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For other uses, see Ultrasound (disambiguation).

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Frequency is a measure of the number of occurrences of a repeating event per unit Time. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults and thus, 20 kHz serves as a useful lower limit in describing ultrasound. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The production of ultrasound is used in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium. The most well known application of this technique is its use in sonography to produce pictures of fetuses in the human womb. There are a vast number of other applications as well.

Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications
Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications
A fetus in its mother's womb, viewed in a sonogram (brightness scan)
A fetus in its mother's womb, viewed in a sonogram (brightness scan)

Contents

Ability to hear ultrasound

The upper frequency limit in humans (approximately 20 kHz) is caused by the middle ear, which acts as a low-pass filter. The middle ear is the portion of the ear internal to the Eardrum, and external to the Oval window of the Cochlea. A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies Ultrasonic hearing can occur if ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear. Ultrasonic hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher Frequency than would ordinarily be audible using the physical The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along Carefully-designed scientific studies have been performed and confirmed what they call the hypersonic effect - that even without consciously hearing it, high-frequency sound can have a measurable effect on the mind. The hypersonic effect is a term coined to describe the phenomenon reported in some scientific studies which demonstrate that although humans cannot consciously hear sounds at Frequencies

It is a fact in psychoacoustics that children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to become lower with age. Psychoacoustics is the study of subjective human Perception of Sounds Alternatively it can be described as the study of the Psychological correlates [1] [2][3] A cell phone company has used this to create ring signals supposedly only able to be heard by younger humans[4]; but many older people claim to be able to hear it, which is likely given the considerable variation of age-related deterioration in the upper hearing threshold.

Some animals – such as dogs, cats, dolphins, bats, and mice – have an upper frequency limit that is greater than that of the human ear and thus can hear ultrasound. The dog ( Canis lupus familiaris) is a domesticated Subspecies of the gray wolf, a Mammal of the Canidae family of the order WikipediaManual of Style (spelling, articles should conform to one overall spelling style of English typically the one most linked to the article topic (if it is geographic Dolphins are Marine mammals that are closely related to Whales and Porpoises There are almost forty species of dolphin in seventeen genera. A mouse (plural mice) is a small Animal that belongs to one The ear is the sense organ that detects Sounds The Vertebrate ear shows a common biology from Fish to Humans with variations

Diagnostic sonography

Sonogram of a fetus at 14 weeks (Profile)
Sonogram of a fetus at 14 weeks (Profile)
A fetus, aged 29 weeks, in a "3D ultrasound"
A fetus, aged 29 weeks, in a "3D ultrasound"
Main article: Medical ultrasonography

Medical sonography (ultrasonography) is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, their size, structure and any pathological lesions with real time tomographic images. 3D ultrasound is a Medical ultrasound technique used during Pregnancy, providing three dimensional images of the Fetus. Medical imaging refers to the techniques and processes used to create Images of the human body (or parts thereof for clinical purposes ( Medical procedures seeking to A lesion is any abnormal tissue found on or in an organism usually damaged by disease or trauma It is also used to visualize a fetus during routine and emergency prenatal care. Prenatal care refers to the medical care recommended for women before and during Pregnancy. Ultrasound scans are performed by medical health care professionals called sonographers. Sonographers are medical professionals who operate ultrasonic imaging devices to produce diagnostic images and scans videos or 3D volumes of anatomy and diagnostic data Obstetric sonography is commonly used during pregnancy. Obstetric sonography (ultrasonography is the application of Medical ultrasonography to Obstetrics, in which ultrasound is used to visualize the Embryo Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female Ultrasound has been used to image the human body for at least 50 years. It is one of the most widely used diagnostic tools in modern medicine. The technology is relatively inexpensive and portable, especially when compared with modalities such as magnetic resonance imaging (MRI) and computed tomography (CT). Computed tomography (CT is a Medical imaging method employing Tomography. As currently applied in the medical environment, ultrasound poses no known risks to the patient. [5] Sonography is generally described as a "safe test" because it does not use ionizing radiation, which imposes hazards, such as cancer production and chromosome breakage. However, ultrasonic energy has two potential physiological effects: it enhances inflammatory response; and it can heat soft tissue. [6] Ultrasound energy produces a mechanical pressure wave through soft tissue. This pressure wave may cause microscopic bubbles in living tissues, and distortion of the cell membrane, influencing ion fluxes and intracellular activity. When ultrasound enters the body, it causes molecular friction and heats the tissues slightly. This effect is very minor as normal tissue perfusion dissipates heat. With high intensity, it can also cause small pockets of gas in body fluids or tissues to expand and contract/collapse in a phenomenon called cavitation (this is not known to occur at diagnostic power levels used by modern diagnostic ultrasound units). The long-term effects of tissue heating and cavitation are not known. [7] There are several studies that indicate the harmful side effects on animal fetuses associated with the use of sonography on pregnant mammals. A noteworthy study in 2006 suggests exposure to ultrasound can affect fetal brain development in mice. This misplacement of brain cells during their development is linked to disorders ranging "from mental retardation and childhood epilepsy to developmental dyslexia, autism spectrum disorders and schizophrenia, the researchers said. However, this effect was only detectable after 30 minutes of continuous scanning. [8] A typical fetal scan, including evaluation for fetal malformations, typically takes 10-30 minutes. [9] There is no link made yet between the test results on animals, such as mice, and the possible outcome to humans. Widespread clinical use of diagnostic ultrasound testing on humans has not been done for ethical reasons. The possibility exists that biological effects may be identified in the future, currently most doctors feel that based on available information the benefits to patients outweigh the risks. [10] Obstetric ultrasound can be used to identify many conditions that would be harmful to the mother and the baby. For this reason many health care professionals consider that the risk of leaving these conditions undiagnosed is much greater than the very small risk, if any, associated with undergoing the scan. According to Cochrane review, routine ultrasound in early pregnancy (less than 24 weeks) appears to enable better gestational age assessment, earlier detection of multiple pregnancies and earlier detection of clinically unsuspected fetal malformation at a time when termination of pregnancy is possible. [11]

