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Medical ultrasonography

Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. There is a plethora of diagnostic and therapeutic applications practiced in medicine.

In physics the term "ultrasound" applies to all acoustic energy with a frequency above human hearing (20,000 hertz or 20 kilohertz). Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, hundreds of times greater than the limit of human hearing. The choice of frequency is a trade-off between spatial resolution of the image and imaging depth: lower frequencies produce less resolution but image deeper into the body.

Orthogonal planes of a 3 dimensional sonographic volume with transverse and coronal measurements for estimating fetal cranial volume. ^[1], ^[2]

Sonography (ultrasonography) is widely used in medicine. It is possible to perform both diagnosis and therapeutic procedures, using ultrasound to guide interventional procedures (for instance biopsies or drainage of fluid collections). Sonographers are medical professionals who perform scans for diagnostic purposes. Sonographers typically use a hand-held probe (called a transducer) that is placed directly on and moved over the patient.

Sonography is effective for imaging soft tissues of the body. Superficial structures such as muscles, tendons, testes, breast and the neonatal brain are imaged at a higher frequency (7-18 MHz), which provides better axial and lateral resolution. Deeper structures such as liver and kidney are imaged at a lower frequency 1-6 MHz with lower axial and lateral resolution but greater penetration.

Medical sonography is used in, for example:

• Cardiology; see echocardiography
• Endocrinology
• Gastroenterology
• Emergency Medicine; many applications, including the Focused Assessment with Sonography for Trauma (FAST) exam for assessing significant hemoperitoneum or pericardial tamponade after trauma.
• Gynaecology; see gynecologic ultrasonography
• Neurology; for assessing blood flow and stenoses in the carotid arteries and the big intracerebral arteries;
• Obstetrics; see obstetric ultrasonography
• Ophthalmology; see A-scan ultrasonography, B-scan ultrasonography
• Urology, to determine, for example, the amount of fluid retained in a patient's bladder.
• Musculoskeletal, tendons, muscles, nerves, and bone surfaces
• Intravascular ultrasound (e.g. ultrasound guided fluid aspiration, fine needle aspiration, guided injections)
• Intervenional; biopsy, emptying fluids, intrauterine transfusion (Hemolytic disease of the newborn)
• Contrast-enhanced ultrasound

A general-purpose sonographic machine may be able to be used for most imaging purposes. Usually specialty applications may be served only by use of a specialty transducer. Most ultrasound procedures are done using a transducer on the surface of the body, but improved diagnostic confidence is often possible if a transducer can be placed inside the body. For this purpose, specialty transducers, including endovaginal, endorectal, and transesophageal transducers are commonly employed. At the extreme of this, very small transducers can be mounted on small diameter catheters and placed into blood vessels to image the walls and disease of those vessels.

Obstetrical ultrasound is commonly used during pregnancy to check on the development of the fetus.

In a pelvic sonogram, organs of the pelvic region are imaged. This includes the uterus and ovaries or urinary bladder. Men are sometimes given a pelvic sonogram to check on the health of their bladder and prostate. There are two methods of performing a pelvic sonography - externally or internally. The internal pelvic sonogram is performed either transvaginally (in a woman) or transrectally (in a man). Sonographic imaging of the pelvic floor can produce important diagnostic information regarding the precise relationship of abnormal structures with other pelvic organs and it represents a useful hint to treat patients with symptoms related to pelvic prolapse, double incontinence and obstructed defecation.^[3]

In abdominal sonography, the solid organs of the abdomen such as the pancreas, aorta, inferior vena cava, liver, gall bladder, bile ducts, kidneys, and spleen are imaged. Sound waves are blocked by gas in the bowel, therefore there are limited diagnostic capabilities in this area. The appendix can sometimes be seen when inflamed eg: appendicitis.

Contents   1 Therapeutic applications 2 From sound to image 2.1 Producing a sound wave 2.2 Receiving the echoes 2.3 Forming the image 3 Sound in the body 4 Modes of sonography 5 Doppler sonography 6 Contrast media 7 Attributes 7.1 Strengths 7.2 Weaknesses 8 Risks and side-effects 8.1 Studies on the safety of ultrasound 9 Regulation 10 Career Information 11 History 11.1 United States 11.2 Sweden 11.3 Scotland 12 See also 13 References 14 External links

 Therapeutic applications

Therapeutic applications use ultrasound to bring heat or agitation into the body. Therefore much higher energies are used than in diagnostic ultrasound. In many cases the range of frequencies used are also very different.

• Ultrasound may be used to clean teeth in dental hygiene.
• Ultrasound sources may be used to generate regional heating and mechanical changes in biological tissue, e.g. in occupational therapy, physical therapy and cancer treatment. However the use of ultrasound in the treatment of musculoskeletal conditions has fallen out of favor.^[4][5]
• Focused ultrasound may be used to generate highly localized heating to treat cysts and tumors (benign or malignant), This is known as Focused Ultrasound Surgery (FUS) or High Intensity Focused Ultrasound (HIFU). These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher energies. HIFU treatment is often guided by MRI.
• Focused ultrasound may be used to break up kidney stones by lithotripsy.
• Ultrasound may be used for cataract treatment by phacoemulsification.
• Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. its ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.
• Procoagulant at 5-12MHz

 From sound to image

The creation of an image from sound is done in three steps - producing a sound wave, receiving echoes, and interpreting those echoes.

 Producing a sound wave

Medical sonographic instrument

A sound wave is typically produced by a piezoelectric transducer encased in a probe. Strong, short electrical pulses from the ultrasound machine make the transducer ring at the desired frequency. The frequencies can be anywhere between 2 and 18 MHz. The sound is focused either by the shape of the transducer, a lens in front of the transducer, or a complex set of control pulses from the ultrasound scanner machine. This focusing produces an arc-shaped sound wave from the face of the transducer. The wave travels into the body and comes into focus at a desired depth.

Older technology transducers focus their beam with physical lenses. Newer technology transducers use phased array techniques to enable the sonographic machine to change the direction and depth of focus. Almost all piezoelectric transducers are made of ceramic.

Materials on the face of the transducer enable the sound to be transmitted efficiently into the body (usually seeming to be a rubbery coating, a form of impedance matching). In addition, a water-based gel is placed between the patient's skin and the probe.

