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Ultrasound is a branch of medical imaging which utilises high frequency sound waves to visualise the internal organs and soft tissues in the human body. The internal organs, such as liver, kidneys, heart, etc. are seen in real time. Ultrasound examination is also ideal for providing information about muscles, joints, tendons and ligaments.
Obstetric sonography is a vital part of ultrasound. This involves the visualisation of the foetuses during routine and emergency prenatal care.
The probe used for scanning is called an ultrasound transducer which both transmits and receives sound waves. The high frequency waves are sent into the human body and are echoed back from the organs. The computer then processes the received data which is then displayed in real time as either a two or three dimensional image, allowing visualisation of a moving foetus or blood flow.
Ultrasound is defined to be a sound with frequencies over 20kHz which cannot be heard with the human ear. Certain animals use ultrasound for communication and navigation, for example, baby rats call to their mothers with high pitched squeaks which people cannot hear. Dolphins and whales use ultrasound to echolocate and find their way around in murky or dark water. Bats have an amazing sonar system, which helps them to navigate their environments and detect prey. The frequency range used in medical ultrasound machines vary between 1MHz and 18MHz.
History of Ultrasound
The first written document dealing with principles of ultrasound physics and echolocation dates back to 1794, when Italian physiologist Lazaro Spallanzani analyzed the basic mechanisms of spatial orientation of the bats. Spallazani demonstrated that blind folded bats could navigate around obstacles in the dark, but bumped against them when their mouths were covered.
The development of ultrasound applications in medicine began with measuring distance under water using sound waves. In 1826 physicist Jean Daniel Colladon proved that sound travelled faster through water than air by calculating the speed of sound through water with an underwater church bell.
In 1880 Pierre and Jacques Curie had discovered the piezo-electric effect in certain crystals, which led to the development of the ultrasound transducer.
Johan Doppler hypothesised that the pitch of a sound would change if the source of the sound was moving. This property is now known as the Doppler Effect and is widely applied in medical ultrasound.
Sinking of the Titanic in 1912 was the impetus for the development of echolocating devices for nautical purposes. SONAR (sound navigation and ranging) systems were developed for the purpose of underwater navigation by submarines in World War I, for submarine detection and avoiding underwater obstacles for ships.
In 1914 Canadian scientist Reginald Fessenden designed and built the first working SONAR system that was capable of detecting an iceberg 2 miles away. Later on an underwater SONAR was invented by Paul Langevin, he called it Hydrophone and it was used for submarine detection.
Back in the 1940’s the ultrasound was considered therapeutic due to the thermal energy it was generating. It was used for arthritic pain, asthma, gastric ulcers, eczema, angina pectoris and urinary incontinence.
The first use of ultrasound as a diagnostic tool dates back to 1942 when a neurologist from the University of Vienna, Karl Dussik tried to locate brain tumours and cerebral ventricles by measuring the transmission of ultrasound beam through the skull.
Systematic use of ultrasound for diagnostic purposes started with George Ludwig diagnosing gallstones in 1948.
The late 1960s and early 1970s were referred to as the sonic boom, when the two-dimensional (2D) echo was introduced by Klaus Bom.
In 1966, the pulsed Doppler technology was developed by Don Baker, Dennis Watkins, and John Reid, which enabled the detection of blood flow in the heart. Don Baker was also involved in developing the colour Doppler and duplex scanning.
In 1980s the real-time ultrasound started to appear and in the 1990s, the scientists have progressed with developing the 3D and 4D images.
Today ultrasound is used to diagnose a wide range of medical conditions:
This is where the solid organs of the abdomen are examined. Liver, gallbladder, pancreas, bile ducts, aorta, inferior vena cava, kidneys and spleen can all be visualised with ultrasound. Sometimes, the appendix can be seen too, especially when it is inflamed (during appendicitis). However, as any imaging technique, it has limitations. Sound waves may be blocked by gas in the bowel and attenuated in different degree by fat, diminishing the diagnostic capabilities in this area.
It is used to examine kidneys, bladder and prostate.
In a pelvic sonogram, organs of the pelvic region are imaged, including the uterus, ovaries and urinary bladder. Pelvic scan can be performed in two methods – externally or internally. The internal pelvic sonogram is performed either trans-vaginally (in women) or trans-rectally (in men). Sonographic imaging of the pelvic floor can produce important diagnostic information regarding the precise relationship of abnormal structures with other pelvic organs.
