Ultrasonic waves can be used for medical imaging. A transducer converts electrical signals to ultrasonic waves and vice versa. The transducer contains a piezoelectric crystal that produces ultrasonic waves when electric current is passed through it and produces an electric current when compressed by ultrasonic waves. The ultrasonic waves travel into the body and bounce off organs and tissues. The echo signals are received by the transducer and converted back to electrical signals that are processed by a computer to produce images.