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Ultrasonography

Ultrasonography

Definition

Ultrasonography is a diagnostic technique that involves directing high frequency sound waves at tissues in the body to generate images of anatomical structures. Ultrasonography is also called sonography, diagnostic sonography, and echocardiography when it is used to image the heart.

Purpose

Ultrasonography has a variety of uses in medical diagnostics. It is most well suited for imaging soft tissues that are solid and uniform or filled with fluid. It does not perform well when imaging calcified objects such as bone or objects filled with air like the bowel. Some of the more common uses for ultrasonography include imaging fetus development during pregnancy, diagnosing gallbladder disease and some forms of cancer, and evaluating abnormalities in the scrotum and prostate, heart, and thyroid gland. Ultrasound can also be used to perform breast exams. A technique called Doppler imaging ultrasonography can also be used to view the movement of blood through blood vessels and to guide needles through anatomical structures for obtaining specimens for biopsy . Three-dimensional ultrasounds provide detailed images of fetuses in the uterus.

The majority of ultrasonic exams are performed externally by running a transducer over the surface of the skin. Usually a gel is applied to the skin on which the transducer will glide during the exam. The gel helps prevent the formation of air pockets between the transducer and the skin that interfere with the ultrasonic signal. Some ultrasound diagnostic tests require the insertion of a probe into a body orifice. For example, during a trans-esophageal echocardiogram a specialized transducer is placed in the esophagus to better image the heart. Trans-rectal exams require a transducer to be inserted into a man's rectum to obtain images of the prostate. Transvaginal ultrasounds are used to provide images of a woman's ovaries and uterus or of a fetus during the early weeks of pregnancy.

Ultrasound is generally a painless procedure. Some discomfort may be felt when the transducer is pressed against the skin or when the transducer is inserted in the body. Most ultrasonic procedures take less than half of an hour.

Cranial ultrasound

Cranial ultrasonography is most often used in infants to diagnose problems with the brain and the ventricles in the brain through which cerebrospinal fluid (the clear fluid that circulates through the brain and spinal cord) flows. These abnormalities are often associated with premature birth. Because ultrasound waves are poorly conducted through bones, cranial ultrasonography must be performed on infants before the fontanel (gaps between the bones of the cranium) have closed. Cranial ultrasonography is also performed on adults during brain surgery to help identify the location of brain tumors. In adults, the skull must be surgically opened in order to use ultrasonography.

In infants, cranial ultrasonography is most often used to diagnose two complications. Intraventricular hemorrhage (IVH) occurs when there is bleeding in the brain. This occurs more commonly in premature babies and is likely to happen within the first week of the infant's life. Periventricular leukomalacia (PVL) occurs when the tissue around the ventricles in the brain is damaged. This complication can occur within several weeks of birth. Both IVH and PVL are associated with mental disabilities and developmental delays. Cranial ultrasonography can also be used to evaluate brain abnormalities in babies, such as congenital hydrocephalus or tumors, or to detect infection.

Description

Ultrasonography relies on sound waves to create an image of the soft tissues in the body. Sound waves are a form of energy called longitudinal pressure waves that result when molecules are pushed together and then become rarified (less dense). The molecules through which the wave passes are not transported by the wave; rather, they vibrate back and forth around a neutral position. The number of times that a molecule moves through a compression and rarification cycle in one second is called the frequency of the wave. The unit of the frequency of a sound wave is the Hertz (Hz). Frequencies between about 20 Hz and 20,000 Hz are audible to the human ear and the greater the frequency, the higher a sound wave sounds. Frequencies above 20,000 Hz are called ultrasonic and the human ear cannot detect these sound waves. The frequencies of sound waves used in ultrasonography are between about one million and 15 million Hz (or one and 15 MHz).

An ultrasound machine typically consists of four parts: the transducer, which allows for the movement of the ultrasound machine over the body; the electronic signal processing unit, which controls the power to the transducer; the display unit, which is usually a computer screen; and a device for storing the images, which is usually a videotape or a camera.