It is used to monitor the development of the foetus during pregnancy and can provide the following information:
- Date the pregnancy (determine gestational age)
- Determine location of the foetus (intrauterine vs ectopic)
- Confirm foetal viability
- Check the location of the placenta in relation to the cervix
- Check for the number of foetuses (multiple pregnancy)
- Check for major physical abnormalities
- Assess foetal growth (for evidence of intrauterine growth restriction (IUGR))
- Check for foetal movement and heartbeat
- Determine the sex of the baby
Arterial sonography – used to assess the patency and possible obstruction of arteries.
Carotid ultrasonography – for assessing the blood flow and stenosis in the carotid arteries.
Venous mapping – can determine the extent and severity of venous insufficiency.
Vascular ultrasound is also well used in examining the major intracerebral arteries and diagnosing the deep vein thrombosis (DVT).
This is when tendons, ligaments, joints and muscles are examined for various conditions, such as an injury, inflammation or oncological problems.
Ultrasound images of the eyes.
This type of ultrasound scan is performed through the soft spots in the skull of an infant (Fontanelle). These completely close at about 1 year of age and form a virtually impenetrable acoustic barrier for the ultrasound. The anterior fontanelle is most commonly used for cranial ultrasound. The quality of the picture is affected by the size of the fontanelle. The smaller the size, the poorer the quality of the scan.
This scan provides the basic assessment of intracerebral structural abnormalities, bleeds, ventriculomegaly or hydrocephalus and anoxic insults (Periventricular leukomalacia).
Ultrasound is also used in thyroid, breast and testicular imaging.
Bi-planar ultrasound is where the probe (transducer) has two 2D planes that are perpendicular to each other, providing more efficient localization and detection of the area of interest.
An omniplane probe is the one that can rotate 180° to obtain multiple images.
In 3D ultrasound, many 2D planes are digitally processed added together with the help of special software to create a 3-dimensional image of the object.
Additional information and measurements can be gained with Doppler Ultrasound. The Doppler effect is employed to assess whether the structures (usually blood) are moving towards or away from the transducer. The machine can then determine the direction and relative speed of the substance (such as flowing blood in an artery or heart valve) by calculating the frequency shift of a particular sample volume. The pulsed Doppler technology is used in all modern ultrasound scanners and is particularly useful in cardiovascular studies (sonography of the vascular system and heart), where it can pick up, for example a reverse blood flow in the liver vasculature in portal hypertension.
Contrast-enhanced ultrasound (CEUS) is the application of a contrast medium (dye) to traditional medical sonography. Contrast medium are gas-filled microbubbles that are administered intravenously to the systemic circulation. Microbubbles have a high degree of echogenicity, which is the ability of an object to reflect the ultrasound waves, which improves the visualisation of cardiac cavities, large vessels and tissue vascularity.
Molecular ultrasonography (ultrasound molecular imaging)
The molecular imaging is believed to be the future of contrast ultrasonography. It has a potential to be clinically applied in cancer screening, detecting tumours in their earliest stages. It uses targeted microbubbles that were originally designed by Dr Alexander Klibanov back in 1997. These microbubbles have an ability to adhere to the microvessels in the tumours allowing for it to be localised and visualised just minutes after the injection.
Elastography (ultrasound elasticity imaging)
This is a relatively new technology which only started to develop in the last decade. It is a medical imaging modality that maps the elastic properties of soft tissues. The concept of this technology lies in the fact that hardness or softness of a tissue can give diagnostic information regarding the presence or status of the disease. For instance, tumours tend to be harder than the surrounding tissue which will allow for them to be differentiated. Another example are diseased livers that often are stiffer and more rigid than the healthy ones.
Risks of Ultrasound
There are no confirmed adverse biological effects on patients or sonographers caused by exposure to ultrasound.
At EastMed Radiology we perform a full range of ultrasound examinations on state of the art equipment:
• Abdominal scanning: gall bladder, liver, pancreas, spleen, bowel, etc.
• Obstetrics ultrasound: dating scan, 12 weeks Nuchal assessment, 20 weeks anatomy assessment, 3rd
trimester scan, biophysical profile for foetal wellbeing.
• Gynaecological scanning: uterine and ovarian pathology.
• Renal scanning: kidneys and bladder assessment.
• Thyroid scanning: for thyroid gland assessment.
• Scrotum scanning: for testicular assessment.
• Soft Tissue scanning: for swellings anywhere on the body, or foreign body localisation.
• Musculoskeletal scanning: we are specialised in musculoskeletal ultrasound and perform examinations of
the shoulders, elbows, wrists, Achilles tendons, ankles, knees, hips, etc.
• Vascular Scanning: assessment of the veins and arteries (aorta, carotid Doppler, venous assessment).\
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