Longitudinal assessment of mouse renal injury using high-resolution anatomic and magnetization transfer MR imaging

Severity of polycystic kidney disease revealed by multiparametric MRI

PURPOSE

We aimed to compare multiple MRI parameters, including relaxation rates (R 1 $$ {R}_1 $$ ,R 2 $$ {R}_2 $$ , andR 1 ρ $$ {R}_{1\rho } $$ ), ADC from diffusion weighted imaging, pool size ratio (PSR) from quantitative magnetization transfer, and measures of exchange from spin-lock imaging (S ρ $$ {S}_{\rho } $$ ), for assessing and predicting the severity of polycystic kidney disease (PKD) over time.

METHODS

Pcy/Pcy mice with CD1 strain, a mouse model of autosomal dominant PKD, were imaged at 5, 9, and 26 wk of age using a 7T MRI system. Twelve-week normal CD1 mice were used as controls. Post-mortem paraffin tissue sections were stained using hematoxylin and eosin and picrosirius red to identify histological changes.

RESULTS

Histology detected segmental cyst formation in the early stage (week 5) and progression of PKD over time in Pcy kidneys. InT 2 $$ {T}_2 $$ -weighted images, small cysts appeared locally in cystic kidneys in week 5 and gradually extended to the whole cortex and outer stripe of outer medulla region from week 5 to week 26. Regional PSR,R 1 $$ {R}_1 $$ ,R 2 $$ {R}_2 $$ , andR 1 ρ $$ {R}_{1\rho } $$ decreased consistently over time compared to normal kidneys, with significant changes detected in week 5. Among all the MRI measures,R 2 $$ {R}_2 $$ andR 1 ρ $$ {R}_{1\rho } $$ allow highest detectability to PKD, while PSR andR 1 $$ {R}_1 $$ have highest correlation with pathological indices of PKD. Using optimum MRI parameters as regressors, multiple linear regression provides reliable prediction of PKD progression.

CONCLUSION

R 2 $$ {R}_2 $$ ,R 1 $$ {R}_1 $$ , and PSR are sensitive indicators of the presence of PKD. Multiparametric MRI allows a comprehensive analysis of renal changes caused by cyst formation and expansion.

Multiparametric magnetic resonance imaging in diagnosis of long-term renal atrophy and fibrosis after ischemia reperfusion induced acute kidney injury in mice

Tubular atrophy and fibrosis are pathological changes that determine the prognosis of kidney disease induced by acute kidney injury (AKI). We aimed to evaluate multiple magnetic resonance imaging (MRI) parameters, including pool size ratio (PSR) from quantitative magnetization transfer, relaxation rates, and measures from spin-lock imaging ( R 1 ρ and S ρ ), for assessing the pathological changes associated with AKI-induced kidney disease. Eight-week-old male C57BL/6 J mice first underwent unilateral ischemia reperfusion injury (IRI) induced by reperfusion after 45 min of ischemia. They were imaged using a 7T MRI system 56 days after the injury. Paraffin tissue sections were stained using Masson trichrome and picrosirius red to identify histopathological changes such as tubular atrophy and fibrosis. Histology detected extensive tubular atrophy and moderate fibrosis in the cortex and outer stripe of the outer medulla (CR + OSOM) and more prominent fibrosis in the inner stripe of the outer medulla (ISOM) of IRI kidneys. In the CR + OSOM region, evident decreases in PSR, R 1 , R 2 , R 1 ρ , and S ρ showed in IRI compared with contralateral kidneys, with PSR and S ρ exhibiting the most significant changes. In addition, the exchange parameter S ρ dropped by the largest degree among all the MRI parameters, whileR 2 * increased significantly. In the ISOM of IRI kidneys, PSR increased while S ρ kept decreasing. R 2 , R 1 ρ , andR 2 * all increased due to more severe fibrosis in this region. Among MRI measures, PSR and R 1 ρ showed the highest detectability of renal changes no matter whether tubular atrophy or fibrosis dominated.R 2 * and S ρ could be more specific to a single pathological event than other MRI measures because onlyR 2 * increased and S ρ decreased consistently when either fibrosis or tubular atrophy dominated, and their correlations with fibrosis scores were higher than other MRI measures. Multiparametric MRI may enable a more comprehensive analysis of histopathological changes following AKI.

