Transesophageal echocardiogram
A transesophageal echocardiogram (TEE; also spelled transoesophageal echocardiogram; TOE in British English) is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient's esophagus.
Source: Wikipedia — Transesophageal echocardiogram (CC BY-SA 4.0)