History and future directions in ultrasonography.

The development of ultrasonography would not be possible without the earlier findings concerning ultrasounds. As early as the thirteenth century Lazzarro Spalanzani observed that bats use hearing rather than sight, considering location in space. In 1938, Donald Griffin described the phenomenon of echolocation in these mammals. In 1880, Pierre and Jaques Curie showed the piezoelectric phenomenon consisting in the creation of an electrical charge inside the crystal quartz or Seignette’s salt (sodium and potassium tartrate), under pressure (1). The name of the phenomenon is derived from the Greek language meaning ‘to push’. The Curie brothers also observed the inverse piezoelectric crystal vibration phenomenon involving the effect of an external electrical field. Piezoelectricity is only present in the crystals, being elementary cells, which do not have a center of symmetry, such as quartz crystals. In the first half of the 20-th century the sonar was constructed-a device using sound waves to track and classify mobile and immobile submerged objects. The first idea for such a device was patented by an English meteorologist, Lewis Richardson in 1912, and one year thereafter, by Alexander Behm in Germany. In 1941, Sproule and Firestone working independently, constructed a device that used ultrasounds to detect defects in the hull of vessels (1). The designed ‘supersonic reflectoscope” by Firestone was soon adapted for the use in shipbuilding. Christian Andreas Doppler (fig. 1), an Austrian physicist and mathematician was the first in 1842 who described the color change under the influence of movement in the system of submerged stars. This effect consists in the development of frequency differences sent by the source and recorded by the observer, who moves in relation to the source, being applied in ultrasonography. Shigeo Satomura was the pioneer of Doppler ultrasonography, a physicist from the Univer-