Dynamic contrast-enhanced MRI measurement of renal function in healthy participants

Renal MRI: From Nephron to NMR Signal

Renal diseases pose a significant socio-economic burden on healthcare systems. The development of better diagnostics and prognostics is well-recognized as a key strategy to resolve these challenges. Central to these developments are MRI biomarkers, due to their potential for monitoring of early pathophysiological changes, renal disease progression or treatment effects. The surge in renal MRI involves major cross-domain initiatives, large clinical studies, and educational programs. In parallel with these translational efforts, the need for greater (patho)physiological specificity remains, to enable engagement with clinical nephrologists and increase the associated health impact. The ISMRM 2022 Member Initiated Symposium (MIS) on renal MRI spotlighted this issue with the goal of inspiring more solutions from the ISMRM community. This work is a summary of the MIS presentations devoted to: 1) educating imaging scientists and clinicians on renal (patho)physiology and demands from clinical nephrologists, 2) elucidating the connection of MRI parameters with renal physiology, 3) presenting the current state of leading MR surrogates in assessing renal structure and functions as well as their next generation of innovation, and 4) describing the potential of these imaging markers for providing clinically meaningful renal characterization to guide or supplement clinical decision making. We hope to continue momentum of recent years and introduce new entrants to the development process, connecting (patho)physiology with (bio)physics, and conceiving new clinical applications. We envision this process to benefit from cross-disciplinary collaboration and analogous efforts in other body organs, but also to maximally leverage the unique opportunities of renal physiology. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

Physiological confounders of renal blood flow measurement

OBJECTIVES

Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI.

METHODS

A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans.

RESULTS

A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement.

CONCLUSION

Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.

Magnetic Resonance Imaging in Clinical Trials of Diabetic Kidney Disease

Chronic kidney disease (CKD) associated with diabetes mellitus (DM) (known as diabetic kidney disease, DKD) is a serious and growing healthcare problem worldwide. In DM patients, DKD is generally diagnosed based on the presence of albuminuria and a reduced glomerular filtration rate. Diagnosis rarely includes an invasive kidney biopsy, although DKD has some characteristic histological features, and kidney fibrosis and nephron loss cause disease progression that eventually ends in kidney failure. Alternative sensitive and reliable non-invasive biomarkers are needed for DKD (and CKD in general) to improve timely diagnosis and aid disease monitoring without the need for a kidney biopsy. Such biomarkers may also serve as endpoints in clinical trials of new treatments. Non-invasive magnetic resonance imaging (MRI), particularly multiparametric MRI, may achieve these goals. In this article, we review emerging data on MRI techniques and their scientific, clinical, and economic value in DKD/CKD for diagnosis, assessment of disease pathogenesis and progression, and as potential biomarkers for clinical trial use that may also increase our understanding of the efficacy and mode(s) of action of potential DKD therapeutic interventions. We also consider how multi-site MRI studies are conducted and the challenges that should be addressed to increase wider application of MRI in DKD.

Reliability of rubidium-82 PET/CT for renal perfusion determination in healthy subjects

Background

Changes in renal perfusion may play a pathophysiological role in hypertension and kidney disease, however to date, no method for renal blood flow (RBF) determination in humans has been implemented in clinical practice. In a previous study, we demonstrated that estimation of renal perfusion based on a single positron emission tomography/computed tomography (PET/CT) scan with Rubidium-82 (82Rb) is feasible and found an approximate 5% intra-assay coefficient of variation for both kidneys, indicative of a precise method.This study’s aim was to determine the day-to day variation of 82Rb PET/CT and to test the method’s ability to detect increased RBF induced by infusion of amino acids.

Methods

Seventeen healthy subjects underwent three dynamic 82Rb PET/CT scans over two examination days comprising: Day A, a single 8-minute dynamic scan and Day B, two scans performed before (baseline) and after RBF stimulation by a 2-hour amino acid-infusion. The order of examination days was determined by randomization. Time activity curves for arterial and renal activity with a 1-tissue compartment model were used for flow estimation; the K1 kinetic parameter representing renal 82Rb clearance. Day-to-day variation was calculated based on the difference between the unstimulated K1 values on Day A and Day B and paired t-testing was performed to compare K1 values at baseline and after RBF stimulation on Day B.

