Ultra Health Dictionary

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Ultrasound

Ultrasound, or ultrasonic, waves comprise very-high-frequency sound waves above 20,000 Hz that the human ear cannot hear. Ultrasound is widely used for diagnosis and also for some treatments. In OBSTETRICS, ultrasound can assess the stage of pregnancy and detect abnormalities in the FETUS (see below). It is a valuable adjunct in the investigation of diseases in the bladder, kidneys, liver, ovaries, pancreas and brain (for more information on these organs and their diseases, see under separate entries); it also detects thromboses (clots) in blood vessels and enables their extent to be assessed. A non-invasive technique that does not need ionising radiation, ultrasound is quick, versatile and relatively inexpensive, with scans being done in any plane of the body. There is little danger to the patient or operator: unlike, for example, XRAYS, ultrasound investigations can be repeated as needed. A contrast medium is not required. Its reliability is dependent upon the skill of the operator.

Ultrasound is replacing ISOTOPE scanning in many situations, and also RADIOGRAPHY. Ultrasound of the liver can separate medical from surgical JAUNDICE in approximately 97 per cent of patients; it is very accurate in detecting and de?ning cystic lesions of the liver, but is less accurate with solid lesions – and yet will detect 85 per cent of secondary deposits (this is less than COMPUTED TOMOGRAPHY [CT] scanning). It is very accurate in detecting gall-stones (see GALL-BLADDER, DISEASES OF) and more accurate than the oral cholecystogram. It is useful as a screening test for pancreatic disease and can di?erentiate carcinoma of the pancreas from chronic pancreatitis with 85 per cent accuracy.

Ultrasound is the ?rst investigation indicated in patients presenting with renal failure, as it can quickly determine the size and shape of the kidney and whether there is any obstruction to the URETER. It is very sensitive to the presence of dilatation of the renal tract and will detect space-occupying lesions, di?erentiating cysts and tumours. It can detect also obstruction of the ureter due to renal stones by showing dilatations of the collecting system and the presence of the calculus. Adrenal (see ADRENAL GLANDS) tumours can be demonstrated by ultrasound, although it is less accurate than CT scanning.

The procedure is now the ?rst test for suspected aortic ANEURYSM and it can also show the presence of clot and delineate the true and false lumen. It is good at demonstrating subphrenic and subhepatic abscesses (see ABSCESS) and will show most intra-abdominal abscesses; CT scanning is however better for the retroperitoneal region. It has a major application in thyroid nodules as it can di?erentiate cystic from solid lesions and show the multiple lesions characteristic of the nodular GOITRE (see also THYROID GLAND, DISEASES OF). It cannot differentiate between a follicular adenoma and a carcinoma, as both these tumours are solid; nor can it demonstrate normal parathyroid glands. However, it can identify adenomas provided that they are more than 6 mm in diameter. Finally, ultrasound can di?erentiate masses in the SCROTUM into testicular and appendicular, and it can demonstrate impalpable testicular tumours. This is important as 15 per cent of testicular tumours metastasise whilst they are still impalpable.

Ultrasonic waves are one of the constituents in the shock treatment of certain types of gallstones and CALCULI in the urinary tract (see LITHOTRIPSY). They are also being used in the treatment of MENIÈRE’S DISEASE and of bruises and strains. In this ?eld of physiotherapy, ultrasonic therapy is proving of particular value in the treatment of acute injuries of soft tissue. If in such cases it is used immediately after the injury, or as soon as possible thereafter, prompt recovery is facilitated. For this reason it is being widely used in the treatment of sports injuries (see also SPORTS MEDICINE). The sound waves stimulate the healing process in damaged tissue.

Doppler ultrasound is a technique which shows the presence of vascular disease in the carotid and peripheral vessels, as it can detect the reduced blood ?ow through narrowed vessels.

Ultrasound in obstetrics Ultrasound has particular applications in obstetrics. A fetus can be seen with ultrasound from the seventh week of pregnancy, and the fetal heart can be demonstrated at this stage. Multiple pregnancy can also be diagnosed at this time by the demonstration of more than one gestation sac containing a viable fetus. A routine obstetric scan is usually performed between the 16th and 18th week of pregnancy when the fetus is easily demonstrated and most photogenic. The fetus can be measured to assess the gestational age, and the anatomy can also be checked. Intra-uterine growth retardation is much more reliably diagnosed by ultrasound than by clinical assessment. The site of the placenta can also be recorded and multiple pregnancies will be diagnosed at this stage. Fetal movements and even the heartbeat can be seen. A second scan is often done between the 32nd and 34th weeks to assess the position, size and growth rate of the baby. The resolution of equipment now available enables pre-natal diagnosis of a wide range of structural abnormalities to be diagnosed. SPINA BIFIDA, HYDROCEPHALUS and ANENCEPHALY are probably the most important, but other anomalies such as multicystic kidney, achondroplasia and certain congenital cardiac anomalies can also be identi?ed. Fetal gender can be determined from 20 weeks of gestation. Ultrasound is also useful as guidance for AMNIOCENTESIS.

