Biometry and volumetry in multi-centric fetal brain MRI: assessing the bias of super-resolution reconstruction

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Abstract Background Super-resolution reconstruction (SRR) of fetal brain magnetic resonance imaging has the potential to enable the development of new imaging biomarkers to better study in utero neurodevelopment. However, potential biases in 2D biometric and 3D volumetric measurements due to different SRR techniques remain understudied. Purpose To assess the consistency of biometric and volumetric measurements across three hospitals using three widely used SRR pipelines. Materials and Methods This retrospective study used T2-weighted (T2w) fetal brain MRI scans acquired in routine clinical practice at three hospitals. MRIs from each subject were reconstructed with each of the 3 SRR methods. Four experts did biometric measurements on each SRR volume blinded to the method used. Automated 3D volumetry was performed using a state-of-the-art segmentation method. A univariate analysis was first carried out with Friedman tests with post-hoc Wilcoxon rank-sum tests, and results were confirmed in a multivariate analysis accounting for the effect of gestational age and different raters, using a t-distributed generalized additive model. An additional qualitative evaluation was performed to assess how likely clinicians would be to use the current SRR volumes in their practice, and whether they would prefer it to low-resolution T2w acquisitions. Differences were assessed with Friedman tests and post-hoc Wilcoxon rank-sum tests. Results 84 healthy subjects were included in three gestational age groups ([21-28): 25.4±1.9, [28-32): 29.3±1.3, [32-36): 33.5±1.2). Statistically significant differences in biometric measurements were found, but consistently remained below voxel width (0.8 mm). Automated 3D volumetry revealed systematic but very small effects (<2.8%). The qualitative evaluation showed systematic differences between SRR methods for the perception of white matter intensity (p=0.02) and sharpness of the image (p=0.01). Conclusion Variations in 2D and 3D quantitative measurements did not show any large systematic bias when using different SRR methods for radiological assessment in clinical routine across multiple centers, scanners, and raters. Summary Different super-resolution reconstruction methods for fetal brain MRI volumes lead to negligible variations in 2D or 3D quantitative measurements; this may help achieve larger sample sizes in prenatal development studies. Key Results - In this multi-centric retrospective study, 252 super-resolution reconstructions (SRR) scans from 84 healthy subjects showed negligible variations in 2D in biometric measures (below the voxel with of 0.8 mm; p<0.001). - 3D measurements revealed small variations ranging from 0.8 % in supratentorial tissues (p<0.001) to 2.8% in the extra-cerebral cerebrospinal fluid (p<0.001). - Clinicians favored having both low resolution and SRR volumes available.

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