Sonography is used routinely in obstetric appointments during pregnancy, but the FDA discourages its use for non-medical purposes such as fetal keepsake videos and photos, even though it is the same technology used in hospitals.

Obstetric ultrasound is primarily used to:

Unfortunately, results are occasionally wrong, producing a false positive (the Cochrane Collaboration is a relevant effort to improve the reliability of health care trials). The Cochrane Collaboration is a group of over 11500 volunteers in more than 90 countries who apply a rigorous systematic process to review the effects of interventions tested in biomedical False detection may result in patients being warned of birth defects when no such defect exists. Sex determination is only accurate after 12 weeks gestation [Ultrasound in Obstetrics and Gynecology 1999]. When balancing risk and reward, there are recommendations to avoid the use of routine ultrasound for low risk pregnancies [ACOG]. In many countries ultrasound is used routinely in the management of all pregnancies.

According to the European Committee of Medical Ultrasound Safety (ECMUS) "Ultrasonic examinations should only be performed by competent personnel who are trained and updated in safety matters. Ultrasound produces heating, pressure changes and mechanical disturbances in tissue. Diagnostic levels of ultrasound can produce temperature rises that are hazardous to sensitive organs and the embryo/fetus. Biological effects of non-thermal origin have been reported in animals but, to date, no such effects have been demonstrated in humans, except when a microbubble contrast agent is present. "[12]

A study on rodent fetus brains that are exposed to ultrasound showed signs of damage. Speculation on human fetuses can be in a range of no significant complications to a variety of mental and brain disorders. The study shows that rodent brain cells failed to grow to their proper position and remained scattered in incorrect parts of the brain. The conditions of this experiment are different from typical fetal scanning because of the long dwell times. [National Institute of Neurological Disorders; Proceedings of the National Academy of Sciences]. Care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain unless specifically indicated in high risk pregnancies.

It should be noted that obstetrics is not the only use of ultrasound. Soft tissue imaging of many other parts of the body is conducted with ultrasound. Other scans routinely conducted are cardiac, renal, liver and gallbladder (hepatic). The liver is a vital organ in the human body and is present in Vertebrates and some other animals Other common applications include musculo-skeletal imaging of muscles, ligaments and tendons, ophthalmic ultrasound (eye) scans and superficial structures such as testicle, thyroid, salivary glands and lymph nodes. The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male The thyroid is one of the largest Endocrine glands in the body The salivary glands in mammals are exocrine glands that produce saliva A Lymph node ( lɪmf noʊd is an organ consisting of many types of cells and is a part of the Lymphatic system. Because of the real time nature of ultrasound, it is often used to guide interventional procedures such as fine needle aspiration FNA or biopsy of masses for cytology or histology testing in the breast, thyroid, liver, kidney, lymph nodes, muscles and joints. "FNA" redirects here For the botanical book series see Flora of North America North of Mexico. A biopsy (in Greek: βίος life and όψη look/appearance is a Medical test involving the removal of cells or tissues Histology (from the Greek = 'tissue' is the study of the microscopic anatomy of cells and tissues of Plants and

Ultrasound scanners using pulsed wave and colour Doppler are used to visualize arteries and veins.

