Diffusion-weighted MRI in the assessment of split renal function: comparison of navigator-triggered prospective acquisition correction and breath-hold acquisition. AJR Am J Roentgenol. 2013;200:113-119. [PMID: 23255749 DOI: 10.2214/ajr.11.8052]

Comparing the clinical utility of single-shot, readout-segmented and zoomit echo-planar imaging in diffusion-weighted imaging of the kidney at 3 T

We compared the clinical utility of single-shot echo-planar imaging (SS-EPI) using different breathing schemes, readout-segmented EPI and zoomit EPI in the repeatability of apparent diffusion coefficient (ADC) measurements, cortico-medullary contrast to noise ratio (c-mCNR) and image quality. In this institutional review board-approved prospective study, some common clinically applicable diffusion-weighted imaging (b = 50, 400, 800 s/mm²) of kidney on 3.0 T MRI were performed on 22 volunteers using SS-EPI with breath-hold diffusion-weighted imaging (BH-DWI), free-breathing (FB-DWI), navigator-triggered (NT-DWI) and respiratory-triggered (RT-DWI), readout-segmented DWI (RS-DWI), and Zoomit DWI (Z-DWI). ADC and c-mCNR were measured in 12 anatomic locations (the upper, middle, and lower pole of the renal cortex and medulla), and image quality was assessed on these DWI sequences. A DWI with the optimal clinical utility was decided by systematically assessing the ADC repeatability, c-mCNR and image quality among the DWIs. For ADC measurements, Z-DWI had an excellent intra-observer agreement (intra-class correlation coefficients (ICCs): 0.876–0.944) and good inter-observer agreement (inter-class ICCs: 0.798–0.856) in six DWI sequences. Z-DWI had the highest ADC repeatability in most of the 12 anatomic locations of the kidneys (mean ADC absolute difference: 0.070–0.111 × 10⁻³ mm²/s, limit of agreement: 0.031–0.056 × 10⁻³ mm²/s). In all DWIs, Z-DWI yielded a slightly higher c-mCNR than other DWIs in most representative locations (P > 0.05), which was significantly higher than BH-DWI and FB-DWI in the middle pole of both kidneys and the upper pole of the left kidney (P < 0.05). In addition, Z-DWI yielded image quality that was similar to RT-DWI and NT-DWI (P > 0.05) and superior to BH-DWI, FB-DWI and RS-DWI (P < 0.05). Our results suggest that Z-DWI provides the highest ADC reproducibility, better c-mCNR and good image quality on 3.0 T MRI, making it the recommended sequence for clinical DWI of the kidney.

Evaluation of Renal Function in Obstructed Ureter Model Using 99mTc-DMSA

BACKGROUND/AIM

Urinary obstruction is a condition of impaired urinary drainage, which may result in progressive renal deterioration. This study applied ^99mTc-labeled dimercaptosuccinic acid (^99mTc-DMSA) renal scintigraphy to a rabbit model of right ureter obstruction and evaluated its utility in studying obstructive renal diseases.

MATERIALS AND METHODS

Complete unilateral ureter obstruction in rabbits was generated by complete ligation of the right ureter. Renal function was investigated during a 4-week post-obstruction period by obtaining planar images of ^99mTc-DMSA activity following ear vein injection. Renal blood perfusion was evaluated by non-invasive scintigraphy in conjunction with parallel histological and hematological examinations.

RESULTS

Renal perfusion was remarkably and rapidly reduced in the ureter-obstructed kidneys. During the experimental period, the size of left kidney appeared normal in the scintigraphic images, but the ureter-obstructed right kidney progressively became larger. Histopathological examination showed flattening and atrophy of tubules, enlargement of interstitial areas, accumulation of extracellular martices and infiltration of inflammatory cells in the obstreucted kidney.

CONCLUSION

^99mTc-DMSA scintigraphy is a sensitive, non-invasive method to assess renal function in unilateral kidney diseases.

