It is based on the fact that sound waves bounce off objects and the reflected wave can be decoded by the computer and converted into images. The sound waves used in medical imaging are between 2 to 20 MHz; thus they are called ultrasound, due to their ultra high frequencies.

Since its first widespread use in the sixties, initially in obstetric cases (pregnant women), no side effects have been reported.  Ultrasound does not involve the use of X-rays and radiation. That is why it is the preferred examination in children and pregnant women. In pregnancy, ultrasound is used to determine the age and overall health of the foetus. Ultrasound is also useful to look at various organs of the body ranging from the brain, heart, organs within the abdomen and pelvis, blood vessels, joints, breasts, etc.  Ultrasound is useful in assessing the brain and spinal cord of newborns and young infants. For the heart, it allows assessment of the function of the heart especially the valves and fluid around the heart without the need for more invasive procedures. This is called echocardiography and it is usually done by the cardiologists. Ultrasound is the investigation of choice to look for gallstones and kidney stones, and is excellent as a screening method to assess the pelvis. Evaluation of blood vessels is done by Doppler studies.

Most radiology and obstetric departments have ultrasound facilities. Some general practitioners have ultrasound machines in their clinics. However, the level of expertise to interpret the scans varies. It is recommended that ultrasound examinations be carried out by specialists who have been trained in the field to get maximum benefit from the examination. Sophisticated examinations like vascular ultrasound examination (Doppler studies) or endoscopic ultrasonography (to examine the inside of the intestine) are however, limited to certain radiological centers.

Ultrasound is readily available and in most cases, can be done instantly. However, in certain situations, preparation is required. In an ultrasound examination of the gallbladder, although preparation is not mandatory, overnight fasting is helpful to distend the gallbladder and allow better assessment. In an ultrasound examination of the pelvis, the patient is required to fill the bladder by drinking plenty of fluid. This is to allow better assessment of structures behind the bladder e.g. the uterus and ovaries. Special and sophisticated ultrasound examinations like intravascular ultrasound or endoscopic ultrasound would require the same preparation as any other angiographic or endoscopic examinations.

At the time of the examination, the patient will be required to lie down, with the part to be examined exposed. Gel is applied on the ultrasound probe and the probe will be moved on the skin surface over the organ of interest. When the gel-coated probe touches the skin surface it may feel cold. The patient may be asked to assume certain positions to allow better visualization of a particular organ, e.g. to turn to the left side when examining the gallbladder or to sit up with the legs over the edge of the table when examining varicose veins in the legs. Occasionally, during the examination, the doctor may exert some pressure with the probe on the skin surface in order to see certain structures better. It does not usually hurt, but if it is painful the patient should inform the doctor. The images will be displaced on the video monitor.

Doppler studies are special ultrasound examinations for examining blood vessels. A thumping sound will be heard during the examination, which is actually the sound of blood flowing in the vessel. Colour can be seen within the vessels on the video monitor. Presently in Malaysia, no injection is used in conjunction with an ultrasound examination. However, in some countries, certain special ultrasound examinations may require the administration of contrast media and a small injection will be given prior to or during the examination.

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Last Updated:
Thursday, 21 August, 2003