Renal tubular dilation and fibrosis after unilateral ureter obstruction revealed by relaxometry and spin-lock exchange MRI

We evaluated the use of quantitative MRI relaxometry, including the dispersion of spin-lock relaxation with different locking fields, for detecting and assessing tubular dilation and fibrosis in a mouse model of unilateral ureter obstruction (UUO). C57BL/6 J and BALB/c mice that exhibit different levels of tubular dilation and renal fibrosis after UUO were subjected to MR imaging at 7 T. Mice were imaged before UUO surgery, and at 5, 10 and 15 days after surgery. We acquired maps of relaxation rates and fit the dispersion of spin-lock relaxation rates R1ρ at different locking fields (frequencies) to a model of exchanging water pools, and assessed the sensitivity of the derived quantities for detecting tubular dilation and fibrosis in kidney. Histological scores for tubular dilation and fibrosis, based on luminal space and positive fibrotic areas in sections, were obtained for comparison. Histology detected extensive tubular dilation and mild to moderate fibrosis in the UUO kidneys, in which enlargement of luminal space, deposition of collagen, and reductions in capillary density were observed in the cortex and outer stripe of the outer medulla. Relaxation rates R1 , R2 and R1ρ clearly decreased in these regions of UUO kidneys longitudinally. While R1 showed the highest detectability to tubular dilation and overall changes in UUO kidneys, Sρ , a parameter derived from R1ρ dispersion data, showed the highest correlation with renal fibrosis in UUO. While relaxation parameters are sensitive to tubular dilation in UUO kidneys, Sρ depends primarily on the average exchange rate between water and other chemically shifted resonances such as hydroxyls and amides, and provides additional specific information for evaluating fibrosis in kidney disease.

Advanced non-invasive diagnostic techniques for visualization and estimation of kidney fibrosis

Kidney fibrosis is marked by excessive extracellular matrix deposition during disease progression. Unfortunately, existing kidney function parameters do not predict the extent of kidney fibrosis. Moreover, the traditional histology methods for the assessment of kidney fibrosis require liquid and imaging biomarkers as well as needle-based biopsies, which are invasive and often associated with kidney injury. The repetitive analyses required to monitor the disease progression are therefore difficult. Hence, there is an unmet medical need for non-invasive and informative diagnostic approaches to monitor kidney fibrosis during the progression of chronic kidney disease. Here, we summarize the modern advances in diagnostic imaging techniques that have shown promise for non-invasive estimation of kidney fibrosis in pre-clinical and clinical studies.

The Vanderbilt O'Brien Kidney Center

The Vanderbilt O'Brien Kidney Center (VOKC) is one of the eight National Institutes of Health P30-funded centers in the United States. The mission of these core-based centers is to provide technical and conceptual support to enhance and facilitate research in the field of kidney diseases. The goal of the VOKC is to provide support to understand mechanisms and identify potential therapies for acute and chronic kidney disease. The services provided by the VOKC are meant to help the scientific community to have the right support and tools as well as to select the right animal model, statistical analysis, and clinical study design to perform innovative research and translate discoveries into personalized care to prevent, diagnose, and cure kidney disease. To achieve these goals, the VOKC has in place a program to foster collaborative investigation into critical questions of kidney disease, to personalize diagnosis and treatment of kidney disease, and to disseminate information about kidney disease and the benefits of VOKC services and research. The VOKC is complemented by state-of-the-art cores and an education and outreach program whose goals are to provide an educational platform to enhance the study of kidney disease, to publicize information about services available through the VOKC, and to provide information about kidney disease to patients and other interested members of the community. In this review, we highlight the major services and contributions of the VOKC.

