INTRODUCTION

Compared to white matter, brain deep gray matter have not received the same critical attentions from diffusion MRI studies, although researches have shown that amyloid deposition begins in the striatum in Alzheimer’s Disease (AD) [1]. We used Diffusion kurtosis imaging (DKI) to evaluate the microstructure changes of brain deep gray matter and to explore its relationship with cognitive function in AD.

METHODS

Twenty-three patients with AD and twenty-four healthy controls (HC) were recruited in this study. DKI and conventional MRI were performed using a 3.0-Tesla MR system. With Functool 2 software in workstation 4.5, bilateral MK, Ka, Kr, MD, Da, Dr and FA values of the head of caudate nucleus, putamen, globus pallidus, thalamus, red nucleus, substantia nigra and hippocampus were measured. Using SPSS 20.0 statistic software for analysis, two independent samples t-test was used to compare the mean values of parameters in all brain regions between the AD and HC groups. Receiver operating characteristic (ROC) analysis were used to assess the ability of regional diffusion metrics to discriminate differences between groups. The correlations between DKI parameters and MMSE score were tested using Pearson's correlation.

RESULTS

Direct comparison between groups revealed significantly reduced MK, Ka, Kr value in the thalamus and MK, Kr value in the hippocampus in AD group. Meanwhile, we found markedly increased MK, Ka, Kr in the substantia nigra and MK value in head of the caudate nucleus in AD. The AD patients showed significant increased MD, Da and Dr value in head of the caudate nucleus, increased MD and Da value in the thalamus and the putamen, increased MD value in the red nucleus, increased Da and Dr value in the globus pallidus, increased Dr value in the hippocampus. FA value in AD group showed significantly decreased in hippocampus, globus pallidus and substantia nigra. Markedly increased FA value was found in head of the caudate nucleus and the red nucleus. The Dr value in hippocampus had an AUC of 0.88 with a cutoff value of 0.79 resulting in 94% and 87% sensitivity and specificity, respectively. Some DKI metrics of the deep grey matter exhibiting significant correlations with MMSE score (P＜0.05), especially Ka value of the hippocampus and Dr value of the globus pallidus.

DISCUSSION

The AD patients showed significant increased MD, Da, Dr value in a number of deep grey matter，which may reflect the pathological changes of AD, that are loss of microstructural compartments such as neuronal cell bodies, axons, synapses, and dendrites[2]. In the meantime, we observed increased MK, Ka, Kr value in the substantia nigra and head of the caudate nucleus, which may be associated with accumulations of beta-amyloid and ferritin [2]. The significant correlations between DKI metrics and MMSE score emphasize the important role of microstructural integrity of these deep gray matter in cognitive function in AD.

Acknowledgements

The authors wish to thank all the subjects for their participation in the study.