Kemp echoes Health Dictionary

A change in the frequency with which sound waves from a given source reach an observer when the source is in rapid motion with respect to the observer.

Approaching sounds appear higher in pitch (frequency) than sounds that are moving away.

This is because the wavelengths of the sound from an approaching source are progressively foreshortened, whereas the wavelengths from a receding source are stretched.

The Doppler effect is used in ultrasound scanning techniques.

An emitter sends out pulses of ultrasound (inaudible highfrequency sound) of a specific frequency.

When these pulses bounce off a moving object (blood flowing through a blood vessel, for example), the frequency of the echoes is changed from that of the emitted sound.

A sensor detects the frequency changes and converts the data into useful information (about how fast the blood flows, for example).

Doppler ultrasound techniques are also used to monitor fetal heartbeat, to detect air bubbles in dialysis and heart–lung machines, and to measure blood pressure.... doppler effect

A method of obtaining an image of the structure and movement of the heart with ultrasound. Echocardiography is a major diagnostic technique used to detect structural, and some functional, abnormalities of the heart wall, heart chambers, heart valves, and large coronary arteries. It is also used to diagnose congenital heart disease (see heart disease, congenital), cardiomyopathy, aneurysms, pericarditis, and blood clots in the heart.

A transducer (an instrument that sends out and receives sound signals) is placed on the chest, or an ultrasound probe is passed into the oesophagus using a flexible endoscope. Ultrasound waves are reflected differently by each part of the heart, resulting in a complex series of echoes, which are viewed on a screen and can be recorded or the results printed out. Developments such as multiple moving transducers and computer analysis give clear anatomical pictures of the heart.

Doppler echocardiography measures the velocity of blood flow through the heart, allowing assessment of structural abnormalities, such as septal defects.... echocardiography

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

adj. (in ultrasound imaging) describing a brighter area, which is usually caused by any structure (e.g. a stone) that reflects the sound waves (echoes) more than the adjacent structure. Compare hypoechoic.... hyperechoic

adj. (in ultrasound imaging) describing a darker area, which is usually caused by any structure (e.g. a cyst) that allows the sound waves to pass through and therefore reflects echoes to a lesser degree than the adjacent structure. Compare hyperechoic.... hypoechoic

adj. (in ultrasound imaging) describing a structure that reflects sound waves (echoes) of the same magnitude as the adjacent structure. Therefore, no contrast between the structures is seen separately, when received by the ultrasound crystal.... isoechoic

(in *ultrasonics) the reflection of sound waves from the surface of an internal structure, which can be used to produce a picture of the surface as a sonogram (see ultrasonography). A specular reflection contrasts with vaguer diffuse echoes produced by minor differences in tissue density.... specular reflection

(OAE, Kemp echoes) tiny sounds that emerge from the inner ear either spontaneously (spontaneous otoacoustic emissions, SOAE) or shortly after the ear is exposed to an external sound (evoked otoacoustic emissions, EOAE). An objective test of hearing has been developed using otoacoustic emissions. The test equipment creates a small sound and then detects any response from the ear. This can be done using a click stimulus (transient otoacoustic emissions, TOAE) or two separate tones (distortion product otoacoustic emissions, DPOAE). A normal response suggests that the ear is functioning and that hearing is satisfactory. All newborn children in the UK are now screened using this technique.... otoacoustic emissions

(sonography) 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. Scans may produce a single stationary image similar to a photograph (static) or multiple sequential images similar to a video (*real-time imaging). The ultrasound waves are transmitted from – and echoes detected by – piezoelectric crystals contained within the scanning probe (see transducer). As far as is known, there are no significant adverse effects from the use of ultrasound at diagnostic energies. Ultrasound waves are blocked by gas, as in the lungs and bowel, which can obscure underlying structures. The detail seen increases with the frequency of the ultrasound but the depth of penetration decreases. Ultrasonography is extensively used in obstetrics, including the diagnosis of pregnancy, assessment of gestational age, diagnosis of *malpresentations, ectopic pregnancies, and *hydatidiform moles, and detection of structural fetal abnormalities (see also transvaginal ultrasonography). It is also used to examine the abdominal organs, urinary tract, blood vessels, muscles, and tendons. More specialized techniques include *echocardiography, *transrectal ultrasonography (TRUS), intraoperative ultrasound (IOUS), and endoscopic ultrasound examinations. See also Doppler ultrasound.... ultrasonography