Until World War II, ultrasound technology was classified military information. The ultrasound frequencies commonly used in echocardiography range from 1 - 10 megaHz. Sound waves behave like a light beam in these ranges, traveling in a straight line. Ultrasound waves are deflected and reflected as they travel through the body from a hand held transducer. The resolution of the images produced varies directly with the frequency and inversely with the wave length of the sound.
Diagnostic ultrasound is used mainly for the imaging of tissue structures.
M mode echocardiography is the earliest modality in ultrasound imaging. It permits the recording of an image and the determination of the rate of motion of a moving object. By moving the transducer in different directions, different structures of the heart can be evaluated. Two dimensional echocardiography revolutionized the way ultrasound is used to image structures in real time. This technology uses an ultrasound beam which is moved mechanically either by oscillating a single transducer or by rotating a series of transducers in a scanning fashion.