Processing strategies for improving cortical thickness correspondence between low-field and high-field MRI in young people

Portable low-field MRI systems are a promising complement to conventional high-field systems, enabling broader access to MRI. However, correspondence in cortical thickness estimates between low- and high-field MRI in young people remains limited despite its importance for neurodevelopment and psychopathology. To evaluate how multiple low-field image processing approaches improve cortical thickness correspondence with high-field MRI in a large sample of young individuals, we collected T1-weighted (T1w) and T2-weighted (T2w) data using both low-field (64mT) and high-field (3T) MRI within one week of each other from a community sample of young people. We applied deep learning-based super-resolution methods (SynthSR v1 and SynthSR v2) followed by recon-all, or other reconstruction methods (recon-all-clinical and recon-any), to low-field data acquired across multiple sequences (T1w and T2w) and orientations (axial, coronal, sagittal, and multi-orientation average), with and without resampling and/or co-registration. We assessed global, lobar, and regional cortical thickness correspondence with 3T MRI measures based on the Desikan-Killiany atlas using Pearson and intraclass correlations. We compared pipelines using Steiger's Z-tests and Fisher's Z-tests. A total of 150 individuals (mean age, 18.63+/-5.07; 80 female) were included. We observed the highest global correspondence with recon-all-clinical applied to coronal T1w images (r=0.40, pFDR=3.02e-05), which significantly exceeded the best global correspondence in our previous study (Fisher's Z=1.99, p=0.047). At the lobar and regional levels, multi-orientation T2w images processed with recon-all-clinical showed the highest correspondence across the greatest number of regions (4/12 lobes; 13/68 regions). This pipeline showed the highest correspondence and largest improvements relative to recon-all alone in frontal, cingulate, and temporal regions, including the right pars triangularis (r=0.52, pFDR=4.78e-11; Steiger's Z=4.78, pFDR=4.25e-06), right caudal anterior cingulate (r=0.47, pFDR=3.83e-09; Steiger's Z=5.46, pFDR=1.32e-07), and left parahippocampal regions (r=0.58, pFDR=2.98e-14; Steiger's Z=5.17, pFDR=6.01e-07). We observed significantly improved cortical thickness correspondence in low-field MRI in young people relative to recon-all alone and our prior work. The recon-all-clinical pipeline yielded moderate correspondence, particularly in frontal, cingulate, and temporal regions. Our results demonstrate a methodological improvement in the use of low-field MRI for assessing cortical thickness in young people, providing a quantitative benchmark for current tools in this area.