The sound wave is partially reflected from the layers between different tissues. Specifically, sound is reflected anywhere there are density changes in the body: e.g. blood cells in blood plasma, small structures in organs, etc. Some of the reflections return to the transducer.

 Receiving the echoes

The return of the sound wave to the transducer results in the same process that it took to send the sound wave, except in reverse. The return sound wave vibrates the transducer, the transducer turns the vibrations into electrical pulses that travel to the ultrasonic scanner where they are processed and transformed into a digital image.

 Forming the image

The sonographic scanner must determine three things from each received echo:

1. How long it took the echo to be received from when the sound was transmitted.
2. From this the focal length for the phased array is deduced, enabling a sharp image of that echo at that depth (this is not possible while producing a sound wave).
3. How strong the echo was. It could be noted that sound wave is not a click, but a pulse with a specific carrier frequency. Moving objects change this frequency on reflection, so that it is only a matter of electronics to have simultaneous Doppler sonography.

Once the ultrasonic scanner determines these three things, it can locate which pixel in the image to light up and to what intensity and at what hue if frequency is processed (see redshift for a natural mapping to hue).

Transforming the received signal into a digital image may be explained by using a blank spreadsheet as an analogy. We imagine our transducer is a long, flat transducer at the top of the sheet. We will send pulses down the 'columns' of our spreadsheet (A, B, C, etc.). We listen at each column for any return echoes. When we hear an echo, we note how long it took for the echo to return. The longer the wait, the deeper the row (1,2,3, etc.). The strength of the echo determines the brightness setting for that cell (white for a strong echo, black for a weak echo, and varying shades of grey for everything in between.) When all the echoes are recorded on the sheet, we have a greyscale image.

For computational details see also: Confocal laser scanning microscopy, Radar, Echo sounding

 Sound in the body

Linear Array Transducer

Ultrasonography (sonography) uses a probe containing one or more acoustic transducers to send pulses of sound into a material. Whenever a sound wave encounters a material with a different density (acoustical impedance), part of the sound wave is reflected back to the probe and is detected as an echo. The time it takes for the echo to travel back to the probe is measured and used to calculate the depth of the tissue interface causing the echo. The greater the difference between acoustic impedances, the larger the echo is. If the pulse hits gases or solids, the density difference is so great that most of the acoustic energy is reflected and it becomes impossible to see deeper.

The frequencies used for medical imaging are generally in the range of 1 to 18 MHz. Higher frequencies have a correspondingly smaller wavelength, and can be used to make sonograms with smaller details. However, the attenuation of the sound wave is increased at higher frequencies, so in order to have better penetration of deeper tissues, a lower frequency (3-5 MHz) is used.

Seeing deep into the body with sonography is very difficult. Some acoustic energy is lost every time an echo is formed, but most of it (approximately ) is lost from acoustic absorption.

The speed of sound is different in different materials, and is dependent on the acoustical impedance of the material. However, the sonographic instrument assumes that the acoustic velocity is constant at 1540 m/s. An effect of this assumption is that in a real body with non-uniform tissues, the beam becomes somewhat de-focused and image resolution is reduced.

To generate a 2D-image, the ultrasonic beam is swept. A transducer may be swept mechanically by rotating or swinging. Or a 1D phased array transducer may be use to sweep the beam electronically. The received data is processed and used to construct the image. The image is then a 2D representation of the slice into the body.

3D images can be generated by acquiring a series of adjacent 2D images. Commonly a specialised probe that mechanically scans a conventional 2D-image transducer is used. However, since the mechanical scanning is slow, it is difficult to make 3D images of moving tissues. Recently, 2D phased array transducers that can sweep the beam in 3D have been developed. These can image faster and can even be used to make live 3D images of a beating heart.

Doppler ultrasonography is used to study blood flow and muscle motion. The different detected speeds are represented in color for ease of interpretation, for example leaky heart valves: the leak shows up as a flash of unique color. Colors may alternatively be used to represent the amplitudes of the received echoes.

 Modes of sonography

Four different modes of ultrasound are used in medical imaging^[6]. These are:

• A-mode: A-mode is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.
• B-mode: In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.
• M-mode: M stands for motion. In m-mode a rapid sequence of B-mode scans whose images follow each other in sequence on screen enables doctors to see and measure range of motion, as the organ boundaries that produce reflections move relative to the probe.
• Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow

 Doppler sonography

Spectral Doppler of Common Carotid Artery

Colour Doppler of Common Carotid Artery

Computer-enhanced transcranial doppler.

Sonography can be enhanced with Doppler measurements, which employ the Doppler effect to assess whether structures (usually blood) are moving towards or away from the probe, and its relative velocity. By calculating the frequency shift of a particular sample volume, for example a jet of blood flow over a heart valve, its speed and direction can be determined and visualised. This is particularly useful in cardiovascular studies (sonography of the vascular system and heart) and essential in many areas such as determining reverse blood flow in the liver vasculature in portal hypertension. The Doppler information is displayed graphically using spectral Doppler, or as an image using color Doppler (directional Doppler) or power Doppler (non directional Doppler). This Doppler shift falls in the audible range and is often presented audibly using stereo speakers: this produces a very distinctive, although synthetic, pulsing sound.

Most modern sonographic machines use pulsed Doppler to measure velocity. Pulsed wave machines transmit and receive series of pulses. The frequency shift of each pulse is ignored, however the relative phase changes of the pulses are used to obtain the frequency shift (since frequency is the rate of change of phase). The major advantages of pulsed Doppler over continuous wave is that distance information is obtained (the time between the transmitted and received pulses can be converted into a distance with knowledge of the speed of sound) and gain correction is applied. The disadvantage of pulsed Doppler is that the measurements can suffer from aliasing. The terminology "Doppler ultrasound" or "Doppler sonography", has been accepted to apply to both pulsed and continuos Doppler systems despite the different mechanisms by which the velocity is measured.