Multiparametric Functional Magnetic Resonance Imaging for Evaluating Renal Allograft Injury

Kidney transplantation is the treatment of choice for patients with end-stage renal disease, as it extends survival and increases quality of life in these patients. However, chronic allograft injury continues to be a major problem, and leads to eventual graft loss. Early detection of allograft injury is essential for guiding appropriate intervention to delay or prevent irreversible damage. Several advanced MRI techniques can offer some important information regarding functional changes such as perfusion, diffusion, structural complexity, as well as oxygenation and fibrosis. This review highlights the potential of multiparametric MRI for noninvasive and comprehensive assessment of renal allograft injury.

Spin-lock relaxation rate dispersion reveals spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney

PURPOSE

To develop and evaluate a reliable non-invasive means for assessing the severity and progression of fibrosis in kidneys. We used spin-lock MR imaging with different locking fields to detect and characterize progressive renal fibrosis in an hHB-EGF^Tg/Tg mouse model.

METHODS

Male hHB-EGF^Tg/Tg mice, a well-established model of progressive fibrosis, and age-matched normal wild type (WT) mice, were imaged at 7T at ages 5-7, 11-13, and 30-40 weeks. Spin-lock relaxation rates R_{1 ρ} were measured at different locking fields (frequencies) and the resultant dispersion curves were fit to a model of exchanging water pools. The obtained MRI parameters were evaluated as potential indicators of tubulointerstitial fibrosis in kidney. Histological examinations of renal fibrosis were also carried out post-mortem after MRI.

RESULTS

Histology detected extensive fibrosis in the hHB-EGF^Tg/Tg mice, in which collagen deposition and reductions in capillary density were observed in the fibrotic regions of kidneys. R₂ and R_{1 ρ} values at different spin-lock powers clearly dropped in the fibrotic region as fibrosis progressed. There was less variation in the asymptotic locking field relaxation rate R 1 ρ ∞ between the groups. The exchange parameter S_ρ and the inflection frequency ω_infl changed by larger factors.

CONCLUSION

Both S_ρ and ω_infl depend primarily on the average exchange rate between water and other chemically shifted resonances such as hydroxyls and amides. Spin-lock relaxation rate dispersion, rather than single measurements of relaxation rates, provides more comprehensive and specific information on spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney.

Noninvasive quantitative magnetization transfer MRI reveals tubulointerstitial fibrosis in murine kidney

Excessive tissue scarring, or fibrosis, is a critical contributor to end stage renal disease, but current clinical tests are not sufficient for assessing renal fibrosis. Quantitative magnetization transfer (qMT) MRI provides indirect information about the macromolecular composition of tissues. We evaluated measurements of the pool size ratio (PSR, the ratio of immobilized macromolecular to free water protons) obtained by qMT as a biomarker of tubulointerstitial fibrosis in a well-established murine model with progressive renal disease. MR images were acquired from 16-week-old fibrotic hHB-EGF^Tg/Tg mice and normal wild-type (WT) mice (N = 12) at 7 T. QMT parameters were derived using a two-pool five-parameter fitting model. A normal range of PSR values in the cortex and outer stripe of outer medulla (CR + OSOM) was determined by averaging across voxels within WT kidneys (mean ± 2SD). Regions in diseased mice whose PSR values exceeded the normal range above a threshold value (tPSR) were identified and measured. The spatial distribution of fibrosis was confirmed using picrosirius red stains. Compared with normal WT mice, scattered clusters of high PSR regions were observed in the OSOM of hHB-EGF^Tg/Tg mouse kidneys. Moderate increases in mean PSR (mPSR) of CR + OSOM regions were observed across fibrotic kidneys. The abnormally high PSR regions (% area) detected by the tPSR were significantly increased in hHB-EGF^Tg/Tg mice, and were highly correlated with regions of fibrosis detected by histological fibrosis indices measured from picrosirius red staining. Renal tubulointerstitial fibrosis in OSOM can thus be assessed by qMT MRI using an appropriate analysis of PSR. This technique may be used as an imaging biomarker for chronic kidney diseases.

