Renal functional MRI: Are we ready for clinical application?

Estimated glomerular filtration rate calculated by serum creatinine lacks precision and accuracy in adults with type 2 diabetes with preserved renal function

AIMS

We evaluated the performance of creatinine-based equations that are currently used to estimate glomerular filtration rate (GFR) in people with type 2 diabetes compared to measured GFR using gold-standard methods.

METHODS

In this post-hoc analysis, 32 participants underwent repeated measurement of GFR by inulin clearance (mGFR). GFR was estimated by serum creatinine using the MDRD (eGFRMDRD) and CKD-EPI (eGFRCKD-EPI) equations four times over the course of one month. Performance was evaluated using measurements of bias (mean difference), precision (SD), and inaccuracy (proportion of eGFR that differed by >20 % of mGFR). Treatment and time effects on bias were evaluated using linear mixed effects models.

RESULTS

At baseline, participants (38 % female) were age 60 ± 8 years, had diabetes duration of 9 ± 7 years, HbA1c 56 ± 9 mmol/mol (7.2 ± 0.8 %), and BMI 31.0 ± 6.2 kg/m2. Mean mGFR was 113 ± 24, mean eGFRMDRD was 93 ± 12, and mean eGFRCKD-EPI was 94 ± 9 mL/min/1.73 m2. When 128 observations (32 participants measured 4 times) were evaluated, both equations substantially underestimated mGFR. For eGFRMDRD, mean bias was -21.5 mL/min/1.73 m2, precision was 22.7 mL/min/1.73 m2, and 46 % of observations differed by >20 %. Results were similar for eGFRCKD-EPI. No time or treatment effects on bias were observed.

CONCLUSIONS

In adults with type 2 diabetes and preserved renal function, eGFR equations underestimated mGFR, lacked precision and accuracy, and performance was lower at higher ranges of mGFR. Current eGFR equations by serum creatinine are inaccurate in adults with type 2 diabetes with preserved renal function, highlighting the necessity to develop new methods to measure kidney function at earlier stages of diabetic kidney disease.

Application of MR Imaging Characteristics in the Differentiation of Renal Changes Between Patients with Stage III Type 2 Diabetic Kidney Disease and Healthy People

Objective

To explore the value of 1.5T magnetic resonance (MR) fat saturation-T2-weighted imaging (FS-T2WI) and apparent diffusion coefficient (ADC) imaging texture features in distinguishing the renal changes of patients with stage III type 2 diabetic kidney disease (DKD) from healthy people.

Methods

This study collected 55 patients with stage III DKD (39 males and 16 females) and 33 healthy controls (13 males and 20 females) from December 2021 to June 2022 in the China-Japan Union Hospital of Jilin University. All subjects were randomly divided in a ratio of 6:4 to extract and screen the FS-T2WI and ADC texture features of the right kidney of the subjects. The area under the curve (AUC) was used to assess the diagnostic accuracy of each model.

Results

There were significant differences between urea, creatinine and sex (p<0.05) of the two groups in the training and test set, and no significant difference in age and body mass index (BMI). We extracted 1409 imaging features from the original ADC sequence and selected them by wavelet and Laplace-Gaussian filter and LASSO algorithm, and using the same methods of FS-T2WI. Finally, FS-T2WI and ADC models were selected to construct the united model, including 3 first-order features and 8 texture features. The AUC values of the training set of FS-T2WI, ADC, FS-T2WI+ADC combined logistic regression model were 0.96, 0.91, 0.98; the AUC values of the test set were 0.91, 0.89 and 0.93, and the specificity and accuracy values of the united model were 0.90 and 0.89, respectively.

Conclusion

FS-T2WI and ADC imaging features based on 1.5 T MR had diagnostic value in the early diagnosis of DKD stage III, and the combined model of FS-T2WI and ADC had high diagnostic efficiency.

Noninvasive assessment of renal dynamics and pH in a unilateral ureter obstruction model using DCE MR‐CEST urography

PURPOSE

To assess the potential of DCE MR CEST urography for assessing renal function in mice with unilateral ureter obstruction (UUO) by simultaneous pH and renal uptake/clearance measurements following injection of iopamidol.

METHODS

The right ureter of nine mice was obstructed via suture ligation. The animals were imaged at day 1, 2, and 3 post-obstruction on an 11.7T MRI scanner. Ninety-six sets of saturated CEST images at 4.3 and 5.5 ppm were collected. Renal pH values were obtained by calculating the signal ratio for these two frequencies and using a pH calibration curve. Renal time activity curves were measured as a percentage change in the post-injection CEST signal at 4.3 ppm relative to the average pre-injection signal.

RESULTS

For the healthy mice, the time activity curves of both kidneys were nearly identical and displayed rapid excretion of contrast. For the UUO mice, the dynamic CEST curves for the obstructed kidneys displayed prolonged time to peak (TTP) values and delayed contrast excretion compared with the contralateral (CL) kidneys. Renal pH maps of the healthy animals showed similar acidic values for both kidneys (pH 6.65 ± 0.04 vs 6.67 ± 0.02), whereas in the obstructed kidneys there was a significant increase in pH values compared with the CL kidneys (pH 6.67 ± 0.08 vs 6.79 ± 0.11 in CL and UUO kidneys, respectively).

CONCLUSION

Our findings indicate that DCE-MR-CEST urography can detect changes in renal uptake/excretion and pH homeostasis and distinguish between obstructed and unobstructed kidney as early as 1 day after UUO.

Kidney morphology in pregnancy using T2-weighted MRI

AIM

To report the morphology of maternal kidneys captured on fetal magnetic resonance imaging (MRI) including kidney length, volume, renal pelvis diameter, and corticomedullary differentiation in pregnancy.

MATERIALS AND METHODS

A retrospective study of maternal kidney morphology captured incidentally on fetal MRI. Women without chronic kidney disease, with a complete view of both kidneys and a singleton pregnancy were included. Kidney length, maximal renal pelvis diameter, kidney volume, and corticomedullary differentiation ratio were measured independently in duplicate. Associations with maternal and pregnancy variables were explored using linear regression.

RESULTS

MRI images from 42 women were performed at 22-32 weeks' gestation. Serum creatinine concentrations are not checked routinely during pregnancy and were available for 15 (36%) women, with a median creatinine of 57 μmol/l (IQR: 50-63 μmol/l). Mean interpolar lengths were 10.9 and 10.4 cm for the left and right kidneys and varied with height. Mean maximal renal pelvis diameters were 9 mm and 12 mm, with upper reference intervals of 17 and 25 mm for the left and right kidneys, respectively. Renal volume in pregnancy was within the non-pregnant reference interval and varied with height and gestation.

CONCLUSIONS

Maternal kidney length and volume in pregnancy are within the normal reference intervals for non-pregnant women. Renal pelvis diameter in pregnancy measured using MRI is substantially higher than described previously by ultrasound, with implications for routine reporting.

Multiparametric Functional MRI of the Kidney: Current State and Future Trends with Deep Learning Approaches

BACKGROUND

 Until today, assessment of renal function has remained a challenge for modern medicine. In many cases, kidney diseases accompanied by a decrease in renal function remain undetected and unsolved, since neither laboratory tests nor imaging diagnostics provide adequate information on kidney status. In recent years, developments in the field of functional magnetic resonance imaging with application to abdominal organs have opened new possibilities combining anatomic imaging with multiparametric functional information. The multiparametric approach enables the measurement of perfusion, diffusion, oxygenation, and tissue characterization in one examination, thus providing more comprehensive insight into pathophysiological processes of diseases as well as effects of therapeutic interventions. However, application of multiparametric fMRI in the kidneys is still restricted mainly to research areas and transfer to the clinical routine is still outstanding. One of the major challenges is the lack of a standardized protocol for acquisition and postprocessing including efficient strategies for data analysis. This article provides an overview of the most common fMRI techniques with application to the kidney together with new approaches regarding data analysis with deep learning.

METHODS

 This article implies a selective literature review using the literature database PubMed in May 2021 supplemented by our own experiences in this field.

RESULTS AND CONCLUSION

 Functional multiparametric MRI is a promising technique for assessing renal function in a more comprehensive approach by combining multiple parameters such as perfusion, diffusion, and BOLD imaging. New approaches with the application of deep learning techniques could substantially contribute to overcoming the challenge of handling the quantity of data and developing more efficient data postprocessing and analysis protocols. Thus, it can be hoped that multiparametric fMRI protocols can be sufficiently optimized to be used for routine renal examination and to assist clinicians in the diagnostics, monitoring, and treatment of kidney diseases in the future.

