Application Of Diffusion Weighted Magnetic Resonance Imaging In The Diagnostic Of Focal Renal Tumors

Part I ADC Histogram Analysis:Differentiation of clear cell Renal Cell Carcinoma from non-clear cell Renal Cell Carcinoma at r-Fov DWIObjective:To explore the utility of ADC histogram analysis for differentiation of clear cell renal cell carcinoma（ccRCC）and non-clear cell renal cell carcinoma（non-ccRCC）at r-Fov DWI.Methods:We retrospectively evaluated 66 renal tumors（46 patients with 47 ccRCCs and 18 patients with 19 non-ccRCCs）in 64 patients who underwent preoperative routine renal MRI sequences and r-FOV DWI.The whole-lesion ADC assessments,including ADC mean、ADC median、ADC₅th、ADC₂5th、ADC₇5th、ADC₉5^th、skew and kurtosis,were performed for each patient.All Histogram-derived ADC parameters between ccRCC and non-ccRCC were compared by using the Student’s t test or Mann–Whitney U test depending on homogeneity of variance.Receiver operating characteristic analysis was used for assessing the diagnostic performance of ADC histogram in distinguishing the 2 groups.Results:ADC histograms of the non-ccRCC group were mostly skewed positively,while the curves of ccRCC were largely skewed negatively.Mean ADC,median ADC,5th percentile ADC,25th percentile ADC,75th percentile ADC,95th percentile ADC（all P<0.05）were significantly lower in non-ccRCC,while skewness was significantly higher in non-ccRCC（P<0.05）.Kurtosis had no significant difference between those 2 groups（P>0.05）.75th percentile ADC achieved the highest AUC（0.987）in differentiating ccRCC and non-ccRCC,with a cutoff value of 1.81×10^-3mm²/s,and a sensitivity of 100.0%and a specificity of 94.7%.Conclusion:ADC histograms of r-FOV DWI might be helpful for differentiating ccRCC from non-ccRCC,and 75th percentile ADC had the highest diagnostic accuracy.Part II Monoexponential,Biexponential,and Stretched exponential Diffusion-weighted Imaging Models: Quantitative Biomarkers for Differentiating Renal Clear Cell Carcinoma and Minimal Fat AngiomyolipomaObjective: To explore various diffusion parameters obtained from monoexponential,biexponential,and stretched exponential Diffusion-weighted imaging models in differentiating between Minimal Fat Angiomyolipoma（MFAML）and clear cell Renal Cell Carcinoma（cc RCC）.Methods: One hundred and thirty-one patients with pathologically confirmed MFAML（n=27）or cc RCC（n=104）underwent multi-b values DWI（0¹700 sec/mm2）imaging at 3.0T MRI.An isotropic apparent diffusion coefficient（ADC）was calculated from diffusion-weighted images by using a monoexponential model.A pseudo-ADC（Dp）,true ADC（Dt）and perfusion fraction（fp）were calculated from diffusion-weighted images by using a biexponential model.A water molecular diffusion heterogeneity index（α）and distributed diffusion coefficient（DDC）were calculated from diffusion-weighted images by using a stretched exponential model.All parameters were compared between MFAML and cc RCC by using the Student’s t test.Receiver operating characteristic and intraclass correlation coefficient analysis were used for statistical evaluations.Results: ADC,Dt,α values were significantly lower in the MFAML group than in the cc RCC group（P <0.001）.Dp,fp and DDC values were slightly higher in the MFAML group than in the cc RCC group,however,the difference was not significant（P=0.136,0.090 and 0.424,respectively）.The AUC values for both α（0.953）and Dt（0.964）were significantly higher than those for ADC（0860）,Dp（0.605）,fp（0.596）and DDC（0.477）in the differentiation of MFAML from cc RCC（P<0.001）.Conclusions: Dt and α may provide additional information and could lead to improved differentiation with better sensitivity and specificity between MFAML and cc RCC compared with conventional diffusion parameters.