10.1007/s10334-019-00800-z) contains supplementary material, which is available to authorized users.

New Device for Noninvasive Telemetric Monitoring of Vital Signs in Healthy and Newly Operated Piglets

Measuring vital signs is central to medical practice, but they are difficult to monitor in awake laboratory animals. We examined the feasibility of a noninvasive device for telemetric assessment of respiration rate, heart rate, temperature and movement in pigs. Awake piglets were monitored continuously for 31 h (interquartile range, 7) before (n = 4) and after (n = 3) surgery. Data quality was sufficient for determination of all parameters. We conclude that continuous, noninvasive monitor- ing of pigs is possible by using the evaluated device.

Autonomous cryogenic RF receive coil for 13 C imaging of rodents at 3 T

PURPOSE

To develop an autonomous, in-bore, MR-compatible cryostat cooled with liquid nitrogen that provides full-day operation, and to demonstrate that the theoretical signal-to-noise benefit can be achieved for ¹³ C imaging at 3 T (32.13 MHz).

METHODS

The cryogenic setup uses a vacuum-insulated fiberglass cryostat, which indirectly cools a cold finger where the RF coil is attached. The cryostat was evacuated before use and had a reservoir of liquid nitrogen for full-day operation. A 30 × 40 mm² copper coil was mounted inside the cryostat with a 3-mm distance to the sample. Two examples of in vivo experiments of rat brain metabolism after a hyperpolarized [1-¹³ C]pyruvate injection are reported.

RESULTS

A coil Q-factor ratio of Q_88K /Q_290K = 550/280 was obtained, and the theoretical SNR enhancement was verified with MR measurements. We achieved a coil temperature of 88 K and a preamplifier temperature of 77 K. A 2-fold overall SNR enhancement was achieved, compared with the best case at room temperature. The thermal performance of the coil was adequate for in vivo experiments, with an autonomy of 5 hours consuming 6 L of LN₂ , extendable to over 12 hours by LN₂ refilling.

CONCLUSION

Cryogenic surface coils can be highly beneficial for ¹³ C imaging, provided that the coil-to-sample distance remains short. An autonomous, in-bore cryostat was developed that achieved the theoretical improvement in SNR.

Consensus-based technical recommendations for clinical translation of renal BOLD MRI

Harmonization of acquisition and analysis protocols is an important step in the validation of BOLD MRI as a renal biomarker. This harmonization initiative provides technical recommendations based on a consensus report with the aim to move towards standardized protocols that facilitate clinical translation and comparison of data across sites. We used a recently published systematic review paper, which included a detailed summary of renal BOLD MRI technical parameters and areas of investigation in its supplementary material, as the starting point in developing the survey questionnaires for seeking consensus. Survey data were collected via the Delphi consensus process from 24 researchers on renal BOLD MRI exam preparation, data acquisition, data analysis, and interpretation. Consensus was defined as ≥ 75% unanimity in response. Among 31 survey questions, 14 achieved consensus resolution, 12 showed clear respondent preference (65-74% agreement), and 5 showed equal (50/50%) split in opinion among respondents. Recommendations for subject preparation, data acquisition, processing and reporting are given based on the survey results and review of the literature. These technical recommendations are aimed towards increased inter-site harmonization, a first step towards standardization of renal BOLD MRI protocols across sites. We expect this to be an iterative process updated dynamically based on progress in the field.

Consensus-based technical recommendations for clinical translation of renal T1 and T2 mapping MRI

To develop technical recommendations on the acquisition and post-processing of renal longitudinal (T1) and transverse (T2) relaxation time mapping. A multidisciplinary panel consisting of 18 experts in the field of renal T1 and T2 mapping participated in a consensus project, which was initiated by the European Cooperation in Science and Technology Action PARENCHIMA CA16103. Consensus recommendations were formulated using a two-step modified Delphi method. The first survey consisted of 56 items on T1 mapping, of which 4 reached the pre-defined consensus threshold of 75% or higher. The second survey was expanded to include both T1 and T2 mapping, and consisted of 54 items of which 32 reached consensus. Recommendations based were formulated on hardware, patient preparation, acquisition, analysis and reporting. Consensus-based technical recommendations for renal T1 and T2 mapping were formulated. However, there was considerable lack of consensus for renal T1 and particularly renal T2 mapping, to some extent surprising considering the long history of relaxometry in MRI, highlighting key knowledge gaps that require further work. This paper should be regarded as a first step in a long-term evidence-based iterative process towards ever increasing harmonization of scan protocols across sites, to ultimately facilitate clinical implementation.

Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI

Objectives

Standardization is an important milestone in the validation of DWI-based parameters as imaging biomarkers for renal disease. Here, we propose technical recommendations on three variants of renal DWI, monoexponential DWI, IVIM and DTI, as well as associated MRI biomarkers (ADC, D, D*, f, FA and MD) to aid ongoing international efforts on methodological harmonization.

Materials and methods

Reported DWI biomarkers from 194 prior renal DWI studies were extracted and Pearson correlations between diffusion biomarkers and protocol parameters were computed. Based on the literature review, surveys were designed for the consensus building. Survey data were collected via Delphi consensus process on renal DWI preparation, acquisition, analysis, and reporting. Consensus was defined as ≥ 75% agreement.

Results

Correlations were observed between reported diffusion biomarkers and protocol parameters. Out of 87 survey questions, 57 achieved consensus resolution, while many of the remaining questions were resolved by preference (65–74% agreement). Summary of the literature and survey data as well as recommendations for the preparation, acquisition, processing and reporting of renal DWI were provided.

Discussion

The consensus-based technical recommendations for renal DWI aim to facilitate inter-site harmonization and increase clinical impact of the technique on a larger scale by setting a framework for acquisition protocols for future renal DWI studies. We anticipate an iterative process with continuous updating of the recommendations according to progress in the field.

Electronic supplementary material

The online version of this article (10.1007/s10334-019-00790-y) contains supplementary material, which is available to authorized users.

Assessment of mouse liver [1-13C]pyruvate metabolism by dynamic hyperpolarized MRS

Hyperpolarized [1-13C]pyruvate magnetic resonance (MR) spectroscopy has the unique ability to detect real-time metabolic changes in vivo owing to its high sensitivity compared with thermal MR and high specificity compared with other metabolic imaging methods. The aim of this study was to explore the potential of hyperpolarized MR spectroscopy for quantification of liver pyruvate metabolism during a hyperinsulinemic-isoglycemic clamp in mice. Hyperpolarized [1-13C]pyruvate was used for in vivo MR spectroscopy of liver pyruvate metabolism in mice. Mice were divided into two groups: (i) non-stimulated 5-h fasted mice and (ii) hyperinsulinemic-isoglycemic clamped mice. During clamp conditions, insulin and donor blood were administered at a constant rate, whereas glucose was infused to maintain isoglycemia. When steady state was reached, insulin-stimulated mice were rapidly infused with hyperpolarized [1-13C]pyruvate for real-time tracking of the dynamic distribution of metabolic derivatives from pyruvate, such as [1-13C]lactate, [1-13C]alanine and [13C]bicarbonate. Isotopomer analysis of plasma glucose confirmed 13C-incorporation from [1-13C]pyruvate into glucose was increased in fasted mice compared with insulin-stimulated mice, demonstrating an increased gluconeogenesis in fasted mice. The AUC ratios for [1-13C]alanine/[1-13C]pyruvate (38.2%), [1-13C]lactate/[1-13C]pyruvate (41.8%) and [13C]bicarbonate/[1-13C]pyruvate (169%) all increased significantly during insulin stimulation. Hyperpolarized [1-13C]pyruvate can be used for in vivo MR spectroscopy of liver pyruvate metabolism during hyperinsulinemic-isoglycemic clamp conditions. Under these conditions, insulin decreased gluconeogenesis and increased [1-13C]alanine, [1-13C]lactate and [13C]bicarbonate after a [1-13C]pyruvate bolus. This application of in vivo spectroscopy has the potential to identify impairments in specific metabolic pathways in the liver associated with obesity, insulin resistance and nonalcoholic fatty liver disease.

Resolving the natural myocardial remodelling brought upon by cardiac contraction; a porcine ex-vivo cardiovascular magnetic resonance study of the left and right ventricle

BACKGROUND

The three-dimensional rearrangement of the right ventricular (RV) myocardium during cardiac deformation is unknown. Previous in-vivo studies have shown that myocardial left ventricular (LV) deformation is driven by rearrangement of aggregations of cardiomyocytes that can be characterised by changes in the so-called E3-angle. Ex-vivo imaging offers superior spatial resolution compared with in-vivo measurements, and can thus provide novel insight into the deformation of the myocardial microstructure in both ventricles. This study sought to describe the dynamic changes of the orientations of the cardiomyocytes in both ventricles brought upon by cardiac contraction, with particular interest in the thin-walled RV, which has not previously been described in terms of its micro-architecture.

METHODS

The hearts of 14 healthy 20 kg swine were excised and preserved in either a relaxed state or a contracted state. Myocardial architecture was assessed and compared between the two contractional states by quantification of the helical, transmural and E3-angles of the cardiomyocytes using high-resolution diffusion tensor imaging.

