Ultrasound is sonic energy with a frequency higher than the audible range of 20,000 Hz. The development of piezoelectric transducers made the application of ultra¬sound possible. A piezoelectric (pressure electric) element is the primary component of an ultrasonic transducer. The shape of a quartz crystal varies with its polarity when an electric current is impressed through the crystal. The expansion and contraction of the crystal produces compres¬sions and rarefactions or sound waves. Most important, when the crystal is struck by reflected ultrasound waves, the crystal creates ultrasound energy and then produces an electric impulse or signal.
Ultrasound, like light, can be focused into a beam that obeys the laws of reflection and refraction. An ultrasound beam travels in a straight line when it traverses a medium of homogeneous density. When the beam hits an inter¬face of different acoustic impedance, part of the energy is reflected. This reflected energy is used to construct an image of the heart.
Figure 1 shows a block diagram of the components of an ultrasonic echograph. The instrument is used to create an image using ultrasound.