KEY POINTS

  · Multiparametric fMRI is a technique performed without the use of radiation, contrast media, and invasive methods.. · Multiparametric fMRI provides more comprehensive insight into pathophysiological processes of kidney diseases by combining functional and structural parameters.. · For broader acceptance of fMRI biomarkers, there is a need for standardization of acquisition, postprocessing, and analysis protocols as well as more prospective studies.. · Deep learning techniques could significantly contribute to an optimization of data acquisition and the postprocessing and interpretation of larger quantities of data..

CITATION FORMAT

· Zhang C, Schwartz M, Küstner T et al. Multiparametric Functional MRI of the Kidney: Current State and Future Trends with Deep Learning Approaches. Fortschr Röntgenstr 2022; DOI: 10.1055/a-1775-8633.

Detection of impaired renal allograft function in paediatric and young adult patients using arterial spin labelling MRI (ASL-MRI)

The study aimed to discriminate renal allografts with impaired function by measuring cortical renal blood flow (cRBF) using magnetic resonance imaging arterial spin labelling (ASL-MRI) in paediatric and young adult patients. We included 18 subjects and performed ASL-MRI on 1.5 T MRI to calculate cRBF on parameter maps. cRBF was correlated to calculated glomerular filtration rate (GFR) and compared between patient groups with good (GFR ≥ 60 mL/min/1.73 m²) and impaired allograft function (GFR < 60 mL/min/1.73 m²). Mean cRBF in patients with good allograft function was significantly higher than in patients with impaired allograft function (219.89 ± 57.24 mL/min/100 g vs. 146.22 ± 41.84 mL/min/100 g, p < 0.008), showing a highly significant correlation with GFR in all subjects (r = 0.75, p < 0.0001). Also, the diffusion-weighted imaging (DWI-MRI) apparent diffusion coefficient (ADC) and Doppler measurements of peak-systolic and end-diastolic velocities and the resistive index (PS, ED, RI) were performed and both methods showed no significant difference between groups. ADC implied no correlation with GFR (r = 0.198, p = 0.464), while PS indicated moderate correlation to GFR (r = 0.48, p < 0.05), and PS and ED moderate correlation to cRBF (r = 0.58, p < 0.05, r = 0.56, p < 0.05, respectively). Cortical perfusion as non-invasively measured by ASL-MRI differs between patients with good and impaired allograft function and correlates significantly with its function.

Diffusion Weighted Imaging and T2 Mapping Detect Inflammatory Response in the Renal Tissue during Ischemia Induced Acute Kidney Injury in Different Mouse Strains and Predict Renal Outcome

To characterize ischemia reperfusion injury (IRI)-induced acute kidney injury (AKI) in C57BL/6 (B6) and CD1-mice by longitudinal functional MRI-measurement of edema formation (T2-mapping) and inflammation (diffusion weighted imaging (DWI)). IRI was induced with unilateral right renal pedicle clamping for 35min. 7T-MRI was performed 1 and 14 days after surgery. DWI (7 b-values) and multiecho TSE sequences (7 TE) were acquired. Parameters were quantified in relation to the contralateral kidney on day 1 (d1). Renal MCP-1 and IL-6-levels were measured by qPCR and serum-CXCL13 by ELISA. Immunohistochemistry for fibronectin and collagen-4 was performed. T2-increase on d1 was higher in the renal cortex (127 ± 5% vs. 94 ± 6%, p < 0.01) and the outer stripe of the outer medulla (141 ± 9% vs. 111 ± 9%, p < 0.05) in CD1, indicating tissue edema. Medullary diffusivity was more restricted in CD1 than B6 (d1: 73 ± 3% vs. 90 ± 2%, p < 0.01 and d14: 77 ± 5% vs. 98 ± 3%, p < 0.01). Renal MCP-1 and IL-6-expression as well as systemic CXCL13-release were pronounced in CD1 on d1 after IRI. Renal fibrosis was detected in CD1 on d14. T2-increase and ADC-reduction on d1 correlated with kidney volume loss on d14 (r = 0.7, p < 0.05; r = 0.6, p < 0.05) and could serve as predictive markers. T2-mapping and DWI evidenced higher susceptibility to ischemic AKI in CD1 compared to B6.

Role of Diffusion Tensor Imaging in renal parenchymal changes

Context:

Diffusion Tensor Imaging (DTI) is a reliable noninvasive tool to assess renal function with medullary Fractional Anisotropy (FA) values showing the most consistent results.

Aims:

Evaluation of FA, Apparent Diffusion Coefficient (ADC) for detecting diabetic nephropathy (DN) using 1.5-Tesla magnetic resonance imaging (MRI). To determine FA and ADC values in chronic kidney disease (CKD) patients and controls, and comparing these with estimated glomerular filtiration rate (eGFR) and categorizing the stage of CKD.

Patients and Methods:

Thirty nondiabetic volunteers underwent DTI. The study included 83 diabetics, 30 frank urine proteinuric, 30 micro-albuminuric, 23 normo-albuminuric with only raised blood sugar patients. Patients were stratified by eGFR into groups: eGFR <60 and eGFR>60ml/min. ADC and FA values in cortex and medulla were compared between controls and study groups.

Statistical Analysis Used:

Analysis of variance and Pearson correlation using SPSS 16 were performed.

Results:

There was significant difference of FA medulla in controls versus albuminuric and micro-albuminuric versus frank proteinuric patients (P < 0.001). Also, there was significant difference between cortical ADC values between normal, microalbuminuric/proteinuric groups (P = 0.010, P =0.000, respectively). Significant difference between medullary FA values of patients with eGFR >60 and eGFR < 60 versus normal controls (P < 0.001) was noted. With declining renal function from normal to CKD category 5, a negative correlation between medullary FA (r= −0.785, P = 0.001) and ADC cortex values (r= −0.436, P = 0.001) was noted. A strong positive correlation between medullary FA and cortex ADC with eGFR (r = 0.598 and 0.344, respectively) was noted.

Conclusion:

Medullary FA of diabetics with relatively intact kidney function were significantly lower than those of controls. Hence, drop in medullary FA values can be an indicator of early nephropathy/patients at risk where eGFR is in near normal range. Cortical ADC and medullary FA demonstrated a significant correlation with eGFR with the latter showing a stronger positive correlation.

Renal transplant evaluation: multimodality imaging of post-transplant complications

With advancements in surgical techniques and immuno-suppression, renal transplantation is established as the most effective treatment option in patients with end-stage renal disease. Early detection of renal allograft complications is important for long-term graft survival. Late clinical presentation often causes diagnostic delays till the time allograft failure is advanced and irreversible. Imaging plays a key role in routine surveillance and in management of acute or chronic transplant dysfunction. Multimodality imaging approach is important with ultrasound-Doppler as the first-line imaging study in immediate, early and late post-transplant periods. Additional imaging studies are often required depending on clinical settings and initial ultrasound. Renal functional MRI is a rapidly growing field that has huge potential for early diagnosis of transplant dysfunction. Multiparametric MRI may be integrated in clinical practice as a noninvasive and comprehensive "one-stop" modality for early diagnosis and longitudinal monitoring of renal allograft dysfunctions, which is essential for guiding appropriate interventions to delay or prevent irreversible renal damage. With rapidly increasing numbers of renal transplantation along with improved patient survival, it is necessary for radiologists in all practice settings to be familiar with the normal appearances and imaging spectrum of anatomical and functional complications in a transplant kidney. Radiologist"s role as an integral part of multidisciplinary transplantation team continues to grow with increasing numbers of successful renal transplantation programs across the globe.

Diffusion Tensor Imaging in early prediction of renal fibrosis in patients with renal disease: Functional and histopathological correlations

AIM

Renal fibrosis (RF) is a well-known marker of chronic kidney disease (CKD) progression. However, renal biopsy is an available tool for evaluation of RF, non-invasive tools are needed not only to detect but also to monitor the progression of fibrosis. The aim of this study is to evaluate the role of diffusion tensor imaging (DTI) in the assessment of renal dysfunction and RF in patients with renal disease.

METHODS

Fifty-six patients with renal disorders and 22 healthy controls were recruited. All participants underwent DTI. Renal biopsy was performed for all patients. Mean renal medullary and cortical fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were compared between patients and healthy controls and correlated to serum creatinine (SCr), estimated glomerular filtration rate (eGFR), 24-h urinary protein (24h-UPRO) and renal histopathological scores.

RESULTS

Cortical FA values were significantly higher (P = .001), while cortical ADC values were significantly lower in the patients' group (P = .002). Cortical FA values positively correlated to SCr (P = .006) and negatively correlated to eGFR (P = .03), while cortical ADC negatively correlated to percentage of sclerotic glomeruli, atrophic tubules and interstitial fibrosis (P = .001 for all variables). Medullary ADC negatively correlated to tubular atrophy (P = .02). The diagnostic performance of DTI for detecting RF was supported by ROC curve. Multiple linear regression analysis revealed that the mean cortex ADC was significantly decreased by 0.199 mg/dL for patients with >50% glomerulosclerosis in renal biopsy.