Results

Day-to-day variation was observed to be 5.5% for the right kidney and 6.0% for the left kidney (n = 15 quality accepted scans). K1 values determined after amino acid-infusion were significantly higher than pre-infusion values (n = 17, p = 0.001). The mean percentage change in K1 from baseline was 13.2 ± 12.9% (range − 10.4 to 35.5) for the right kidney; 12.9 ± 13.2% (range − 15.7 to 35.3) for the left kidney.

Conclusion

Day-to-day variation is acceptably low. A significant K1 increase from baseline is detected after application of a known RBF stimulus, indicating that 82Rb PET/CT scanning can provide a precise method for evaluation of RBF and it is able to determine changes herein.

Clinical Trial Registration

EU Clinical Trials Register, 2017-005008-88. Registered 18/01/2018.

Birth Weight Is Associated With Kidney Size in Middle-Aged Women

Introduction

Low birth weight (LBW) is associated with increased risk of kidney disease due to lower nephron endowment leading to hyperfiltration and subsequent nephron loss. Kidney size is commonly used as a proxy for nephron number. We compared kidney volume measured by magnetic resonance imaging (MRI) with measured glomerular filtration rate (mGFR) in adults with either normal birth weight (NBW) or low birth weight (LBW).

Methods

Healthy individuals aged 42 to 52 years with LBW (1100−2300 g) and NBW (3500 −4000 g) were invited to participate. The GFR was measured using plasma clearance of iohexol. Kidney volume was measured on magnetic resonance images using axial T2 images and coronal T1 images with fat saturation without contrast enhancement; calculations were performed according to the ellipsoid formula π/6 × length × width × depth.

Results

We included 102 individuals (54 LBW and 48 NBW). Total kidney volume was 302 ± 51 ml for female NBW vs 258 ± 48 ml for female LBW individuals (P = 0.002). For male individuals, total kidney volume was 347 ± 51 ml vs. 340 ± 65 ml (P = 0.7). The mGFR was significantly associated with kidney volume, with r = 0.52 (P < 0.001) for women and r = 0.39 (P = 0.007) for men. A mediation analysis showed that the association between birth weight and mGFR (significant in total sample and women) was mediated by kidney volume.

Conclusion

Healthy female individuals born with LBW have smaller kidneys than healthy females born with NBW. The previously shown associations between LBW and lower mGFR in adult women might be explained by smaller kidney volume.

Healthy Kidney Segmentation in the Dce-Mr Images Using a Convolutional Neural Network and Temporal Signal Characteristics

Quantification of renal perfusion based on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) requires determination of signal intensity time courses in the region of renal parenchyma. Thus, selection of voxels representing the kidney must be accomplished with special care and constitutes one of the major technical limitations which hampers wider usage of this technique as a standard clinical routine. Manual segmentation of renal compartments—even if performed by experts—is a common source of decreased repeatability and reproducibility. In this paper, we present a processing framework for the automatic kidney segmentation in DCE-MR images. The framework consists of two stages. Firstly, kidney masks are generated using a convolutional neural network. Then, mask voxels are classified to one of three regions—cortex, medulla, and pelvis–based on DCE-MRI signal intensity time courses. The proposed approach was evaluated on a cohort of 10 healthy volunteers who underwent the DCE-MRI examination. MRI scanning was repeated on two time events within a 10-day interval. For semantic segmentation task we employed a classic U-Net architecture, whereas experiments on voxel classification were performed using three alternative algorithms—support vector machines, logistic regression and extreme gradient boosting trees, among which SVM produced the most accurate results. Both segmentation and classification steps were accomplished by a series of models, each trained separately for a given subject using the data from other participants only. The mean achieved accuracy of the whole kidney segmentation was 94% in terms of IoU coefficient. Cortex, medulla and pelvis were segmented with IoU ranging from 90 to 93% depending on the tissue and body side. The results were also validated by comparing image-derived perfusion parameters with ground truth measurements of glomerular filtration rate (GFR). The repeatability of GFR calculation, as assessed by the coefficient of variation was determined at the level of 14.5 and 17.5% for the left and right kidney, respectively and it improved relative to manual segmentation. Reproduciblity, in turn, was evaluated by measuring agreement between image-derived and iohexol-based GFR values. The estimated absolute mean differences were equal to 9.4 and 12.9 mL/min/1.73 m² for scanning sessions 1 and 2 and the proposed automated segmentation method. The result for session 2 was comparable with manual segmentation, whereas for session 1 reproducibility in the automatic pipeline was weaker.

