Abstract
There have been several MR imaging biomarkers of Alzheimer’s disease (AD) for early diagnosis. Cortical mean diffusivity (MD) is one of them for the study of the cortical microstructural change in AD. However, several factors may overshadow the feasibility of MD as AD biomarker. Thus, current study investigated feasible gray matter microstructure biomarker with higher sensitivity for early AD detection. With the aim of facilitating the early detection of AD, the Alzheimer’s Disease Neuroimaging Initiative (ADNI) proposed two stages based on the memory performance: early mild cognitive impairment (EMCI) and late mild cognitive impairment (LMCI). We propose single shell DTI measure, ‘ radiality ’, for early AD biomarker. It is a dot product between cortical surface normal vector and primary diffusion direction, which presumably reflects the fiber orientation within the cortical column.
Here, we gathered images from ADNI phase 2 & 3; 78 cognitive normal, 51 EMCI, 34 LMCI, and 39 AD patients. Then, we evaluated cortical thickness (CTh), MD, amount of amyloid and tau accumulations using PET, which are conventional AD biomarkers. Radiality was projected on gray matter surface to compare and validate the changes along other neuroimage biomarkers.
Results showed decreased radiality primarily in entorhinal, insula, frontal and temporal cortex as disease progress onward. Especially, radiality could delineate the difference between cognitive normal and EMCI group while other biomarkers could not. We looked into the relationship between the radiality and other biomarkers to validate its pathological evidence in AD. Overall, radiality showed high association with conventional biomarkers. Additional ROI analysis exhibit dynamics of AD related changes as stages onward.
In conclusion, radiality in cortical gray matter showed AD specific changes and relevance with other conventional AD biomarkers with higher sensitivity. Besides, it could show group differences in early AD changes from EMCI which show advantage for early diagnosis than using conventional biomarkers. We provide the evidence of structure changes with cognitive impairment and suggest radiality as a sensitive biomarker for early diagnose and progress monitor AD.
Biomarkers, mild cognitive impairment and early diagnosis of Alzheimer's disease