CONCLUSION

DTI appears to represent a valuable tool for the non-invasive assessment of renal dysfunction and renal fibrosis.

Renal Damages in Deoxycorticosterone Acetate-Salt Hypertensive Rats: Assessment with Diffusion Tensor Imaging and T2-mapping

PURPOSE

This study aimed to investigate the feasibility of diffusion tensor imaging (DTI) and T2-mapping to assess temporal renal damage in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats and compare the results with histopathologic and immunohistochemical findings.

PROCEDURES

After baseline renal magnetic resonance imaging (MRI), 24 out of 30 uninephrectomized Sprague-Dawley rats with DOCA-salt-induced hypertension were divided equally into four groups. Group 1 had renal MRI at weeks 2, 4, 6, and 8, and groups 2, 3, and 4 had MRI at weeks 2, 4, and 6, respectively. The remaining 6 rats were used as sham controls. The renal cortex and outer and inner stripes of the outer medulla were examined over time using fractional anisotropy (FA), apparent diffusion coefficient (ADC), and T2-mapping, and the results were compared with baseline values. The degree of glomerular and tubular injury, endothelial cell thickening, hyaline arteriolosclerosis, macrophage infiltration, microcyst formation, and fibrosis in different zones at different time points in the DOCA-salt rats were compared with controls.

RESULTS

Compared with baseline values, DOCA-salt rats demonstrated a significant decrease in renal cortical FA from week 4 to week 8 (0.244 ± 0.015 vs 0.172 ± 0.014-0.150 ± 0.016, P = 0.018-0.002), corresponding to significantly more glomerular damage, arteriolosclerosis, macrophage infiltration, and fibrosis. The DOCA-salt rats had significantly increased cortical ADC and T2 values at weeks 6 and 8 (1.778 ± 0.051 × 10^-3 mm²/s vs 1.872 ± 0.058-1.917 ± 0.066 × 10^-3 mm²/s; 93.7 ± 4.9 ms vs 98.0 ± 2.9-100.7 ± 4.0 ms, respectively, all P < 0.05), consistent with excessively fluid-filled microcysts (aquaporin-2+). Despite DOCA-salt rats harbored markedly increased fibrosis in outer and inner stripes of the outer medulla at weeks 6 and 8, only nonsignificant decreases in FA were observed in comparison with the controls suggesting that only limited microstructural changes were present.

CONCLUSIONS

Renal cortical FA is useful for the early detection and monitoring of renal damage in DOCA-salt hypertensive rats.

The Role of Diffusion-Weighted MRI and Apparent Diffusion Coefficient in Assessment of Diabetic Kidney Disease: Preliminary Experience Study

Background

Diabetic kidney disease is the most common cause of ESRD. There is poor correlation between the degree of renal fibrosis and current screening markers. A noninvasive imaging technique is needed to assess the degree of structural changes in the kidney. The aim of this study was to assess the role of apparent diffusion coefficient (ADC) in the diagnosis of diabetic kidney disease. Forty adult diabetic patients with chronic kidney disease as well as 20 age- and sex-matched adult healthy controls were recruited from Nephrology Department of our University Hospital. All patients underwent renal MR-DWI and ADC mapping on a 1.5-T scanner (Philips Achieva) using phased array body coil.

Results

Among the studied 40 diabetic patients, five groups of patients were resulted 8 patients for each and the ADC values were inversely correlated with advancement in renal parenchymal affection, ie, in late stages of the disease the ADC values were lower than in early stages. The mean ADC values of renal parenchyma in patients with diabetic kidney disease were considerably lower than that of healthy controls with normal renal function (2.1±0.3x10^-3 mm²/s vs 2.4±0.1x10^-3 mm²/s with p<0.001).

Conclusion

ADC value is a possible noninvasive technique in evaluating the stage of renal dysfunction with assessment of disease progression.

DWI as a biomarker of renal function in children with CKD: what is the potential?

Background

Evaluation of renal microstructure is pivotal for diagnosing and monitoring chronic renal disease. DWI has been proved to be practicable and reliable examination for the assessment of renal function and parenchymal damage in some renal diseases. Our aim is to appraise DWI sequence and ADC measurement as a potential tool of renal function assessment as well as establishing a possible relationship between the different CKD stages and the renal parenchymal ADC values changes.

Results

Regarding the cause of CKD, nine patients (45%) had glomerulonephritis, 5 patients (25%) had hemolytic uremic syndrome, 2 patients (10%) had lupus nephritis, 2 patients (10%) had nepheronophthisis, and 1 patient (1.5%) had infantile nepherosis, whereas the cause of CKD was unknown in 1 patient (1.5%).

The stages of CKD were classified according to KIDGO guidelines: 6 patients (30%) were stage 1, 4 patients (20%) were stage 2, 3 patients (15%) were stage 3, 2 patients (10%) were stage 4, and 5 patients (25%) were stage 5. The patients’ group (group A) had a mean ADC value (1.85 × 10−3 ± 0.24) which was significantly lower than that of the control group (group B) (2.21 × 10−3 ± 0.12). As for the correlation between stage of CKD and ADC, we found it to be a moderate negative one with r’ value of − .655 and a significant p value of < 0.001.

Conclusion

DWI is recognized as a promising imaging tool that can take part in the assessment of the morphological and functional changes in diffuse renal parenchymal disease, hence playing an important role in the early diagnosis and staging of chronic kidney disease.

R, R. S. Role of Diffusion Tensor Imaging in Functional Assessment of Transplant Kidneys at 3-Tesla MRI

Objectives The main purpose of this article is to measure the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of cortex and medulla of renal allograft using 3-Tesla diffusion tensor imaging (DTI) in renal transplant patients with normal and graft dysfunction and to assess the correlation between diffusion tensor parameters (ADC and FA) and the estimated glomerular filtration rate (eGFR) value.

Materials and Methods Fifty renal transplant recipients who received either living or cadaveric renal allografts were included in the study. Blood samples for serum creatinine and eGFR value were taken on the same day prior to the magnetic resonance study and the patients were assigned to three groups (A, B, C) according to allograft function (eGFR levels). The mean ADC and FA values of the cortex/medulla in upper, mid, and lower poles were calculated from the DTI sequence. Statistical analysis was performed using paired sample Student’s t-test and one-way analysis of variance test.

Results The mean ADC values of the cortex were higher than the medulla that was statistically significant. However, the mean FA values were significantly higher in the medulla than the cortex. Mean ADCs and FA of the renal cortex and medulla were significantly higher in group A patients with normal renal function than in group B and C with poor renal functions. The corticomedullary difference in the FA values was more in group A. However, this difference was lower in group B and more so in group C.

Conclusion ADC and FA values in the renal cortex and medulla exhibit a good correlation with allograft function and were significantly lower in transplants with dysfunction than those with good function. FA values appear to be more sensitive than eGFR and ADC for detection of early pathological changes in the graft dysfunction.

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.

Correlation Between Apparent Diffusion Coefficient Values of the Renal Parenchyma and Estimated Glomerular Filtration Rates on 3-T Diffusion-Weighted Echo-Planar Magnetic Resonance Imaging

OBJECTIVE

To evaluate the relationship between the apparent diffusion coefficient (ADC) values of renal parenchyma and estimated glomerular filtration rates (eGFR).

METHODS

Data on 216 patients examined by 3-T magnetic resonance imaging for various reasons were retrospectively collected.

RESULTS

There was a significant linear correlation between the ADC values and eGFRs (r = 0.254, P < 0.001). The ADC values in patients with an eGFR of less than 60 mL/min per 1.73 m were significantly lower than those with an eGFR of 60 mL/min per 1.73 m or greater. The mean ADC value of patients with grouped stage 2 disease was significantly higher than those with grouped stage 3 of chronic kidney disease (P < 0.01).

CONCLUSIONS

The ADC value of renal parenchyma may be a promising marker for the determination of patients with normal to mild reduction in renal function (eGFR ≥60 mL/min per 1.73 m) versus those with a moderate to severe reduction in renal function (eGFR <60 mL/min per 1.73 m).

Efficacy Evaluation and Tracking of Bone Marrow Stromal Stem Cells in a Rat Model of Renal Ischemia-Reperfusion Injury

Objectives

The aim of this study was to evaluate the effects of bone marrow stromal stem cells (BMSCs) on renal ischemia-reperfusion injury (RIRI) and dynamically monitor engrafted BMSCs in vivo for the early prediction of their therapeutic effects in a rat model.