Analysis Protocol for Dynamic Contrast Enhanced (DCE) MRI of Renal Perfusion and Filtration

Here we present an analysis protocol for dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) data of the kidneys. It covers comprehensive steps to facilitate signal to contrast agent concentration mapping via T1 mapping and the calculation of renal perfusion and filtration parametric maps using model-free approaches, model free analysis using deconvolution, the Toft's model and a Bayesian approach.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This analysis protocol chapter is complemented by two separate chapters describing the basic concept and experimental procedure.

A Multi-Layer Perceptron Network for Perfusion Parameter Estimation in DCE-MRI Studies of the Healthy Kidney

Background: Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is an imaging technique which helps in visualizing and quantifying perfusion—one of the most important indicators of an organ’s state. This paper focuses on perfusion and filtration in the kidney, whose performance directly influences versatile functions of the body. In clinical practice, kidney function is assessed by measuring glomerular filtration rate (GFR). Estimating GFR based on DCE-MRI data requires the application of an organ-specific pharmacokinetic (PK) model. However, determination of the model parameters, and thus the characterization of GFR, is sensitive to determination of the arterial input function (AIF) and the initial choice of parameter values. Methods: This paper proposes a multi-layer perceptron network for PK model parameter determination, in order to overcome the limitations of the traditional model’s optimization techniques based on non-linear least-squares curve-fitting. As a reference method, we applied the trust-region reflective algorithm to numerically optimize the model. The effectiveness of the proposed approach was tested for 20 data sets, collected for 10 healthy volunteers whose image-derived GFR scores were compared with ground-truth blood test values. Results: The achieved mean difference between the image-derived and ground-truth GFR values was 2.35 mL/min/1.73 m2, which is comparable to the result obtained for the reference estimation method (−5.80 mL/min/1.73 m2). Conclusions: Neural networks are a feasible alternative to the least-squares curve-fitting algorithm, ensuring agreement with ground-truth measurements at a comparable level. The advantages of using a neural network are twofold. Firstly, it can estimate a GFR value without the need to determine the AIF for each individual patient. Secondly, a reliable estimate can be obtained, without the need to manually set up either the initial parameter values or the constraints thereof.

One-stop assessment of renal function and renal artery in hypertensive patients with suspected renal dysfunction: non-enhanced MRI using spatial labeling with multiple inversion pulses

OBJECTIVES

To assess whether spatial labeling with multiple inversion pulses (SLEEK) sequence can be employed as a one-stop assessment method for evaluating renal function and displaying renal artery in hypertensive patients with suspected renal dysfunction.

METHODS

A total of 78 patients with suspected hypertensive renal damage were enrolled in this retrospective study. All patients underwent MRI examinations, and both SLEEK and DWI sequences were performed simultaneously. According to estimated glomerular filtration rate (eGFR), patients were divided into three groups (Group 1, eGFR> 90; Group 2, eGFR = 60-90; Group 3, eGFR< 60). Twenty-two of these patients also underwent CT angiography (CTA) examination. Comparison between CTA, DWI, and eGFR was performed to assess the value of SLEEK in evaluating renal function and displaying renal artery.

RESULTS

The performance of SLEEK to display renal artery was highly consistent with the results of CTA (kappa = 0.713). The corticomedullary contrast ratio positively correlated with eGFR (p = 0.004, r = 0.322) and was significantly higher in SLEEK images than in DWI images in all three groups (p < 0.001). There was no significant difference in corticomedullary contrast ratio in SLEEK images between Group 1 and Group 2 (p = 0.285). However, the minimal renal cortical thickness, which significantly correlated with eGFR (p < 0.001, r = 0.866), was significantly different between Group 1 and Group 2 (p < 0.001). ROC analysis showed good diagnostic performance when differentiating patients with eGFR> 60 from those with eGFR< 60.

CONCLUSIONS

The SLEEK sequence could evaluate simultaneously renal function through corticomedullary differentiation and renal arteries, enabling one-stop assessment in hypertensive patients with suspected renal dysfunction.

KEY POINTS

• Spatial labeling with multiple inversion pulses (SLEEK) improves renal corticomedullary differentiation in hypertensive patients with renal dysfunction compared with DWI. • SLEEK clearly displays renal artery in hypertensive patients with renal dysfunction. • SLEEK could be utilized as a one-stop assessment method for evaluating renal function and renal artery in hypertensive patients.

