Diffusional kurtosis imaging of kidneys in patients with hyperuricemia: initial study

Renal MRI: From Nephron to NMR Signal

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

Preliminary Feasibility Study on Diffusion Kurtosis Imaging to Monitor the Early Functional Alterations of Kidneys in Streptozocin-Induced Diabetic Rats

RATIONALE AND OBJECTIVES

The aim of this study was to investigate the potential of diffusion kurtosis imaging (DKI) to assess the early renal functional undulation of diabetic mellitus (DM).

MATERIALS AND METHODS

Fifty-seven Sprague-Dawley (SD) rats were randomly divided into two groups and eventually 48 rats were included in this study: the normal control (CON) group and diabetic mellitus (DM) group. Weeks 0, 4, 8, and 12 after the diabetes model was successfully established, all the rats were scanned on the 3.0T MRI. The DKI derived parameters of renal parenchyma, including fractional anisotropy (FAco, FAme), mean diffusivity (MDco, MDme), and mean kurtosis (MKco, MKme) were measured. Their alteration over time was analyzed and then correlated with urine volume (UV), blood urea nitrogen (BUN), and serum creatinine (Scr) using Pearson correlation analysis. Finally, hematoxylin and eosin (H&E) staining was performed on the kidneys of the two groups.

RESULT

There was a decreasing trend in FA, MK, and MD values over time in diabetic rats. Also, the gradually worsening histological damage of kidneys was noted over time in diabetic rats. The cortical FA and MK values and medullary FA, MK and MD values of diabetic rats were significantly lower than those of controls at most time points after DM induction. In addition, negative correlations were revealed between the BUN and FAco (r = -0.43, p = 0.03) or FAme value (r = -0.49, p = 0.01). The cortical MK value was moderately correlated with UV (r = -0.46, p = 0.03) and BUN (r = -0.55, p = 0.01).

CONCLUSION

The preliminary findings suggest that DKI might be an effective and sensitive tool to assess the early changes of renal function impairment in diabetic rats. The FA values of the cortex and medulla and the MK value of the cortex are sensitive markers in detecting renal injury in diabetic rats.

Renal functional and interstitial fibrotic assessment with non-Gaussian diffusion kurtosis imaging

OBJECTIVES

To evaluate the application value of diffusion kurtosis imaging (DKI) for monitoring renal function and interstitial fibrosis.

METHODS

Forty-two patients suspected of having primary nephropathy, hypertension or diabetes with impaired renal function were examined with DKI. DKI metrics of renal cortex and medulla on both sides of each patient were measured, including mean kurtosis (MK), axial kurtosis (Ka), radial kurtosis (Kr), mean diffusivity (MD) and fractional anisotropy (FA). The differences in DKI metrics between stable and impaired estimated glomerular filtration rate (eGFR) patients as well as between mild and severe interstitial fibrosis patients were compared. Correlations of DKI metrics with clinical indicators and pathology were analyzed. Diagnostic performance of DKI to assess the degree of renal dysfunction was analyzed.

RESULTS

Cortical MK, parenchymal Ka, MD and medullary FA were different in stable vs impaired eGFR patients and mild vs severe interstitial fibrosis patients (all p < .05). Negative correlation was found between Ka and eGFR (cortex: r = - 0.579; medulla: r = - 0.603), between MD and interstitial fibrosis (cortex: r = - 0.899; medulla: r = - 0.770), and positive correlation was found between MD and eGFR (cortex: r = 0.411; medulla: r = 0.344), between Ka and interstitial fibrosis (cortex: r = 0.871; medulla: r = 0.844) (all p < .05). DKI combined with mean arterial blood pressure (MAP) and urea showed good diagnostic power for assessing the degree of renal dysfunction (sensitivity: 90.5%; specificity: 89.5%).

CONCLUSIONS

Noninvasive DKI has certain application value for monitoring renal function and interstitial fibrosis.

Pathological assessment of chronic kidney disease with DWI: Is there an added value for diffusion kurtosis imaging?

BACKGROUND

Chronic kidney disease (CKD) is a worldwide health problem, precise functional and pathological assessment is beneficial to better treatment. Diffusion kurtosis imaging (DKI) can evaluate non-Gaussian diffusion and may help to assess renal pathology and function.

PURPOSE

To assess pathological and functional alterations in CKD using DKI compared with diffusion-weighted imaging (DWI).

STUDY TYPE

Prospective study.

POPULATION

70 CKD patients and 20 healthy volunteers.

FIELD STRENGTH

1.5 T.

ASSESSMENT

All participants underwent DKI, and apparent diffusion coefficient (ADC), mean diffusivity (MD), and mean kurtosis (MK) of renal parenchyma were acquired. Correlation between renal parenchymal ADC, MD, MK, and estimated glomerular filtration rate (eGFR), pathological scores were assessed. The diagnostic efficacy of ADC, MD, and MK for assessing the degree of renal pathological injury were compared.

STATISTICAL TESTS

ANOVA, Spearman correlation analysis, and ROC curve analysis.

RESULTS

The cortical ADC, MD were significantly higher than medulla for all participants, whereas medullary MK was significantly higher than cortex (P < 0.01). Whether eGFR reduced or not, renal parenchymal MK were significantly higher in patients than controls (P < 0.05). Positive correlation was found between eGFR and ADC (cortex, r = 0.562; medulla, r = 0.527), and negative correlation between eGFR and MK (cortex, r = -0.786; medulla, r = -0.709) (all P < 0.001). There was positive correlation between MK and glomerular injury (cortex, r = 0.681; medulla, r = 0.652), tubulointerstitial lesion (cortex, r = 0.650; medulla, r = 0.599) (all P < 0.001). For discrimination between mild and m-s renal injury group, the AUC values of ADC, MD, MK were cortex: 0.723, 0.655, 0.864 and medulla: 0.718, 0.581, 0.829. The AUC values of ADC, MD, MK were cortex: 0.708, 0.679, 0.770 and medulla: 0.713, 0.830, 0.780 for differentiating control group from mild renal injury group.

DATA CONCLUSION

DKI is practicable for noninvasive assessment of renal pathology and function of CKD, DKI offer better diagnostic performance than DWI. Evidence Level 1 Technical Efficacy 2.

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.