Spatiotemporal trajectories of quantitative magnetization transfer measurements in injured spinal cord using simplified acquisitions

Purpose

This study aims to systematically evaluate the accuracy and precision of pool size ratio (PSR) measurements from quantitative magnetization transfer (qMT) acquisitions using simplified models in the context of assessing injury-associated spatiotemporal changes in spinal cords of non-human primates. This study also aims to characterize changes in the spinal tissue pathology in individual subjects, both regionally and longitudinally, in order to demonstrate the relationship between regional tissue compositional changes and sensorimotor behavioral recovery after cervical spinal cord injury (SCI).

Methods

MRI scans were recorded on anesthetized monkeys at 9.4 T, before and serially after a unilateral section of the dorsal column tract. Images were acquired following saturating RF pulses at different offset frequencies. Models incorporating two pools of protons but with differing numbers of variable parameters were used to fit the data to derive qMT parameters. The results using different amounts of measured data and assuming different numbers of variable model parameters were compared. Behavioral impairments and recovery were assessed by a food grasping-retrieving task. Histological sections were obtained post mortem for validation of the injury.

Results

QMT fitting provided maps of pool size ratio (PSR), the relative amounts of immobilized protons exchanging magnetization compared to the “free” water. All the selected modeling approaches detected a lesion/cyst at the site of injury as significant reductions in PSR values. The regional contrasts in the PSR maps obtained using the different fittings varied, but the 2-parameter fitting results showed strong positive correlations with results from 5-parameter modeling. 2-parameter fitting results with modest (>3) RF offsets showed comparable sensitivity for detecting demyelination in white matter and loss of macromolecules in gray matter around lesion sites compared to 5-parameter fitting with fully-sampled data acquisitions. Histology confirmed that decreases of PSR corresponded to regional demyelination around lesion sites, especially when demyelination occurred along the dorsal column on the injury side. Longitudinally, PSR values of injured dorsal column tract and gray matter horns exhibited remarkable recovery that associated with behavioral improvement.

Conclusion

Simplified qMT modeling approaches provide efficient and sensitive means to detect and characterize injury-associated demyelination in white matter tracts and loss of macromolecules in gray matter and to monitor its recovery over time.

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Simplified 2-parameter and fully sampled 5-parameter qMT modeling achieved comparable accuracy and precision of PSR values.

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Successfully tracked and differentiated myelination states of specific WM tracts and macromolecular changes in GM horns.

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Recovery of WM and GM pathology assessed by qMT correlated with improvements in hand uses after injury.

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High translational potential for clinical studies of human patients with spinal cord injury.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T1/T2 mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

Assessment of renal fibrosis in murine diabetic nephropathy using quantitative magnetization transfer MRI

PURPOSE

Renal fibrosis is a hallmark of progressive renal disease; however, current clinical tests are insufficient for assessing renal fibrosis. Here we evaluated the utility of quantitative magnetization transfer MRI in detecting renal fibrosis in a murine model of progressive diabetic nephropathy (DN).

METHODS

The db/db eNOS-/- mice, a well-recognized model of progressive DN, and normal wild-type mice were imaged at 7T. The quantitative magnetization transfer data were collected in coronal plane using a 2D magnetization transfer prepared spoiled gradient echo sequence with a Gaussian-shaped presaturation pulse. Parameters were derived using a two-pool fitting model. A normal range of cortical pool size ratio (PSR) was defined as Mean±2SD of wild-type kidneys (N = 20). The cortical regions whose PSR values exceeded this threshold (threshold PSR) were assessed. The correlations between the PSR-based and histological (collagen IV or picrosirius red stain) fibrosis measurements were evaluated.

RESULTS

Compared with wild-type mice, moderate increases in mean PSR values and scattered clusters of high PSR region were observed in cortex of DN mouse kidneys. Abnormally high PSR regions (% area) that were detected by the threshold PSR were significantly increased in renal cortexes of DN mice. These regions progressively increased on aging and highly correlated with histological fibrosis measures, while the mean PSR values correlated much less.

CONCLUSION

Renal fibrosis in DN can be assessed by the quantitative magnetization transfer MRI and threshold analysis. This technique may be used as a novel imaging biomarker for DN and other renal diseases.

