Common ultrasound scan techniques, types and uses
An ultrasound scan examination has a variety of uses. The most commonly associated use is scans done periodically throughout a woman’s pregnancy. These images of a developing baby while in the womb afford both the medical professional and expectant parents the first views of an unborn child and are used to monitor foetal development and identify any potential health issues in utero.
An ultrasound scan can be done:
- Externally: A transducer is used on the outside of the body, and moved over the skin. An external examination can be used to assess the heart, liver, kidneys and various other organs in the abdomen and pelvis, as well as muscles and joints of the body or the development of an unborn baby in the uterus of a pregnant woman.
- Internally: A small transducer is attached to a probe or catheter (thin tube) and inserted into a natural bodily opening such as the rectum or vagina. The prostate gland, uterus and/or ovaries are some of most common examined portions of the body using an internal ultrasound.
- Endoscopically: During an endoscopic ultrasound (EUS) a long thin, flexible probe or catheter is used with an endoscope and is passed deeper into the body, as needed, to reach areas that are otherwise difficult to view such as the lungs and gastrointestinal tract. Sound waves then create images in the same way as they would during an external examination. When the ultrasound is being passed through the mouth and down the throat, sedatives and mouth guards will be used to relax a patient and assist with keeping the mouth open (to avoid biting down on the scope) during the procedure.
What type of ultrasound transducers are used internally?
When the need arises to obtain clearer and more informative images, a transducer may be used inside the body. Some examples include:
- A transoesophageal transducer (passed down the throat / oesophagus)
- An endorectal transducer (used in the rectum)
- An endovaginal transducer (used in the vagina)
A doctor can also make use of very small transducer devices at the end of a catheter (thin, flexible tube) for insertion into blood vessels. These are useful for examination of blood vessels.
General uses for ultrasound scans
- Pregnancy (obstetric ultrasonography): An ultrasound scan can be used to confirm and date a pregnancy during the first trimester. Ultrasounds can also detect a number of developing foetuses in the womb (multiples, such as twins or triplets), as well as rule out an ectopic pregnancy (when a fertilised egg implants outside the uterine wall lining) during the early stages. Throughout pregnancy, ultrasound scans are used as valuable screening tools for the detection of concerns or complications, such as placental problems (position of the placenta), some birth defects, the amount of amniotic fluid surrounding the foetus or the breech positioning of a baby. They are also valuable for assessing maternal health and overall state of pregnancy, as well as the opening or shortening of the cervix. Ultrasound scans can help to determine the sex of an unborn baby midway through pregnancy and are also useful for estimating the size of a baby closer to delivery (birth).
- Diagnostics: Many medical conditions result in symptoms which a doctor may opt to examine using an ultrasound scan. Symptoms of pain, inflammation or swelling may be indicative of internal organ problems and various other health concerns involving the soft tissues. Using an ultrasound, a doctor can clearly view the quality and functionality of the brain (in infants), blood vessels, eyes, the thyroid gland, lymph nodes, liver, kidneys, heart, gallbladder, bladder, pancreas, spleen, appendix, uterus, ovaries, or testicles. A scan can assist with the diagnostic process of diseases, determine abnormalities (such as tumours, cysts or stones in the gallbladder or kidneys), evaluate a particular lump or tumour (determining whether it is malignant or benign i.e. cancerous or non-cancerous), as well as the flow of fluids in blood vessels, or abnormal widening of blood vessels / aneurysms. An ultrasound can help to determine problems with the body’s muscles, joints and tendons and potentially diagnose problems such as carpal tunnel syndrome (numbness or tingling in the hand and arm caused by a pinched nerve), frozen shoulder (stiffness and pain in the shoulder joints), tennis elbow (irritation of tissue in the forearm muscle connecting to the elbow) or Morton’s neuroma (a thickening of tissue around the nerves leading to the toes). An ultrasound is sometimes used on a new-born baby by placing a transducer on the fontanelle (the soft spot of the top of a baby’s head or skull). The scan is used to assess potential abnormalities in the brain, such as periventricular leukomalacia (injury to the white matter of the brain) or hydrocephalus (accumulation of spinal fluid in the brain). There are, however, diagnostic limitations. An ultrasound scan is not an effective screening / examination tool for dense bone or the bowel (where the body holds air or gas) as sound waves generally don’t transmit well in these areas.
- Medical procedures: Needle biopsies (internal) are used in conjunction with ultrasound scans in order to determine the precise area from which to extract tissue samples when these are needed for lab analysis. An ultrasound is also useful for anaesthetists when guiding needles to administer anaesthetic near nerves. Emergency medicine also benefits from ultrasound scans when assessing various health problems and conditions, such as fluid build-up around the heart or pericardial tamponade (compression of the heart due to fluid in the surrounding sac), a traumatic injury, or blood leakage in the abdomen (hemoperitoneum).
- Therapeutic applications: Soft tissue injuries have also been known to be detected and treated with ultrasound scan technology.