Dual assessment of kidney perfusion and pH by exploiting a dynamic CEST-MRI approach in an acute kidney ischemia-reperfusion injury murine model

Several factors can lead to acute kidney injury, but damage following ischemia and reperfusion injuries is the main risk factor and usually develops into chronic disease. MRI has often been proposed as a method with which to assess renal function. It does so by measuring the renal perfusion of an injected Gd-based contrast agent. The use of pH-responsive agents as part of the CEST (chemical exchange saturation transfer)-MRI technique has recently shown that pH homeostasis is also an important indicator of kidney functionality. However, there is still a need for methods that can provide more than one type of information following the injection of a single contrast agent for the characterization of renal function. Herein we propose, for the first time, dynamic CEST acquisition following iopamidol injection to quantify renal function by assessing both perfusion and pH homeostasis. The aim of this study is to assess renal functionality in a murine unilateral ischemia-reperfusion injury model at two time points (3 and 7 days) after acute kidney injury. The renal-perfusion estimates measured with iopamidol were compared with those obtained with a gadolinium-based agent, via a dynamic contrast enhanced (DCE)-MRI approach, to validate the proposed method. Compared with the contralateral kidneys, the clamped ones showed a significant decrease in renal perfusion, as measured using the DCE-MRI approach, which is consistent with reduced filtration capability. Dynamic CEST-MRI findings provided similar results, indicating that the clamped kidneys displayed significantly reduced renal filtration that persisted up to 7 days after the damage. In addition, CEST-MRI pH imaging showed that the clamped kidneys displayed significantly increased pH values, reflecting the disturbance to pH homeostasis. Our results demonstrate that a single CEST-MRI contrast agent can provide multiple types of information related to renal function and can discern healthy kidneys from pathological ones by combining perfusion measurements with renal pH mapping.

Prospective pediatric study comparing glomerular filtration rate estimates based on motion-robust dynamic contrast-enhanced magnetic resonance imaging and serum creatinine (eGFR) to 99mTc DTPA

BACKGROUND

Current methods to estimate glomerular filtration rate (GFR) have shortcomings. Estimates based on serum creatinine are known to be inaccurate in the chronically ill and during acute changes in renal function. Gold standard methods such as inulin and ^99mTc diethylenetriamine pentaacetic acid (DTPA) require blood or urine sampling and thus can be difficult to perform in children. Motion-robust radial volumetric interpolated breath-hold examination (VIBE) dynamic contrast-enhanced MRI represents a novel tool for estimating GFR that has not been validated in children.

OBJECTIVE

The purpose of our study was to determine the feasibility and accuracy of GFR measured by motion-robust radial VIBE dynamic contrast-enhanced MRI compared to estimates by serum creatinine (eGFR) and ^99mTc DTPA in children.

MATERIALS AND METHODS

We enrolled children, 0-18 years of age, who were undergoing both a contrast-enhanced MRI and nuclear medicine ^99mTc DTPA glomerular filtration rate (NM-GFR) within 2 weeks of each other. Enrolled children consented to an additional 6-min dynamic contrast-enhanced MRI scan using the motion-robust high spatiotemporal resolution prototype dynamic radial VIBE sequence (Siemens, Erlangen, Germany) at 3 tesla (T). The images were reconstructed offline with high temporal resolution (~3 s/volume) using compressed sensing image reconstruction including regularization in temporal dimension to improve image quality and reduce streaking artifacts. Images were then automatically post-processed using in-house-developed software. Post-processing steps included automatic segmentation of kidney parenchyma and aorta using convolutional neural network techniques and tracer kinetic model fitting using the Sourbron two-compartment model to calculate the MR-based GFR (MR-GFR). The NM-GFR was compared to MR-GFR and estimated GFR based on serum creatinine (eGFR) using Pearson correlation coefficient and Bland-Altman analysis.

RESULTS

Twenty-one children (7 female, 14 male) were enrolled between February 2017 and May 2018. Data from six of these children were not further analyzed because of deviations from the MRI protocol. Fifteen patients were analyzed (5 female, 10 male; average age 5.9 years); the method was technically feasible in all children. The results showed that the MR-GFR correlated with NM-GFR with a Pearson correlation coefficient (r-value) of 0.98. Bland-Altman analysis (i.e. difference of MR-GFR and NM-GFR versus mean of NM-GFR and MR-GFR) showed a mean difference of -0.32 and reproducibility coefficient of 18 with 95% confidence interval, and the coefficient of variation of 6.7% with values between -19 (-1.96 standard deviation) and 18 (+1.96 standard deviation). In contrast, serum creatinine compared with NM-GFR yielded an r-value of 0.73. Bland-Altman analysis (i.e. difference of eGFR and NM-GFR versus mean of NM-GFR and eGFR) showed a mean difference of 2.9 and reproducibility coefficient of 70 with 95% confidence interval, and the coefficient of variation of 25% with values between -67 (-1.96 standard deviation) and 73 (+1.96 standard deviation).

