Multi-system repeatability and reproducibility of apparent diffusion coefficient measurement using an ice-water phantom

Purpose: To determine quantitative quality control proce-dures to evaluate technical variability in multi-center measurements of the diffusion coefficient of water as a prerequisite to use of the biomarker apparent diffusion coefficient (ADC) in multi-center clinical trials. Materials and Methods: A uniform data acquisition pro-tocol was developed and shared with 18 participating test sites along with a temperature-controlled diffusion phan-tom delivered to each site. Usable diffusion weighted imaging data of ice water at five b-values were collected on 35 clinical MRI systems from three vendors at two field strengths (1.5 and 3 Tesla [T]) and analyzed at a central processing site. Results: Standard deviation of bore-center ADCs mea-sured across 35 scanners was <2%; error range: 2 % to þ5 % from literature value. Day-to-day repeatability of the measurements was within 4.5%. Intra-exam repeatability at the phantom center was within 1%. Excluding one out-lier, inter-site reproducibility of ADC at magnet isocenter was within 3%, although variability increased for off-center measurements. Significant (>10%) vendor-specific and system-specific spatial nonuniformity ADC bias was detected for the off-center measurement that was consist-ent with gradient nonlinearity. Conclusion: Standardization of DWI protocol has improved reproducibility of ADC measurements and allowed identifying spatial ADC nonuniformity as a source of error in multi-site clinical studies