Methods

A rat model of RIRI was prepared by clamping the left renal artery for 45 min. One week after renal artery clamping, 2 × 10⁶ superparamagnetic iron oxide- (SPIO-) labeled BMSCs were injected into the renal artery. Next, MR imaging of the kidneys was performed on days 1, 7, 14, and 21 after cell transplantation. On day 21, after transplantation, serum creatinine (Scr) and urea nitrogen (BUN) levels were assessed, and HE staining and TUNEL assay were also performed.

Results

The body weight growth rates in the SPIO-BMSC group were significantly higher than those in the PBS group (P < 0.05), and the Scr and BUN levels were also significantly lower than those in the PBS group (P < 0.05). HE staining showed that the degree of degeneration and vacuole-like changes in the renal tubular epithelial cells in the SPIO-BMSC group was significantly better than that observed in the PBS group. The TUNEL assay showed that the number of apoptotic renal tubular epithelial cells in the SPIO-BMSC group was significantly lower than that in the PBS group. The T2 value of the renal lesion was the highest on day 1 after cell transplantation, and it gradually decreased with time in both the PBS and SPIO-BMSC groups but was always the lowest in the SPIO-BMSC group.

Conclusion

SPIO-labeled BMSC transplantation can significantly promote the recovery of RIRI and noninvasive dynamic monitoring of engrafted cells and can also be performed simultaneously with MRI in vivo for the early prediction of therapeutic effects.

Pilot study on renal magnetic resonance diffusion tensor imaging: are quantitative diffusion tensor imaging values useful in the evaluation of children with ureteropelvic junction obstruction?

BACKGROUND

Ureteropelvic junction (UPJ) obstruction is a common cause of renal injury in children. Indications for surgery are still controversial. Currently, there is no threshold to differentiate patients with suspected UPJ obstruction requiring surgery from the ones that do not, or to predict renal outcome after surgery. Several studies have demonstrated that diffusion tensor imaging (DTI) results may correlate with microstructural changes in the kidneys.

OBJECTIVE

To evaluate the feasibility of using DTI to identify UPJ obstruction kidneys.

MATERIALS AND METHODS

We analyzed functional MR urography (fMRU) with renal DTI (b=0 and b=400, 20 directions, 1.5 Tesla, no respiratory triggering) in 26 kidneys of 19 children (mean age: 6.15 years) by comparing 13 kidneys with UPJ obstruction configuration that underwent pyeloplasty following the fMRU, and 13 anatomically normal age- and gender-matched kidneys. DTI tractography was reconstructed using a fractional anisotropy threshold of 0.10 and an angle threshold of 55°. User-defined regions of interest (ROIs) of the renal parenchyma (excluding collecting system) were drawn to quantify DTI parameters: fractional anisotropy, apparent diffusion coefficient (ADC), track length and track volume. The failure rate was evaluated.

RESULTS

All DTI parameters changed with age; fractional anisotropy decreased (P<0.032). Track volume and track length increased (P<0.05). ADC increased with age in normal kidneys (P<0.001) but not in UPJ obstruction kidneys (P=0.11). After controlling for age, the fractional anisotropy (UPJ obstruction mean: 0.18, normal kidney mean: 0.21; P=0.001) and track length (UPJ obstruction mean: 11.9 mm, normal kidney mean: 15.4 mm; P<0.001) were lower in UPJ obstruction vs. normal kidneys. There was a trend toward a higher ADC in UPJ obstruction kidneys vs. normal kidneys (P=0.062). The failure rate in UPJ obstruction kidneys due to technical limitations of DTI was 13/26 (50%).

CONCLUSION

We demonstrated that fractional anisotropy is lower in UPJ obstruction than in normal kidneys. It is necessary to improve this technique to increase the success rate and to perform more studies to evaluate if a decrease in fractional anisotropy can differentiate UPJ obstruction kidneys from hydronephrotic kidneys without UPJ obstruction.

Measurement of single kidney glomerular filtration rate in dogs using dynamic contrast-enhanced magnetic resonance imaging and the Rutland-Patlak plot technique

Background

Nephropathies are among the most common diseases in dogs. Regular examination of the kidney function plays an important role for an adequate treatment scheme. The determination of the glomerular filtration rate (GFR) is seen as the gold standard in assessing the kidney status. Most of the tests have the disadvantage that only the complete glomerular filtration rate of both kidneys can be assessed and not the single kidney glomerular filtration rate. Imaging examination techniques like dynamic contrast-enhanced magnetic resonance imaging have the potential to evaluate the single kidney GFR. There are studies in human medicine describing the determination of the single kidney GFR using this technique. To our knowledge there are no such studies for dogs.

Results

An exponential fit was found to describe the functional interrelation between signal intensity and contrast medium concentrations. The changes of contrast medium concentrations during the contrast medium bolus propagation were calculated. The extreme values of contrast medium concentrations in the kidneys were reached at nearly the same time in every individual dog (1st maximum aorta 8.5 s, 1st maximum in both kidneys after about 14.5 s; maximum concentration values varied between 17 and 125 µmol/mL in the aorta and between 4 and 15 µmol/mL in the kidneys). The glomerular filtration rate was calculated from the concentration changes of the contrast medium using a modified Rutland-Patlak plot technique. The GFR was 12.7 ± 2.9 mL/min m² BS for the left kidney and 12.0 ± 2.2 mL/min/m² BS for the right kidney. The mean values of the coefficient of determination of the regression lines were averagely 0.91 ± 0.08.

Conclusions

The propagation of contrast medium bolus could be depicted well. The contrast medium proceeded in a similar manner for every individual dog. Additionally, the evaluation of the single kidney function of the individual dogs is possible with this method. A standardized examination procedure would be recommended in order to minimize influencing parameters.

Electronic supplementary material

The online version of this article (10.1186/s13028-018-0423-3) contains supplementary material, which is available to authorized users.

Renal Functional MRI and Its Application

Renal function varies according to the nature and stage of diseases. Renal functional magnetic resonance imaging (fMRI), a technique considered superior to the most common method used to estimate the glomerular filtration rate, allows for noninvasive, accurate measurements of renal structures and functions in both animals and humans. It has become increasingly prevalent in research and clinical applications. In recent years, renal fMRI has developed rapidly with progress in MRI hardware and emerging postprocessing algorithms. Function-related imaging markers can be acquired via renal fMRI, encompassing water molecular diffusion, perfusion, and oxygenation. This review focuses on the progression and challenges of the main renal fMRI methods, including dynamic contrast-enhanced MRI, blood oxygen level-dependent MRI, diffusion-weighted imaging, diffusion tensor imaging, arterial spin labeling, fat fraction imaging, and their recent clinical applications.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:863-881.

Methods of Blood Oxygen Level-Dependent Magnetic Resonance Imaging Analysis for Evaluating Renal Oxygenation

Blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) has recently been utilized as a noninvasive tool for evaluating renal oxygenation. Several methods have been proposed for analyzing BOLD images. Regional ROI selection is the earliest and most widely used method for BOLD analysis. In the last 20 years, many investigators have used this method to evaluate cortical and medullary oxygenation in patients with ischemic nephropathy, hypertensive nephropathy, diabetic nephropathy, chronic kidney disease (CKD), acute kidney injury and renal allograft rejection. However, clinical trials of BOLD MRI using regional ROI selection revealed that it was difficult to distinguish the renal cortico-medullary zones with this method, and that it was susceptible to observer variability. To overcome these deficiencies, several new methods were proposed for analyzing BOLD images, including the compartmental approach, fractional hypoxia method, concentric objects (CO) method and twelve-layer concentric objects (TLCO) method. The compartmental approach provides an algorithm to judge whether the pixel belongs to the cortex or medulla. Fractional kidney hypoxia, measured by using BOLD MRI, was negatively correlated with renal blood flow, tissue perfusion and glomerular filtration rate (GFR) in patients with atherosclerotic renal artery stenosis. The CO method divides the renal parenchyma into six or twelve layers of thickness in each coronal slice of BOLD images and provides a R2* radial profile curve. The slope of the R2* curve associated positively with eGFR in CKD patients. Indeed, each method invariably has advantages and disadvantages, and there is generally no consensus method so far. Undoubtedly, analytic approaches for BOLD MRI with better reproducibility would assist clinicians in monitoring the degree of kidney hypoxia and thus facilitating timely reversal of tissue hypoxia.

Blood oxygen level dependent magnetic resonance imaging for detecting pathological patterns in lupus nephritis patients: a preliminary study using a decision tree model

BACKGROUND

Precise renal histopathological diagnosis will guide therapy strategy in patients with lupus nephritis. Blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) has been applicable noninvasive technique in renal disease. This current study was performed to explore whether BOLD MRI could contribute to diagnose renal pathological pattern.

