by Barnaby Meins

Created on: June 06, 2008

Ultrasound imaging has its beginnings in the 1880s when Pierre Curie introduced simple echo sounding methods. This led to the discovery of Sound Navigating and Ranging (SONAR), the technique of sending sound waves through the water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators. Shortly after the second World War, researchers in Japan began to explore medical diagnostic capabilities of ultrasound. The US and Europe became aware of this new diagnostic technique in the 1950s when Japan presented their findings on the use of ultrasound to detect gallstones, breast masses, and tumors.

US pioneers contributed many innovations and important discoveries to the field in the following decades. In the early 1970s, there were the gray scale static images of internal organs. In mid 1970s, real-time imaging emerged. The early 1980s saw the advert of spectral Doppler and color Doppler, also producing a hand-held contact scanner for clinical use. When they are used to monitor carotid artery, it is known as carotid doppler ultrasound

In the 1980s, ultrasound technique was technologically more advanced than the computer technology. Due to this, Samuel H. Maslak developed the 128-channel Computed Sonography platform, allowing for black-and-white and color ultrasound images with superior resolution and clarity. US is better known for its diagnostic capabilities, but it was initially used for therapy rather than diagnosis. Ultrasonic waves emit heat that can create disruptive effects on animal tissue and destroy malignant tissue.

The basic principle of ultrasound imaging is described as follow. A pulse is propagated and its reflection is received both by the transducer. The key assumption is that sound waves have an almost constant velocity of 1540 m/s in water and soft tissue. Size of reflected pulse detected gives acoustic impedance & brightness. The transducer is made of piezoelectric crystal creates sound waves aimed at a specific area of the body. Differences in tissue density reflect the sound waves and the echoes are recorded. Delay of reflected signal and amplitude determines the position of the tissue. There can be still images or a moving picture of the inside of the body

In ultrasound scanning, there is an array of 200 piezoelectric crystals. Each is activated sequentially to scan beam over 2D field. The pulse rate is roughly 3000 per second and the frequency of each pulse is about 1- 15 MHz. Generally, high

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