What is echocardiography?
Echocardiography is the ultrasound imaging of the heart. The device used for echocardiography is called and echocardiograph. An imaging probe known as transducer is used to send ultrasound (high frequency sound waves above the audible range) beams to the heart and receive the echo. It has its origin from SONAR (sound navigation and ranging) used for tracking underwater torpedoes and submarines. The beam scans the heart just like a torch light being swept across a dark room. From the echo received, the computer algorithm of the echocardiograph can exactly locate the depth and size of the structures within the heart which are reflecting the sound beam back. Blood usually does not give back much echo and is hence seen as black in the usual echocardiogram. Using high frequency transducers it is possible to get high resolution images of the heart valves, their movements, various chambers and blood vessels of the heart and their movement. Real time imaging of the heart is possible even at the bedside small hand held devices. Portable echocardiographs appear like a laptop while the regular echocardiographs have multiple transducers of varying frequency and are typically used in a stationary location (echocardiography laboratory, echo lab).
What are the different modes of echocardiography?
Starting from the early single dimensional (M-Mode) echocardiographs, the technology has advanced to provide real time 3 dimensional imaging (4-D). Simple two dimensional imaging is known as 2D echocardiography. It images the structure and movement of the heart in various angles. Next mode to be introduced was Doppler echocardiography. Doppler is used to assess the velocity of blood flow in various parts of the heart. When Doppler information is displayed in a two dimensional mode with color coding, it is known as Color Doppler echocardiography. In Color Doppler, blood flowing towards the ultrasound probe is coded as red and that flowing away as red. A velocity blood jet will be imaged as a mixture of colours known as a mosaic jet. From two dimensional imaging, then came three dimensional reconstructions, which was done by offline software and was not ‘live’. Still later when the computer processing speed increased, live three dimensional reconstruction is possible, known as 4-D imaging. 4-D imaging is very useful in assessing structural defects of the heart and its valves. Images from various angles and profiles obtained by 4-D imaging is very useful for the heart surgeon to study the heart well before opening up the chest. He can plan the surgery meticulously beforehand.
What is transesophageal echocardiography (TEE)?
Usually echocardiography is done using the probe kept at various locations on the chest. But in transesophageal echocardiography the probe is at the tip of an endoscope (cylindrical) like device, so that it can be introduced into the food pipe (esophagus). The advantage is that the food pipe passes just behind the heart, very close to it. So it is possible to get excellent images of the structure and function of the heart using this mode of echocardiography. Only disadvantage is that is a bit ‘invasive’ as many find introduction of the device into the food pipe a bit of a discomfort.