[Transesophageal echocardiography (Part 1): Basic concepts in two-dimensional imaging and M-mode].

Transesophageal echocardiography has features suitable for intraoperative use. It enables intraoperative evaluation of cardiac or thoracic aortic lesions before and after surgical intervention. It also provides real-time information on cardiac performance throughout the operation without interfering with surgical procedures. Anatomical relationship of the esophagus and the heart allows the use of high frequency ultrasound, which is advantageous to increase the resolution of echo images. An ultrasound beam emitted by a transducer is absorbed, reflected and scattered as it progresses in inhomogeneous living tissues. The reflected ultrasound waves reach the transducer, and their mechanical vibrations are converted to electronic signals. These signals are further processed by the ultrasound imaging system, and echo images are displayed on a video screen. Ultrasound imaging techniques include M-mode, two-dimensional imaging and Doppler techniques. M-mode is the most basic technique, which displays a scroll of the echo signals along a single ultrasound beam on a video screen. It has higher temporal resolution than other modes, and is therefore useful for precise timing of events and quantitative measurements of size or distance within the cardiac cycle. Two-dimensional mode produces a real-time cross-sectional view of cardiac structures, which can be easily interpreted. It is suited to visualization of anatomic structures.