In gynaecology, POLYCYSTIC OVARY SYNDROME can readily be detected as well as FIBROID and ovarian cysts. Ultrasound can monitor follicular growth when patients are being treated with infertility drugs. It is also useful in detecting ECTOPIC PREGNANCY. (See also PREGNANCY AND LABOUR.)... ultrasound

Ultrasonography

The use of ULTRASOUND to produce images of structures in the body that can be viewed on a television screen and transferred to photographic ?lm.... ultrasonography

Ultrafiltration

Filtration carried out under pressure. Blood undergoes ultra?ltration in the KIDNEYS to remove the waste products, urea and surplus water that constitute URINE.... ultrafiltration

Ultraviolet Rays (uvr)

Invisible light rays of very short wavelength beyond the violet end of the sun’s spectrum. Ultraviolet-C (UVC) (wavelength <290 nm [nanometre – see APPENDIX 6: MEASUREMENTS IN MEDICINE]) is entirely absorbed by the earth’s atmosphere and would otherwise be lethally damaging. Ultraviolet-B (UVB – 290– 320 nm) intensity increases with altitude: it is greatest in midsummer and at midday and penetrates cirrhus cloud. UVB causes sunburn and also tanning. Ultraviolet-A (UVA – 320– 400 nm) penetrates deeper into our skins but does not cause sunburn; it is implicated in many photochemical reactions and PHOTODERMATOSES and in CARCINOGENESIS. UVR helps the skin to synthesise vitamin D.

Ultraviolet lamps produce UVR and are used to tan skin but, because of the risk of producing skin cancer (see SKIN, DISEASES OF), the lamps must be used with great caution.... ultraviolet rays (uvr)

Ultrasound Scanning

A diagnostic technique in which very high frequency sound waves are passed into the body and the reflected echoes analysed to build a picture of the internal organs or of a fetus in the uterus. The procedure is painless and considered safe.Ultrasonic waves are emitted by a transducer, which is placed on the skin over the part of the body to be viewed. The transducer contains a crystal that converts an electric current into sound waves. These pass readily through soft tissues and fluids, making this procedure useful for examining fluid-filled or soft organs.

One of the most common uses of ultrasound is to view the uterus and fetus, at any time during pregnancy, but often at 18–20 weeks. The age, size, and growth rate of the fetus can be determined; multiple pregnancies detected; and certain problems, such as neural tube defects, diagnosed. Scans may be taken early in pregnancy if problems, such as an ectopic pregnancy, are suspected.

Ultrasound scanning can also be used in newborn babies to examine the brain through a gap in the skull (for example, to investigate hydrocephalus). Ultrasound can help to diagnose disorders such as cirrhosis, gallstones, hydronephrosis, and pancreatitis, as well as problems in the thyroid gland, breasts, bladder, testes, ovaries, spleen, and eyes. The technique is also used during needle biopsy to help guide the needle.Doppler ultrasound is a modified form of ultrasound that uses the Doppler effect to investigate moving objects.

This can be used to examine the fetal heartbeat and to obtain information about the rate of blood flow in vessels.... ultrasound scanning

Ultraviolet Light

Invisible light from the part of the electromagnetic spectrum immediately beyond the violet end of the visible light spectrum. Long wavelength ultraviolet light is termed , intermediate , and short.

Ultraviolet light occurs in sunlight, but much of it is absorbed by the ozone layer. The ultraviolet light (mainly ) that reaches the earth’s surface causes the tanning effects of sunlight and the production of vitamin D in the skin. It can have harmful effects, such as skin cancer (see sunlight, adverse effects of).

Ultraviolet light is sometimes used in phototherapy.

A mercury-vapour lamp (Wood’s light) can also produce ultraviolet light.

This is used to diagnose skin conditions such as tinea because it causes the infected area to fluoresce.... ultraviolet light

Doppler Ultrasound

a diagnostic technique that utilizes the fact that the frequency of sound or light waves changes when they are reflected from a moving surface (the Doppler effect). It is used to study the flow in blood vessels and the movement of blood in the heart. The frequency detector may be part of an ultrasound imaging probe, which displays an image of the anatomy on a monitor. Simultaneously the Doppler signal from a particular point on the ultrasound image can be displayed superimposed on the anatomical position (duplex imaging). Using electronic techniques, direction and velocity of blood flow can each be allocated different colours and displayed on a colour monitor over the anatomical image (colour flow ultrasound imaging). Power Doppler, a modification of this technique, is more sensitive at detecting flow but does not give information on direction of flow. Doppler ultrasound is a valuable technique to detect vessel thrombosis, such as deep vein thrombosis, and can be safely used in pregnancy without the risk of ionizing radiation. It is extensively used in vascular surgery to assess the status of the blood vessels before surgery, especially in carotid surgery. Doppler measurement of the fetal middle cerebral vessels (MCA Doppler) can predict fetal anaemia as the resistance in these vessels is increased. This noninvasive technique has supplanted serial amniocentesis/fetal cord blood sampling in cases of *haemolytic disease of the newborn. Doppler of other fetal vessels (e.g. the ductus venosus) is used as a screening method for fetal chromosomal and cardiac defects and, later, fetal growth restriction. [C. J. Doppler (1803–53), Austrian physicist]... doppler ultrasound