The transducer is the most technologically interesting part of the ultrasonography machine. It is usually a hand-held device that can be pushed against the skin or inserted into an orifice. The transducer is made up of a plastic or ceramic material that has piezoelectric properties. This means that it is capable of generating and detecting ultrasound waves. If pulses of electric current are applied to the surface of a transducer, the piezoelectric surface will change in thickness in response to the pulses. This change in thickness causes a change in pressure in the molecules surrounding the piezoelectric surface, generating sound waves. If the pulses occur between one and 15 million times a second, then the result is a sound wave with an ultrasonic frequency. Similarly, the piezoelectric surface acts as a receptor for return waves. When sound waves collide with the piezoelectric surface, they cause a change in its thickness. This change in thickness is converted to a change in the electric current in the transducer, which is then interpreted as various shades of gray and used to form an image on the display unit. The electronics of the transducer are constructed so that ultrasound beams are generated, followed by a pause during which the return waves are detected; this cycle continues during the entire diagnostic procedure.

An ultrasonic wave that is directed out of the transducer and into tissues of the body has one of four outcomes: it can be absorbed by the material, in which case the transducer will receive no return signal; it can be reflected back to the transducer, in which case the transducer will receive a strong return signal; it can be refracted so that it changes direction and only a part of the signal will return to the transducer; finally, the wave can be scattered, greatly reducing the signal received by the transducer. At various tissue interfaces, different amounts of the wave energy are returned to the transducer as a result of various combinations of absorption, reflection, refraction, and scattering. For example, at a fat-muscle interface, about 1% of the incident wave is returned to the transducer, while at a bone-muscle interface, about 40% of the incident wave is returned. At any interface that involves air, such as a gas bubble in the bowel, nearly 100% of the incident wave will be returned to the transducer. Similarly, bones and other calcified objects like kidney stones and gallstones result in very high reflection of the incident wave. Because air acts as such a strong reflector of an ultrasonic wave, gel or some other lubricant is usually placed between the transducer and the skin during an ultrasonic exam.

Some ultrasonic machines take advantage of the Doppler effect in order to display color images of the flow of blood or other fluids. When an ultrasound wave is directed at a stationary object, the return wave will remain the same frequency as the incident wave, although it will be attenuated depending upon the structures with which it interacts. On the other hand, when an ultrasound wave is directed at a moving object, the return wave will have a different frequency than the incident wave depending on whether the moving object is in the same direction as, or in the opposite direction from, the incident wave. This change in frequency can be interpreted, for example, as the speed of blood flow within a vessel.

The recent development of color Doppler sonography (CDS) has improved several diagnostic exams. In this technique, a black and white image of the anatomical structures resulting from traditional ultrasonography is overlaid with a color image showing the flow of a fluid within the tissues generated from a Doppler ultrasonograph. CDS has proven extremely useful for evaluating the blood flow to the placenta and uterus during pregnancy. It has also been used to quantify the blood flow to various tumors; malignant tumors tend to have greater rates of blood flow and longer residence times than benign ones.

Several other new technologies associated with ultrasonography are becoming available as diagnostic tools. Some physicians are using ultrasonography in conjunction with contrast agents that provide better resolution of internal structures. This is particularly useful for visualizing the heart and kidneys more effectively. Harmonic imaging is a technique that is used to improve the signal-to-noise ratio of an ultrasonic image. It is based on the idea that the tissues of the body resonate harmonically, similar to a musical instrument. Therefore, taking advantage of sound waves at two and three times the frequency of the incident wave should provide additional information about the internal structures of the body. For example, if the incident wave of the transducer is 4 MHz, then using return waves that are 8 MHz should improve the resolution of the image. Finally, three-dimensional sonography is available on some machines. In some cases, the three-dimensional image is reconstructed from several sweeps of the transducer at different levels through the body. In others, two transducers that are oriented perpendicular to each other are used to build a three-dimensional image. This technology has been used most frequently to visualize fetuses in the uterus.

Preparation

Preparation for ultrasonography differs depending on the type of exam being performed. For some exams, no preparation is necessary. For others, fasting and abstaining from drinking for up to 12 hours prior to the exam is required. Some exams, like the transabdominal ultrasound, require that the patient have a full bladder because the ultrasonic waves are best transmitted through fluid. If a biopsy is required, antibiotics may be administered prior to the test. The physician or technician performing the exam usually provides instructions on proper preparation prior to the exam.