It should be noted here that there are no standards for the display of color Doppler. Some laboratories insist on showing arteries as red and veins as blue, as medical illustrators usually show them, even though, as a result, a torturous vessel may have portions with flow toward and away relative to the transducer. This can result in the illogical appearance of blood flow that appears to be in both directions in the same vessel. Other laboratories use red to indicate flow toward the transducer and blue away from the transducer which is the reverse of 150 years of astronomy literature. Still other laboratories prefer to display the sonographic Doppler color map more in accord with the prior published physics with the red shift representing longer waves of echoes (scattered) from blood flowing away from the transducer; and with blue representing the shorter waves of echoes reflecting from blood flowing toward the transducer. Because of this confusion and lack of standards in the various laboratories, the sonographer must understand the underlying acoustic physics of color Doppler and the physiology of normal and abnormal blood flow in the human body. See: -->^[7][8][9]

 Contrast media

The use of microbubble contrast media in medical sonography to improve ultrasound signal backscatter is known as contrast-enhanced ultrasound. This technique is currently used in echocardiography, and may have future applications in molecular imaging and drug delivery.

 Attributes

As with all imaging modalities, ultrasonography has in list of positive and negative attributes.

 Strengths

• It images muscle, soft tissue, and bone surfaces very well and is particularly useful for delineating the interfaces between solid and fluid-filled spaces.
• It renders "live" images, where the operator can dynamically select the most useful section for diagnosing and documenting changes, often enabling rapid diagnoses. Live images also allow for ultrasound-guided biopsies or injections, which can be cumbersome with other imaging modalities.
• It shows the structure of organs.
• It has no known long-term side effects and rarely causes any discomfort to the patient.
• Equipment is widely available and comparatively flexible.
• Small, easily carried scanners are available; examinations can be performed at the bedside.
• Relatively inexpensive compared to other modes of investigation, such as computed X-ray tomography, DEXA or magnetic resonance imaging.
• Spatial resolution is better in high frequency ultrasound transducers than it is in most other imaging modalities.

 Weaknesses

• Sonographic devices have trouble penetrating bone. For example, sonography of the adult brain is very limited though improvements are being made in transcranial ultrasonography.
• Sonography performs very poorly when there is a gas between the transducer and the organ of interest, due to the extreme differences in acoustic impedance. For example, overlying gas in the gastrointestinal tract often makes ultrasound scanning of the pancreas difficult, and lung imaging is not possible (apart from demarcating pleural effusions).
• Even in the absence of bone or air, the depth penetration of ultrasound may be limited depending on the frequency of imaging. Consequently, there might be difficulties imaging structures deep in the body, especially in obese patients.
• The method is operator-dependent. A high level of skill and experience is needed to acquire good-quality images and make accurate diagnoses.
• There is no scout image as there is with CT and MR. Once an image has been acquired there is no exact way to tell which part of the body was imaged.

 Risks and side-effects

Ultrasonography is generally considered a "safe" imaging modality.^[10] However slight detrimental effects have been occasionally observed (see below). Diagnostic ultrasound studies of the fetus are generally considered to be safe during pregnancy. This diagnostic procedure should be performed only when there is a valid medical indication, and the lowest possible ultrasonic exposure setting should be used to gain the necessary diagnostic information under the "as low as reasonably achievable" or ALARA principle.

World Health Organizations technical report series 875(1998).^[11] supports that ultrasound is harmless: "Diagnostic ultrasound is recognized as a safe, effective, and highly flexible imaging modality capable of providing clinically relevant information about most parts of the body in a rapid and cost-effective fashion". Although there is no evidence ultrasound could be harmful for the fetus, US Food and Drug Administration views promotion, selling, or leasing of ultrasound equipment for making "keepsake fetal videos" to be an unapproved use of a medical device.

 Studies on the safety of ultrasound

• A study at the Yale Medical School found a correlation between prolonged and frequent use of ultrasound and abnormal neuronal migration in mice.^[12]
• A study published in 2001 by a team working at the Karolinska Institute in Stockholm found a correlation between the number of scans received by male fetuses and subsequent left-handedness. ^[13]
• A meta-analysis of several ultrasonography studies found no statistically significant harmful effects from ultrasonography, but mentioned that there was a lack of data on long-term substantive outcomes such as neurodevelopment.^[14]

 Regulation

Diagnostic and therapeutic ultrasound equipment is regulated in the USA by the FDA, and worldwide by other national regulatory agencies. The FDA limits acoustic output using several metrics. Generally other regulatory agencies around the world accept the FDA-established guidelines.

Currently New Mexico is the only state the USA which regulates diagnostic medical sonographers. Certification examinations for sonographers are available in the US from three organizations: The American Registry of Diagnostic Medical Sonography,Cardiovascular Credentialing International and the American Registry of Radiological Technologists.

The primary regulated metrics are MI (Mechanical Index) a metric associated with the cavitation bio-effect, and TI (Thermal Index) a metric associated with the tissue heating bio-effect. The FDA requires that the machine not exceed limits that they have established. This requires self-regulation on the part of the manufacturer in terms of the calibration of the machine. The established limits are reasonably conservative so as to maintain diagnostic ultrasound as a safe imaging modality.^{[citation needed]}

 Career Information

According to the Society of Diagnostic Medical Sonography, a diagnostic medical sonographer earns an average of $66,768 (2008). Sonographers work in a variety of settings including hospitals, clinics, physician offices, and mobile labs. Some even use their skills and knowledge in veterinary offices. Information about a career in Diagnostic Medical Sonography is available from the Society of Diagnostic Medical Sonography. The US Department of Labor also provides information about the field in its Occupation Outlook Handbook.

 History

 United States

Ultrasonic energy was first applied to the human body for medical purposes by Dr. George Ludwig at the Naval Medical Research Institute, Bethesda, Maryland in the late 1940s.^[15][16]

In 1962, after about two years of work, Joseph Holmes, William Wright, and Ralph Meyerdirk developed the first compound contact B-mode scanner. Their work had been supported by U.S. Public Health Services and the University of Colorado. Wright and Meyerdirk left the University to form Physionic Engineering Inc., which launched the first commercial hand-held articulated arm compound contact B-mode scanner in 1963. This was the start of the most popular design in the history of ultrasound scanners. ^[17]

The first demonstration of color Doppler was by Geoff Stevenson, who was involved in the early developments and medical use of Doppler shifted ultrasonic energy.^[18]

 Sweden

Medical ultrasonography was used 1953 at Lund University by cardiologist Inge Edler and Carl Hellmuth Hertz, the son of Gustav Ludwig Hertz, who was a graduate student at the department of nuclear physics.

Edler had asked Hertz if it was possible to use radar to look into the body, but Hertz said this was impossible. However, he said, it might be possible to use ultrasonography. Hertz was familiar with using ultrasonic reflectoscopes for nondestructive materials testing, and together they developed the idea of using this method in medicine.