Renal Diffusion-Weighted Imaging (DWI) for Apparent Diffusion Coefficient (ADC), Intravoxel Incoherent Motion (IVIM), and Diffusion Tensor Imaging (DTI): Basic Concepts

The specialized function of the kidney is reflected in its unique structure, characterized by juxtaposition of disorganized and ordered elements, including renal glomerula, capillaries, and tubules. The key role of the kidney in blood filtration, and changes in filtration rate and blood flow associated with pathological conditions, make it possible to investigate kidney function using the motion of water molecules in renal tissue. Diffusion-weighted imaging (DWI) is a versatile modality that sensitizes observable signal to water motion, and can inform on the complexity of the tissue microstructure. Several DWI acquisition strategies are available, as are different analysis strategies, and models that attempt to capture not only simple diffusion effects, but also perfusion, compartmentalization, and anisotropy. This chapter introduces the basic concepts of DWI alongside common acquisition schemes and models, and gives an overview of specific DWI applications for animal models of renal disease.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by two separate chapters describing the experimental procedure and data analysis.

Comparison of free breathing and respiratory triggered diffusion-weighted imaging sequences for liver imaging

BACKGROUND

Diffusion-weighted imaging (DWI) has become a useful tool in the detection, characterization, and evaluation of response to treatment of many cancers, including malignant liver lesions. DWI offers higher image contrast between lesions and normal liver tissue than other sequences. DWI images acquired at two or more b-values can be used to derive an apparent diffusion coefficient (ADC). DWI in the body has several technical challenges. This include ghosting artifacts, mis-registration and susceptibility artifacts. New DWI sequences have been developed to overcome some of these challenges. Our goal is to evaluate 3 new DWI sequences for liver imaging.

AIM

To qualitatively and quantitatively compare 3 DWI sequences for liver imaging: free-breathing (FB), simultaneous multislice (SMS), and prospective acquisition correction (PACE).

METHODS

Magnetic resonance imaging (MRI) was performed in 20 patients in this prospective study. The MR study included 3 separate DWI sequences: FB-DWI, SMS-DWI, and PACE-DWI. The image quality, mean ADC, standard deviations (SD) of ADC, and ADC histogram were compared. Wilcoxon signed-rank tests were used to compare qualitative image quality. A linear mixed model was used to compare the mean ADC and the SDs of the ADC values. All tests were 2-sided and P values of < 0.05 were considered statistically significant.

RESULTS

There were 56 lesions (50 malignant) evaluated in this study. The mean qualitative image quality score of PACE-DWI was 4.48. This was significantly better than that of SMS-DWI (4.22) and FB-DWI (3.15) (P < 0.05). Quantitatively, the mean ADC values from the 3 different sequences did not significantly differ for each liver lesion. FB-DWI had a markedly higher variation in the SD of the ADC values than did SMS-DWI and PACE-DWI. We found statistically significant differences in the SDs of the ADC values for FB-DWI vs PACE-DWI (P < 0.0001) and for FB-DWI vs SMS-DWI (P = 0.03). The SD of the ADC values was not statistically significant for PACE-DWI and SMS-DWI (P = 0.18). The quality of the PACE-DWI ADC histograms were considered better than the SMS-DWI and FB-DWI.

CONCLUSION

Compared to FB-DWI, both PACE-DWI and SMS-DWI provide better image quality and decreased quantitative variability in the measurement of ADC values of liver lesions.

