Impact of Free Water Correction on the Mean Diffusivity of Glioblastoma is Regional and b-value Dependent: A Retrospective Study on Open-source Datasets

Abstract

Purpose: To investigate the effects of free-water (FW) correction on mean diffusivity (MD) values in glioblastomas using diffusion tensor imaging (DTI) with different b-value settings. We also examined regional differences between contrast-enhanced (CE) tumor and peritumoral fluid-attenuated inversion recovery (FLAIR) hyperintense regions.

Methods: DTI data from 787 participants with glioblastoma were obtained from 2 open-source datasets: the University of California, San Francisco Preoperative Diffuse Glioma MRI (UCSF-PDGM; b-value, 2000) and the Multi-parametric Magnetic Resonance Imaging Scans for De Novo Glioblastoma Patients from the University of Pennsylvania Health System (UPENN-GBM; b-value, 1000). Conventional and FW-corrected MD maps were generated, and median MD values were calculated from CE and FLAIR hyperintense regions. The impact of FW correction was assessed via the Wilcoxon matched-pairs signed rank test, Bland–Altman plot, and Spearman’s correlation analysis. Multivariate Cox regression was used to evaluate prognostic significance, adjusting for age and CE volume.

Results: Both median MD values were significantly lower in the CE regions than in the FLAIR hyperintense regions. In the UCSF-PDGM dataset, FW correction caused a greater reduction of MD in the CE regions, whereas the greater reduction occurred in the FLAIR hyperintense regions in the UPENN-GBM dataset. Bland–Altman plot also indicated lesions with lower MD values showing greater FW correction in the UCSF-PDGM dataset, whereas those with relatively high MD values showed greater FW correction in the UPENN-GBM dataset. The correlation between both MD values was high (Rs > 0.98). Neither conventional MD nor FW-corrected MD values in the CE regions were significantly associated with overall survival. (Ps > 0.30).

Conclusion: A paradoxical relationship of MD values with and without FW correction was identified depending on regional characteristics and b-value settings, underscoring the importance of acquisition parameters when interpreting FW correction.