The first successful measurement of heart activity was made on October 29, 1953 using a device borrowed from the ship construction company Kockums in Malmö. On December 16 the same year, the method was used to generate an echo-encephalogram (ultrasonic probe of the brain). Edler and Hertz published their findings in 1954.

 Scotland

Parallel developments in Glasgow, Scotland (coincidentally also a major shipbuilding centre) by Professor Ian Donald and colleagues at the Glasgow Royal Maternity Hospital (GRMH) led to the first diagnostic applications of the technique. Donald was an obstetrician with a self-confessed "childish interest in machines, electronic and otherwise", who, having treated the wife of one of the company's directors, was invited to visit the Research Department of boilermakers Babcock & Wilcox at Renfrew, where he used their industrial ultrasound equipment to conduct experiments on various morbid anatomical specimens and assess their ultrasonic characteristics. Together with the medical physicist Tom Brown and fellow obstetrician Dr John MacVicar, Donald refined the equipment to enable differentiation of pathology in live volunteer patients. These findings were reported in The Lancet on 7 June 1958 as "Investigation of Abdominal Masses by Pulsed Ultrasound" - possibly one of the most important papers ever published in the field of diagnostic medical imaging.

At GRMH, Professor Donald and Dr James Willocks then refined their techniques to obstetric applications including fetal head measurement to assess the size and growth of the fetus. With the opening of the new Queen Mother's Hospital in Yorkhill in 1964, it became possible to improve these methods even further. Dr Stuart Campbell's pioneering work on fetal cephalometry led to it acquiring long-term status as the definitive method of study of fetal growth. As the technical quality of the scans was further developed, it soon became possible to study pregnancy from start to finish and diagnose its many complications such as multiple pregnancy, fetal abnormality and placenta praevia. Diagnostic ultrasound has since been imported into practically every other area of medicine.

 See also

• Emergency ultrasound
• 3D Ultrasound
• Duplex ultrasonography
• Doppler fetal monitor
• EMMI European Master in Molecular Imaging

 References

• Donald I, MacVicar J, Brown TG. Investigation of abdominal masses by pulsed ultrasound. Lancet 1958;1(7032):1188-95. PMID 13550965
• Edler I, Hertz CH. The use of ultrasonic reflectoscope for the continuous recording of movements of heart walls. Kungl Fzsiogr Sallsk i Lund Forhandl. 1954;24:5. Reproduced in Clin Physiol Funct Imaging 2004;24:118-36. PMID 15165281.
• S. A. Kana (2003). Introduction to physics in modern medicine. Tsylor & Francis. ISBN 0-415-30171-8. 
• C. Kasai et al. Real-time two-dimensional blood flow imaging using an autocorrelation technique. IEEE Transactions on Sonics and Ultrasonics 1985:458-464.
• Ohanyido FO,. Basic Sonology for Doctors in Low Income Settings. Healthquest 2005;3:23.
• Bushberg JT (2002). The essential physics of medical imaging. Lippincott Williams & Wilkins. ISBN 0-683-30118-7. 

1. ^ ""Fetal Biometry: Vertical Calvarial Diameter and Calvarial Volume ". July 2000". https://jdm.sagepub.com/cgi/content/abstract/1/5/205. Retrieved on 2008-09-27. 
2. ^ ""3D BPD Correction". July 2000". https://www.obgyn.net/us/cotm/0007/3d-bpd-correction.htm. Retrieved on 2008-09-27. 
3. ^ Sonography of the female pelvic floor Clinical indications and techniques
4. ^ A Review of Therapeutic Ultrasound: Effectiveness Studies, Valma J Robertson, Kerry G Baker, Physical Therapy . Volume 81 . Number 7 . July 2001
5. ^ A Review of Therapeutic Ultrasound: Biophysical Effects, , Kerry G Baker, et al., Physical Therapy . Volume 81 . Number 7 . July 2001
6. ^ The Gale Encyclopedia of Medicine, 2nd Edition Volume 1 A-B. Page no.4
7. ^ "Wikipedia: “Red Shift”". https://en.wikipedia.org/wiki/Redshift. Retrieved on January 25 2008. 
8. ^ "Ellis, George FR, Williams, Ruth M.; “Flat and Curved Space-Times“ 2nd Edition; Oxford University Press, 2000”". https://www.amazon.com/gp/reader/0198506562/ref=sib_dp_ptu#reader-link. Retrieved on January 25 2008. 
9. ^ "“Doppler Ultrasound History”". https://www.obgyn.net/ultrasound/ultrasound.asp?page=feature/doppler_history/history_ultrasound. Retrieved on January 25 2008. 
10. ^ Merritt, CR (01 November 1989). "Ultrasound safety: what are the issues?". Radiology 173 (2): 304–306. PMID 2678243. https://radiology.rsnajnls.org/cgi/reprint/173/2/304. Retrieved on 2008-01-22. 
11. ^ Template:Cite WHO
12. ^ Ang Jr., ES; Gluncic V, Duque A et al. (2006). "Prenatal exposure to ultrasound waves impacts neuronal migration in mice". Proc Natl Acad Sci USA 103 (34): 12903–10. doi:10.1073/pnas.0605294103. PMID 16901978. https://www.pnas.org/cgi/content/full/103/34/12903. Retrieved on 2008-01-22. 
13. ^ Kieler H, Cnattingius S, Haglund B, Palmgren J, Axelsson O (2001). "Sinistrality--a side-effect of prenatal sonography: a comparative study of young men". Epidemiology (Cambridge, Mass.) 12 (6): 618–23. PMID 11679787. 
14. ^ Bricker L, Garcia J, Henderson J, et al. (2000). "Ultrasound screening in pregnancy: a systematic review of the clinical effectiveness, cost-effectiveness and women's views". Health technology assessment (Winchester, England) 4 (16): i-vi, 1–193. PMID 11070816. https://www.hta.ac.uk/execsumm/summ416.htm. 
15. ^ "History of the AIUM". https://www.aium.org/aboutAIUM/timeline/1950.asp. Retrieved on November 15 2005. 
16. ^ "The History of Ultrasound: A collection of recollections, articles, interviews and images". www.obgyn.net. https://www.obgyn.net/us/us.asp?page=/us/news_articles/ultrasound_history/asp-history-toc. Retrieved on 2006-05-11. 
17. ^ Woo, Joseph (2002). "A short History of the development of Ultrasound in Obstetrics and Gynecology". ob-ultrasound.net. https://www.ob-ultrasound.net/history1.html. Retrieved on 2007-08-26. 
18. ^ "Doppler Ultrasound History". www.obgyn.net. https://www.obgyn.net/displayarticle.asp?page=/us/feature/doppler_history/history_ultrasound. Retrieved on 2006-05-11. 