The Accuracy of Renal Function Measurements in Obstructive Hydronephrosis Using Dynamic Contrast-Enhanced MR Renography

OBJECTIVE. The objective of our study was to assess the accuracy of glomerular filtration rate (GFR) evaluation in patients with obstructive hydronephrosis using dynamic contrast-enhanced MR renography (DCE-MRR). MATERIALS AND METHODS. A group of 28 adult volunteers were enrolled in this study: 13 without hydronephrosis, eight with low-grade hydronephrosis, and seven with high-grade hydronephrosis. The GFR obtained from DCE-MRR (GFR_MRR) and the GFR obtained from renal scintigraphy (GFR_RS) were compared with the reference GFR (GFR_Ref) acquired using the two plasma sample method. The correlation and agreement between GFR_MRR and GFR_Ref, GFR_RS and GFR_Ref, and single-kidney GFR_MRR (skGFR_MRR) and single-kidney GFR_RS (skGFR_RS) were assessed. The interrater reliability of DCE-MRR and the interrater reliability of renal scintigraphy (RS) were measured. RESULTS. Both GFR_MRR and GFR_RS correlated well with GFR_Ref. In patients with hydronephrosis, DCE-MRR and RS overestimated GFR by 12.8 ± 13.9 mL/min (mean ± SD) and 11.5 ± 12.3 mL/min, respectively. The skGFR_RS was higher than skGFR_MRR by 5.7 ± 3.8 mL/min in high-grade hydronephrotic kidneys (p = 0.004). Good interrater reliability was observed for skGFR_MRR (intraclass correlation coefficient [ICC] = 0.82-0.92) and skGFR_RS (ICC = 0.79-0.90) for both nonhydronephrotic kidneys and hydronephrotic kidneys. The overall mean SDs of repeated measurements from three investigators were 4.0 and 3.8 mL/min for skGFR_MRR and skGFR_RS, respectively. CONCLUSION. Both DCE-MRR and RS tend to overestimate GFR in patients with hydronephrosis. RS-derived skGFR is slightly higher than that of DCE-MRR in kidneys with high-grade hydronephrosis. DCE-MRR is comparable to RS and may serve as an alternative noninvasive method for GFR measurement.

Diffusion-weighted magnetic resonance imaging to assess diffuse renal pathology: a systematic review and statement paper

Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive method sensitive to local water motion in the tissue. As a tool to probe the microstructure, including the presence and potentially the degree of renal fibrosis, DWI has the potential to become an effective imaging biomarker. The aim of this review is to discuss the current status of renal DWI in diffuse renal diseases. DWI biomarkers can be classified in the following three main categories: (i) the apparent diffusion coefficient-an overall measure of water diffusion and microcirculation in the tissue; (ii) true diffusion, pseudodiffusion and flowing fraction-providing separate information on diffusion and perfusion or tubular flow; and (iii) fractional anisotropy-measuring the microstructural orientation. An overview of human studies applying renal DWI in diffuse pathologies is given, demonstrating not only the feasibility and intra-study reproducibility of DWI but also highlighting the need for standardization of methods, additional validation and qualification. The current and future role of renal DWI in clinical practice is reviewed, emphasizing its potential as a surrogate and monitoring biomarker for interstitial fibrosis in chronic kidney disease, as well as a surrogate biomarker for the inflammation in acute kidney diseases that may impact patient selection for renal biopsy in acute graft rejection. As part of the international COST (European Cooperation in Science and Technology) action PARENCHIMA (Magnetic Resonance Imaging Biomarkers for Chronic Kidney Disease), aimed at eliminating the barriers to the clinical use of functional renal magnetic resonance imaging, this article provides practical recommendations for future design of clinical studies and the use of renal DWI in clinical practice.

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.

Renal fat fraction and diffusion tensor imaging in patients with early-stage diabetic nephropathy

OBJECTIVE

To investigate the renal fat fraction and water molecular diffusion features in patients with early-stage DN using Dixon imaging and diffusion tensor imaging (DTI).

METHODS

Sixty-one type 2 diabetics (normoalbuminuria: n = 40; microalbuminuria: n = 21) and 34 non-diabetic volunteers were included. All participants received three-point Dixon imaging and DTI using a 3.0-T magnetic resonance imager. The fat fraction [FF] and DTI features [fractional anisotropy (FA), apparent diffusion coefficient (ADC), tract counts and length from DTI tractography] were collected. All image features were compared between cohorts using one-way ANOVA with Bonferroni post-hoc analysis.

