Acquisition matters - how do scan parameters affect apparent diffusion coefficient estimates in pediatric rhabdomyosarcoma

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Abstract Background The apparent diffusion coefficient (ADC) derived from diffusion-weighted imaging (DWI) is a potential biomarker for treatment response in pediatric rhabdomyosarcoma. Due to its rarity, investigations into this marker require multicenter approaches, which can result in variability in acquisition parameters. Objective To evaluate the impact of different acquisition parameters on ADC estimates in a multicenter dataset of rhabdomyosarcoma patients. Materials and methods We included 114 pediatric and adolescent rhabdomyosarcoma patients from 22 treatment centers (195 scans). Median age: 6.0 years (0.3–21.8). We evaluated the impact of voxel size, (number of) b-values, and echo time on tumor ADC values. The effect of the highest b-value was separately investigated on a subset of scans with five or more b-values. Results We observed a large variability in key acquisition parameters in the overall cohort, and for individual imaging centers. No parameter showed a significant effect on ADC estimates of the whole cohort when corrected for multiple-comparisons. Decreasing the highest b-value within the same acquisition caused ADC to decrease on average by 2.8% per 100 s mm-2. Differing b-values between scans at diagnosis and treatment response yielded significant changes in the longitudinal ADC for each patient (P<0.05). Conclusion While we observed wide variation of acquisition parameters within a multicenter cohort, this did not lead to significant cross-sectional differences of tumor ADC. However, we found that modifying the highest b-value between baseline and follow-up can impact longitudinal ADC estimates. As such, we recommend the highest b-value to remain constant. This retrospective study was reviewed and approved by the Internal Review Board (UMC Utrecht, reference ID: 18-412). Graphical Abstract

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