Development and comprehensive evaluation of high‐resolution 0.5 mm isotropic T2‐weighted, PD‐weighted, T2 map and FLAIR templates of the MIITRA atlas.

Abstract

AbstractBackgroundVoxel‐wise, disease‐monitoring and other MRI investigations involving T2‐weighted(T2w), PD‐weighted(PDw), T2 map and FLAIR templates typically utilize young adult templates such as those of the ICBM atlas. Moreover, a comprehensive assessment of how such available standardized templates perform on aging population has not yet been performed. Here, a high‐resolution older‐adult population based T2w, PDw T2 map and FLAIR templates of the MIITRA atlas was developed using theories of super‐resolution and sparse‐representation and compared to other available standardized templates in terms of image quality, spatial normalization accuracy and representativeness of the older adult brain.MethodT1‐weighted MPRAGE of isotropic 1mm resolution, five spin‐echo(0.5×0.5×0.5 mm3,TE = 20,40,60,80,100ms) and FLAIR data (0.5×0.5×4 mm3) were collected on 3T MRI scanners for 400 non‐demented older adults (50% male; 65‐95 years of age, 54% white and 43% black) participating in the construction of the MIITRA atlas. The subject T2 maps and PD‐weighted data were computed by fitting the T2 decay equation. The template construction technique involved upsampling the images to 0.5×0.5×0.5 mm3 using non‐local upsampling, and converting the T2‐weighted(TE = 60ms) to synthetic T1‐weighted, followed by linear registration to upsampled T1‐weighted data using ANTs. Next, the resulting transformations concatenated with the combined iterative T1w and DTI driven MIITRA atlas deformations were used to forward map each participant to exact physical locations in the MIITRA space. Finally, sparse representation data fusion technique was utilized on the transformed signals to construct the templates at isotropic 0.5mm resolution (Figure.1). MIITRA third echo T2‐weighted and FLAIR template was compared to available standardized templates (Figure. 2) in terms of inter‐subject spatial normalization accuracy when used for spatial normalization of 400 ADNI T2‐weighted and FLAIR participants respectively.ResultThe T2‐weighted and FLAIR templates of the MIITRA atlas exhibited higher image sharpness exemplified by higher spatial frequency content of the normalized power spectra(Figure. 2). MIITRA templates demonstrated higher inter‐subject spatial normalization accuracy and required the least deformations for spatial normalization of ADNI data(Figure. 3)ConclusionThe new T2w, PDw, and FLAIR templates of the MIITRA atlas exhibited superior image quality, required lower deformations, facilitating higher spatial normalization accuracy for use in studies on older adults such as the ADNI datasets.