Medical ultrasound
A contrast medium for medical ultrasonography is a formulation of encapsulated gaseous microbubbles to increase echogenicity of blood, discovered by Dr Raymond Gramiak in 1968 and named contrast-enhanced ultrasound. This contrast medical imaging modality is clinically used throughout the world, in particular for echocardiography in the United States and for ultrasound radiology in Europe and Asia.
Ultrasound
Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less.