A technique using 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, X-RAYS, ultrasound investigations can be repeated as needed. A CONTRAST MEDIUM is not required. Its reliability is dependent upon the skill of the operator as the images are seen in real-time and the saved images may not reflect the entirety of the examination
Ultrasound has replaced ISOTOPE scanning in most situations, as well as reducing the need for X-rays. Ultrasound of the liver can separate medical from surgical JAUNDICE in approximately 97 per cent of patients; it is very accurate in detecting and defining 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) [CT] scanning). It is very accurate in detecting gall-stones (see GALL-BLADDER, DISEASES OF) and more accurate than oral CHOLECYSTOGRAPHY. It is useful as a screening test for pancreatic disease and can differentiate carcinoma of the pancreas from chronic PANCREATITIS with 85 per cent accuracy. It is often used to confirm a suspicion of acute appendicitis.
Ultrasound is the first 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, differentiating cysts and tumours. It can also detect 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 the first 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 although CT scanning is better for the RETROPERITONEAL region. Ultrasound has a major application in thyroid nodules, as it can differentiate cystic from solid lesions and show the multiple lesions characteristic of the nodular GOITRE (THYROID GLAND, DISEASES OF); however, it cannot differentiate between a follicular ADENOMA and a CARCINOMA as both these tumours are solid; nor can it demonstrate normal parathyroid glands. It can identify adenomas provided that they are more than 6 mm in diameter. Finally, ultrasound can differentiate masses in the SCROTUM into testicular and appendicular, and it can demonstrate impalpable testicular tumours. This is important as 15 per cent of malignant testicular tumours metastasise whilst they are still impalpable.
Separately from their role in imaging, ultrasonic waves are one of the constituents in the shock treatment of certain types of gall-stones (see above) and CALCULI in the urinary tract (see LITHOTRIPSY). In the field of physiotherapy, ultrasonics are used in the treatment of acute injuries of soft tissue, bruises and strains on the basis that it stimulates damaged tissue to heal. Thus it is widely employed in treating sports injuries (SPORTS MEDICINE).
is a technique which shows the presence of vascular disease in the carotid and peripheral vessels, as it can detect the reduced blood flow through narrowed vessels.
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. Foetal 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. 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 identified. Foetal 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 a 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.)