Figures released for the period 2005-2006 by UK Government (Department of Health) show that non-obstetric ultrasound examinations contributed to more than 65% of the total number of ultrasound scans conducted.

Biomedical ultrasonic applications

Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions:[13]

Industrial ultrasound

Main article: Ultrasonic testing
Non-destructive testing of a swing shaft showing spline cracking
Non-destructive testing of a swing shaft showing spline cracking

Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects. In ultrasonic testing, very short ultrasonic pulse-waves with center frequencies ranging from 0 In ultrasonic testing, very short ultrasonic pulse-waves with center frequencies ranging from 0 Nondestructive testing ( NDT) also called nondestructive examination ( NDE) and nondestructive inspection ( NDI) is testing that does Frequencies of 2 to 10 MHz are common but for special purposes other frequencies are used. Inspection may be manual or automated and is an essential part of modern manufacturing processes. Most metals can be inspected as well as plastics and aerospace composites. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products This article is about the field of research and industry for the corporation see The Aerospace Corporation Aerospace comprises the Composite materials (or composites for short are engineered Materials made from two or more constituent materials with significantly different physical or chemical Lower frequency ultrasound (50 kHz to 500 kHz) can also be used to inspect less dense materials such as wood, concrete and cement. Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together

Ultrasound can also be used for heat transfer in liquids. [19]

Researchers recently employed ultrasound in dry corn milling plant to enhance ethanol production. [20]

Ultrasonic cleaning

Ultrasonic cleaners, sometimes mistakenly called supersonic cleaners, are used at frequencies from 20-40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments, diving regulators and industrial parts. An ultrasonic cleaner is a cleaning device that uses Ultrasound (usually from 15-400 KHz) and an appropriate cleaning solution to clean delicate items For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Jewellery (also spelled jewelry, see spelling differences) is a personal Ornament, such as a necklace ring or bracelet made from Gemstones A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging A watch is a timepiece that is made to be worn on a person The term now usually refers to a wristwatch, which is worn on the wrist with a strap or Bracelet. Dentistry' is the "evaluation diagnosis prevention and/or treatment (nonsurgical surgical or related procedures of diseases disorders and/or conditions of the oral cavity A surgical instrument is a specially designed tool or device for performing specific actions of carrying out desired effects during a Surgery or operation such as modifying A diving regulator is a Pressure regulator used in a Scuba set that supplies the diver with breathing gas For other uses of this term see Industry (disambiguation An industry (from Latin industrius, "diligent industrious" An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure The bubbles made by cavitation collapse forming tiny jets directed at the surface. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure Home ultrasonic cleaners are available and cost about US $60 or more.

Ultrasonic humidifier

The ultrasonic humidifier, one type of nebulizer (a device that creates a very fine spray), is a popular type of humidifier. A humidifier is a household Appliance that increases Humidity (moisture in a single room or in the entire home In Medicine, a nebulizer is a device used to administer medication to people in the form of a mist inhaled into the lungs It works by vibrating a metal plate at ultrasonic frequencies to nebulize (sometimes incorrectly called "atomize") the water. Because the water is not heated for evaporation, it produces a cool mist. The ultrasonic pressure waves nebulize not only the water but also materials in the water including calcium, other minerals, viruses, fungi, bacteria[21], and other impurities. Illness caused by impurities that reside in a humidifier's reservoir fall under the heading of "Humidifier Fever".

