There will be 200 participants, who aged 30 years or older with TBI in 1,5,10,15 years ago and GCS=13-15 will be recruited. Another group of 200 participants with the same age and gender and without TBI will be recruited as the controls. All of them will undergo AD8 questionnaire for dementia screening and APOE4 genotyping. Further CASI and CDR will be tested for the confirmation of dementia diagnosis for the individuals with AD8 scaore >/=2. 10 TBI with dementia, 20 TBI without dementia and 10 controls will be selected randomly for AV45 amylid PET study.