Using Ultrahigh b -Value Diffusion-Weighted Imaging to Noninvasively Assess Renal Fibrosis in a Rabbit Model of Renal Artery Stenosis.

OBJECTIVE: This study aimed to investigate the feasibility of diffusion-weighted imaging with ultrahigh b values ( ub DWI) for the evaluation of renal fibrosis (RF) induced by renal artery stenosis (RAS) in a rabbit model. METHODS: Thirty-two rabbits underwent left RAS operation, whereas 8 rabbits received sham surgery. All rabbits underwent ub DWI ( b = 0-4500 s/mm 2 ). The standard apparent diffusion coefficient (ADC st ), molecular diffusion coefficient ( D ), perfusion fraction ( f ), perfusion-related diffusion coefficient ( D *) and ultrahigh apparent diffusion coefficient (ADC uh ) were longitudinally assessed before operation and at weeks 2, 4, and 6 after operation. The degree of interstitial fibrosis and the expression of aquaporin (AQP) 1 and AQP2 were determined through pathological examination. RESULTS: In the stenotic kidney, the ADC st , D , f , and ADC uh values of the renal parenchyma significantly decreased compared with those at baseline (all P < 0.05), whereas the D * values significantly increased after RAS induction ( P < 0.05). The ADC st , D , D *, and f were weakly to moderately correlated with interstitial fibrosis as well as with the expression of AQP1 and AQP2. Furthermore, the ADC uh negatively correlated with interstitial fibrosis ( ρ = -0.782, P < 0.001) and positively correlated with AQP1 and AQP2 expression ( ρ = 0.794, P < 0.001, and ρ = 0.789, P < 0.001, respectively). CONCLUSIONS: Diffusion-weighted imaging with ultrahigh b values shows the potential for noninvasive assessment of the progression of RF in rabbits with unilateral RAS. The ADC uh derived from ub DWI could reflect the expression of AQPs in RF.

Particle size distribution inversion using the Weibull-distribution adaptive-parameters cuckoo search algorithm.

A Weibull-distribution adaptive-parameters cuckoo search (WACS) algorithm is proposed, which can converge quickly and prevent falling into local optimal values, and thus improve the global search performance of a cuckoo search (CS) algorithm. In simulations, particle size inversions were performed using the proposed algorithm for unimodal and bimodal particle systems obeying Johnson's SB, Rosin-Rammler, and normal distribution, and the results were compared to the original CS algorithm, Weibull-distribution CS algorithm, and adaptive-parameters CS algorithm. Among them, the WACS algorithm has the best accuracy. The relative root mean squared error (RRMSE) was three to four orders of magnitude lower than the CS algorithm. The noise immunity of the algorithm was verified by comparing the particle size inversion error. Random noise [1%, 10%] was added to the scattered light energy of the target function, in 1% noise increments. The WACS algorithm prevailed, and the advantage became more obvious as the noise increased. A small-angle forward scattering experimental platform was built, and ferric tetroxide particles were selected as the measured particles. Experimental measurements were carried out on a unimodal particle system (50 µm) and bimodal particle system (50 and 100 µm), while the WACS algorithm was used on particle size distribution inversion. Compared to the CS algorithm, the RRMSE of the WACS algorithm was approximately 51% lower on unimodal and 66% lower on bimodal particle population inversions.

Value of T2 Mapping in the Dynamic Evaluation of Renal Ischemia-Reperfusion Injury.