Multiparametric magnetic resonance imaging of experimental chronic kidney disease: A quantitative correlation study with histology

Objectives

In human chronic kidney disease (CKD) the extent of renal tubulointerstitial fibrosis correlates with progressive loss of renal function. However, fibrosis can so far only be assessed by histology of kidney biopsies. Magnetic resonance imaging (MRI) can provide information about tissue architecture, but its potential to assess fibrosis and inflammation in diseased kidneys remains poorly defined.

Materials and methods

We evaluated excised kidneys in a murine adenine-induced nephropathy model for CKD by MRI and correlated quantitative MRI parameters (T1, T2, and T2* relaxation times, apparent diffusion coefficient and fractional anisotropy) with histological hallmarks of progressive CKD, including renal fibrosis, inflammation, and microvascular rarefaction. Furthermore, we analyzed the effects of paraformaldehyde fixation on MRI parameters by comparing kidney samples before and after fixation with paraformaldehyde.

Results

In diseased kidneys T2 and T2* relaxation times, apparent diffusion coefficient and fractional anisotropy in the renal cortex and/or outer medulla were significantly different from those in control kidneys. In particular, T2 relaxation time was the best parameter to distinguish control and CKD groups and correlated very well with the extent of fibrosis, inflammatory infiltrates, tubular dilation, crystal deposition, and loss of peritubular capillaries and normal tubules in the renal cortex and outer medulla. Fixation with paraformaldehyde had no impact on T2 relaxation time and fractional anisotropy, whereas T1 times significantly decreased and T2* times and apparent diffusion coefficients increased in fixed kidney tissue.

Conclusions

MRI parameters provide a promising approach to quantitatively assess renal fibrosis and inflammation in CKD. Especially T2 relaxation time correlates well with histological features of CKD and is not influenced by paraformaldehyde fixation of kidney samples. Thus, T2 relaxation time might be a candidate parameter for non-invasive assessment of renal fibrosis in human patients.

Magnetization Transfer Magnetic Resonance Imaging Noninvasively Detects Renal Fibrosis in Swine Atherosclerotic Renal Artery Stenosis at 3.0 T

OBJECTIVES

Renal fibrosis is a useful biomarker for diagnosis and evaluation of therapeutic interventions of renal diseases but often requires invasive testing. Magnetization transfer magnetic resonance imaging (MT-MRI), which evaluates the presence of macromolecules, offers a noninvasive tool to probe renal fibrosis in murine renal artery stenosis (RAS) at 16.4 T. In this study, we aimed to identify appropriate imaging parameters for collagen detection at 3.0 T MRI and to test the utility of MT-MRI in measuring renal fibrosis in a swine model of atherosclerotic RAS (ARAS).

MATERIALS AND METHODS

To select the appropriate offset frequency, an MT-MRI study was performed on a phantom containing 0% to 40% collagen I and III with offset frequencies from -1600 to +1600 Hz and other MT parameters empirically set as pulse width at 16 milliseconds and flip angle at 800 degrees. Then selected MT parameters were used in vivo on pigs 12 weeks after sham (n = 8) or RAS (n = 10) surgeries. The ARAS pigs were fed with high-cholesterol diet to induce atherosclerosis. The MT ratio (MTR) was compared with ex vivo renal fibrosis measured using Sirius-red staining.

RESULTS

Offset frequencies at 600 and 1000 Hz were selected for collagen detection without direct saturation of free water signal, and subsequently applied in vivo. The ARAS kidneys showed mild cortical and medullary fibrosis by Sirius-red staining. The cortical and medullary MTRs at 600 and 1000 Hz were both increased. Renal fibrosis measured ex vivo showed good linear correlations with MTR at 600 (cortex: Pearson correlation coefficient r = 0.87, P < 0.001; medulla: r = 0.70, P = 0.001) and 1000 Hz (cortex: r = 0.75, P < 0.001; medulla: r = 0.83, P < 0.001).

CONCLUSIONS

Magnetization transfer magnetic resonance imaging can noninvasively detect renal fibrosis in the stenotic swine kidney at 3.0 T. Therefore, MT-MRI may potentially be clinically applicable and useful for detection and monitoring of renal pathology in subjects with RAS.

