Medical sonography, high intensity focused ultrasound (HIFU), and ultrasound-enhanced systemic thrombolysis are just three of the medical applications of the natural phenomenon of ‘ultrasound,' high frequency sound waves that are undetectable to the human ear. Ultrasound waves have a number of physical and dynamic properties that make them suitable for both diagnostic and therapeutic applications in medicine. This report will describe these properties underlying ultrasound technology. Then it will go on to describe the mechanisms of interaction between ultrasound waves and the biological tissue that they pass through, and it will discuss some of the bioeffects that result from these interactions.Ultrasound technology in medical diagnostics dates back to the late 1940's, while its use in therapeutic settings dates back even earlier to the 1920's. (http://www.ob- ultrasound.net/history1.html) Medical ultrasound technology is made possible by discoveries in navigation by sound (SONAR) and the discovery in 1880 of the piezo-electric effect by Pierre and Jacques Curie.
[...] (Bamber, 1998: 64-72) Mechanisms of Interaction with Biological Tissue and Resulting Bioeffects The physical mechanism that makes ultrasound technology suitable for diagnosing and treating various medical conditions has a number of effects on biological tissue. While most of the effects that ultrasound has on biological tissues are innocuous, some high intensity doses of ultrasound waves can pose a danger. Primary mechanisms of concern in ultrasound diagnostic technology include heating and cavitation. While in some instances, these effects are actively sought out for their therapeutic properties, in a diagnostic capacity they are to be avoided. [...]
[...] Some of the unique dangers associated with ultrasound diagnostics have also been examined, such as thermal effects on living tissue and cavitation of microbubbles in the living medium leading to mechanical stress or damage to surrounding cellular structures. While these dangers have been shown to be clinically significant (Karagöz, Biri, Babacan, & Kavutçu, 2006), and other researchers have pointed out the importance of understanding the exponential relationship between temperature and time of exposure in ultrasound examinations (Church, 2007), it could be argued that the adverse effects on living tissues caused by thermal and cavitation mechanisms do not pose nearly as much of a danger as other imaging methods, especially those involving electromagnetic radiation. [...]
[...] 1149-1166. Haar, G. (2006). “Therapeutic Applications of Ultrasound.” Progress in Biophysics and Molecular Biology 111-129. Hand, J. (1998). “Ultrasound Hypothermia and the Prediction of Heating.” Chapter 8. Ultrasound in Medicine. Duck, F., Baker, A., & Starritt, H., eds. IOP Publishing Ltd. Hsu, S., Huang, T., Chuang, S., Tsai, I., & Chen, D. (2005). “Ultrasound Preexposure Improves Endothelial Cell Binding and Retention on Biomaterial Surfaces.” [...]
[...] For example, the success of ultrasound in sonothrombolysis is believed to be due to the cavitation effects it has on living media. (Haar, 2007:117) A therapeutic treatment that relies on the thermal properties of ultrasound is in physiotherapy and enhanced healing treatments. (Haar, 2007: 113) In its diagnostic role, however, these phenomena are to be carefully controlled, if not avoided altogether. Diagnostic ultrasound uses primarily short pulses. This is because the aim of diagnostic ultrasound is to find out information about the patient's body without inducing any significant biological changes in the body, which long pulses are able to do in therapeutic uses of the technology. [...]
[...] Increasing tissue temperature by 2 or 3 degrees above normal can bring with it physiological benefits, such as increased blood flow and cell activity. (Haar, 113) Another, less common mode of action induced by ultrasound that some therapeutic techniques rely upon is “acoustic cavitation,” the “action of ultrasonically driven microbubbles (Haar, 113) While this is often seen as a side-effect of diagnostic ultrasound to be avoided, in therapeutic ultrasound, the mechanism of cavitation enhances the effects of sonophoresis and gene transfection. (Haar, 113) Sonophoresis is the process whereby ultrasound is used to assist in allowing topically applied pharmaceuticals to penetrate through the skin. [...]
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