Abstract: The characteristics of the diffusion-weighted imaging (DWI) apparent diffusion coefficient of patients with subclinical hypothyroidism (SCH) were analyzed to explore the relationship with their cognitive function. 180 patients with SCH were selected as subjects. After the evaluation of their 901 cognitive function with MMSE scale, HDS scale and MoCA scale, 82 patients with normal cognitive function were divided into control group, 66 patients with mild cognitive impairment were divided into mild group, and 32 patients with dementia were divided into dementia group. All the patients were underwent MR-DWI examination to measure the ADC values of each anatomical part of the head. The data showed that, the differences in age, MoCA, MMSE, and HDS scores between three groups were statistically significant (P<0.05). The ADC values of MR-DWI in the right hippocampus area, left internal capsule area and left half-oval center all increased with the increase of cognitive dysfunction, and the ADC values of the mild group and dementia group were significantly higher than the control group (P<0.05). The results show that increasing age will increase the risk of cognitive dysfunction. The impairment of cognitive function is closely related to the metabolism and structural changes of the hippocampus, internal capsule, and regional semi-oval center. The hippocampus is a sensitive area where is related to mild cognitive dysfunction, and the internal capsule area is a sensitive area where is related to dementia.

Key words: subclinical hypothyroidism, DWI, apparent diffusion coefficient, cognitive function