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

Abstract

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 mm² /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.

Keywords: diffusion weighted imaging (DWI); fibrosis; intravoxel incoherent motion (IVIM); pancreas; pancreas adenocarcinoma (PAC); stromal desmoplasia.