Assessment of unilateral ureter obstruction with multi-parametric MRI

PURPOSE

Quantitative multi-parametric MRI (mpMRI) methods may allow the assessment of renal injury and function in a sensitive and objective manner. This study aimed to evaluate an array of MRI methods that exploit endogenous contrasts including relaxation rates, pool size ratio (PSR) derived from quantitative magnetization transfer (qMT), chemical exchange saturation transfer (CEST), nuclear Overhauser enhancement (NOE), and apparent diffusion coefficient (ADC) for their sensitivity and specificity in detecting abnormal features associated with kidney disease in a murine model of unilateral ureter obstruction (UUO).

METHODS

MRI scans were performed in anesthetized C57BL/6N mice 1, 3, or 6 days after UUO at 7T. Paraffin tissue sections were stained with Masson trichrome following MRI.

RESULTS

Compared to contralateral kidneys, the cortices of UUO kidneys showed decreases of relaxation rates R₁ and R₂ , PSR, NOE, and ADC. No significant changes in CEST effects were observed for the cortical region of UUO kidneys. The MRI parametric changes in renal cortex are related to tubular cell death, tubular atrophy, tubular dilation, urine retention, and interstitial fibrosis in the cortex of UUO kidneys.

CONCLUSION

Measurements of multiple MRI parameters provide comprehensive information about the molecular and cellular changes produced by UUO. Magn Reson Med 79:2216-2227, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Noninvasive Assessment of Renal Fibrosis with Magnetization Transfer MR Imaging: Validation and Evaluation in Murine Renal Artery Stenosis

Purpose To test the utility of magnetization transfer imaging in detecting and monitoring the progression of renal fibrosis in mice with unilateral renal artery stenosis. Materials and Methods This prospective study was approved by the Institutional Animal Care and Use Committee. Renal artery stenosis surgery (n = 10) or sham surgery (n = 5) was performed, and the stenotic and contralateral kidneys were studied longitudinally in vivo at baseline and 2, 4, and 6 weeks after surgery. After a 16.4-T magnetic resonance imaging examination, magnetization transfer ratio was measured as an index of fibrosis (guided by parameters selected in preliminary phantom studies). In addition, renal volume, perfusion, blood flow, and oxygenation were assessed. Fibrosis was subsequently measured ex vivo by means of histologic analysis and hydroxyproline assay. The Wilcoxon rank sum or signed rank test was used for statistical comparisons between or within groups, and Pearson and Spearman rank correlation was used to compare fibrosis measured in vivo and ex vivo. Results In the stenotic kidney, the median magnetization transfer ratio showed progressive increases from baseline to 6 weeks after surgery (increases of 13.7% [P = .0006] and 21.3% [P = .0005] in cortex and medulla, respectively), which were accompanied by a progressive loss in renal volume, perfusion, blood flow, and oxygenation. The 6-week magnetization transfer ratio map showed good correlation with fibrosis measured ex vivo (Pearson r = 0.9038 and Spearman ρ = 0.8107 [P = .0002 vs trichrome staining]; r = 0.9540 and ρ = 0.8821 [P < .0001 vs Sirius red staining]; and r = 0.8429 and ρ = 0.7607 [P = .001 vs hydroxyproline assay]). Conclusion Magnetization transfer imaging was used successfully to measure and longitudinally monitor the progression of renal fibrosis in mice with unilateral renal artery stenosis. ^© RSNA, 2016 Online supplemental material is available for this article.

MRI tools for assessment of microstructure and nephron function of the kidney

MRI can provide excellent detail of renal structure and function. Recently, novel MR contrast mechanisms and imaging tools have been developed to evaluate microscopic kidney structures including the tubules and glomeruli. Quantitative MRI can assess local tubular function and is able to determine the concentrating mechanism of the kidney noninvasively in real time. Measuring single nephron function is now a near possibility. In parallel to advancing imaging techniques for kidney microstructure is a need to carefully understand the relationship between the local source of MRI contrast and the underlying physiological change. The development of these imaging markers can impact the accurate diagnosis and treatment of kidney disease. This study reviews the novel tools to examine kidney microstructure and local function and demonstrates the application of these methods in renal pathophysiology.