Ultrasound Identification (USID)

Ultrasound Identification (USID) is a Real Time Locating System (RTLS) or Indoor Positioning System (IPS) technology used to automatically track and identify the location of objects in real time using simple, inexpensive nodes (badges/tags) attached to or embedded in objects and devices, which then transmit an ultrasound signal to communicate their location to microphone sensors. Ultrasound Identification is a Real Time Locating System (RTLS or Indoor Positioning System (IPS technology used to automatically track and identify the location This page specifically concerns operational aspects of RTLS. For methodology issues see Locating engine. Indoor Positioning Systems (IPS locate and track objects in buildings

Ultrasound and animals

Bats

Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. Echolocation, also called biosonar, is the biological Sonar used by several Animals such as Dolphins Shrews most Bats They can detect frequencies as high as 100 kHz, although there is some disagreement on the upper limit. [22]

Dogs

Dogs can hear sound at higher frequencies than humans can. The dog ( Canis lupus familiaris) is a domesticated Subspecies of the gray wolf, a Mammal of the Canidae family of the order A dog whistle exploits this by emitting a high frequency sound to call to a dog. For the use of political code words see Dog-whistle politics. Many dog whistles emit sound in the upper audible range of humans, but some, such as the silent whistle, emit ultrasound at a frequency in the range of 18 kHz to 22 kHz. For the use of political code words see Dog-whistle politics.

Dolphins and whales

It is well known that some whales can hear ultrasound and have their own natural sonar system. Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate Some whales use the ultrasound as a hunting tool (for both detection of prey and as an attack).

Fish

Several types of fish can detect ultrasound. Of the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e. Clupeiformes is the order of ray-finned fish that includes the Herring family Clupeidae, and the Anchovy family Engraulidae. The shads or river herrings comprise the Genus Alosa, Fishes related to Herring in the family Clupeidae g. herrings) can hear only up to 4 kHz. Herring are small Oily fish of the genus Clupea found in the shallow temperate waters of the North Atlantic, the Baltic Sea, the North [23]

Moths

There is evidence that ultrasound in the range emitted by bats causes flying moths to make evasive manoeuvres because bats eat moths. A moth is an Insect closely related to the Butterfly, both being of the order Lepidoptera. Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop a few inches in its flight to evade attack. The Noctuidae or Owlet moths are a family of robustly-built Moths that includes more than 35000 known species out of possibly 100000 total in more than 4200 genera [1]

Rodents/insects

Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work. Rodentia is an order of Mammals also known as rodents, characterised by two continuously-growing incisors in the upper and lower jaws which must Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Laboratory tests conducted by Kansas State University did show positive results for products from specific manufacturers. Controlled tests on some of the systems have shown that rodents quickly learn that the speakers are harmless.

Sonochemistry

Main article: Sonochemistry

Power ultrasound in the 20-100 kHz range is used in chemistry. In Chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties The ultrasound does not interact directly with molecules to induce the chemical change, as its typical wavelength (in the millimeter range) is too long compared to the molecules. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Instead:

Both of these make the reaction faster.

Ultrasonic disintegration

Some sorts of ultrasound can disintegrate biological cells including bacteria. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have This has uses in biological science and in killing bacteria in sewage. Foundations of modern biology There are five unifying principles Sewage is the mainly liquid Waste containing some solids produced by humans which typically consists of washing water Feces, Urine, laundry waste and other High power ultrasound at frequency of around 20 kHz produces cavitation that facilitates particle disintegration. Dr. Samir Khanal of Iowa State University employed high power ultrasound to disintegrate corn slurry to enhance liquefaction and saccharification for higher ethanol yield in dry corn milling plants.

See examples:-

Ultrasonic range finding

Main article: sonar

A common use of ultrasound is in range finding; this use is also called SONAR, (sound navigation and ranging). Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate A rangefinder is a device that measures distance from the observer to a target for the purposes of Surveying, determining focus in Photography, or Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate This works similarly to RADAR (radio detection and ranging): An ultrasonic pulse is generated in a particular direction. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an echo and can be detected through the receiver path. In Audio signal processing and Acoustics, an echo (plural echoes) is a reflection of sound arriving at the listener some time after the direct By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine how far away the object is.

The measured travel time of SONAR pulses in water is strongly dependent on the temperature and the salinity of the water. Ultrasonic ranging is also applied for measurement in air and for short distances. Such method is capable for easily and rapidly measuring the layout of rooms.

Although range finding underwater is performed at both sub-audible and audible frequencies for great distances (1 to several ten kilometers), ultrasonic range finding is used when distances are shorter and the accuracy of the distance measurement is desired to be finer. Ultrasonic measurements may be limited through barrier layers with large salinity, temperature or vortex differentials. Ranging in water varies from about hundreds to thousands of meters, but can be performed with centimeters to meters accuracy.

