Reduced Field-of-View Diffusion-Weighted Magnetic Resonance Imaging of the Pancreas: Comparison with Conventional Single-Shot Echo-Planar Imaging

Objective: To investigate the image quality (IQ) and apparent diffusion coefficient (ADC) of reduced field-of-view (FOV) di-ffusion-weighted imaging (DWI) of pancreas in comparison with full FOV DWI. Materials and Methods: In this retrospective study, 2 readers independently performed qualitative analysis of full FOV DWI (FOV, $38{\times}38cm$; b-value, 0 and $500m^2/sec$) and reduced FOV DWI (FOV, $28{\times}8.5cm$; b-value, 0 and $400mm^2/sec$2). Both procedures were conducted with a two-dimensional spatially selective radiofrequency excitation pulse, in 102 patients with benign or malignant pancreatic diseases (mean size, $27.5{\pm}14.4mm$). The study parameters included 1) anatomic structure visualization, 2) lesion conspicuity, 3) artifacts, 4) IQ score, and 5) subjective clinical utility for confirming or excluding initially considered differential diagnosis on conventional imaging. Another reader performed quantitative ADC measurements of focal pancreatic lesions and parenchyma. Wilcoxon signed-rank test was used to compare qualitative scores and ADCs between DWI sequences. Mann Whitney U-test was used to compare ADCs between the lesions and parenchyma. Results: On qualitative analysis, reduced FOV DWI showed better anatomic structure visualization ($2.76{\pm}0.79$ at $b=0s/mm^2$ and $2.81{\pm}0.64$ at $b=400s/mm^2$), lesion conspicuity ($3.11{\pm}0.99$ at $b=0s/mm^2$ and $3.15{\pm}0.79$ at $b=400s/mm^2$), IQ score ($8.51{\pm}2.05$ at $b=0s/mm^2$ and $8.79{\pm}1.60$ at $b=400s/mm^2$), and higher clinical utility ($3.41{\pm}0.64$), as compared to full FOV DWI (anatomic structure, $2.18{\pm}0.59$ at $b=0s/mm^2$ and $2.56{\pm}0.47$ at $b=500s/mm^2$; lesion conspicuity, $2.55{\pm}1.07$ at $b=0s/mm^2$ and $2.89{\pm}0.86$ at $b=500s/mm^2$; IQ score, $7.13{\pm}1.83$ at $b=0s/mm^2$ and $8.17{\pm}1.31$ at $b=500s/mm^2$; clinical utility, $3.14{\pm}0.70$) (p < 0.05). Artifacts were significantly improved on reduced FOV DWI ($2.65{\pm}0.68$) at $b=0s/mm^2$ (full FOV DWI, $2.41{\pm}0.63$) (p < 0.001). On quantitative analysis, there were no significant differences between the 2 DWI sequences in ADCs of various pancreatic lesions and parenchyma (p > 0.05). ADCs of adenocarcinomas ($1.061{\times}10^{-3}mm^2/s{\pm}0.133$ at reduced FOV and $1.079{\times}10^{-3}mm^2/s{\pm}0.135$ at full FOV) and neuroendocrine tumors ($0.983{\times}10^{-3}mm^2/s{\pm}0.152$ at reduced FOV and $1.004{\times}10^{-3}mm^2/s{\pm}0.153$ at full FOV) were significantly lower than those of parenchyma ($1.191{\times}10^{-3}mm^2/s{\pm}0.125$ at reduced FOV and $1.218{\times}10^{-3}mm^2/s{\pm}0.103$ at full FOV) (p < 0.05). Conclusion: Reduced FOV DWI of the pancreas provides better overall IQ including better anatomic detail, lesion conspicuity and subjective clinical utility.