CONCLUSION

MR-GFR is a technically feasible and reliable method of measuring GFR when compared to the reference standard, NM-GFR by serum ^99mTc DTPA, and MR-GFR is more reliable than estimates based on serum creatinine.

Multiparametric Renal MRI: An Intrasubject Test-Retest Repeatability Study

Background

Renal multiparametric magnetic resonance imaging (MRI) is a promising tool for diagnosis, prognosis, and treatment monitoring in kidney disease.

Purpose

To determine intrasubject test–retest repeatability of renal MRI measurements.

Study Type

Prospective.

Population

Nineteen healthy subjects aged over 40 years.

Field Strength/Sequences

T₁ and T₂ mapping, R₂* mapping or blood oxygenation level‐dependent (BOLD) MRI, diffusion tensor imaging (DTI), and intravoxel incoherent motion (IVIM) diffusion‐weighted imaging (DWI), 2D phase contrast, arterial spin labelling (ASL), dynamic contrast enhanced (DCE) MRI, and quantitative Dixon for fat quantification at 3T.

Assessment

Subjects were scanned twice with ~1 week between visits. Total scan time was ~1 hour. Postprocessing included motion correction, semiautomated segmentation of cortex and medulla, and fitting of the appropriate signal model.

Statistical Test

To assess the repeatability, a Bland–Altman analysis was performed and coefficients of variation (CoVs), repeatability coefficients, and intraclass correlation coefficients were calculated.

Results

CoVs for relaxometry (T₁, T₂, R₂*/BOLD) were below 6.1%, with the lowest CoVs for T₂ maps and highest for R₂*/BOLD. CoVs for all diffusion analyses were below 7.2%, except for perfusion fraction (F_P), with CoVs ranging from 18–24%. The CoV for renal sinus fat volume and percentage were both around 9%. Perfusion measurements were most repeatable with ASL (cortical perfusion only) and 2D phase contrast with CoVs of 10% and 13%, respectively. DCE perfusion had a CoV of 16%, while single kidney glomerular filtration rate (GFR) had a CoV of 13%. Repeatability coefficients (RCs) ranged from 7.7–87% (lowest/highest values for medullary mean diffusivity and cortical F_P, respectively) and intraclass correlation coefficients (ICCs) ranged from −0.01 to 0.98 (lowest/highest values for cortical F_P and renal sinus fat volume, respectively).

Data Conclusion

CoVs of most MRI measures of renal function and structure (with the exception of F_P and perfusion as measured by DCE) were below 13%, which is comparable to standard clinical tests in nephrology.

Level of Evidence

2

Technical Efficacy

Stage 1

Does image normalization and intensity resolution impact texture classification?

Image texture is a very important component in many types of images, including medical images. Medical images are often corrupted by noise and affected by artifacts. Some of the texture-based features that should describe the structure of the tissue under examination may also reflect, for example, the uneven sensitivity of the scanner within the tissue region. This in turn may lead to an inappropriate description of the tissue or incorrect classification. To limit these phenomena, the analyzed regions of interest are normalized. In texture analysis methods, image intensity normalization is usually followed by a reduction in the number of levels coding the intensity. The aim of this work was to analyze the impact of different image normalization methods and the number of intensity levels on texture classification, taking into account noise and artifacts related to uneven background brightness distribution. Analyses were performed on four sets of images: modified Brodatz textures, kidney images obtained by means of dynamic contrast-enhanced magnetic resonance imaging, shoulder images acquired as T2-weighted magnetic resonance images and CT heart and thorax images. The results will be of use for choosing a particular method of image normalization, based on the types of noise and distortion present in the images.

Accurate Therapeutic Response Assessment of Pancreatic Ductal Adenocarcinoma Using Quantitative Dynamic Contrast-Enhanced Magnetic Resonance Imaging With a Point-of-Care Perfusion Phantom: A Pilot Study

OBJECTIVES

The aim of this study was to test the feasibility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with concurrent perfusion phantom for monitoring therapeutic response in patients with pancreatic ductal adenocarcinoma (PDAC).

