Can diffusion‐weighted imaging serve as a biomarker of fibrosis in pancreatic adenocarcinoma?

Purpose To assess the relationship between diffusion‐weighted imaging (DWI) and intravoxel incoherent motion (IVIM)‐derived quantitative parameters (apparent diffusion coefficient [ADC], perfusion fraction [f], D slow , diffusion coefficient [D], and D fast , pseudodiffusion coefficient [D*]) and histopathology in pancreatic adenocarcinoma (PAC). Materials and Methods Subjects with suspected surgically resectable PAC were prospectively enrolled in this Health Insurance Portability and Accountability Act (HIPAA)‐compliant, Institutional Review Board‐approved study. Imaging was performed at 1.5T with a respiratory‐triggered echo planar DWI sequence using 10 b values. Two readers drew regions of interest (ROIs) over the tumor and adjacent nontumoral tissue. Monoexponential and biexponential fits were used to derive ADC 2b , ADC all , f, D, and D*, which were compared to quantitative histopathology of fibrosis, mean vascular density, and cellularity. Two biexponential IVIM models were investigated and compared: 1) nonlinear least‐square fitting based on the Levenberg–Marquardt algorithm, and 2) linear fit using a fixed D* (20 mm 2 /s). Statistical analysis included Student's t ‐test, Pearson correlation ( P < 0.05 was considered significant), intraclass correlation, and coefficients of variance. Results Twenty subjects with PAC were included in the final cohort. Negative correlation between D and fibrosis (Reader 2: r = –0.57 P = 0.01; pooled P = –0.46, P = 0.04) was observed with a trend toward positive correlation between f and fibrosis ( r = 0.44, P = 0.05). ADC 2b was significantly lower in PAC with dense fibrosis than with loose fibrosis ADC 2b ( P = 0.03). Inter‐ and intrareader agreement was excellent for ADC, D, and f. Conclusion In PAC, D negatively correlates with fibrosis, with a trend toward positive correlation with f suggesting both perfusion and diffusion effects contribute to stromal desmoplasia. ADC 2b is significantly lower in tumors with dense fibrosis and may serve as a biomarker of fibrosis architecture. Level of Evidence: 1 Technical Efficacy : Stage 2 J. MAGN. RESON. IMAGING 2017;46:393–402