Low Intensity Focused Ultrasound Stimulation in Stroke Patients - Parameter Optimization

Inclusion Criteria: * age \>=21 years old of any gender or race * First-ever ischemic or hemorrhagic stroke (neuroimaging verified) at least 6 months from the stroke onset of symptoms * Unilateral arm weakness measured by the Fugl-Meyer Upper-Extremity Scale ≤ 62/64 * Inducible rest motor threshold and testing motor threshold recorded from the affected abductor pollicis brevis muscle Exclusion Criteria: * Bilateral strokes (infarcts and/or hematoma) * Other co-existent neuromuscular disorders affecting upper extremity motor impairment * History of medically uncontrolled depression or other neuropsychiatric disorders despite medications either before or after a stroke that may affect the subject's ability to participate in the study * History of confirmed dementia or taking dementia drugs * Uncontrolled hypertension despite medical treatment(s) at the time of enrollment, defined as SBP≥185 mmHg or DBP≥110 mmHg (patient can be treated, reassessed and enrolled later) * Presence of any MRI/TMS/LIFUS risk factors * Concurrent enrollment in another interventional stroke recovery study * Concerns that the subject cannot comply with study procedures and visits * Pregnant