Current MRI techniques for the assessment of renal disease

PURPOSE OF REVIEW

Over the past decade, a variety of MRI methods have been developed and applied to many kidney diseases. These MRI techniques show great promise, enabling the noninvasive assessment of renal structure, function and injury in individuals. This review will highlight the current applications of functional MRI techniques for the assessment of renal disease and discuss future directions.

RECENT FINDINGS

Many pathological (functional and structural) changes or factors in renal disease can be assessed by advanced MRI techniques. These include renal vascular structure and function (contrast-enhanced MRI, arterial spin labelling), tissue oxygenation (blood oxygen level dependent MRI), renal tissue injury and fibrosis (diffusion or magnetization transfer imaging, magnetic resonance elastography), renal metabolism (chemical exchange saturation transfer, spectroscopic imaging), nephron endowment (cationic-contrast imaging), sodium concentration (23Na-MRI) and molecular events (targeted-contrast imaging).

SUMMARY

Current advances in MRI techniques have enabled the noninvasive investigation of renal disease. Further development, evaluation and application of the MRI techniques should facilitate better understanding and assessment of renal disease, and the development of new imaging biomarkers, enabling the intensified treatment of high-risk populations and a more rapid interrogation of novel therapeutic agents and protocols.

Mapping murine diabetic kidney disease using chemical exchange saturation transfer MRI

PURPOSE

Diabetic nephropathy (DN) is the leading cause of renal failure; however, current clinical tests are insufficient for assessing this disease. DN is associated with changes in renal metabolites, so we evaluated the utility of chemical exchange saturation transfer (CEST) imaging to detect changes characteristic of this disease.

METHODS

Sensitivity of CEST imaging at 7 Tesla to DN was evaluated by imaging diabetic mice [db/db, db/db endothelial nitric oxide synthase (eNOS)-/-] that show different levels of nephropathy as well as by longitudinal imaging (8 to 24 weeks). Nondiabetic (db/m) mice were used as controls.

RESULTS

Compared with nondiabetic mice, the CEST contrasts of hydroxyl metabolites that correspond to glucose and glycogen were significantly increased in papilla (P), inner medulla (IM), and outer medulla (OM) in db/db and db/db eNOS-/- kidneys at 16 weeks. The db/db eNOS-/- mice that showed advanced nephropathy exhibited greater CEST effects in OM and significant CEST contrasts were also observed in cortex. Longitudinally, db/db mice exhibited progressive increases in hydroxyl signals in IM+P and OM from 12 to 24 weeks and an increase was also observed in cortex at 24 weeks.

CONCLUSION

CEST MRI can be used to measure changes of hydroxyl metabolites in kidney during progression of DN. Magn Reson Med 76:1531-1541, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Current MRI techniques for the assessment of renal disease

PURPOSE OF REVIEW

Over the past decade, a variety of MRI methods have been developed and applied to many kidney diseases. These MRI techniques show great promise, enabling the noninvasive assessment of renal structure, function and injury in individuals. This review will highlight the current applications of functional MRI techniques for the assessment of renal disease and discuss future directions.

RECENT FINDINGS

Many pathological (functional and structural) changes or factors in renal disease can be assessed by advanced MRI techniques. These include renal vascular structure and function (contrast-enhanced MRI, arterial spin labelling), tissue oxygenation (blood oxygen level dependent MRI), renal tissue injury and fibrosis (diffusion or magnetization transfer imaging, magnetic resonance elastography), renal metabolism (chemical exchange saturation transfer, spectroscopic imaging), nephron endowment (cationic-contrast imaging), sodium concentration (23Na-MRI) and molecular events (targeted-contrast imaging).

SUMMARY

Current advances in MRI techniques have enabled the noninvasive investigation of renal disease. Further development, evaluation and application of the MRI techniques should facilitate better understanding and assessment of renal disease, and the development of new imaging biomarkers, enabling the intensified treatment of high-risk populations and a more rapid interrogation of novel therapeutic agents and protocols.