RESULTS

The differences between the two states of contraction were most pronounced in the endocardium where the E3-angle decreased from 78.6° to 24.8° in the LV and from 82.6° to 68.6° in the RV. No significant change in neither the helical nor the transmural angle was found in the cardiomyocytes of the RV. In the endocardium of the LV, however, the helical angle increased from 35.4° to 47.8° and the transmural angle increased from 3.1° to 10.4°.

CONCLUSION

The entire myocardium rearranges through the cardiac cycle with the change in the orientation of the aggregations of cardiomyocytes being the predominant mediator of myocardial wall thickening. Interestingly, differences also exist between the RV and LV, which helps in the explanation of the different physiological capabilities of the ventricles.

Metabolic consequences of lactate dehydrogenase inhibition by oxamate in hyperglycemic proximal tubular cells

Diabetic kidney disease (DKD) is associated with altered metabolic patterns, leading to increased lactate production even in the presence of sufficient oxygen supply. Studies have shown hyperglycemia to be an important factor in determining development of DKD. Here we explore the metabolic consequences of lactate dehydrogenase (LDH) inhibition exerted by the LDH inhibitor, oxamate, in the isolated rat renal proximal tubular cells (NRK-52E) under hyperglycemic conditions. Cells treated with oxamate (100 mM) for 24 h, with or without high D-glucose (25 mM) load, were investigated with hyperpolarized [1-¹³C]pyruvate in a 1T NMR system. Respiratory measurements using an oxygen microsensor system was conducted. Oxamate treatment of cells with or without the presences of high D-glucose, reduced the lactate production/accumulation with 36.5% or 22.5% respectively. Reduced proliferation, hypertrophic effects, as well as elevated vascular endothelial growth factor (VEGF) expression in the NRK-52E cells were found. The increased glycolytic flux in high D-glucose cultured NRK-52E cells resulted in an upregulation of the cellular oxygen consumption rate upon treatment with oxamate. Our findings suggested that in vitro cultured NRK-52E cells exposed to hyperglycemic conditions, could redirect the glycolytic flux towards oxidative phosphorylation by LDH inhibition. This link between aerobic and anaerobic metabolism may be determined by the redox balance (NAD+/NADH ratio). In conclusion, hyperglycemic conditions and oxamate treatment alters the metabolic phenotype of NRK-52E cells towards increased oxygen utilization mediated by a decreased NAD+/NADH ratio, which in turn decreases cell proliferation/survival.

Hyperpolarized 13C MRI: Path to Clinical Translation in Oncology

This white paper discusses prospects for advancing hyperpolarization technology to better understand cancer metabolism, identify current obstacles to HP (hyperpolarized) 13C magnetic resonance imaging's (MRI's) widespread clinical use, and provide recommendations for overcoming them. Since the publication of the first NIH white paper on hyperpolarized 13C MRI in 2011, preclinical studies involving [1-13C]pyruvate as well a number of other 13C labeled metabolic substrates have demonstrated this technology's capacity to provide unique metabolic information. A dose-ranging study of HP [1-13C]pyruvate in patients with prostate cancer established safety and feasibility of this technique. Additional studies are ongoing in prostate, brain, breast, liver, cervical, and ovarian cancer. Technology for generating and delivering hyperpolarized agents has evolved, and new MR data acquisition sequences and improved MRI hardware have been developed. It will be important to continue investigation and development of existing and new probes in animal models. Improved polarization technology, efficient radiofrequency coils, and reliable pulse sequences are all important objectives to enable exploration of the technology in healthy control subjects and patient populations. It will be critical to determine how HP 13C MRI might fill existing needs in current clinical research and practice, and complement existing metabolic imaging modalities. Financial sponsorship and integration of academia, industry, and government efforts will be important factors in translating the technology for clinical research in oncology. This white paper is intended to provide recommendations with this goal in mind.

Glucagon infusion alters the hyperpolarized 13 C-urea renal hemodynamic signature

Renal urea handling is central to the urine concentrating mechanism, and as such the ability to image urea transport in the kidney is an important potential imaging biomarker for renal functional assessment. Glucagon levels associated with changes in dietary protein intake have been shown to influence renal urea handling; however, the exact mechanism has still to be fully understood. Here we investigate renal function and osmolite distribution using [¹³ C,¹⁵ N] urea dynamics and ²³ Na distribution before and 60 min after glucagon infusion in six female rats. Glucagon infusion increased the renal [¹³ C,¹⁵ N] urea mean transit time by 14%, while no change was seen in the sodium distribution, glomerular filtration rate or oxygen consumption. This change is related to the well-known effect of increased urea excretion associated with glucagon infusion, independent of renal functional effects. This study demonstrates for the first time that hyperpolarized ¹³ C-urea enables monitoring of renal urinary excretion effects in vivo.