METHODS

Adult patients with lupus nephritis renal pathological diagnosis were recruited for this study. Renal biopsy tissues were assessed based on the lupus nephritis ISN/RPS 2003 classification. The Blood oxygen level dependent magnetic resonance imaging (BOLD-MRI) was used to obtain functional magnetic resonance parameter, R2* values. Several functions of R2* values were calculated and used to construct algorithmic models for renal pathological patterns. In addition, the algorithmic models were compared as to their diagnostic capability.

RESULTS

Both Histopathology and BOLD MRI were used to examine a total of twelve patients. Renal pathological patterns included five classes III (including 3 as class III + V) and seven classes IV (including 4 as class IV + V). Three algorithmic models, including decision tree, line discriminant, and logistic regression, were constructed to distinguish the renal pathological pattern of class III and class IV. The sensitivity of the decision tree model was better than that of the line discriminant model (71.87% vs 59.48%, P < 0.001) and inferior to that of the Logistic regression model (71.87% vs 78.71%, P < 0.001). The specificity of decision tree model was equivalent to that of the line discriminant model (63.87% vs 63.73%, P = 0.939) and higher than that of the logistic regression model (63.87% vs 38.0%, P < 0.001). The Area under the ROC curve (AUROCC) of the decision tree model was greater than that of the line discriminant model (0.765 vs 0.629, P < 0.001) and logistic regression model (0.765 vs 0.662, P < 0.001).

CONCLUSIONS

BOLD MRI is a useful non-invasive imaging technique for the evaluation of lupus nephritis. Decision tree models constructed using functions of R2* values may facilitate the prediction of renal pathological patterns.

Measured GFR in Routine Clinical Practice-The Promise of Dried Blood Spots

Accurate determination of glomerular filtration rate (GFR) is crucial for the diagnosis of kidney disease. Estimated GFR (eGFR) calculated by serum creatinine and/or cystatin C is a mainstay in clinical practice and epidemiologic research but lacks precision and accuracy until GFR <60 mL/min/1.73 m². Furthermore, eGFR may not precisely and accurately represent changes in GFR longitudinally. The lack of precision and accuracy is of concern in populations at high risk for kidney disease, as the dissociation between changes in eGFR and GFR may lead to missed diagnoses of early kidney disease. Therefore, improved methods to quantify GFR are needed. Whereas direct measures of GFR have been too cumbersome for screening and ambulatory care, a practical method of measuring GFR by iohexol clearance using dried capillary blood spots exists. In this review, we examine the current literature and data addressing GFR measurements by dried capillary blood spots and its potential application in high-risk groups.

Innovative Perspective: Gadolinium-Free Magnetic Resonance Imaging in Long-Term Follow-Up after Kidney Transplantation

Since the mid-1980s magnetic resonance imaging (MRI) has been investigated as a non- or minimally invasive tool to probe kidney allograft function. Despite this long-standing interest, MRI still plays a subordinate role in daily practice of transplantation nephrology. With the introduction of new functional MRI techniques, administration of exogenous gadolinium-based contrast agents has often become unnecessary and true non-invasive assessment of allograft function has become possible. This raises the question why application of MRI in the follow-up of kidney transplantation remains restricted, despite promising results. Current literature on kidney allograft MRI is mainly focused on assessment of (sub) acute kidney injury after transplantation. The aim of this review is to survey whether MRI can provide valuable diagnostic information beyond 1 year after kidney transplantation from a mechanistic point of view. The driving force behind chronic allograft nephropathy is believed to be chronic hypoxia. Based on this, techniques that visualize kidney perfusion and oxygenation, scarring, and parenchymal inflammation deserve special interest. We propose that functional MRI mechanistically provides tools for diagnostic work-up in long-term follow-up of kidney allografts.

Blood Oxygenation Level-Dependent Functional MRI of Early Evidences of Brain Plasticity after Hemodialysis Session by Helixone Membrane of Patients with Indices of Adrenal Deficiency

BACKGROUND

Various alterations of hypothalamic-pituitary-adrenal axis function have been described in patients with chronic renal failure. Nevertheless, controversial evidences were stated about the association between adrenal function deficiency (AD) and hemodialysis (HD).

PURPOSE

The goal of this paper was to estimate indirect indices of the adrenal gland dysfunction which is potentially influenced by oxidative stress (OS) that still generates brain plasticity and reorganization of the functional control.

METHODS

Two male patients undergoing HD by the synthetic Helixone membrane for more than 6 months at the HD Center of the University Hospital of Fez, Fez, Morocco, were recruited. They underwent identical assessment immediately before and after the full HD session; this consisted of a blood ionogram revealing rates of sodium and calcium, and brain blood oxygenation level-dependent functional MRI (BOLD-fMRI) using a motor paradigm in block design.

RESULTS

The blood ionogram revealed hypercalcemia and hyponatremia in both patients. Both biological assessment and BOLD-fMRI study results revealed a high level of OS that induced activation of a significantly large brain volume area suggesting the occurrence of possible brain plasticity and functional control reorganization induced by free radicals and enhanced by AD.

CONCLUSION

The occurrence of brain plasticity and functional control reorganization was demonstrated in both patients studied who were undergoing HD by BOLD-fMRI with a notable sensitivity; this plasticity is induced by elevated OS occasioned by HD technique itself and probably amplified by AD. Similar results were found in a previous study performed on the same patients undergoing HD by a polysulfone membrane.

Non-gaussian diffusion evaluation of the human kidney by Padé exponent model

PURPOSE

To evaluate the feasibility of renal diffusion quantification using the Padé exponent model (PEM) in healthy subjects.

MATERIALS AND METHODS

Diffusion measurements were completed in 10 healthy subjects (mean age, 32.4 ± 8.9 years) on a 3T MRI scanner (Magnetom Trio, Siemens AG, Germany). A respiratory-triggered echo planar imaging sequence (15 slices with 6 mm thickness; 16 b-values [0-750 s/mm² ]; three diffusion directions; field of view: 400 × 375 mm; Matrix 192 × 192; repetition time/echo time: 3000/74 ms) was acquired in the coronal direction. Parameter maps were calculated for the monoexponential, biexponential, kurtosis models, and the PEM. A regression analysis using an R² -test and corrected Akaike information criterion (AICc) was performed to identify the best mathematical fitting to the measured diffusion-weighted imaging signal decay.

RESULTS

The mathematical accuracy of the PEM was significantly higher than for the other three-parameter and the monoexponential model (P < 0.05), which enables more precise information about the deviation of the Gaussian behavior of the diffusion signal by the PEM. The biexponential model showed better fitting to the diffusion signal (medullar Rbi2 0.989 ± 0.008, AICc_bi 113.3 ± 6.6; cortical Rbi2 0.992 ± 0.006, AICc_bi 113.3 ± 5.2) than the three-parameter models (medullar RPadé2 0.965 ± 0.016, AICc_Padé 122.6 ± 6.4, RK2 0.954 ± 0.019, AICc_K 128.5 ± 6.0; cortical RPadé2 0.989 ± 0.005, AICc_Padé 116.3 ± 4.4, RK2 0.985 ± 0.007, AICc_K 120.4 ± 4.8). The monoexponential model fits least to the diffusion signal in the kidney (medullar Rmono2 0.898 ± 0.039, AICc_mono 141.4 ± 5.6; cortical Rmono2 0.961 ± 0.013, AICc_mono 135.4 ± 4.8).

CONCLUSION

The PEM is a novel promising approach to quantify diffusion properties in the human kidney and might further improve functional renal MR imaging.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:160-167.

Gd-Dots with Strong Ligand-Water Interaction for Ultrasensitive Magnetic Resonance Renography

Magnetic resonance imaging contrast agents with both significantly enhanced relaxivity and minimal safety risk are of great importance for sensitive clinical diagnosis, but have rarely been reported. Herein, we present a simple strategy to improve relaxivity by introducing surface ligands with strong interaction to water molecules. As a proof of concept, NaGdF₄ nanoparticles (NPs) capped by poly(acrylic acid) (PAA) show superior relaxivity to those capped by polyethylenimine and polyethylene glycol, which is attributed to the strong hydrogen-bond capacity of PAA to water molecules as revealed by theoretical calculation. Furthermore, benefiting from PAA and ultrasmall particle size, Gd-dots, namely PAA-capped GdOF NPs (2.1 ± 0.2 nm), are developed as a high-performance contrast agent, with a remarkable ionic relaxivity of ∼75 mM^-1 s^-1 in albumin solution at 0.5 T. These Gd-dots also exhibit efficient renal clearance with <3% of injected amount left 12 h post-injection. Ultrasensitive MR renography achieved with Gd-dots strongly suggests their great potential for practical applications.