OBJECTIVE: To explore the value of T2 mapping in the dynamic quantitative evaluation of renal ischemia- reperfusion injury (IRI). MATERIALS AND METHODS: Forty-eight healthy New Zealand rabbits were randomly divided into IRI group (n = 40) and control group (n = 8). Rabbits in the IRI group underwent left renal artery clamping for 60 minutes. Rabbits underwent MRI examinations (T2WI and T2 mapping) before and 1, 12, 24, and 48 hours after IRI. The inter-observer and intra-observer reproducibility of the T2 values were assessed using the intraclass correlation coefficient (ICC) with 95% confidence interval (CI). Correlations between the T2 value of the renal outer medulla and injury scores were assessed by Spearman correlation analysis. The repeated measures analysis of variance was used to compare the differences in T2 values of the IRI and control group across the different time points. RESULTS: Both of the intra-observer (ICC = 0.97, 95% CI 0.95-0.99) and inter-observer reproducibility (ICC = 0.92, 95% CI 0.86-0.96) were excellent for T2 values. The T2 value of the renal outer medulla was moderately positive correlated with tubular epithelial edema (ρ = 0.686, p < 0.001). In IRI group, T2 values of the renal outer medulla were increase at 1 h after IRI (p = 0.001) and were decrease from 1 h to 12 h (p = 0.002). At 1 h after IRI, the T2 values of the renal outer medulla for the IRI group were higher than those for the control group (p < 0.001). CONCLUSION: T2 mapping can reflect the dynamic changes of renal parenchyma in an animal model of IRI and be used to assess the early renal IRI.

Evaluation of renal ischemia-reperfusion injury by magnetic resonance imaging texture analysis: An experimental study.

PURPOSE: To explore the value of MRI texture analysis in evaluating the presence and severity of early renal ischemia-reperfusion injury (IRI). METHODS: Healthy New Zealand rabbits were used (IRI group, N = 54; control group, N = 8). Rabbits in the IRI group underwent left renal artery clamping for 60 minutes. Magnetic resonance imaging was performed before and at 1, 12, 24, and 48 hours after IRI. The relationship between MRI texture features and histopathology parameters was assessed using Pearson's correlation coefficients. The diagnostic performance of texture features in kidney differentiation at different time points was assessed by receiver operating characteristic curve analysis. RESULTS: T2 WI_S(3,-3)Inverse_Difference_Moment had the strongest correlation with brush border destruction, tubular epithelial edema, necrosis, and cast (r = 0.56, -0.58, 0.62, and 0.69, respectively; all P < .001). BOLD_S(4,-4)Correlation had the strongest correlation with interstitial inflammatory cell infiltration (r = 0.63, P < .001). SWI_S(4,4)Difference_Entropy had the strongest correlation with microvessel density (r = 0.61, P < .001). The areas under the curve for T2 WI_S(3,-3)Inverse_Difference_Moment, SWI_S(4,4)Difference_Entropy, and BOLD_S(4,-4)Correlation in kidney differentiation before IRI and that at 1 and 12 hours after reperfusion were 0.76, 0.72, and 0.70, respectively; the values before IRI and at 24 and 48 hours after reperfusion were 0.84, 0.81, and 0.69, respectively. The area under the curve for T2 WI_S(3,-3)Inverse_Difference_Moment in kidney differentiation at 1 and 12 hours after reperfusion and that at 24 and 48 hours after reperfusion was 0.66. CONCLUSION: Magnetic resonance imaging texture analysis can be used for evaluating the presence and severity of early renal IRI.

The role of MRI texture analysis based on susceptibility-weighted imaging in predicting Fuhrman grade of clear cell renal cell carcinoma.

BACKGROUND: The Fuhrman nuclear grade system is one of the most important independent indicators in patients with clear cell renal cell carcinoma (ccRCC) for aggressiveness and prognosis. Preoperative assessment of tumor aggressiveness is important for surgical decision-making. PURPOSE: To explore the role of magnetic resonance imaging (MRI) texture analysis based on susceptibility-weighted imaging (SWI) in predicting Fuhrman grade of ccRCC. MATERIAL AND METHODS: A total of 45 patients with SWI and surgically proven ccRCC were divided into two groups: the low-grade group (Fuhrman I/II, n = 29) and the high-grade group (Fuhrman III/IV, n = 16). Texture features were extracted from SWI images. Feature selection was performed, and multivariable logistic regression analysis was performed to develop the SWI-based texture model for grading ccRCCs. Receiver operating characteristic (ROC) curve analysis and leave-group-out cross-validation (LGOCV) were performed to test the reliability of the model. RESULTS: A total of 396 SWI-based texture features were extracted from each SWI image. The SWI-based texture model developed by multivariable logistic regression analysis was: SWIscore = -0.59 + 1.60 * ZonePercentage. The area under the ROC curve of the SWI-based texture model for differentiating high-grade ccRCC from low-grade ccRCC was 0.81 (95% confidence interval 0.67-0.94), with 80% accuracy, 56.25% sensitivity, and 93.10% specificity. After 100 LGOCVs, the mean accuracy, sensitivity, and specificity were 90.91%, 91.83%, and 89.89% for the training sets, and 77.29%, 80.52%, and 71.44% for the test sets, respectively. CONCLUSION: SWI-based texture analysis might be a reliable quantitative approach for differentiating high-grade ccRCC from low-grade ccRCC.