MATERIALS AND METHODS

A prospective pilot study was conducted with 8 patients (7 men and 1 woman) aged 46 to 78 years (mean age, 66 years). Participants had either locally advanced (n = 7) or metastatic (n = 1) PDAC, and had 2 DCE-MRI examinations: one before and one 8 ± 1 weeks after starting first-line chemotherapy. A small triplicate perfusion phantom was imaged with each patient, serving as an internal reference for accurate quantitative image analysis. Tumor perfusion was measured with K using extended Tofts model before and after phantom-based data correction. Results are presented as mean ± SD and 95% confidence intervals (CIs). Statistical difference was evaluated with 1-way analysis of variance.

RESULTS

Tumor-size change of responding group (n = 4) was -12% ± 4% at 8 weeks of therapy, while that of nonresponding group (n = 4) was 18% ± 15% (P = 0.0100). Before phantom-based data correction, the K change of responding tumors was 69% ± 23% (95% CI, 32% to 106%) at 8 weeks, whereas that of nonresponding tumors was -1% ± 41% (95% CI, -65% to 64%) (P = 0.0247). After correction, the data variation in each group was significantly reduced; the K change of responding tumors was 73% ± 6% (95% CI, 64% to 82%) compared with nonresponding tumors of -0% ± 5% (95% CI, -7% to 8%) (P < 0.0001).

CONCLUSIONS

Quantitative DCE-MRI measured the significant perfusion increase of PDAC tumors responding favorably to chemotherapy, with decreased variability after correction using a perfusion phantom.

Hyperfiltration in ubiquitin C-terminal hydrolase L1-deleted mice

Neuronal ubiquitin C-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme that maintains intracellular ubiquitin pools and promotes axonal transport. Uchl1 deletion in mice leads to progressive axonal degeneration, affecting the dorsal root ganglion that harbors axons emanating to the kidney. Innervation is a crucial regulator of renal hemodynamics, though the contribution of neuronal UCHL1 to this is unclear. Immunofluorescence revealed significant neuronal UCHL1 expression in mouse kidney, including periglomerular axons. Glomerular filtration rate trended higher in 6-week-old Uchl1-/- mice, and by 12 weeks of age, these displayed significant glomerular hyperfiltration, coincident with the onset of neurodegeneration. Angiotensin converting enzyme inhibition had no effect on glomerular filtration rate of Uchl1-/- mice indicating that the renin–angiotensin system does not contribute to the observed hyperfiltration. DCE-MRI revealed increased cortical renal blood flow in Uchl1-/- mice, suggesting that hyperfiltration results from afferent arteriole dilation. Nonetheless, hyperglycemia, cyclooxygenase-2, and nitric oxide synthases were ruled out as sources of hyperfiltration in Uchl1-/- mice as glomerular filtration rate remained unchanged following insulin treatment, and cyclooxygenase-2 and nitric oxide synthase inhibition. Finally, renal nerve dysfunction in Uchl1-/- mice is suggested given increased renal nerve arborization, decreased urinary norepinephrine, and impaired vascular reactivity. Uchl1-deleted mice demonstrate glomerular hyperfiltration associated with renal neuronal dysfunction, suggesting that neuronal UCHL1 plays a crucial role in regulating renal hemodynamics.

Repeatability of Contrast-Enhanced Ultrasonography of the Kidneys in Healthy Cats

Contrast-enhanced ultrasound can be used to image and quantify tissue perfusion. It holds great potential for the use in the diagnosis of various diffuse renal diseases in both human and veterinary medicine. Nevertheless, the technique is known to have an inherent relatively high variability, related to various factors associated with the patient, the contrast agent and machine settings. Therefore, the aim of this study was to assess week-to-week intra- and inter-cat variation of several perfusion parameters obtained with CEUS of both kidneys of 12 healthy cats. Repeatability was determined by calculating the coefficient of variation (CV). The contrast-enhanced ultrasound parameters with the lowest variation for the renal cortex were time-to-peak (CV 6.0%), rise time (CV 13%), fall time (CV 19%) and mean transit time (24%). Intensity-related parameters and parameters related to the slope of the time-intensity curve had a CV of >35%. Lower repeatability was present for perfusion parameters derived from the renal medulla compared with the renal cortex. Normalization to the inter-lobar artery does not cause a reduction in variation. In conclusion, time-related parameters for the cortex show a reasonable repeatability; whereas poor repeatability is present for intensity-related parameters and parameters related to in- and outflow of contrast agent. Poor repeatability is also present for all perfusion parameters for the renal medulla, except for time to peak, which has a good repeatability.