Detection of Ultrasound Contrast Signals in the Cerebral Circulation

Inclusion Criteria: * male or female age \>19 years of age * scheduled for a stress echocardiogram * negative urine pregnancy test within two hours of ultrasound contrast administration required for females of childbearing age unless post-menopausal or with evidence of surgical sterilization * be conscious and coherent, and able to communicate effectively with trial personnel Exclusion Criteria: * pregnant or lactation * life expectancy of less than 2 months or terminally ill * Known or suspected hypersensitivity to ultrasound contrast agent used for the study * complicated hemodynamic instability * Known left main disease