History of Ultrasound of Physics and the Properties of the Transducer

Physics -- History of Ultrasound Physics and Properties of Transducer

The history of Ultrasound Physics has involved contributions from many professions from a number of countries over hundreds of years. The first developments, dating as far back as 1794, were made by scientists outside the medical profession and were often disconnected from each other. As science progressed and scientists combined these discoveries, the medical profession gradually realized the value of ultrasound for detection, diagnosis and treatment. From the first uses of ultrasound physics with large, clumsy and limited equipment, ultrasound has been so refined that ultrasound can now be accomplished with easily portable equipment at the site of care, far from any hospital or laboratory.

A vital part of these ultrasound developments that is still used today is the transducer, a device that efficiently converts electrical energy into images. Consisting of a sensor and the associated circuitry, the type of transducer used in modern medicine depends on the depth of the object to be imaged. High frequency transducers give clearer images but do not penetrate as deeply while lower frequency transducers penetrate more deeply but give images that are less clear. No matter which type of transducer is used, modern transducers are commonly made of either piezoelectric or multi-element arrays.

Introduction

Ultrasound Physics developed over hundreds of years from the contributions of many individuals from different countries over hundreds of years. Though the first developments were made by scientists outside the medical profession, as those developments came together, the medical profession gradually realized that ultrasound could be effectively used to detect, diagnose and treat a number of human illnesses. The value of ultrasound physics for humanity can be seen in its continual refinement, including the continual refinement and use of the transducer. This technology has become so refined that ultrasound can now be quickly used with portable equipment at the point of care in remote locations.

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History of Ultrasound Physics

Ultrasound Physics has developed with contributions from many countries over hundreds of years. Though this type of science has steadily developed and continues to steadily develop, there are historical highlights in its growth. The first developments were made outside the medical profession and were often disconnected discoveries. Ultrasound Physics began in 1794 with a certain observation by an Italian physiologist named Lazzaro Spallanzani. Spallanzani noticed that flying bats use ultrasound in the form of "echolocation" to guide them (Tsung, 2011, p. 3). Echolocation is the process of making a sound, receiving the echo from the sound hitting and bouncing back from an object, and using that echo to determine the structure, size and location of that object (Echolocation, 2013). In 1826, a French physicist named Jean Daniel Colladon used a submerged church bell to determine the speed of underwater sound to prove that sound moves faster in water than in air (Tsung, 2011, p. 4). In 1880, Pierre Curie and Jacques Curie discovered the Piezo-Electric Effect (Tsung, 2011, p. 5), which is an electrical charge created by mechanical stress (Piezo Systems, Inc., n.d.). The Curies discovered that certain prepared crystals developed surface charges when mechanical stress was applied to them (Piezo Systems, Inc., n.d.). The sinking of the Titanic in 1912 lead to the 1915 invention of the hydrophone -- the first transducer -- developed by French Physicist Paul Langevin to recognize icebergs, and later used in World War I to detect enemy submarines (Tsung, 2011, p. 6). As scientists gradually discovered and developed technologies based on necessity, they were forming the bases for modern medical ultrasound.

The basic technology of ultrasound physics was adopted by the medical profession as it sought to detect, diagnose and treat human illnesses. The basic technology continued to develop from 1915 to 1942, when Austrian Neurologist and Psychiatrist, Karl Dussik, began using ultrasound to detect and diagnose brain tumors (Tsung, 2011, p. 7). The United States' first notable historic contribution to Ultrasound Physics occurred in 1948, when an Internist named George Ludwig explained using ultrasound to detect and diagnose gallstones and other foreign objects (Tsung, 2011, p. 8). By 1958, Scottish doctor, Ian Donald, began using ultrasound for OB-GYN (Tsung, 2011, p. 9). Then in the 1950's, American physicians Douglass Howry and Joseph Holmes developed two-dimensional B-mode ultrasound, particularly the "pan scanner." The pan scanner was a significant breakthrough in that it did not require a subject to be fully immersed in order to use a focused sound beam and compound scanning for two-dimensional results (Posakony, n.d.). Ultrasound continued to be refined and gradually used widely in the medical profession; for example, in 1989, French physician Daniel Lichtenstein began using lung ultrasound at the point of care in ICU units (Tsung, 2011, p. 22). The technology developed and was refined continually until point-of-care ultrasound became possible with portable equipment in circumstances far from any laboratory or hospital, even to the point of transmitting real-time ultrasound images to iPhones (Tsung, 2011, pp. 28-9). From very early clumsy and limited technologies, scientists and the medical profession have continually refined ultrasound physics into a common and effective tool of modern medicine.

Properties of the Transducer

The term "transducer" means "a device that transfers power from one system to another in the same or in the different form" (Anonymous, n.d.). In its basic form, a transducer includes a sensor and all the related circuitry. The transducer, which is an essential part of modern ultrasound physics, accepts a form of input energy or signal and converts it to another form of output energy or signal, as the following diagram shows:

(Anonymous, n.d.)

Based on the piezo-electric effect discovered by the Curies, transducer crystals give output energy or a signal in the form of a visual or readable image (Carlson, 2009, p. 3). This technology allows modern medical science, for example, to penetrate a patient's skull with energy, which is then converted by a transducer crystal into a real-time image of a tumor or other foreign body in the brain. Variations of the transducer have been developed as a matter of necessity. For example, after the Titanic's sinking in 1912, the "hydrophone" was developed to detect icebergs, and eventually was used to detect submarines during the First World War (Tsung, 2011, p. 6). Modern medicine uses different transducers, though modern transducers are made of "piezoelectric linear or multi-element phased arrays" (Carlson, 2009, p. 3). The specific type of transducer used depends on how deeply the energy must penetrate a subject in order to obtain the desired image. Higher frequency transducer crystals cannot penetrate as deeply but give clearer images while lower frequency transducer crystals penetrate more deeply but give less clear images (Visualsonics, n.d., p. 4).