ultrasound

/ˈʌltrəsaʊnd/ noun

Definition

SOUND WAVES [U] › very high sound waves, especially those that are used in medical examinations to produce an image of something inside your body: an ultrasound scan

MEDICAL EXAMINATION [C] › a medical examination which produces an image of something that is inside the body, especially a baby, using sound waves: An ultrasound revealed a perfectly healthy baby.

(Definition of ultrasound noun from the Cambridge Learner's Dictionary © Cambridge University Press)