 External links

• American Institute of Ultrasound in Medicine Professional Association
• About the discovery of medical ultrasonography
• History of medical sonography (ultrasound)
• medical sonography in India (ultrasound)
• Procedures in Ultrasound (Sonography) for patients, from RadiologyInfo.org
• Careers in the vascular ultrasound field
• Sonography of the female pelvic floor:clinical indications and techniques Illustrate the clinical utility of this non-invasive diagnostic technique.

Ultrasound

.

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. 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 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.^[1]:34-35

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)

An ultrasound examination in Germany

Contents   1 Ability to hear ultrasound 2 Diagnostic sonography 3 Biomedical ultrasonic applications 4 Industrial ultrasound 5 Ultrasonic cleaning 6 Ultrasonic humidifier 7 Ultrasound Identification (USID) 8 Ultrasound and animals 8.1 Bats 8.2 Dogs 8.3 Dolphins and whales 8.4 Fish 8.5 Moths 8.6 Rodents/insects 9 Sonochemistry 10 Ultrasonic disintegration 11 Ultrasonic range finding 12 Other uses 13 Nonlinear propagation effects 14 Safety 15 See also 16 References 17 Further reading

 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. Ultrasonic hearing can occur if ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear. Carefully-designed scientific studies have been performed supporting what the authors call the hypersonic effect — that even without consciously hearing it, high-frequency sound can have a measurable effect on the mind.^[2]

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.^[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.

 Diagnostic sonography

Sonogram of a fetus at 14 weeks (Profile)

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. It is also used to visualize a fetus during routine and emergency prenatal care. Ultrasound scans are performed by medical health care professionals called sonographers. Obstetric sonography is commonly used during pregnancy. 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). 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] As of May 23, 2008, the AIUM published an article called "American Institute of Ultrasound in Medicine Consensus Report on Potential Bioeffects of Diagnostic Ultrasound: Executive Summary" stating that there are indeed some potential dangers to the fetus in administering ultrasound tests. They are: "Postnatal thermal effects, fetal thermal effects, postnatal mechanical effects, fetal mechanical effects, and bioeffects considerations for ultrasound contrast agents."^[7] 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 have shown decrease in size of red blood cells in cattle when exposed to intensity higher than diagnostic levels.^[8] However, long term effects due to ultrasound exposure at diagnostic intensity is not known.^[9] 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. ^[10] A typical fetal scan, including evaluation for fetal malformations, typically takes 10–30 minutes.^[11] 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.^[12] 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.^[13]

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:

• Date the pregnancy (gestational age)
• Confirm fetal viability
• Determine location of fetus, intrauterine vs ectopic
• Check the location of the placenta in relation to the cervix
• Check for the number of fetuses (multiple pregnancy)
• Check for major physical abnormalities.
• Assess fetal growth (for evidence of intrauterine growth restriction (IUGR))
• Check for fetal movement and heartbeat.
• Determine the sex of the baby

Unfortunately, results are occasionally wrong,^{[citations needed]} producing a false positive (the Cochrane Collaboration is a relevant effort to improve the reliability of health care trials). 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."^[14]

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). 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. 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.

Ultrasound scanners have different Doppler-techniques to visualize arteries and veins. The most common is colour doppler or power doppler, but also other techniques like b-flow are used to show bloodflow in an organ. By using pulsed wave doppler or continuous wave doppler bloodflow velocities can be calculated.

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.

Ultrasound is also increasingly being used in trauma and first aid cases, with emergency ultrasound becoming a staple of most EMT response teams.

 Biomedical ultrasonic applications

Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions:^[15]

• According to RadiologyInfo,^[16] ultrasounds are useful in the detection of pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men.
• Treating benign and malignant tumors and other disorders via a process known as high intensity focused ultrasound (HIFU), also called focused ultrasound surgery (FUS). In this procedure, a generally lower frequencies than medical diagnostic ultrasound is used (250-2000 kHz), but significantly higher time-averaged intensities. The treatment is often guided by magnetic resonance imaging (MRI)—this is called Magnetic resonance-guided focused ultrasound (MRgFUS). Delivering chemotherapy to brain cancer cells and various drugs to other tissues is called acoustic targeted drug delivery (ATDD).^[17] These procedures generally use high frequency ultrasound (1-10 MHz) and a range of intensities (0-20 watts/cm²). The acoustic energy is focused on the tissue of interest to agitate its matrix and make it more permeable for therapeutic drugs.^[18][19]
  Enhanced drug uptake using acoustic targeted drug delivery (ATDD).
• Therapeutic ultrasound, a technique that uses more powerful ultrasound sources to generate cellular effects in soft tissue has fallen out of favor as research has shown a lack of efficacy^[20] and a lack of scientific basis for proposed biophysical effects.^[21] Ultrasound has been used in cancer treatment.
• Cleaning teeth in dental hygiene.
• Focused ultrasound sources may be used for cataract treatment by phacoemulsification.
• Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. the ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.
• Ultrasound is essential to the procedures of ultrasound-guided sclerotherapy and endovenous laser treatment for the non-surgical treatment of varicose veins.
• Ultrasound-assisted lipectomy is lipectomy assisted by ultrasound. Liposuction can also be assisted by ultrasound.
• Doppler ultrasound is being tested for use in aiding tissue plasminogen activator treatment in stroke sufferers in the procedure called ultrasound-enhanced systemic thrombolysis.
• Low intensity pulsed ultrasound is used for therapeutic tooth and bone regeneration.
• Ultrasound can also be used for elastography. This can be useful in medical diagnoses, as elasticity can discern healthy from unhealthy tissue for specific organs/growths. In some cases unhealthy tissue may have a lower system Q, meaning that the system acts more like a large heavy spring as compared to higher values of system Q (healthy tissue) that respond to higher forcing frequencies. Ultrasonic elastography is different from conventional ultrasound, as a transceiver (pair) and a transmitter are used instead of only a transceiver. One transducer acts as both the transmitter and receiver to image the region of interest over time. The extra transmitter is a very low frequency transmitter, and perturbs the system so the unhealthy tissue oscillates at a low frequency and the healthy tissue does not. The transceiver, which operates at a high frequency (typically MHz) then measures the displacement of the unhealthy tissue (oscillating at a much lower frequency). The movement of the slowly oscillating tissue is used to determine the elasticity of the material, which can then be used to distinguish healthy tissue from the unhealthy tissue.
• Ultrasound has been shown to act synergistically with antibiotics in bacterial cell killing.^[22]
• Ultrasound has been postulated to allow thicker eukaryotic cell tissue cultures by promoting nutrient penetration.Scientific Article
• Ultrasound in the low MHz range in the form of standing waves is an emerging tool for contactless separation, concentration and manipulation of microparticles and biological cells, a method referred to as acoustophoresis. The basis is the acoustic radiation force, a non-linear effect which causes particles to be attracted to either the nodes or anti-nodes of the standing wave depending on the acoustic contrast factor, which is a function of the sound velocities and densities of the particle and of the medium in which the particle is immersed.