Risks

Because ultrasonography uses high frequency sound waves, and not x rays or other forms of radiation , there are very few risks associated with its use. Sound waves are either reflected back to the transducer, or the tissues of the body absorb them and they dissipate as heat. There may be a slight increase in heat in the body as a result, but no negative effects of this heat have been documented.

Normal results

Results of ultrasonic tests are usually sent to a physician and possibly to a radiologist. They are usually made available to the patient within one to two days.

Resources

BOOKS

Fleischer, Arthur C., et al. Sonography in Obstetrics and Gynecology: Principles and Practice, 6th ed. New York: McGraw-Hill Companies, Inc. 2001.

Fleischer, Arthur C., and Donna M. Kepple. Diagnostic Sonography: Principles and Clinical Applications, 2nd ed. Philadelphia: W. B. Saunders Company, 1995.

OTHER

"Ultrasound Imaging." The Mayo Clinic. January 3, 2004 (April 4, 2004). <http://www.mayoclinic.com/invoke.cfm?objectid=2F0F9036-342F-4723-9DDBAB9FAEA73A77>.

Moyer, Paula. "3-D Ultrasound: Do You Really Need It?" WebMDHealth. February 2, 2004 (April 4, 2004). <http://my.webmd.com/content/article/21/1728_55256.htm?lastselectedguid={5FE84E90-BC77-4056-A91C-9531713CA348}>.

"Ultrasound." Medline Plus National Library of Medicine. December 3, 2003 (April 4, 2004). <http://www.nlm.nih.gov/medlineplus/tutorials/ultrasound/rd209101.html>.

Juli M. Berwald, PhD

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Berwald, Juli. "Ultrasonography." Gale Encyclopedia of Neurological Disorders. 2005. Encyclopedia.com. 1 Sep. 2016 <http://www.encyclopedia.com>.

Berwald, Juli. "Ultrasonography." Gale Encyclopedia of Neurological Disorders. 2005. Encyclopedia.com. (September 1, 2016). http://www.encyclopedia.com/doc/1G2-3435200364.html

Berwald, Juli. "Ultrasonography." Gale Encyclopedia of Neurological Disorders. 2005. Retrieved September 01, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3435200364.html

Ultrasonography

Ultrasonography

Definition

Ultrasonography is the study of internal organs or blood vessels using high-frequency sound waves. The actual test is called an ultrasound scan or sonogram. Duplex ultrasonography uses Doppler technology to study blood cells moving through major veins and arteries. There are several types of ultrasound. Each is used in diagnosing specific parts of the body.

Purpose

An ultrasound is a noninvasive, safe method of examining a patient's eyes, pelvic or abdominal organs, breast, heart, or arteries and veins. It is often used to diagnosis disease, locate the source of pain, or look for stones in the kidney or gallbladder. Ultrasound produces images in real time. Images appear on the screen instantly. It may also be used to guide doctors who are performing a needle biopsy to locate a mass. (Needle biopsies are often used to obtain a sample of breast tissue to test for cancer cells.) Duplex/Doppler ultrasound aids in diagnosing a blockage in or a malformation of the vessel. Different color flows aid in identifying problem areas in smaller vessels. Endoscopic ultrasound combines a visual endoscopic exam, during which a flexible tube called an endoscope is threaded down the throat, with an ultrasound test. The ultrasound probe is attached to the end of the endoscope. An endoscopic ultrasound is helpful in determining how deeply a tumor has grown into normal tissues or the gastrointestinal tract. During a transvaginal ultrasound , the ultrasound probe is inserted into the vagina to obtain better images of the ovaries and uterus. Color flow Doppler imaging, using a transvaginal probe, is being performed to detect abnormal blood flow patterns associated with ovarian cancer .

Precautions

Ultrasound is considered safe with no known risks or precautions. The exam uses no radiation. Under nor mal circumstances the exam is normally painless. However, if the patient has a full bladder, pressure exerted during the exam may feel uncomfortable. An ultrasound conducted in conjunction with an invasive exam carries the same risks as the invasive exam.