RESULTS

Renal FF in the microalbuminuric group was significantly higher than in the normoalbuminuric and control groups (5.6% ± 1.3%, 4.7% ± 1.1% and 4.3% ± 0.5%, respectively; p < 0.001). Medullary FA in the microalbuminuric group was the lowest (0.31 ± 0.06) in all cohorts. The tract counts and length in the renal medulla were significantly lower in the microalbuminuric group than in the other two groups.

CONCLUSIONS

Dixon imaging and DTI are able to detect renal lipid deposition and water molecule diffusion abnormalities in patients with early-stage DN. Both techniques have the potential to noninvasively evaluate early renal impairment in type 2 diabetes.

KEY POINTS

• Dixon imaging demonstrated renal fat deposition in early-stage DN; • Renal fractional anisotropy decreased in patients with early-stage DN; • Renal tractography demonstrated reduced track counts and length in early-stage DN.

Estimation of Split Renal Function With 99mTc-DMSA SPECT: Comparison Between 3D Volumetric Assessment and 2D Coronal Projection Imaging

OBJECTIVE

Split renal function (SRF) can be estimated with ^99mTc-labeled dimercaptosuccinic acid (DMSA) SPECT cortical renal scintigraphy on either 2D projected images or 3D images. The purpose of this study was to determine whether there is a significant difference between SRF values calculated with the 2D method and those calculated with the 3D method.

MATERIALS AND METHODS

This retrospective study was performed with ^99mTc-DMSA SPECT images of 316 patients (age range, 1-26 years). All images were reconstructed by filtered back projection. An automated computational method was developed to estimate SRF using both 2D projection images and direct 3D images. A paired t test was used to evaluate the difference between SRFs determined with the two methods and the association between the magnitude of the differences and kidney size, patient age, and SRF.

RESULTS

There was strong correlation between SRFs estimated with the 2D and 3D methods (r = 0.94, p < 0.001). There was small significant difference (0.14% ± 0.86%, p = 0.003) in SRFs obtained with the two methods. The difference was clinically negligible and independent of renal length (p = 0.698), volume (p = 0.297), and patient age (p = 0.768) but was associated with SRF (p = 0.018).

CONCLUSION

For determination of split renal function, ^99mTc-DMSA SPECT renal scintigraphy 2D coronal projection images perform as well as and are simpler to analyze than 3D images.

Renal function impairment in liver cirrhosis: preliminary results with diffusion-weighted imaging at 3 T

OBJECTIVE

The purpose of this study was to investigate the utility of diffusion-weighted MRI (DWI) at 3 T for assessing renal function impairment in patients with liver cirrhosis.

MATERIALS AND METHODS

Sixty-four patients with liver cirrhosis who underwent both DWI at 3 T and renal function testing were retrospectively included. Twenty-two patients had moderate or severe renal function impairment (group A, estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m(2)) and 42 had good renal function or mild renal function impairment (group B, eGFR ≥ 60 mL/min/1.73 m(2)). Cortical and medullary apparent diffusion coefficients (ADCs) of both kidneys were measured. AUC was assessed for predicting group A with ADC. The correlation between renal ADC and eGFR or serum creatinine was analyzed. The reproducibility of ADC measurement was investigated.

RESULTS

Both cortical and medullary ADCs were lower in group A than in group B, (both, p < 0.05). In all patients, AUCs were 0.784 and 0.737 with cortical and medullary ADCs, respectively, for predicting group A. Both cortical and medullary ADCs had linear correlation with eGFR or serum creatinine (both, p < 0.05). The reproducibility of measurement was excellent for cortex (intraclass coefficient [ICC] = 0.808) and good for medulla (ICC = 0.692), with 1.6% or less variability.

CONCLUSION

DWI may have potential for assessing renal function impairment in patients with liver cirrhosis.