Assessment of delayed graft function using susceptibility-weighted imaging in the early period after kidney transplantation: a feasibility study.

PURPOSE: This study aimed to explore the feasibility of susceptibility-weighted imaging (SWI) for evaluating delayed graft function (DGF) during the early posttransplantation period. METHODS: Sixty-nine recipients who accepted allograft renal transplantation underwent SWI during the second posttransplantation week. Renal allograft function was estimated via the glomerular filtration rate. Recipients with and without DGF were identified. For each transplanted kidney, the presence of abnormal signal intensity lesions (ASILs), excluding benign lesions, on SWI was assessed. Renal allograft function was compared between the recipients with and without ASILs. The correlation between ASILs and renal allograft function was tested by Spearman's rank correlation analysis. RESULTS: Thirty-four recipients were diagnosed with DGF, while 35 recipients showed no DGF. In the DGF group, 16 recipients had low-intensity ASILs, primarily at the corticomedullary junction of transplanted kidneys on SWI, and no ASILs were found in 18 recipients. In the non-DGF group, none of the recipients showed ASILs on SWI. In the DGF group, the renal allograft function among the 16 recipients with low-intensity ASILs was significantly lower than that among the other 18 recipients (8.5 ± 4.2 vs. 19.7 ± 9.7 mL/min, P < 0.001). The presence of low-intensity ASILs on SWI showed a moderate negative correlation with renal allograft function in recipients with DGF (r = - 0.553, P = 0.001). CONCLUSION: SWI can be used to evaluate DGF in the early post-kidney transplantation period.

Evaluating Renal Fibrosis with R2* Histogram Analysis of the Whole Cortex in a Unilateral Ureteral Obstruction Model.

RATIONALE AND OBJECTIVES: The aim of this study was to use histogram analysis to assess the correlation between blood oxygen-level dependent magnetic resonance imaging (BOLD-MRI) and renal fibrosis induced by unilateral ureteral obstruction (UUO) in an animal model for a long experimental period. MATERIALS AND METHODS: The rabbits were randomly divided into a control group (n = 6) and a UUO group (n = 30). The rabbits in the UUO group underwent left ureteral obstruction surgery. BOLD-MRI examinations were performed at 2, 4, 6, and 8 weeks after ligation. After the examinations, nephrectomy was performed for histologic evaluation. Histogram analysis of the left renal cortex (C) R2* values was performed to measure the mean, median, 10th percentile, 90th percentile, skewness, and kurtosis for all kidneys. Masson trichrome staining was used to assess the percentage of fibrotic area. RESULTS: The histogram R2* values of the mean, median, 10th percentile, and 90th percentile at week 2 were all lower than those at baseline. Over the course of UUO progression, there were statistical differences between the histogram R2* values at any other two time points, except between weeks 4 and 6, and weeks 6 and 8. A close correlation was found between the percentage of fibrotic area and R2* values (mean: F = 21.49, p = 0.0001, R2 = 0.49, median: F = 30.07, p < 0.0001, R2 = 0.58, 10th percentile: F = 31.02, p < 0.0001, R2 = 0.59, 90th percentile: F = 24.13, p < 0.0001, R2 = 0.52). CONCLUSION: BOLD-MRI could reflect the formation and progression of renal fibrosis in a rabbit UUO model; however, the value of BOLD-MRI in the long-term evaluation of fibrosis is limited.

Fat status detection and histotypes differentiation in solid renal masses using Dixon technique.