Fast diffusion kurtosis imaging of fibrotic mouse kidneys

Diffusion kurtosis imaging (DKI) is sensitive to tissue microstructure and may therefore be useful in the diagnosis and monitoring of disease in brain and body organs. Generally, diffusion magnetic resonance imaging (dMRI) in the body is challenging because of the heterogeneous body composition, which can cause image artefacts as a result of chemical shifts and susceptibility differences. In addition, the abdomen possesses physiological factors (e.g. breathing, heartbeat, blood flow) which may severely reduce image quality, especially when echo planar imaging is employed, as is typical in dMRI. Collectively, these challenging measurement conditions impede the use and exploration of DKI in the body. This impediment is further exacerbated by the traditionally large amount of data required for DKI and the low signal-to-noise ratio at the b-values needed to effectively probe the kurtosis regime. Recently introduced fast DKI techniques reduce the challenge of DKI in the body by decreasing the data requirement substantially, so that, for example, triggering and breath-hold techniques may be applied for the entire DKI acquisition without causing unfeasible scan times. One common pathological condition for which body DKI may be of immediate clinical value is kidney fibrosis, which causes progressive changes in organ microstructure. With its sensitivity to microstructure, DKI is an obvious candidate for a non-invasive evaluation method. We present preclinical evidence indicating that the rapidly obtainable tensor-derived mean kurtosis ( W̅) distinguishes moderately fibrotic kidneys from healthy controls. The presence and degree of fibrosis are confirmed by histology, which also indicates fibrosis as the main driver behind the DKI differences observed between groups. We therefore conclude that fast kurtosis is a likely candidate for an MRI-based method for the detection and monitoring of renal fibrosis. We provide protocol recommendations for fast renal DKI in humans based on a b-value optimisation performed using data acquired at 3 T in normal human kidney.

Evaluation of renal allografts function early after transplantation using intravoxel incoherent motion and arterial spin labeling MRI

PURPOSE

To evaluate renal allografts function early after transplantation using intravoxel incoherent motion (IVIM) and arterial spin labeling (ASL) MRI.

METHODS

This prospective study was approved by the local ethics committee, and written informed consent was obtained from all participants. A total of 82 participants with 62 renal allograft recipients (2-4weeks after kidney transplantation) and 20 volunteers were enrolled to be scanned using IVIM and ASL MRI on a 3.0T MR scanner. Recipients were divided into two groups with either normal or impaired function according to the estimated glomerular filtration rate (eGFR) with a threshold of 60ml/min/1.73m(2). The apparent diffusion coefficient (ADC) of pure diffusion (ADCslow), the ADC of pseudodiffusion (ADCfast), perfusion fraction (PF), and renal blood flow (RBF) of cortex were compared among three groups. The correlation of ADCslow, ADCfast, PF and RBF with eGFR was evaluated. The receiver operating characteristic (ROC) curve and binary logistic regression analyses were performed to assess the diagnostic efficiency of using IVIM and ASL parameters to discriminate allografts with impaired function from normal function. P<0.05 was considered statistically significant.

RESULTS

In allografts with normal function, no significant difference of mean cortical ADCslow, ADCfast, and PF was found compared with healthy controls (P>0.05). Cortical RBF in allografts with normal function was statistically lower than that of healthy controls (P<0.001). Mean cortical ADCslow, ADCfast, PF and RBF were lower for allografts with impaired function than that with normal function (P<0.05). Mean cortical ADCslow, ADCfast, PF and RBF showed a positive correlation with eGFR (all P<0.01) for recipients. The combination of IVIM and ASL MRI showed a higher area under the ROC curve (AUC) (0.865) than that of ASL MRI alone (P=0.02).

CONCLUSION

Combined IVIM and ASL MRI can better evaluate the diffusion and perfusion properties for allografts early after kidney transplantation.

Prospective MR image alignment between breath-holds: Application to renal BOLD MRI

PURPOSE

To present an image registration method for renal blood oxygen level-dependent (BOLD) measurements that enables semiautomatic assessment of parenchymal and medullary R2* changes under a functional challenge.

METHODS

In a series of breath-hold acquisitions, three-dimensional data were acquired initially for prospective image registration of subsequent BOLD measurements. An algorithm for kidney alignment for BOLD renal imaging (KALIBRI) was implemented to detect the positions of the left and right kidney so that the kidneys were acquired in the subsequent BOLD measurement at consistent anatomical locations. Residual in-plane distortions were corrected retrospectively so that semiautomatic dynamic R2* measurements of the renal cortex and medulla become feasible. KALIBRI was tested in six healthy volunteers during a series of BOLD experiments, which included a 600- to 1000-mL water challenge.

RESULTS

Prospective image registration and BOLD imaging of each kidney was achieved within a total measurement time of about 17 s, enabling its execution within a single breath-hold. KALIBRI improved the registration by up to 35% as found with mutual information measures. In four volunteers, a medullary R2* decrease of up to 40% was observed after water ingestion.

CONCLUSION

KALIBRI improves the quality of two-dimensional time-resolved renal BOLD MRI by aligning local renal anatomy, which allows for consistent R2* measurements over many breath-holds. Magn Reson Med 77:1573-1582, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

The relationship of ADC values of renal parenchyma with CKD stage and serum creatinine levels

Purpose

To evaluate the relationship of apparent diffusion coefficient (ADC) values of renal parenchyma with chronic kidney disease (CKD) stage and serum creatinine levels.

Materials and methods

One hundred and ten patients who had undergone magnetic resonance imaging of the upper abdomen for different reasons were retrospectively studied. A region of interest (ROI) was placed on the renal parenchyma for measurement of ADC values of both kidneys, without any preference for cortex or medulla. Three circular ROIs were placed-one each in the upper pole, interpolar region and lower pole of both kidneys. The mean ADC values were recorded for each patient and the relationship between ADC values and stage of CKD and serum creatinine levels were evaluated.

Results

Statistically significant difference was determined between the ADC values of the cases according to CKD stages (p < 0.001). Paired comparisons performed to determine the group that caused the difference revealed that median ADC values of healthy subjects who formed the control group was statistically significantly higher than that of the cases with stage 3, stage 4 and stage 5 CKD (p: 0.008; p: 0.008; and p: 0.002, respectively). Sensitivity and specificity were found to be 75.44% and 69.81%, respectively in detecting stage 3, stage 4 and stage 5 CKD among the cases with ADC values of 1151 and lower.

Conclusion

ADC values can play a role in the evaluation of renal dysfunction. However, population-and protocol-based cut-off ADC values are needed to identify renal dysfunction and to distinguish between different stages of CKD.

Quantitative high-resolution renal perfusion imaging using 3-dimensional through-time radial generalized autocalibrating partially parallel acquisition

OBJECTIVES

Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) examinations of the kidneys provide quantitative information on renal perfusion and filtration. However, these examinations are often difficult to implement because of respiratory motion and their need for a high spatiotemporal resolution and 3-dimensional coverage. Here, we present a free-breathing quantitative renal DCE-MRI examination acquired with a highly accelerated stack-of-stars trajectory and reconstructed with 3-dimensional (3D) through-time radial generalized autocalibrating partially parallel acquisition (GRAPPA), using half and quarter doses of gadolinium contrast.

MATERIALS AND METHODS

Data were acquired in 10 asymptomatic volunteers using a stack-of-stars trajectory that was undersampled in-plane by a factor of 12.6 with respect to Nyquist sampling criterion and using partial Fourier of 6/8 in the partition direction. Data had a high temporal (2.1-2.9 seconds per frame) and spatial (approximately 2.2 mm) resolution with full 3D coverage of both kidneys (350-370 mm × 79-92 mm). Images were successfully reconstructed with 3D through-time radial GRAPPA, and interframe respiratory motion was compensated by using an algorithm developed to automatically use images from multiple points of enhancement as references for registration. Quantitative pharmacokinetic analysis was performed using a separable dual-compartment model.

RESULTS

Region-of-interest (ROI) pharmacokinetic analysis provided estimates (mean (SD)) of quantitative renal parameters after a half dose: 218.1 (57.1) mL/min per 100 mL; plasma mean transit time, 4.8 (2.2) seconds; renal filtration, 28.7 (10.0) mL/min per 100 mL; and tubular mean transit time, 131.1 (60.2) seconds in 10 kidneys. The ROI pharmacokinetic analysis provided estimates (mean (SD)) of quantitative renal parameters after a quarter dose: 218.1 (57.1) mL/min per 100 mL; plasma mean transit time, 4.8 (2.2) seconds; renal filtration, 28.7 (10.0) mL/min per 100 mL; and tubular mean transit time, 131.1 (60.2) seconds in the 10 kidneys. Three-dimensional pixelwise parameter maps were also evaluated.

