Comparison of Biexponential and Monoexponential Model of Diffusion-Weighted Imaging for Distinguishing between Common Renal Cell Carcinoma and Fat Poor Angiomyolipoma

Abstract

Objective: To compare the diagnostic accuracy of intravoxel incoherent motion (IVIM)-derived parameters and apparent diffusion coefficient (ADC) in distinguishing between renal cell carcinoma (RCC) and fat poor angiomyolipoma (AML).

Materials and methods: Eighty-three patients with pathologically confirmed renal tumors were included in the study. All patients underwent renal 1.5T MRI, including IVIM protocol with 8 b values (0-800 s/mm²). The ADC, diffusion coefficient (D), pseudodiffusion coefficient (D^*), and perfusion fraction (f) were calculated. One-way ANOVA was used for comparing ADC and IVIM-derived parameters among clear cell RCC (ccRCC), non-ccRCC and fat poor AML. The diagnostic performance of these parameters was evaluated by using receiver operating characteristic (ROC) analysis.

Results: The ADC were significantly greater in ccRCCs than that of non-ccRCCs and fat poor AMLs (each p < 0.010, respectively). The D and D^* among the three groups were significantly different (all p < 0.050). The f of non-ccRCCs were less than that of ccRCCs and fat poor AMLs (each p < 0.050, respectively). In ROC analysis, ADC and D showed similar area under the ROC curve (AUC) values (AUC = 0.955 and 0.964, respectively, p = 0.589) in distinguishing between ccRCCs and fat poor AMLs. The combination of D > 0.97 × 10^-3 mm²/s, D^* < 28.03 × 10^-3 mm²/s, and f < 13.61% maximized the diagnostic sensitivity for distinguishing non-ccRCCs from fat poor AMLs. The final estimates of AUC (95% confidence interval), sensitivity, specificity, positive predictive value, negative predictive value and accuracy for the entire cohort were 0.875 (0.719-0.962), 100% (23/23), 75% (9/12), 88.5% (23/26), 100% (9/9), and 91.4% (32/35), respectively.

Conclusion: The ADC and D showed similar diagnostic accuracy in distinguishing between ccRCCs and fat poor AMLs. The IVIM-derived parameters were better than ADC in discriminating non-ccRCCs from fat poor AMLs.

Keywords: Angiomyolipoma; DWI; Diffusion-weighted imaging; Intravoxel incoherent motion; Renal cell carcinoma.

Fig. 1. Box-and-whisker plots of ADC (A), D (B), D^* (C), and f (D) values for ccRCC, non-ccRCC, and fat poor AML.

Bottom and top of boxes indicate 25th and 75th percentiles of values, respectively. Horizontal line inside box indicates median values. ADC = apparent diffusion coefficient, AML = angiomyolipomas, ccRCC = clear cell renal cell carcinoma, non-ccRCC = papillary RCC and chromophobe RCC

Fig. 2. MR images in 37-year-old man with 3.7 cm surgically verified ccRCC in right kidney.

Diffusion-weighted image with b value of 800 s/mm² (A), and IVIM-derived parametric maps (D, D^*, and f, respectively) (B-D) calculated from IVIM-DWI data. Calculated mean values of ADC, D, D^*, and f for manually drawn ROIs for ccRCC were 1.85 × 10^-3 mm²/s, 1.49 × 10^-3 mm²/s, 31.10 × 10^-3 mm²/s, and 22.9%, respectively. ADC = apparent diffusion coefficient, ccRCC = clear cell renal cell carcinoma, DWI = diffusion-weighted imaging, IVIM = intravoxel incoherent motion, MR = magnetic resonance, ROIs = region of interests

Fig. 3. MR images in 52-year-old man with 3.5 cm surgically proven chRCC in left kidney.

Diffusion-weighted image with b value of 800 s/mm² (A), and IVIM-derived parametric maps (D, D^*, and f, respectively) (B-D) calculated from IVIM-DWI data. Calculated mean values of ADC, D, D^*, and f for manually drawn ROIs for non-ccRCC were 0.92 × 10^-3 mm²/s, 0.74 × 10^-3 mm²/s, 16.87 × 10^-3 mm²/s, and 13.9%, respectively. ADC = apparent diffusion coefficient, chRCC = chromophobe renal cell carcinoma, DWI = diffusion-weighted imaging, IVIM = intravoxel incoherent motion, MR = magnetic resonance, ROIs = region of interests

Fig. 4. MR images in 36-year-old woman with 11.2 cm pathologically proven fat poor AML in right kidney.

Diffusion-weighted image with b value of 800 s/mm² (A), and IVIM-derived parametric maps (D, D^*, and f, respectively) (B-D) calculated from IVIM-DWI data. Calculated mean values of ADC, D, D^*, and f for manually drawn ROIs for fat poor AML were 1.16 × 10^-3 mm²/s, 0.81 × 10^-3 mm²/s, 50.55 × 10^-3 mm²/s, and 22.8%, respectively. ADC = apparent diffusion coefficient, AML = angiomyolipomas, DWI = diffusion-weighted imaging, IVIM = intravoxel incoherent motion, MR = magnetic resonance, ROIs = region of interests

Fig. 5. ROC curves for ADC and IVIM-derived parameters in differentiating renal cell carcinomas and fat poor AMLs.

A. Graph shows comparison of ROC curve analysis for discriminating ccRCC and fat poor AMLs with ADC and IVIM-derived parameters. AUCs for ADC, D, D^*, and f were 0.955, 0.964, 0.668, and 0.506, respectively. B. Graph shows comparison of ROC curve analysis for differentiation between non-ccRCC and fat poor AMLs with ADC and IVIM-derived parameters. AUCs for ADC, D, D^*, and f were 0.634, 0.757, 0.822, and 0.783, respectively. ADC = apparent diffusion coefficient, AML = angiomyolipomas, AUC = area under the receiver operating characteristic curve, ccRCC = clear cell renal cell carcinoma, IVIM = intravoxel incoherent motion, ROC = receiver operating characteristic