High-intensity Focused Ultrasound

see HIFU; ultrasound.... high-intensity focused ultrasound

Intravascular Ultrasound

(IVUS) a technique in which a micro *ultrasound transducer is mounted on a catheter, which is then advanced over a guidewire into a blood vessel. IVUS is used to accurately assess the diameter of the blood vessels before any treatment, to assess any internal abnormality within the blood vessels, or to help mark the blood vessel branches during any stent placement.... intravascular ultrasound

Transrectal Ultrasonography

(TRUS) an *ultrasonography technique for examination of the prostate gland and seminal vesicles by placing an ultrasound probe through the anus to lie directly behind these structures in the rectum. Because of the close proximity of the probe, excellent detail is seen. The technique enables transrectal or transperineal biopsies of the prostate to be taken in a systematic manner in the diagnosis of cancer. See also vesiculography.... transrectal ultrasonography

Ultrasound Treatment

The use of ultrasound to treat soft-tissue injuries (such as injuries to ligaments, muscles, and tendons). Ultrasound treatment reduces inflammation and speeds up healing. It is thought to work by improving blood flow in tissues under the skin.... ultrasound treatment

Colour Flow Ultrasound Imaging

see Doppler ultrasound.... colour flow ultrasound imaging

Transvaginal Ultrasonography

an *ultrasonography technique for examination of the female pelvis using a vaginal probe instead of an abdominal transducer. It allows the use of a higher frequency, thus providing superior resolution and therefore a more detailed anatomy of the female pelvis and an earlier and more accurate identification of fetal structures.... transvaginal ultrasonography

Ultracentrifuge

n. a *centrifuge that works at extremely high speeds of rotation: used for separating large molecules, such as proteins.... ultracentrifuge

Endoscopic Ultrasound

the fusion of endoscopy with ultrasonography. An ultrasound probe is incorporated into the endoscope in order to deliver highly detailed images from within the body. Endoscopic ultrasound is used predominantly by gastroenterologists, to assess internal structures or organs within the upper gastrointestinal tract, or by respiratory physicians in the assessment of bronchial disease. It may be used for diagnostic purposes, to accurately stage a confirmed diagnosis of cancer or to obtain tissue samples using fine-needle aspiration. Therapeutic indications include drainage of a pancreatic *pseudocyst, the common bile duct, or the pancreatic duct, and coeliac plexus neurolysis, a technique used to deliver pain relief in cases of intractable abdominal pain, usually resulting from chronic pancreatitis.... endoscopic ultrasound

Ultradian

adj. denoting a biological rhythm or cycle that occurs more frequently than once in 24 hours. Compare circadian, nyctohemeral.... ultradian

Ultrafiltration

n. filtration under pressure. In the kidney, blood is subjected to ultrafiltration to remove the unwanted water, urea, and other waste material that goes to make up urine.... ultrafiltration

Ultramicroscope

n. a microscope for examining particles suspended in a gas or liquid under intense illumination from one side. Light is scattered or reflected from the particles, which can be seen through the eyepiece as bright objects against a dark background.... ultramicroscope

Ultramicrotome

n. an instrument for cutting extremely thin sections of tissue (not more than 0.1 ?m thick) for electron microscopy. See also microtome.... ultramicrotome

Ultrasonics

n. the study of the uses and properties of sound waves of very high frequency (see ultrasound). —ultrasonic adj.... ultrasonics

Ultrasound Marker

the appearance, on *ultrasonography of a pregnant woman, of a feature suggesting an abnormality in the fetus. Such markers can be classified as major fetal structural abnormalities or minor ultrasound features called soft markers. The latter are usually transient and may resolve spontaneously, but they may indicate the risk of a serious chromosomal abnormality in the fetus. An example is increased nuchal translucency (see nuchal translucency scanning).... ultrasound marker

Ultraviolet Rays

invisible short-wavelength radiation beyond the violet end of the visible spectrum. Sunlight contains ultraviolet rays, which are responsible for the production of both suntan and – on overexposure – *sunburn. The dust and gases of the earth’s atmosphere absorb most of the ultraviolet radiation in sunlight (see ozone). If this did not happen, the intense ultraviolet radiation from the sun would be lethal to living organisms.... ultraviolet rays

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