 Industrial ultrasound

Non-destructive testing of a swing shaft showing spline cracking

See also: Macrosonic and Ultrasonic testing

Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects. 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. Lower frequency ultrasound (50 kHz to 500 kHz) can also be used to inspect less dense materials such as wood, concrete and cement.

Ultrasound can also be used for heat transfer in liquids.^[23]

Researchers recently employed ultrasound in dry corn milling plant to enhance ethanol production.^[24]

 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 works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. The bubbles made by cavitation collapse forming tiny jets directed at the surface. 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. 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,^[25] 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 and animals

 Bats

Bats use ultrasounds to move in the darkness.

Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies as high as 100 kHz, although there is some disagreement on the upper limit.^[26]

 Dogs

Dogs can hear sound at higher frequencies than humans can. A dog whistle exploits this by emitting a high frequency sound to call to a dog. 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.

 Dolphins and whales

It is well known that some whales can hear ultrasound and have their own natural sonar system. Some whales use the ultrasound as a hunting tool (for both detection of prey and as an attack).^[27]

 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.g. herrings) can hear only up to 4 kHz.^[28]

 Moths

There is evidence that ultrasound in the range emitted by bats causes flying moths to make evasive manoeuvres because bats eat moths. Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop a few inches in its flight to evade attack.^{[29][dead link]}

 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. 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.^{[citation needed]}

 Sonochemistry

Main article: Sonochemistry

Power ultrasound in the 20-100 kHz range is used in chemistry. 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. Instead:

• It causes cavitation which causes local extremes of temperature and pressure in the liquid where the reaction happens.
• It breaks up solids and removes passivating layers of inert material to give a larger surface area for the reaction to occur over.

Both of these make the reaction faster.

• It is used in extraction, using different frequencies.

 Ultrasonic disintegration

Some sorts of ultrasound can disintegrate biological cells including bacteria. This has uses in biological science and in killing bacteria in sewage. High power ultrasound at frequency of around 20 kHz produces cavitation that facilitates particle disintegration.^{[citations needed]} 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:-

• Ultrasound pre-treatment of waste activated sludge
• Retooling ethanol industries: integrating ultrasonics into dry corn milling to enhance ethanol yield
• Enhancement of anaerobic sludge digestion by ultrasonic disintegration

 Ultrasonic range finding

Principle of an active sonar

Main article: sonar

A common use of ultrasound is in range finding; this use is also called SONAR, (sound navigation and ranging). This works similarly to RADAR (radio detection and ranging): An ultrasonic pulse is generated in a particular direction. 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. 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. This phenomenon is being investigated partly because of the possibility of bubble fusion (a nuclear fusion reaction hypothesized to occur during sonoluminescence).

Recently researchers at the University of Alberta in Canada have successfully used ultrasound to regenerate dental material^[30].

Ultrasound is used when characterizing particulates through the technique of ultrasound attenuation spectroscopy or by observing electroacoustic phenomena.

In rheology, an acoustic rheometer relies on the principle of ultrasound. In fluid mechanics, fluid flow can be measured using an ultrasound flow meter.

Ultrasound also plays a role in Sonic weaponry.

High and ultra high ultrasound waves are used in Acoustic microscopy

Audio can be propagated by modulated ultrasound.

 Nonlinear propagation effects

Because of their high amplitude to wavelength ratio, ultrasonic waves commonly display nonlinear propagation.

 Safety

Occupational exposure to ultrasound in excess of 120dB may lead to hearing loss. Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death.^[31]

 See also

• Acoustics
• Bat detector
• Infrasound — sound at extremely low frequencies
• Light
• Medical ultrasonography
• Picosecond Ultrasonics
• Sound
• Sound from ultrasound (also known as Hypersonic sound)
• Waves
• Sonomicrometry
• Zone sonography technology