CONCLUSIONS

Highly undersampled data were successfully reconstructed with 3D through-time radial GRAPPA to achieve a high-resolution 3-dimensional renal DCE-MRI examination. The acquisition was completely free breathing, and the images were registered to compensate for respiratory motion. This allowed for an accurate high-resolution 3D quantitative renal functional mapping of perfusion and filtration parameters.

Measurement of single-kidney glomerular filtration function from magnetic resonance perfusion renography

Glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidney, and is considered to be the reference standard in the evaluation of renal function. There are many ways to test the GFR clinically, such as serum creatinine concentration, blood urea nitrogen and SPECT renography, however, they're all not a good standard to evaluate the early damage of renal function. In recent years, the improvement of MRI hardware and software makes it possible to reveal physiological characteristics such as renal blood flow or GFR by dynamic contrast enhancement magnetic resonance perfusion renography (DEC MRPR). MRPR is a method used to monitor the transit of contrast material, typically a gadolinium chelate, through the renal cortex, the medulla, and the collecting system. This review outlines the basics of DCE MRPR included acquisition of dynamic MR perfusion imaging, calculation of the contrast concentration from signal intensity and compartment models, and some challenges of MRPR method faced in prospective clinical application.

Assessment of hemodialysis impact by Polysulfone membrane on brain plasticity using BOLD-fMRI

PURPOSE

Hemodialysis (HD) is considered the most common alternative for overcoming renal failure. Studies have shown the involvement of HD membrane in the genesis of oxidative stress (OS) which has a direct impact on the brain tissue and is expected to be involved in brain plasticity and also reorganization of brain function control. The goal of this paper was to demonstrate the sensitivity of the blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) to characterize the OS before and after the HD session.

PATIENTS, MATERIALS AND METHODS

Twelve male patient-volunteers following chronic HD for more than 6months were recruited among 86 HD-patients. All patients underwent identical assessment immediately before and after the full HD-session. This consisted of full biological assessment, including malondialdehyde (MDA) and total antioxidant activity (TAOA); and brain BOLD-fMRI using the motor paradigm in block-design.

RESULTS

Functional BOLD-fMRI maps of motor area M1 were obtained from the HD patient before and after the hemodialysis session, important decrease in the intensity of brain activation of the motor area after HD, and important increase of the size of the volume of brain activation were observed, these changes are reflecting brain plasticity that is well correlated to OS levels. Individual patients MDA and TAOA before and after the hemodialysis sessions demonstrated a clear and systematic increase of the OS after HD (P-value=0.03). Correlation of BOLD-fMRI maximal signal intensity and volume of activated cortical brain area behaviors to MDA and total TAOA were close to 1.

CONCLUSION

OS is systematically increased in HD-patients after the HD-process. Indeed, the BOLD-fMRI shows a remarkable sensitivity to brain plasticity studied cortical areas. Our results confirm the superiority of the BOLD-fMRI quantities compared to the biological method used for assessing the OS while not being specific, and reflect the increase in OS generated by the HD. BOLD-fMRI is expected to be a suitable tool for evaluating the plasticity process evolution in hemodialysis brain patients.

Diffusion weighted imaging and blood oxygen level-dependent MR imaging of kidneys in patients with lupus nephritis

BACKGROUND

Lupus nephritis (LN) is one of most common secondary glomerulonephritis. There is no ideal method to simultaneously assess renal structure and function in patients with LN. The aim of this study is to investigate the utility of diffusion weighted imaging (DWI) and blood oxygen level-dependent (BOLD) MR imaging in the assessment of renal involvement and pathological changes in patients with LN.

METHODS

Sixty-five patients with LN and 16 healthy volunteers underwent coronal echo-planar DWI and BOLD MR imaging of the kidneys. The apparent diffusion coefficient (ADC) and R2* values of the kidneys were calculated with b values of 0 and 500 s/mm(2). The relationship between the renal injury variables and the ADCs or R2* values were evaluated. And 16 of 65 patients with LN underwent a repeated evaluation after the induction treatment for 9 to 12 months.

RESULTS

The mean ADC values of kidneys in patients with LN were 2.40 ± 0.25 × 10(-3) mm(2)/s, the mean R2* values of the renal cortex and medulla were 11.03 ± 1.60/sec and 14.05 ± 3.38/sec respectively, which were all significantly lower than that in volunteers. In patients with LN, the mean ADC values were correlated with eGFR (r = 0.510, p < 0.01). There was a negative correlation between the mean ADC values and renal pathology chronicity indexes (r = -0.249, p < 0.05), the R2* values of the renal medulla and proteinuria (r = -0.244, p < 0.05), and the degree of tubulointerstitial lesions (r = -0.242, p < 0.05). The ADC and R2* values of kidneys were significantly higher than those of pre-treatment in complete remission patients.

CONCLUSIONS

DWI and BOLD MR imaging of kidneys may be used to noninvasively monitor the disease activity and evaluate therapeutic efficacy in lupus nephritis.

Chronic kidney disease: pathological and functional assessment with diffusion tensor imaging at 3T MR

OBJECTIVE

Our objective was to evaluate pathological and functional changes in chronic kidney disease (CKD) using diffusion tensor imaging (DTI) at 3 T.

METHODS

There were fifty-one patients with CKD who required biopsy and 19 healthy volunteers who were examined using DTI at 3 T. The mean values of fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) were obtained from the renal parenchyma (cortex and medulla). Correlations between imaging results and the estimated glomerular filtration rate (eGFR), as well as pathological damage (glomerular lesion and tubulointerstitial injury), were evaluated.

RESULTS

The renal cortical FA was significantly lower than the medullary in both normal and affected kidneys (p < 0.001). The parenchymal FA was significantly lower in patients than healthy controls, regardless of whether eGFR was reduced. There were positive correlations between eGFR and FA (cortex, r = 0.689, p = 0.000; and medulla, r = 0.696, p = 0.000), and between eGFR and ADC (cortex, r = 0.310, p = 0.017; and medulla, r = 0.356, p = 0.010). Negative correlations were found between FA and the glomerular lesion (cortex, r = -0.499, p = 0.000; and medulla, r = -0.530, p = 0.000), and between FA and tubulointerstitial injury (cortex, r = -0.631, p = 0.000; and medulla, r = -0.724, p = 0.000).

CONCLUSION

DTI is valuable for noninvasive assessment of renal function and pathology in patients with CKD. A decrease in FA could identify the glomerular lesions, tubulointerstitial injuries, and eGFR.

Assessment of renal fibrosis in chronic kidney disease using diffusion-weighted MRI

AIM

To assess the performance of diffusion-weighted magnetic resonance imaging (MRI) for the assessment of renal fibrosis in chronic kidney disease (CKD), with histopathology as a reference standard.

MATERIALS AND METHODS

Forty patients with CKD and 30 healthy volunteers were recruited for the study. All participants underwent diffusion-weighted MRI. Renal biopsy was performed in 25 patients with CKD. Mean renal medullary and cortical apparent diffusion coefficient (ADC) values were compared between CKD patients and the healthy volunteers. Pearson's correlation coefficient was calculated to investigate the relationship between ADC values, serum creatinine (SCr), estimated glomerular filtration rate (eGFR), 24 h urinary protein (24h-UPRO), and renal histopathological scores.

RESULTS

Cortical and medullary ADC values in the CKD group were significantly lower compared to those in the healthy controls. In the CKD group, a significant negative correlation was found between cortical ADC values and SCr/24h-UPRO, and significant positive correlation was found between cortical ADC and eGFR. There was also a significant negative correlation between medullary ADC values and SCr. Both cortical and medullary ADC values were significantly correlated with histopathological fibrosis score.

CONCLUSION

Renal ADC values strongly correlate with histological measures of fibrosis, and have the potential to enhance the non-invasive monitoring of chronic kidney disease.

Image registration for triggered and non-triggered DTI of the human kidney: reduced variability of diffusion parameter estimation

BACKGROUND

To investigate if non-rigid image-registration reduces motion artifacts in triggered and non-triggered diffusion tensor imaging (DTI) of native kidneys. A secondary aim was to determine, if improvements through registration allow for omitting respiratory-triggering.

METHODS

Twenty volunteers underwent coronal DTI of the kidneys with nine b-values (10-700 s/mm(2) ) at 3 Tesla. Image-registration was performed using a multimodal nonrigid registration algorithm. Data processing yielded the apparent diffusion coefficient (ADC), the contribution of perfusion (FP ), and the fractional anisotropy (FA). For comparison of the data stability, the root mean square error (RMSE) of the fitting and the standard deviations within the regions of interest (SDROI ) were evaluated.