PURPOSE: To detect fat status and differentiate histotypes of renal masses by using Dixon technique. MATERIALS AND METHODS: This study included 134 solid renal masses. Signal intensity index (SII) and fat fraction (FF) in different histotypes were compared. RESULTS: Only angiomyolipoma (AML), clear cell renal cell carcinoma (RCC), and papillary RCC were confirmed to contain fat. The FF of 16.8% can effectively differentiate AML from clear cell RCC, so did the SII of 9.2% can differentiate clear cell RCC from non-clear cell RCC and rare benign histotypes. CONCLUSION: Dixon technique successfully evaluated the fat status and histotypes of renal masses.

Longitudinal assessment of rabbit renal fibrosis induced by unilateral ureteral obstruction using two-dimensional susceptibility weighted imaging.

BACKGROUND: Previous studies indicated that two-dimensional-susceptibility weighted imaging (2D-SWI) could serve as a useful biomarker for differentiating the grade of liver fibrosis. PURPOSE: To evaluate the feasibility of 2D-SWI in the dynamic quantification of renal fibrosis in a rabbit model. STUDY TYPE: Longitudinal study. ANIMAL MODEL: Twenty-Four New Zealand White Rabbits including control group (n = 4); and renal fibrosis group (n = 20), by means of a unilateral ureteral obstruction (UUO) model. FIELD STRENGTH/SEQUENCE: The 3.0 T SWI using a 2D gradient-echo sequence. ASSESSMENT: The relative SWI signal ratio(r) of cortical and medulla (r = SIrenal /SImuscle ) was longitudinally assessed before ligation and on weeks 2, 4, 6, and 8 following ligation. Sirius Red staining was used to assess the degree of fibrosis in five high-power fields. STATISTICAL TESTS: The repeated measures of analysis of variance and linear regression analysis. RESULTS: Both the cortical and medullary r values were significantly higher in the UUO kidneys at week 2 compared with the kidneys before ligation. Over the course of UUO progression, significant changes occurred in the cortical and medullary r values in vivo and fibrosis scores in vitro (all P values < 0.05). The r values gradually decreased, while the fibrosis scores gradually increased over 8 weeks following ligation. The linear regression analysis showed a strong and significant correlation between cortical and medullary r values and the pathologic fibrosis scores (R2 = 0.91, 0.81, respectively). DATA CONCLUSION: The SWI sequence could provide a quantitative evaluation of renal fibrosis during UUO progression. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:1572-1577.

[Evaluate the early changes of renal ischemia-reperfusion by susceptibility weighted imaging:primary experiment study].

OBJECTIVE: To explore whether susceptibility weighted imaging (SWI) could diagnose the early changes of renal IRI in vivo by modeling the renal ischemia-reperfusion (IRI) of rabbit. METHODS: Thrity four New Zealand white rabbits were chosen, the vesseles of the left kidney of rabbits were ligated for 60 minutes, then the renal ischemia-reperfusion model was established. Respectively, the rabbits before ligation, 0.5, 24 and 48 h after the ligation, were examined with MR, then the signal of the cortex and medulla was analyzed in SWI and T2WI, the imaging features were compared with histopathology. RESULTS: The inner medullary of renal showed high signal, low signal in the outer medulla and mildly high in the cortex before ligation in T2WI sequence, which showed the typical three-band signal distribution, while the outer medulla showed wildly hypo-signal in SWI, the remnants showed high signal; kidney swelled significantly 0.5 hour after ligation, the stripe of cortex became thin, however, the inner medulla and outer medulla widened. The hypo-signal of the outer medulla faded, while the signal of inner medullary and cortical slightly elevated. The signal intensity of outer medulla lowered more obviously in SWI, the margin of the cortex and medulla became more clearly 24 and 48 h after ligation,However the signal of the outer medulla was higher than normal kidney in the SWI, and punctuate or stripe haemorrhage occurred in the outer medulla. Respectively, the number of punctuate, stripe haemorrhage detected by SWI in the out medulla of kidney 0.5, 24 and 48 h after ligation were 0, 2.50, 6.75 (F=52.17, P<0.01), Meanwhile, the number detected by T2WI was 0, 1.13, 2.88 (F=15.65, P<0.01); the number of hemorrhage which was detected by SWI and T2WI in the outer medulla among different timepoint have the statistical significance (t=4.83, P<0.01). CONCLUSION: SWI can clearly show early changes in IRI-renal, especially in the outer medulla of the renal, the technique was helpful to assess the early changes of renal IRI.