 References

1. ^ Novelline, Robert. Squire's Fundamentals of Radiology. Harvard University Press. 5th edition. 1997. ISBN 0674833392.
2. ^ Details of the results are given with citations at hypersonic effect.
3. ^ Takeda, S et al (1992). "Age variation in the upper limit of hearing". European Journal of Applied Physiology 65 (5): 403–408. https://www.springerlink.com/content/m638p784x2112475/. Retrieved on 2008-11-17.  edit
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. ^ AIUM. (2008). " JOURNAL OF ULTRASOUND IN MEDICINE FEATURES BIOEFFECTS CONSENSUS REPORT ". (see here for more articles and information)
8. ^ Japanese Journal of Applied Physics - Fundamental Examination of Cattle Red Blood Cells Damage with Ultrasound Exposure Microscopic System (UEMS)
9. ^ FDA Radiological Health - Ultrasound Imaging
10. ^ Ultrasound Can Affect Fetal Brain Development | LiveScience
11. ^ https://www.obgyn.net/femalepatient/femalepatient.asp?page=levi_tfp "Ultrasonographic Screening for Fetal Malformations"
12. ^ Patient Information - Ultrasound Safety
13. ^ "Ultrasound for fetal assessment in early pregnancy". https://www.cochrane.org/reviews/en/ab000182.html. 
14. ^ https://www.efsumb.org/efsumb/committees/Safety_Committee/Safety_Eng/Clinical Safety Statement 2006.pdf
15. ^ Essentials of Medical Ultrasound: A Practical Introduction to the Principles, Techniques and Biomedical Applications, edited by M. H. Rapacholi, Humana Press 1982
16. ^ "Ultrasound - Pelvis". https://www.radiologyinfo.org/en/info.cfm?pg=pelvus&bhcp=1. 
17. ^ "Acoustic targeted drug delivery in neurological tissue". https://scitation.aip.org/vsearch/servlet/VerityServlet?KEY=ASADL&smode=strresults&sort=rel&maxdisp=25&threshold=0&pjournals=ARLOFJ,JASMAN,NOCOAN,SOUCAU,PMARCW,ASASTR&possible1=george+lewis&possible1zone=article&OUTLOG=NO&viewabs=JASMAN&key=DISPLAY&docID=1&page=0&chapter=0. 
18. ^ "A phantom feasibility study of acoustic enhanced drug delivery to neurological tissue". https://www.ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=4400869&arnumber=4400886&count=67&index=16. 
19. ^ "Acoustics and brain cancer". https://www.eurekalert.org/pub_releases/2007-11/aiop-hou110607.php. 
20. ^ A Review of Therapeutic Ultrasound: Effectiveness Studies, Valma J Robertson, Kerry G Baker, Physical Therapy . Volume 81 . Number 7 . July 2001
21. ^ A Review of Therapeutic Ultrasound: Biophysical Effects, , Kerry G Baker, et al, Physical Therapy . Volume 81 . Number 7. July 2001
22. ^ "Citation list". https://jba.sagepub.com/cgi/content/refs/18/4/237. 
23. ^ Milton B. Larson, Study of the Effects of Ultrasonic Vibrations on Convective Heat Transfer in Liquids, (1960)
24. ^ Using Infrared To See If You're Lit
25. ^ Microbial contamination by ultrasonic humidifier
26. ^ Cancel, Juan (1998). "Frequency of Bat Sonar". The Physics Factbook. https://hypertextbook.com/facts/1998/JuanCancel.shtml. 
27. ^ Voices in the Sea
28. ^ Mann DA, et al. (2001) Ultrasound detection by clupeiform fishes. JASA 109 (6), 3048-3054 | doi:10.1121/1.1368406
29. ^ https://www.irysec.vic.edu.au/sci/goneill/butterflyevo.htm
30. ^ Toothsome research may hold key to repairing dental disasters - ExpressNews - University of Alberta
31. ^ Guidelines for the Safe Use of Ultrasound Part II - Industrial & Commercial Applications - Safety Code 24. Health Canada. 1991. ISBN 0-660-13741-0. https://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/safety-code_24-securite/health-sante-eng.php#a2.2. 

 Further reading

• Kundu, Tribikram. Ultrasonic nondestructive evaluation: engineering and biological material characterization. Boca Raton, FL: CRC Press, c2004. ISBN 0849314623.
• Guidelines for the Safe Use of Ultrasound: valuable insight on the boundary conditions tending towards abuse of ultrasound.
• High-frequency hearing risk for operators of industrial ultrasonic devices:
• Safety Issues in Fetal Ultrasound:
• Damage to red blood cells induced by acoustic cavitation(ultrasound):

Echocardiography

 

An echocardiogram. Image shows that the human heart has four chambers. Apical view - left side of the heart to the right. Anatomically correct image - heart's apex at bottom. The trace in the lower left shows the cardiac cycle and the red mark the time in the cardiac cycle that the image was captured.

An abnormal echocardiogram. Image shows a mid-muscular ventricular septal defect. The trace in the lower left shows the cardiac cycle and the red mark the time in the cardiac cycle that the image was captured. Colors are used to represent the velocity and direction of blood flow.

An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart. Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart. The latest ultrasound systems now employ 3D real-time imaging.

In addition to creating two-dimensional pictures of the cardiovascular system, an echocardiogram can also produce accurate assessment of the velocity of blood and cardiac tissue at any arbitrary point using pulsed or continuous wave Doppler ultrasound. This allows assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), and calculation of the cardiac output as well as the ejection fraction.

Echocardiography was an early medical application of ultrasound. Echocardiography was also the first application of intravenous contrast-enhanced ultrasound. This technique injects gas-filled microbubbles into the venous system to improve tissue and blood delineation. Contrast is also currently being evaluated for its effectiveness in evaluating myocardial perfusion. It can also be used with Doppler ultrasound to improve flow-related measurements (see Doppler echocardiography).

Echocardiography is either performed by cardiac sonographers or doctors trained in cardiology.

Contents   1 Purpose 2 Transthoracic echocardiogram 3 Transesophageal echocardiogram 4 3-dimensional echocardiography 5 Accreditation 6 See also 7 References 8 External links

 Purpose

Echocardiography is used to diagnose cardiovascular diseases. In fact, it is one of the most widely used diagnostic tests for heart disease. It can provide a wealth of helpful information, including the size and shape of the heart, its pumping capacity and the location and extent of any damage to its tissues. It is especially useful for assessing diseases of the heart valves. It not only allows doctors to evaluate the heart valves, but it can detect abnormalities in the pattern of blood flow, such as the backward flow of blood through partly closed heart valves, known as regurgitation. By assessing the motion of the heart wall, echocardiography can help detect the presence and assess the severity of coronary artery disease, as well as help determine whether any chest pain is related to heart disease. Echocardiography can also help detect hypertrophic cardiomyopathy. The biggest advantage to echocardiography is that it is noninvasive (doesn't involve breaking the skin or entering body cavities) and has no known risks or side effects.

 Transthoracic echocardiogram

A standard echocardiogram is also known as a transthoracic echocardiogram (TTE), or cardiac ultrasound. In this case, the echocardiography transducer (or probe) is placed on the chest wall (or thorax) of the subject, and images are taken through the chest wall. This is a non-invasive, highly accurate and quick assessment of the overall health of the heart. A cardiologist can quickly assess a patient's heart valves and degree of heart muscle contraction (an indicator of the ejection fraction). The images are displayed on a monitor, and are recorded either by videotape (analog) or by digital techniques.

