Inclusion Criteria:  Men or women between the ages of 18 and 75; Diagnostic criteria for mild subclinical hypothyroidism :TSH>10mIU/L, thyroxine and free thyroxine levels were normal Positive thyroglobulin antibody and/or Thyroperoxidase antibody No previous use of drugs affecting thyroid function  Exclusion Criteria:  The contraindications indicated in the Chinese instructions of the drug Liver function impairment Renal function impairment Claustrophobia Mental disorders