RESULTS

RMSEs decreased significantly after registration for triggered and also for non-triggered scans (P < 0.05). SDROI for ADC, FA, and FP were significantly lower after registration in both medulla and cortex of triggered scans (P < 0.01). Similarly the SDROI of FA and FP decreased significantly in non-triggered scans after registration (P < 0.05). RMSEs were significantly lower in triggered than in non-triggered scans, both with and without registration (P < 0.05).

CONCLUSION

Respiratory motion correction by registration of individual echo-planar images leads to clearly reduced signal variations in renal DTI for both triggered and particularly non-triggered scans. Secondarily, the results suggest that respiratory-triggering still seems advantageous.

New magnetic resonance imaging methods in nephrology

Established as a method to study anatomic changes, such as renal tumors or atherosclerotic vascular disease, magnetic resonance imaging (MRI) to interrogate renal function has only recently begun to come of age. In this review, we briefly introduce some of the most important MRI techniques for renal functional imaging, and then review current findings on their use for diagnosis and monitoring of major kidney diseases. Specific applications include renovascular disease, diabetic nephropathy, renal transplants, renal masses, acute kidney injury, and pediatric anomalies. With this review, we hope to encourage more collaboration between nephrologists and radiologists to accelerate the development and application of modern MRI tools in nephrology clinics.

Why and how we determine nephron number

The total number of glomeruli (nephrons) in a kidney is an important microanatomical parameter for at least three reasons: it provides an index of the success/extent of nephrogenesis and can thereby provide insights into the roles of specific genes and feto-maternal environmental factors in nephrogenesis; low nephron number has been linked to an increased risk of cardiovascular and renal disease in adulthood; and knowledge of quantitative kidney microanatomy can illuminate our understanding of physiological mechanisms in health and disease. A range of methods has been used to count glomeruli in kidneys over the past 100 years, with design-based stereology (the physical disector/fractionator combination) considered the gold standard. However, this approach is labor-intensive and expensive, and therefore is not utilized by most laboratories. A new method for counting and sizing every glomerulus in the kidney has recently been described. This method involves in vivo labeling of glomeruli with cationic ferritin, and then magnetic resonance imaging (MRI) of the ex vivo kidney. Values are obtained in one sixth of the time of disector-based approaches. This new MRI method holds great promise for studies of glomerular number and size ex vivo and in vivo.

Quantitative sodium MR imaging of native versus transplanted kidneys using a dual-tuned proton/sodium (1H/ 23Na) coil: initial experience

OBJECTIVES

To compare sodium ((23)Na) characteristics between native and transplanted kidneys using dual-tuned proton ((1)H)/sodium MRI.

METHODS

Six healthy volunteers and six renal transplant patients (3 normal function, 3 acute allograft rejection) were included. Proton/sodium MRI was obtained at 3 T using a dual-tuned coil. Signal to noise ratio (SNR), sodium concentration ([(23)Na]) and cortico-medullary sodium gradient (CMSG) were measured. Reproducibility of [(23)Na] measurement was also tested. SNR, [(23)Na] and CMSG of the native and transplanted kidneys were compared.

RESULTS

Proton and sodium images of kidneys were successfully acquired. SNR and [(23)Na] measurements of the native kidneys were reproducible at two different sessions. [(23)Na] and CMSG of the transplanted kidneys was significantly lower than those of the native kidneys: 153.5 ± 11.9 vs. 192.9 ± 9.6 mM (P = 0.002) and 8.9 ± 1.5 vs. 10.5 ± 0.9 mM/mm (P = 0.041), respectively. [(23)Na] and CMSG of the transplanted kidneys with normal function vs. acute rejection were not statistically different.

CONCLUSIONS

Sodium quantification of kidneys was reliably performed using proton/sodium MRI. [(23)Na] and CMSG of the transplanted kidneys were lower than those of the native kidneys, but without a statistically significant difference between patients with or without renal allograft rejection.

KEY POINTS

Dual-tuned proton/sodium RF coil enables co-registered proton and sodium MRI. Structural and sodium biochemical property can be acquired by dual-tuned proton/sodium MRI. Sodium and sodium gradient of kidneys can be measured by dual-tuned MRI. Sodium concentration was lower in transplanted kidneys than in native kidneys. Sodium gradient of transplanted kidneys was lower than for native kidneys.

Assessment with unenhanced MRI techniques of renal morphology and hemodynamic changes during acute kidney injury and chronic kidney disease in mice

BACKGROUND/AIMS

Changes in renal oxygenation and perfusion have been identified as common pathways to the development and progression of renal disease. Recently, the sensitivity of hemodynamic response imaging (HRI) was demonstrated; this is a functional magnetic resonance imaging (MRI) method combined with transient hypercapnia and hyperoxia for the evaluation of renal perfusion and vascular reactivity. The aim of this study was to utilize HRI for the noninvasive evaluation of changes in renal hemodynamics and morphology during acute, chronic and acute-on-chronic renal failures.

METHODS

Renal-HRI maps and true fast imaging with steady-state precession (True-FISP) images were used to evaluate renal perfusion, morphology and corticomedullary differentiation (CMD). MR images were acquired on two mouse models of kidney injury: adenine-induced chronic kidney disease (CKD) and rhabdomyolysis-induced acute kidney injury (AKI). Serum urea was measured from these mice in order to determine renal function.

RESULTS

Renal-HRI maps revealed a blunted response to hypercapnia and hyperoxia with evolving kidney dysfunction in both models, reflecting hampered renal vascular reactivity and perfusion. True-FISP images showed a high sensitivity to renal morphological changes, with different patterns characterizing each model. Calculated data obtained from HRI and True-FISP during the evolution of renal failure and upon recovery, with and without protective intervention, closely correlated with the degree of renal impairment.

CONCLUSIONS

This study suggests the potential combined usage of two noninvasive MRI methods, HRI and True-FISP, for the assessment of renal dysfunction without the potential risk associated with contrast-agents administration. HRI may also serve as a research tool in experimental settings, revealing the hemodynamic changes associated with kidney dysfunction.

Perfluorocarbon nanoparticles for physiological and molecular imaging and therapy

Herein, we review the use of non-nephrotoxic perfluorocarbon nanoparticles (PFC NPs) for noninvasive detection and therapy of kidney diseases, and we provide a synopsis of other related literature pertinent to their anticipated clinical application. Recent reports indicate that PFC NPs allow for quantitative mapping of kidney perfusion and oxygenation after ischemia-reperfusion injury with the use of a novel multinuclear (1)H/(19)F magnetic resonance imaging approach. Furthermore, when conjugated with targeting ligands, the functionalized PFC NPs offer unique and quantitative capabilities for imaging inflammation in the kidney of atherosclerotic ApoE-null mice. In addition, PFC NPs can facilitate drug delivery for treatment of inflammation, thrombosis, and angiogenesis in selected conditions that are comorbidities for kidney failure. The excellent safety profile of PFC NPs with respect to kidney injury positions these nanomedicine approaches as promising diagnostic and therapeutic candidates for treating and following acute and chronic kidney diseases.

Functional evaluation of transplanted kidneys using arterial spin labeling MRI

PURPOSE

To investigate non-contrast-enhanced arterial spin labeling (ASL) MRI for functional assessment of transplanted kidneys at 1.5 Tesla (T) and 3T.

MATERIALS AND METHODS

This study was approved by the local ethics committee, and written informed consent was obtained from all participants. Ninety eight renal allograft recipients (mean age, 51.5 ± 14.6 years) were prospectively included in this study. ASL MRI was performed at 1.5T (n = 65) and 3T (n = 33) using a single-slice flow-sensitive alternating inversion recovery true-fast imaging with steady-state precession (FAIR True-FISP) sequence in the paracoronal plane. ASL perfusion was regional analyzed for the renal cortex on parameter maps. ASL was compared between patients with good or moderate allograft function (Group a; estimated glomerular filtration rate [eGFR] > 30 mL/min/1.73 m(2)) and patients with heavily impaired allograft function (Group b; eGFR ≤ 30 mL/min/1.73 m(2)) and correlated to renal function as determined by eGFR.

RESULTS

ASL perfusion and eGFR were comparable at 1.5T (246.9 ± 66.8 mL/100 g/min and 41.9 ± 22.7 mL/min/1.73 m(2)) and 3T (236.5 ± 102.3 mL/100 g/min and 35.9 ± 22.9 mL/min/1.73 m(2)). ASL perfusion was significantly higher in group a (282.7 ± 60.8 mL/100 g/min) as compared to group b (178.2 ± 63.3 mL/100 g/min) (P < 0.0001). ASL perfusion values exhibited a significant correlation with renal function as determined by eGFR (r = 0.59; P < 0.0001).

CONCLUSION

Cortical ASL perfusion values differ between patients with good or moderate allograft function and poor allograft function and correlate significantly with allograft function. Our results highlight the potential of ASL MRI for functional evaluation of renal allografts.