Description

The patient will be asked to lie still on an exam table in a darkened room. The darkness helps the technician see images on a screen, which is similar to a computer monitor. Sometimes the patients are positioned so they can watch the screen. The technician will apply a lubricating gel to the skin over the area to be studied. Ultrasound uses high-frequency sound waves to produce an image. A small wand-like device called a transducer produces sound waves that are sent into the body when the device is pressed against the skin. The gel helps transmit the sound waves, which do not travel through the air. Neither the patient nor the technician can hear the sound waves. The technician moves the device across the skin in the area to be studied. The sound waves bounce off the fluids and tissues inside the body. The transducer picks up the return echo and records any changes in the pitch or direction of the sound. The image is immediately visible on the screen. The technician may print a still picture of any significant images for later review by the radiologist.

Preparation

Depending on the type of ultrasound ordered, patients may not need to do anything prior to the test. Other ultrasound studies may require that the patient not eat or drink anything for up to 12 hours prior to the exam, in order to decrease the amount of gas in the bowel. Intestinal gas may interfere in obtaining accurate results. The patient must have a full bladder for some exams and an empty bladder for others.

Aftercare

Remove any gel still left on the skin. No other after-care is required following an ultrasound.

Risks

Standard, diagnostic ultrasound is considered risk-free. Risks may be associated with invasive tests conducted at the same time, such as an endoscopic ultrasound or an ultrasound-guided needle biopsy.

Normal results

An ultrasound scan is considered normal when the image depicts normally shaped organs or normal blood flow.

Abnormal results

Abnormal echo patterns may represent a condition requiring treatment. Any masses, tumors, enlarged organs or blockages in the blood vessel are considered abnormal. Additional testing may be ordered.

See Also Upper gastrointestinal endoscopy

Resources

BOOKS

Pfenninger, John L. Procedures for Primary Care Physicians, 2nd edition. St. Louis, MO: Mosby-Year Book, Inc, 2000.

Rosen, Peter. Emergency Medicine: Concepts and Clinical Practice. St. Louis, MO: Mosby-Year Book, Inc. 1999.

Schull, Patricia. Illustrated Guide to Diagnostic Tests. Spring-house, PA: Springhouse Corporation, 1997.

ORGANIZATION

American Cancer Society (National Headquarters). 1599Clifton Road, NE Atlanta, Georgia 30329. (800) 227-2345. <http://www.cancer.org>

National Cancer Institute. 9000 Rockville Pike, Building 31, Room 10A31, Bethesda, Maryland, 20892. (800) 422-6237. <http://wwwicic.nci.nih.gov>

Radiological Society of North America (RSNA). 820 Jorie Boulevard, Oak Brook, IL 60523-2251. <http:www.radiologyinfo.org>

Debra Wood, R.N.

KEY TERMS

Biopsy

Removal of a tissue sample for examination under a microscope to check for cancer cells.

Endoscopy

Examination of the upper gastrointestinal tract using a thin, flexible instrument called an endoscope.

Radiologist

Doctor who has received special training and is experienced in performing and analyzing ultrasounds and other radiology exams.

QUESTIONS TO ASK THE DOCTOR

  • Did you see any abnormalities?
  • What future care will I need?

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Wood, Debra. "Ultrasonography." Gale Encyclopedia of Cancer. 2002. Retrieved September 01, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3405200469.html

ultrasound

ultrasound or sonography, in medicine, technique that uses sound waves to study and treat hard-to-reach body areas. In scanning with ultrasound, high-frequency sound waves are transmitted to the area of interest and the returning echoes recorded (for more detail, see ultrasonics). First developed in World War II to locate submerged objects, the technique is now widely used in virtually every branch of medicine. In obstetrics it is used to study the age, sex, and level of development of the fetus and to determine the presence of birth defects or other potential problems. Its use to determine fetal sex has led to the widespread abortion of female fetuses in some countries, such as China and India, where male offspring are more highly valued. Ultrasound is used in cardiology to detect heart damage and in ophthalmology to detect retinal problems. It is also used to heat joints, relieving arthritic joint pain, and for such procedures as lithotripsy, in which shock waves break up kidney stones, eliminating the need for surgery. Ultrasound is noninvasive, involves no radiation, and avoids the possible hazards—such as bleeding, infection, or reactions to chemicals—of other diagnostic methods.

