Development of the MIITRA QSM template: a high‐resolution magnetic susceptibility template of the older adult brain in the MIITRA atlas space

Background A QSM template of the older‐adult brain is not yet available. This study constructed a high resolution QSM template of the older‐adult brain for the MITRA atlas using data from a large, diverse, community cohort of non‐demented older‐adults. Method Magnetic susceptibility maps were generated for the 400 older‐adult paricipants used in the construction of MIITRA using the Morphology Enabled Dipole Inversion(MEDI) on the 3D 5‐echo GRE data(0.7×0.7×1.3mm3) and upsampled to 0.7×0.7×0.65mm3 using nonlocal upsampling. The first GRE echo of each participant were N4 bias field corrected, then upsampled to 0.7×0.7×0.65mm3 using non‐local upsampling and converted to synthetic T1w images using mri_synthsr. The original 3D T1w MPRAGE(1×1×1mm3) data were upsampled to 0.5×0.5×0.5mm3. The synthetic T1w images were linearly registered to the upsampled T1w data and the resulting transformations were used to forward‐map magnetic susceptibility values from the native space of each participant to exact physical locations in MIITRA space. A sparse representation based data‐fusion approach was used on the transformed signals to generate the final 0.5×0.5×0.5mm3 resolution template, denoted as MIITRA_QSM(Fig.1). Since no other magnetic susceptibility template of the older‐adult brain is currently available, we compared MIITRA_QSM to a young adult template named MuSus‐100(1×1×1mm3,100 participants,mean age 24 years) in terms of image quality and magnetic susceptibility properties. Result Visual showed that MIITRA_QSM template includes fine details, has the expected QSM contrast, highest values in subcortical, brainstem, and cerebellar structures known for their high magnetic susceptibility(especially in older adults), lower values in the white compared to gray matter, and higher values in white matter of the frontal lobe compared to parietal and occipital lobes. When compared to MuSus‐100, MIITRA_QSM showed better delineation of cortical structures and higher image sharpness(Fig.2), as well as higher magnetic susceptibility values in most subcortical brain structures(Fig.3A), Cortical structures from the two templates exhibited more similar magnetic susceptibility values(Fig.3B). Conclusion Magnetic susceptibility values in specific subcortical, brainstem and cerebellar structures are higher in the MIITRA_QSM template compared to a young adult template, probably due to increased metal deposition in these structures with aging. The new template is expected to greatly en