Effect of b values and size of region of interest on apparent diffusion coefficient measurement and its reproducibility in liver diffusion-weighted MRI

ObjectivesTo investigate the effect of b value and size of region of interest (ROI) on apparent diffusion coefficient (ADC) measurement and its reproducibility in liver diffusion-weighted imaging (DWI).MethodsThirty-six volunteers underwent liver DWI twice with b values of 0, 100, 500, and 800 s/mm(2). ADCs were measured with ROI of 50 mm(2) on ADC maps generated with different b values of (0, 100), (0, 500), (0, 800), (0, 100, 500), (0, 100, 800), (0, 500, 800), and (0, 100, 500, 800) s/mm(2). ADCs from b values of (0, 800) s/mm(2) were measured with 4 ROI sizes (50, 100, 200 and 300 mm(2)). ANOVA analysis was used to compare differences of ADCs among different ROI sizes and different combined b values. Bland-Altman method was used to assess reproducibility of ADC measurement.ResultsADCs with larger ROI size were slightly higher than those with smaller one, while no statistical difference was found (P > 0.05). And reproducibility of ADC measurement with different ROI sizes was comparable (LOA 7.0-8.2% for right lobe, 14.15-17.4% for left lobe). ADCs statistically decreased with increased maximum b values (P < 0.05). ADC measurement achieved the best reproducible with maximum b value of 800 s/mm(2) regardless of the number of b values.ConclusionsThe b values influence ADC measurement and its reproducibility, while the ROI sizes do not affect them. Two b values of (0, 800) s/mm(2) and ROI of 50 mm(2) are recommended for liver ADC measurement.