A longitudinal structural brain MRI template for non‐demented older adults

Background One of the major challenges in constructing a longitudinal structural template of the older adult brain is to ensure spatio‐temporal consistency. Here, a new method was introduced to construct a spatio‐temporally consistent longitudinal template of the older adult brain using high‐quality cross‐sectional older adult data from a large cohort. The new template was compared to templates generated with previously published methods in terms of spatio‐temporal consistency and image quality and showed superior performance. Method T1‐weighted MPRAGE brain data collected on a 3T MRI scanner from 222 non‐demented older adults (65‐95 age‐range, male: female=1:1) participating in the Memory and Aging Project were used for longitudinal template construction. In Method 1, 10 years wide kernel with constant weight was moved to cover eight age‐ranges (65‐75,68‐78,71‐81,74‐84,77‐87,80‐90,86‐95), each including 58 participants with male:female=1:1. Each age‐ranged data were normalized (SyGN) and averaged, resulting into a longitudinal template with eight time‐points:R age‐range (Fig.1 steps 1,2,3). Method 2 was a variant of Method 1 and included an initial affine‐registration of individual datasets to the same initial template to limit group biases. This method resulted into a second longitudinal template:A age‐range . The proposed method first builds a common population template using data from all participants(65‐95 age‐range) using SyGN registration(Fig.1 steps 1,2,3). Next, the inverse of the non‐linear deformations and the inverse of the shape‐update deformation for participants in each age‐range were concatenated and averaged separately. Each resulting deformation was applied to data from corresponding sub‐group and were averaged, resulting into the proposed longitudinal template:L age‐range. The three longitudinal templates were compared in terms of spatio‐temporal consistency and image quality. Result The longitudinal template constructed using the proposed method resulted in the highest spatio‐temporal consistency as illustrated both visually (Figs.2,3) and quantitatively for gray matter, white matter and the lateral ventricles (Fig. 4). Image sharpness was similar across methods (Fig.3). No image artifacts were detected. Conclusion We introduced a new method for the development of a longitudinal structural template of the older adult brain that exhibited higher spatio‐temporal consistency compared to two previously published methods and was characterized by high image sharpness and no image artifacts. The new longitudinal template is part of the MIITRA atlas (www.nitrc.org/projects/miitra).