Currently, the main treatment method for Alzheimer's disease (AD) is chemotherapy. However, the effectiveness of drugs is moderate and there are several side effects. In this clinical trial, the investigators would like to activate the brain by the transcranial ultrasound stimulation (TUS). This is a feasibility study to evaluate the safety and initial effectiveness of TUS for the treatment of patients with mild AD.

The purpose of this study is to verify the feasibility of low intensity transcranial ultrasound stimulation (TUS) for patients with mild Alzheimer's disease (AD). As a secondary aim, the investigators will explore whether the TUS is associated with improvement in cognitive functioning six and forty-six weeks following the intervention.

Subjects will be randomly assigned to one of two experimental groups which with or without the TUS administration.

The investigators will study up to 20 subjects with mild AD. Initially, subjects will undergo a screening assessment with a study physician to determine medical and psychiatric history, establish AD diagnosis, and undergo a bold draw. Subjects that meet criteria and agree to participate in the study will undergo a follow-up visit. In the baseline measurement visit, participants will first undergo neuropsychological testing. Participants will be randomly assigned to one of two groups. Participants will then be administrated TUS treatment for six weeks. Subsequently, participants will undergo a series of neuropsychological test. A final follow-up assessment will be administered at forty-six weeks.

Inclusion Criteria:

1. Age between 55 and 90 years old
2. Weight greater than 50 kg
3. Male or Female
4. Good understanding of written and verbal Chinese
5. Geriatric Depression Scale (GDS) score of < 8
6. Mild AD patients (Mini-Mental State Examination (MMSE) 20-26)
7. Probable AD consistent with NIA/AA criteria
8. The blood flow of bilateral middle cerebral artery M1 can be detected by Transcranial Color Doppler (TCD)
9. Caregiver spending at least 10 hours per week with the patient
10. Agreement to obey the rules of this study
11. Use of cholinesterase inhibitors for AD (Aricept, Namenda, etc.) will be allowed as long as the participant has been on a stable dose for at least six months
12. Does have a reliable caregiver in frequent contact with the patient and can accompany the patient to the clinic and treatment

Exclusion Criteria:

1. Evidence of any other major neurologic or other physical illness that could produce cognitive deterioration, except for mild cognitive impairment (MCI) and any history of stroke or diabetes
2. History of myocardial infarction within the previous year or unstable cardiac disease
3. Any contraindications to MRI scanning such as metallic implants, claustrophibia or too large for MRI scanner
4. History of liver disease or severely impaired renal function
5. The blood flow of either unilateral middle cerebral artery M1 can't be detected by Transcranial Color Doppler (TCD)
6. Major psychiatric disorders, such as bipolar disorder or schizophrenia, or persons with current untreated major depression
7. Pregnant or breastfeeding women