The importance of ultrasound

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The Doctor Says
By Dr MILTON LUM

Ultrasound has now become an integral part of medical practice.

ANYONE who has seen films about the sea battles in World War II would not have failed to notice the use of sonar, which is an acronym for SOund Navigation And Ranging. It refers to the use of sound propagation to navigate, communicate with, or detect other sea vessels, particularly submarines.

Ultrasound, which is ubiquitous in medicine today, is an extension of sonar. It involves the use of high frequency sound waves which are produced by a handheld sensor called a transducer that is placed on a body surface, e.g. skin, vagina, and rectum.

When the sound waves from the transducer hit a body part, it is bounced back towards the transducer, which is connected to a computer that converts the reflected sound waves into an image of the body part.

Hear, hear: External ultrasound involves placing the transducer on the skin and moving it over the body part that is to be examined.

It is used for diagnosis of many medical conditions as well as the assessment of treatment.

The diagnostic applications of ultrasound were pioneered by Ian Donald who contemplated its use in medicine after he saw its use by the shipyards of Glasgow for the detection of metallic faults in ships. His paper, Investigation Of Abdominal Masses By Pulsed Ultrasound, published in The Lancet on June 7, 1958, was a seminal article.

James Willocks, a colleague of Ian Donald, who authored Medical Ultrasound – A Glasgow Development Which Swept The World, in 1996, had this to say: “Ultrasound scanning is a household word. Every mother knows it and many have pictures to prove it. It is painless, safe and reliable. Its success since its beginnings 40 years ago is truly astonishing. It started in Glasgow in the University Department of Midwifery under Professor Ian Donald and seemed a rather crazy experiment at the time.

“Ian Donald was no backroom boffin, but a full-blown flamboyant consultant at the sharp edge of one of medicine’s most acute specialities – a colourful character of Johnsonian richness for whom I am a very inadequate Boswell.”

The initial ultrasound machines produced by the medical device industry about half a century ago were large and cumbersome, with limited features. With the passage of time, more sophisticated ultrasound machines were developed. The machines today are more compact, with several features including mobility and a wide range of diagnostic applications.

Different types

There are different types of ultrasound scans, i.e. external, internal, and endoscopic, depending on the part of the body that is examined.

External ultrasound involves placing the transducer on the skin and moving it over the body part that is to be examined. A gel is applied to the skin to facilitate smooth movement of the transducer and to ensure that there is continuous contact between the transducer sensor and the skin.

The ultrasound waves which are produced by the transducer in pulses pass through the skin into the body and are reflected back by various body parts. The reflected waves are detected by the transducer sensor and are converted by a computer connected to the transducer to produce images which can be seen on a monitor, which is similar to a TV monitor.

In addition, video recordings of the movements of body parts can be made.

The common uses of an external ultrasound scan are the examination of the developing foetus in the pregnant mother’s uterus, the reproductive organs, heart, liver, gallbladder, and kidneys.

A full bladder is required for a scan done in the first three months of pregnancy. This is due to the fact that the uterus is still small. The full bladder helps to place the uterus into a position that is not so deep in the pelvis, thereby enabling better imaging of the foetus in the uterus.

Once the pregnancy is more than three months, the uterus is no longer confined to the pelvis and can be felt in the lower abdomen, making visualisation of the developing foetus easier without a full bladder.

Ultrasound of the gall bladder and pancreas would involve the patient having to consume no food or drinks for four hours or so before the examination is carried out.

There is no discomfort from an external ultrasound. However, the lubricating gel may feel sticky and cold. A full bladder may be uncomfortable to some people.

Internal ultrasound involves placing an ultrasound probe into the vagina or rectum. The transvaginal probe enables better visualisation of the uterus even if the bladder is empty.

The transrectal probe enables more detailed examination of the prostate gland and can include targeted biopsy of the prostate. There may be some discomfort with internal ultrasound, but there is usually no pain.

Endoscopic ultrasound involves the insertion of an instrument called an endoscope, which is a thin, long, and flexible tube through the mouth to examine the gullet (oesophagus), stomach, or small bowel (duodenum). The endoscope has a light source and ultrasound probe at one end.

Upon insertion, the ultrasound waves produced by the probe create images in the same manner as in external or internal ultrasound.

Endoscopy may be uncomfortable. Patients are usually given a sedative and painkiller prior to commencement of the procedure.

Uses

There are multiple diagnostic uses of ultrasound.

Until ultrasound came along, doctors could only listen to the foetal heart, on which presence was assumed to be an indicator of foetal well-being.

With the advent of ultrasound, the information available to the pregnant patients’ attending doctors has increased markedly. Doctors are able measure the size of the foetus, which helps in determining when delivery of the baby would be expected; monitor growth of the developing foetus; check for structural abnormalities of foetus, e.g. head, and spine between 18 and 20 weeks of pregnancy; locate the site of the placenta; check for evidence of foetal well being or compromise with examinations of the foetal heart and even perform procedures on the foetus.

The detection and assessment of growths in the female reproductive tract like fibroids, tubal or ovarian masses, cancers etc is another use of ultrasound.

Ultrasound is used in the detection and assessment of conditions in the heart. It is used to examine the size, shape, and movement of the heart, including its valves and chambers as well as the blood flow through the heart. This type of ultrasound is called an echocardiogram, which can even be used to diagnose cardiac abnormalities in foetuses prior to their birth (foetal echocardiography).

Ultrasound is used in the diagnosis of deep vein thrombosis (DVT), which is a condition in which there is blood clot formation (thrombi) in the deep veins. The thrombi can break loose and travel to the lungs, causing pulmonary embolism, which is a life threatening condition.

Abnormal conditions in other organs that can be detected and assessed by ultrasound include the liver, gallbladder, pancreas, kidneys, bladder, prostate, testes, breasts, thyroid, lymph nodes, skin, joints, and eyes.

Procedures like biopsies, in which tissue samples are taken for analysis, can be carried out under ultrasound guidance. The ultrasound is used as a guide to the correct location of the site for the biopsy to be carried out. Examples include breast and prostate biopsies.

Limitations

The limitations to the use of ultrasound are due to its properties, viz: ultrasound waves cannot pass through bone, air, or gas. Therefore, it is not possible to produce detailed images of some parts of the body like the brain, which is surrounded by bone.

Doctors utilise other imaging methods like CT scans and magnetic resonance imaging (MRI) scans to examine parts of the body that are not suitable for ultrasound examination.

Category: Milton's Corner
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