Other uses

Ultrasound when applied in specific configurations can produce short bursts of light in an exotic phenomenon known as sonoluminescence. Sonoluminescence is the emission of short bursts of Light from imploding bubbles in a Liquid when excited by Sound. This phenomenon is being investigated partly because of the possibility of bubble fusion (a nuclear fusion reaction hypothesized to occur during sonoluminescence). Bubble fusion, also known as sonofusion, is the non-technical name for a Nuclear fusion reaction hypothesized to occur during Sonoluminescence, an extreme In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus

Recently researchers at the University of Alberta in Canada have successfully used ultrasound to regenerate dental material. The University of Alberta (U of A is a public research University located in Edmonton, Alberta, Canada.

Ultrasound is used when characterizing particulates through the technique of ultrasound attenuation spectroscopy or by observing electroacoustic phenomena. Ultrasound attenuation spectroscopy is a method for characterizing properties of Fluids and Dispersed particles. Electroacoustic phenomena arises when Ultrasound propagates through a Fluid containing Ions.

In rheology, an acoustic rheometer relies on the principle of ultrasound. Rheology is the study of the flow of matter mainly liquids but also soft solids or solids under conditions in which they flow rather than deform elastically Acoustic rheometer employes Piezo-electric Crystal that can easily launch a successive Wave of extensions and contractions into the Fluid In fluid mechanics, fluid flow can be measured using an ultrasound flow meter. Fluid mechanics is the study of how Fluids move and the Forces on them A ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using acoustic sensors

Ultrasound also plays a role in Sonic weaponry. Sonic and ultrasonic weapons (USW are weapons of various types that use sound to injure incapacitate or kill an opponent

Audio can be propagated by modulated ultrasound. Ultrasound can be modulated to carry an audio signal (like radio signals are modulated

Nonlinear propagation effects

Because of their high amplitude to wavelength ratio, ultrasonic waves commonly display nonlinear propagation. This article is about sound waves being distorted as they travel

See also

References

  1. ^ Takeda S et al (1992)
  2. ^ Age variation in the upper limit of hearing. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids Infrasound is Sound with a Frequency too low to be heard by the human Ear. Sound from ultrasound is the name given here to situations when Modulated ultrasound can make its carried signal audible without needing a receiver set When an ultrashort light pulse (duration ~ 100 fs energy Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700
  3. ^ European Journal of Applied Physiology 65(5), 403-408
  4. ^ "A Ring Tone Meant to Fall on Deaf Ears" (New York Times article)
  5. ^ AAPM/RSNA Physics Tutorial for Residents: Topics in US: B-mode US: Basic Concepts and New Technology - Hangiandreou 23 (4): 1019 - RadioGraphics
  6. ^ Watson, T. (2006). "Therapeutic Ultrasound". (see here for a pdf version with the author and date information)
  7. ^ FDA Radiological Health - Ultrasound Imaging
  8. ^ Ultrasound Can Affect Fetal Brain Development | LiveScience
  9. ^ http://www.obgyn.net/femalepatient/femalepatient.asp?page=levi_tfp "Ultrasonographic Screening for Fetal Malformations"
  10. ^ Patient Information - Ultrasound Safety
  11. ^ Ultrasound for fetal assessment in early pregnancy.
  12. ^ http://www.efsumb.org/efsumb/committees/Safety_Committee/Safety_Eng/Clinical%20Safety%20Statement%202006.pdf
  13. ^ Essentials of Medical Ultrasound: A Practical Introduction to the Principles, Techniques and Biomedical Applications, edited by M. H. Rapacholi, Humana Press 1982
  14. ^ Ultrasound - Pelvis.
  15. ^ Acoustic targeted drug delivery in neurological tissue.
  16. ^ A phantom feasibility study of acoustic enhanced drug delivery to neurological tissue.
  17. ^ Acoustics and brain cancer.
  18. ^ Citation list.
  19. ^ Milton B. Larson, Study of the Effects of Ultrasonic Vibrations on Convective Heat Transfer in Liquids, (1960)
  20. ^ Using Infrared To See If You're Lit
  21. ^ Microbial contamination by ultrasonic humidifier
  22. ^ Cancel, Juan (1998). Frequency of Bat Sonar. The Physics Factbook.
  23. ^ Mann DA, et al. (2001) Ultrasound detection by clupeiform fishes. JASA 109 (6), 3048-3054 | doi:10. 1121/1. 1368406

Further reading

Dictionary

ultrasound

-noun

  1. sound with a frequency greater than the upper limit of human hearing; approximately 20 kilohertz
  2. (medicine) The use of ultrasonic waves for diagnostic or therapeutic purposes
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