Medical ultrasound in healthcare enables doctors to carry out a wide range of exploratory and diagnostic processes involving the soft tissue structures in the body. Ultrasound originated with industrial applications, and the first practical medical use was in the 1950s. Today, most areas of healthcare use them in some way.
Ultrasound equipment uses a handheld transducer or probe that produces a beam of ultrasound waves. These waves pass through tissues and are reflected back to the transducer, much like echoes bouncing off walls. When the reflected waves return to the transducer, they generate electrical signals the machine translates into an ultrasound image on a screen. The ultrasound waves are generated by piezoelectric crystals, ceramic crystal materials that generate sound waves when an electric field is applied to them. The sound waves are at a frequency of 2 to 18 megahertz, which humans cannot detect.
The ultrasound waves bounce back to the transducer when they hit boundaries between different types of tissues, like that between fluid and soft tissue. The machine measures the time it takes for each wave to return after it has bounced off a tissue boundary. Using the known speed of sound and the time for the ultrasound wave to return, the scanner calculates the distance from the transducer to the tissue boundary, creating a real-time two-dimensional image of tissues and organs.
Medical ultrasound can aid doctors in investigating diseases and making diagnoses. Anatomical ultrasound requires placing the probe on the skin and visualizing the anatomy of organs, including their size and shape. The probe can also enter the body, such as the stomach, esophagus (gullet), or vagina, to gain optimal views of some organs. During operations, ultrasounds can assess inaccessible areas.
Functional ultrasound assesses the functioning of organs and blood flow, the condition of the lining of arteries, the movement of the walls of organs, and the health of the tissues of organs. These types of scans are sometimes called Doppler ultrasound scans.
Ultrasound is also valuable in guiding physician interventions. It allows the doctor to see the tip of the needle they are inserting during a biopsy or an anesthetic nerve block. The insertion of a chest drainage tube through the chest wall can be made safer by ultrasound guidance of the procedure.
Therapeutic or interventional ultrasound is a relatively recent area of development. Ultrasound waves of high-intensity are focussed on an area of diseased tissue and destroy it, avoiding the need for more invasive procedures such as surgery.
Ultrasound scans diagnose and assess a vast range of medical conditions. There are very few organs that are not suitable for scanning by ultrasound. The method can also help in the investigation of symptoms such as pain, infections, and swelling. Ultrasound scanning can help assess trauma patients to determine the extent of injury to organs and whether there are collections of blood in the abdomen. Ultrasound scanning can investigate gastrointestinal issues by imaging the abdominal organs. For people with conditions of the lungs, ultrasound may help identify abnormalities or guide procedures such as biopsies or the insertion of chest drainage tubes.
The wide spectrum of use of ultrasound scans means that many people, at some time, will benefit from their use.
This was one of the first areas of medicine to benefit from the introduction of ultrasound techniques. During pregnancy, ultrasound monitors the health of the unborn baby. It can identify conditions that could threaten mother or baby and enable doctors to take measures to reduce the risks. Additional benefits include confirming the fetus' gestational age, the health of the placenta, the number and position of the babies, and any major physical abnormalities. The doctor can also monitor the baby’s heartbeat, and determine the sex. The use of ultrasound in pregnancy purely for “keepsake” videos with no medical indication is generally discouraged.
Ultrasound assessment of the heart — echocardiography — is a common method to evaluate the function of the heart valves and chambers. It can provide information on the strength of the heart muscle and the thickness of the walls of the chambers, ventricles, and atria. