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Leighton, T. G. (2007). What is ultrasound? Progress in Biophysics and Molecular Biology, 93(1–3), 3–83. 
Added by: Mark Grimshaw-Aagaard (3/27/22, 10:23 AM)   Last edited by: Mark Grimshaw-Aagaard (4/6/22, 12:16 PM)
Resource type: Journal Article
Peer reviewed
DOI: 10.1016/j.pbiomolbio.2006.07.026
BibTeX citation key: Leighton2007
View all bibliographic details
Categories: General
Keywords: Health, Ultrasound
Creators: Leighton
Publisher: Elsevier (Amsterdam)
Collection: Progress in Biophysics and Molecular Biology
Views: 6/23
Abstract
"This paper is based on material presented at the start of a Health Protection Agency meeting on ultrasound and infrasound. In answering the question ‘what is ultrasound?’, it shows that the simple description of a wave which transports mechanical energy through the local vibration of particles at frequencies of 20 kHz or more, with no net transport of the particles themselves, can in every respect be misleading or even incorrect. To explain the complexities responsible for this, the description of ultrasound is first built up from the fundamental properties of these local particle vibrations. This progresses through an exposition of the characteristics of linear waves, in order to explain the propensity for, and properties of, the nonlinear propagation which occurs in many practical ultrasonic fields. Given the Health Protection environment which framed the original presentation, explanation and examples are given of how these complexities affect issues of practical importance. These issues include the measurement and description of fields and exposures, and the ability of ultrasound to affect tissue (through microstreaming, streaming, cavitation, heating, etc.). It is noted that there are two very distinct regimes, in terms of wave characteristics and potential for bioeffect. The first concerns the use of ultrasound in liquids/solids, for measurement or material processing. For biomedical applications (where these two processes are termed diagnosis and therapy, respectively), the issue of hazard has been studied in depth, although this has not been done to such a degree for industrial uses of ultrasound in liquids/solids (sonar, non-destructive testing, ultrasonic processing etc.). However, in the second regime, that of the use of ultrasound in air, although the waves in question tend to be of much lower intensities than those used in liquids/solids, there is a greater mismatch between the extent to which hazard has been studied, and the growth in commercial applications for airborne ultrasound."
  
Quotes
p.5   "Foetal ultrasonic scanning is now so established in industrialised nations that it would now be difficult to find a control group for epidemiological studies."   Added by: Mark Grimshaw-Aagaard
Keywords:   Health Ultrasound
p.6   "The limiting feature for the use of ultrasound in air is the severe absorption which rapidly reduces the amplitude of the field, as it propagates away from the source, to levels which are too low for most processing activities, or even to provide sufficient signal-to-noise ratios (SNRs) for many diagnostic applications. There is however one exception, the manifestation of which illustrates a key point which must be appreciated in the assessment of the safety of ultrasound in air.
"The human ear is an extremely sensitive sensor for acoustic waves. Intensities which are low by the standards used for ultrasonic diagnostic technology, and certainly for ultrasonic processing, are generally very much higher than the maximum intensities which the human ear can sustain at audio frequencies without damage. Therefore when ultrasound is used to generate signals to which the ear can responds [sic] (which may not necessarily be restricted to audio frequencies—see Section 6), whilst the resulting intensities may be thought of as ‘low’ from the perspective of many ultrasonic technologies, they may be ‘high’ from the perspective of the ear. This point is discussed further in Section 7."   Added by: Mark Grimshaw-Aagaard
Keywords:   Health Ultrasound
p.30   "Given the paucity of information on the safe levels for human exposure to ultrasound in air (Section 6), and the lack of traceability for the measurement of such fields (see Section 2.3), this could be a safety issue."   Added by: Mark Grimshaw-Aagaard
Keywords:   Health Ultrasound
Paraphrases
pp.64-65   Leighton suggests three categories of exposure to ultrasound production, the first of which he classifies as ultrasonic noise exposure:
  1. ultrasound generated by some device as a byproduct of its operation (unintended exposure)
  2. ultrasound generated explicitly by some device and fundamental to its operation (unintended exposure e.g., ultrasonic rangefinder, automatic door openers)
  3. ultrasound generated in order to have an effect on humans and/or to change their behaviour (intended exposure).
  Added by: Mark Grimshaw-Aagaard
Keywords:   Health Ultrasound
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