An echocardiogram can be used to evaluate all four chambers of the heart. It can determine strength of the heart, the condition of the heart valves, the lining of the heart (the pericardium), and the aorta. It can be used to detect a heart attack, enlargement or hypertrophy of the heart, infiltration of the heart with an abnormal substance. Weakness of the heart, cardiac tumors, and a variety of other findings can be diagnosed with an echocardiogram. With advanced measurements of the movement of the tissue with time (tissue doppler), it can measure diastolic function, fluid status^[1], and dys-synchrony.

The TTE is highly accurate for identifying vegetations (masses consisting of a mixture of bacteria and blood clots), but the accuracy can be reduced in up to 20% of adults because of obesity, chronic obstructive pulmonary disease, chest-wall deformities, or otherwise technically difficult patients. TTE in adults is also of limited use for the structures at the back of the heart, such as the left atrial appendage. Transesophageal echocardiography may be more accurate than TTE because it excludes the variables previously mentioned and allows closer visualization of common sites for vegetations and other abnormalities. Transesophageal echocardiography also affords better visualization of prosthetic heart valves.

 Transesophageal echocardiogram

This is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient's esophagus. This allows image and Doppler evaluation which can be recorded. This is known as a transesophageal echocardiogram, or TEE (TOE in the United Kingdom). The advantage of TEE over TTE is usually clearer images, especially of structures that are difficult to view transthoracicly (through the chest wall). The explanation for this is that the heart rests directly upon the esophagus leaving only millimeters that the ultrasound beam has to travel. This reduces the attenuation (weakening) of the ultrasound signal, generating a stronger return signal, ultimately enhancing image and Doppler quality. Comparatively, transthoracic ultrasound must first traverse skin, fat, ribs and lungs before reflecting off the heart and back to the probe before an image can be created. All these structures, along with the increased distance the beam must travel, weaken the ultrasound signal thus degrading the image and Doppler quality.

In adults, several structures can be evaluated and imaged better with the TEE, including the aorta, pulmonary artery, valves of the heart, both atria, atrial septum, left atrial appendage, and coronary arteries. TEE has a very high sensitivity for locating a blood clot inside the left atrium.^[2] While TTE can be performed quickly, easily and without pain to the patient, TEE requires a fasting patient, (the patient must not eat or drink after midnight on the day before the procedure), a team of medical personnel, takes longer to perform, is uncomfortable for the patient and has some risks associated with the procedure (esophageal perforation -- 1 in 10,000, and adverse reactions to the medication).

Before inserting the probe, conscious sedation is induced in the patient to ease the discomfort and to decrease the gag reflex, thus making the ultrasound probe easier to pass into the esophagus. Conscious sedation is a light sedation usually using the medications midazolam (a benzodiazepine with sedating, amnesiac qualities) and fentanyl. Sometimes a local anesthetic spray is used for the back of the throat, such a xylocaine and/or a jelly/lubricant anesthetic for the esophagus. Children are anesthetized. Unlike the TTE, the TEE is considered an invasive procedure and is thus performed by physicians in the U.S., not sonographers.

 3-dimensional echocardiography

3D echocardiogram of a heart viewed from the apex

3-D echocardiography is now possible, using an ultrasound probe with an array of transducers and an appropriate processing system. This enables detailed anatomical assessment of cardiac pathology, particularly valvular defects,^[3] and cardiomyopathies.^[4] The ability to slice the virtual heart in infinite planes in an anatomically appropriate manner and to reconstruct 3-dimensional images of anatomic structures make 3D echocardiography unique for the understanding of the congenitally malformed heart. ^[5]

 Accreditation

The "Intersocietal Commission for the Accreditation of Echocardiography Laboratories" (ICAEL) sets standards for the echo labs, cardiologists and technologists in the US to comply to. Once all requirements have been met, the lab will receive ICAEL certification. A lab that has received the certification may also receive higher reimbursement from insurance companies such as Medicare and United Healthcare. https://www.icael.org/icael/index.htm
In the UK, accreditation is done by the British Society of Echocardiography. Accredited technologists or other professionals from the echocardiography field will have completed a logbook and passed an exam.

It can be used for diseases like artherosclerosis, myocardial infarction and other coronory heart diseases.

At a European level,individual and laboratory accreditation is provided by the European Association of Echocardiography (EAE). Three subspecialties for individual accreditation: Adult Transthoracic Echocardiography (TTE), Adult Transesophageal Echocardiography (TEE) and Congenital Heart Disease Echocardiography (CHD).

 See also

• Angiogram
• Aortic valve area calculation
• Electrocardiogram
• Fetal echocardiography

 References

1. ^ Ommen SR, Nishimura RA, Appleton CP, Miller FA, Oh JK, Redfield MM, Tajik AJ. (2000). "Clinical utility of Doppler echocardiography and tissue Doppler imaging in the estimation of left ventricular filling pressures: A comparative simultaneous Doppler-catheterization study" (PDF). Circulation 102 (15): 1788–94. PMID 11023933. https://circ.ahajournals.org/cgi/reprint/102/15/1788.pdf. 
2. ^ www.heartsite.com
3. ^ Poh KK, Levine RA, Solis J, Shen L, Flaherty M, Kang YJ, Guerrero JL, Hung J. (2008). "Assessing aortic valve area in aortic stenosis by continuity equation: a novel approach using real-time three-dimensional echocardiography". Eur Heart J 29: 2526. doi:10.1093/eurheartj/ehn022. PMID 18263866. 
4. ^ Goland S, Czer LS, Luthringer D, Siegel RJ. (2008). "A case of arrhythmogenic right ventricular cardiomyopathy". Can J Cardiol 24 (1): 61–2. PMID 18209772. 
5. ^ Impact of Multiplanar Review of Three-Dimensional Echocardiographic Data on Management of Congenital Heart Disease. Ann. Thorac. Surg., September 2008; 86: 875 - 881)

 

 External links

• Echo Film of Torn Mitral Valve
• American Society of Echocardiography
• British Society of Echocardiography
• International Society of Cardiovascular Ultrasound
• Echocardiography Library
• Information on congenital echocardiography
• European Association of Echocardiography
• 3D Echo Box: Interpretation of 3 Dimensional Echocardiography images and derive information online
• VIRTUAL TEE - online self-study and teaching resource
• Echobasics - free online echocardiography tutorial
• Algorithms and System for Digital Echocardiogram Video Indexing and Su

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