In 1880 the Curie brothers discovered the piezoelectric effect in quartz. Converse piezoelectricity was mathematically deduced from fundamental thermodynamic principles by Lippmann in 1881.

In 1917, Paul Langevin (France) and his coworkers developed an underwater sonar system (called hydrophone) that uses the piezoelectric effect to detect submarines through echo location.

In 1935, the first RADAR system was produced by the British physicist Robert Watson-Wat. Also about 1935, developments began with the objective to use ultrasonic power therapeutically, utilizing its heating and disruptive effects on living tissues. In 1936, Siemens markets the first ultrasonic therapeutic machine, the Sonostat.

Shortly after the World War II, researchers began to explore medical diagnostic capabilities of ultrasound. Karl Theo Dussik (Austria) attempted to locate the cerebral ventricles by measuring the transmission of ultrasound beam through the skull. Other researchers try to use ultrasound to detect gallstones, breast masses, and tumors. These first investigations were performed with A-mode.

Shortly after the World War II, researchers in Europe, the United States and Japan began to explore medical diagnostic capabilities of ultrasound. Karl Theo Dussik (Austria) attempted to locate the cerebral ventricles by measuring the transmission of ultrasound beam through the skull. Other researchers, e.g. George Ludwig (United States) tried to use ultrasound to detect gallstones, breast masses, and tumors. This first experimentally investigations were performed with A-mode. Ultrasound pioneers contributed innovations and important discoveries, for example the velocity of sound transmission in animal soft tissues with a mean value of 1540 m/sec (still in use today), and determined values of the optimal scanning frequency of the ultrasound transducer.

In the early 50`s the first B-mode images were obtained. Images were static, without gray-scale information in simple black and white and compound technique. Carl Hellmuth Hertz and Inge Edler (Sweden) made in 1953 the first scan of heart activity. Ian Donald and Colleagues (Scotland) were specialized on obstetric and gynecologic ultrasound research. By continuous development it was possible to study pregnancy and diagnose possible complications.

After about 1960 two-dimensional compound procedures were developed. The applications in obstetric and gynecologic ultrasound boomed worldwide from the mid 60's with both, A-scan and B-scan equipment. In the late 60's B-mode ultrasonography replaced A-mode in wide parts.

In the 70's gray scale imaging became available and with progress of computer technique ultrasonic imaging gets better and faster.

After continuous work, in the 80's fast realtime B-mode gray-scale imaging was developed. Electronic focusing and duplex flow measurements became popular. A wider range of applications were possible.

In the 90's, high resolution scanners with digital beamforming, high transducer frequencies, multi-channel focus and broad-band transducer technology became state of the art. Optimized tissue contrast and improved diagnostic accuracy lead to an important role in breast imaging and cancer detection. Color Doppler and Duplex became available and sensitivity for low flow was continuously improved.

Actually, machines with advanced ultrasound system performance are equipped with realtime compound imaging, tissue harmonic imaging, contrast harmonic imaging, vascular assessment, matrix array transducers, pulse inversion imaging, 3D and 4D ultrasound with panoramic view.

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The sound velocity in the examined tissue is homogeneous and constant (around 1540 m/s).

The propagation of ultrasound is straight ahead.

The ultrasound beam is infinite thin in its thickness and lateral direction.

The detected echo comes from the shortest sound path between reflector and transducer.

The ultrasound echo is originated by the last generated sound pulse.

The amplitudes of the echoes are proportional to the difference of the acoustical impedance caused by different tissue layers.