Transesophageal echocardiography

Technical concepts Physics of ultrasound In ultrasonography, the heart and great vessels are insonated with ultrasound, which is sound above the human audible range. The ultrasound is sent into the area of interest and is partially reflected by the structures. From these reflections, distance, velocity, and density of objects are derived. Wavelength, frequency, and velocity An ultrasound beam is a continuous or intermittent train of sound waves emitted by a transducer or wave generator. It is composed of density or pressure waves and can exist in any medium, with the exception of a vacuum. Ultrasound waves are characterized by their wavelength, frequency, and velocity. Wavelength is the distance between the two nearest points of equal pressure or density in an ultrasound beam, and velocity is the speed at which the waves propagate through a medium. As the waves travel past any fixed point in an ultrasound beam, the pressure cycles regularly and continuously between a high and a low value. The number of cycles per second (hertz) is called the frequency of the wave. Ultrasound is sound with frequencies above 20,000 Hz, which is the upper limit of the human audible range.