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ultrasonography

ultrasonography (sonography) (ultră-sonn-og-răfi) n. the use of ultrasound to produce images of structures in the human body. The ultrasound probe sends out a short pulse of high-frequency sound and detects the reflected waves (echoes) occurring at interfaces within the organs. The direction of the pulse can then be moved across the area of interest with each pulse to build up a complete image. As far as is known, there are no adverse effects from the use of ultrasound at diagnostic energies. Ultrasonography is used extensively in obstetrics and also to examine the abdominal organs, urinary tract, blood vessels, muscles, and tendons. transrectal u. (TRUS) ultrasonography for examination of the prostate gland and seminal vesicle, in which the ultrasound probe is placed through the anus to lie directly behind these structures. transvaginal u. ultrasonography using a vaginal probe, which provides a detailed anatomy of the female pelvis and early accurate identification of fetal structures.
www.cancerhelp.org.uk/help/default.asp?page=150 Further explanation of the procedure from CancerHelp UK

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"ultrasonography." A Dictionary of Nursing. 2008. Encyclopedia.com. 1 Sep. 2016 <http://www.encyclopedia.com>.

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ultrasound

ultrasound Waves of higher frequency than audible sound waves. Reflection of ultrasound waves was applied to underwater detection during World War II, and subsequently to imaging the body. The harmless waves (>100 Mhz) are aimed at the part to be examined, and reflections are detected from tissue components in proportion to their acoustic impedance. These signals can be processed to create two- or three-dimensional images. The most common use is for viewing the fetus in early pregnancy, but there are also many other diagnostic applications.

Treatment by ultrasound (ultrasonics) is widely used by physiotherapists, particularly for soft tissue injuries but also for a variety of more chronic conditions, with a view to promoting healing and relieving pain. Most commonly frequencies of 1–3 MHz are used. There are differences of opinion and practice, related to whether the intended action should be primarily thermal or non-thermal, but there is a lack of controlled trials on the efficacy of the different methods used.

J. K. Davidson, and Stuart Judge


See imaging techniques; sonogram.

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COLIN BLAKEMORE and SHELIA JENNETT. "ultrasound." The Oxford Companion to the Body. 2001. Encyclopedia.com. 1 Sep. 2016 <http://www.encyclopedia.com>.

COLIN BLAKEMORE and SHELIA JENNETT. "ultrasound." The Oxford Companion to the Body. 2001. Encyclopedia.com. (September 1, 2016). http://www.encyclopedia.com/doc/1O128-ultrasound.html

COLIN BLAKEMORE and SHELIA JENNETT. "ultrasound." The Oxford Companion to the Body. 2001. Retrieved September 01, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O128-ultrasound.html

ultrasound

ultrasound (ultrasonic waves) (ul-tră-sownd) n. sound waves of high frequency (above 20 kHz), inaudible to the human ear. Ultrasound in the range 2–20 MHz can be used to produce images of the interior of the body as the waves reflect off structures back to the probe (see ultrasonography). The vibratory effect of ultrasound can also be used to break up stones (see lithotripsy) and cataracts (see phacoemulsification), to remove calculus from the teeth, to destroy tumours (high-intensity focused u.; HIFU), and in the treatment of rheumatic conditions.

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ultrasound

ul·tra·sound / ˈəltrəˌsound/ • n. sound or other vibrations having an ultrasonic frequency, particularly as used in medical imaging. ∎  an ultrasound scan, esp. one of a pregnant woman to examine the fetus.

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ultrasound

ultrasoundabound, aground, around, astound, bound, compound, confound, dumbfound, expound, found, ground, hound, impound, interwound, mound, pound, profound, propound, redound, round, sound, stoneground, surround, theatre-in-the-round (US theater-in-the-round), underground, wound •spellbound • westbound • casebound •eastbound • windbound • hidebound •fogbound • stormbound •northbound • housebound •outbound • southbound • snowbound •weatherbound • earthbound •hellhound • greyhound • foxhound •newshound • wolfhound •bloodhound • background •battleground • campground •fairground • playground •whip-round • foreground •showground • merry-go-round •runaround • turnaround • ultrasound •pre-owned, unowned •unchaperoned • poind • untuned •Lund

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