A transesophageal echocardiogram (TEE) uses echocardiography to assess the structure and function of the heart. During the procedure, a transducer (like a microphone) sends out ultrasonic sound waves. When the transducer is placed at certain locations and angles, the ultrasonic sound waves move through the skin and other body tissues to the heart tissues, where the waves bounce or “echo” off of the heart structures. The transducer picks up the reflected waves and sends them to a computer. The computer displays the echoes as images of the heart walls and valves.
A traditional echocardiogram is done by putting the transducer on the surface of the chest. This is called a transthoracic echocardiogram. A transesophageal echocardiogram is done by inserting a probe with a transducer down the esophagus. This provides a clearer image of the heart because the sound waves do not have to pass through skin, muscle, or bone tissue. The TEE probe is much closer to the heart since the esophagus and heart are right next to each other. (Source: Hopkins Medicine link below)
What is a transesophageal echocardiogram (TEE)? | Hopkins Medicine
Transesophageal Echocardiography | American Heart Association