Ultrasound image techniques
1. Doppler ultrasound
A Doppler ultrasound is primarily used to assess blood flow and speed within the blood vessels (arteries, veins or capillaries), but can also be used to identify other blood circulatory problems such as obstructions in the system as well as aid in the measurement of blood pressure. This type of ultrasound is commonly incorporated into many other forms of scans so as to evaluate blood flow or supply, or the lack thereof throughout the body’s tissues.
High-frequency sound waves are bounced off blood cells which are in motion in the body’s blood vessels, creating what is known as the ‘Doppler effect’. Changes in frequency are then recorded as echoes, converting the data into a visual representation of the nature of blood. A doctor can then see how quickly or slowly blood flow is, as well as the direction in which it is flowing. This is a valuable diagnostic screening tool for most ultrasound testing and is preferred by most medical professionals as it does not require the injection of contrast dye into a person (as is the case with X-ray angiography).
Colour Doppler ultrasonography is a subtype of this form of scan which is used in addition to the usual, more routine grayscale visual imaging. A wide range of colours are used to visualise blood flow measurements, which are then ingrained into a two-dimensional visual of bodily structures or tissues. In this way, a doctor can obtain a more pronounced or comprehensive visual representation of blood flow, its direction and speed, than can be achieved in grayscale. Colour techniques can also help a doctor to plot out changes in blood flow (speed and or / direction) on a graph during the scan for diagnostic or evaluation purposes.
Another subtype is the Power Doppler, which also utilises colour imaging techniques to provide highly detailed visual representations. A power Doppler is more sensitive and can represent detailed blood flow measurements, but cannot determine the direction of flow.
The third variation of Doppler, is the Spectral Doppler. This type uses conventional and colour techniques to determine both blood flow and direction, representing the data in a detailed graphic form, instead of in grayscale form with colour detail (such as in the other subtypes).
An example of a Doppler ultrasound is an echocardiogram (ECG) which is useful for creating images of the cardiovascular system (showing the state of cardiac valves, possible heart abnormalities, blood leakage, or valvular regurgitation), as well as determining cardiac tissue movement in specific areas.
A doctor can make use of this ultrasound to assess the walls of blood vessels, check for an aneurysm (ballooning or weakening in the circulatory system), deep vein thrombosis (DVT), plaque build-up or blood clots (hindering sufficient blood flow), arterial narrowing or blockages. Sometimes, an ultrasound can determine blood flow that is greater than normal, circulating the body and reaching the organs, often due to an infection.
Blood flow in the arteries and veins of the arms, legs, abdomen, neck and brain (of infants and young children) can be assessed using a doppler ultrasound. A doppler ultrasound can also assess the foetal heartbeat of an unborn baby during pregnancy, helping a doctor to determine any possible abnormalities in blood vessels, as well as congenital vascular malformations and tumours, or the heart.
Other obstetrical uses include the monitoring of a developing embryo or foetus, an evaluation of blood flow in the umbilical cord, developing foetus or placenta, and the overall condition of a mother’s uterus (womb) and ovaries. In males, a Doppler ultrasound can also be useful to assess the potential twisting (torsion) of a testicle (which can cause blood flow / circulatory problems).
Sometimes mild discomfort during an ultrasound scan may be experienced but this should not be painful. Not all foetal abnormalities can be identified with a Doppler ultrasound scan. If necessary, other testing procedures to detect abnormalities in a developing foetus can be performed, such as an amniocentesis, chorionic villus sampling or blood tests.
2. Duplex ultrasound
A duplex ultrasound combines the techniques used with traditional technology and a Doppler. Traditional techniques create images of the solid tissue mass that is being assessed or examined, representing a visual that is usually grey. In contrast, blood flow is represented in colour (Doppler). An example would be the examination of an artery (represented in grey) and blood flow (colour).
A duplex ultrasound is valuable for the examination of blood flow in the body’s arteries and veins, and can quickly detect blockages, clots, narrowing or widening of blood vessels, venous insufficiency (difficulties in blood being returned or pumped back to the heart) or varicose veins.
Ultrasound visual imaging types
There are several kinds of ultrasound imaging types which can be used depending on the nature of the scan, and which one will achieve the best visual result for the examination. These include:
- Two-dimensional ultrasound images (2D ultrasound): This is the most common type of visual image used. A 2D image uses a series of flat, two-dimensional cross section visuals of the area of the body being scanned. This type of image is used for most obstetric and diagnostic evaluations.
- Three-dimensional ultrasound images (3D ultrasound): Two-dimensional visuals can also be projected onto those of three-dimensional representation. Tissue is scanned in cross sections from numerous angles. Data is then reconstructed into a three-dimensional image. A 3D scan can help to provide a more comprehensive visual, which can be more realistic. A common use for such a visual is during a woman’s pregnancy when viewing and monitoring a developing foetus (unborn baby).
- Four-dimensional ultrasound images (4D ultrasound): Three-dimensional visuals can be updated in rapid succession, creating a fourth dimension (i.e. motion). Movement can create a more realistic representation of the area being viewed. A 4D visual can sometimes reveal abnormalities not easily detected by a 2D visual. A 4D scan also provides expectant parents with a fairly realistic visual of their unborn baby.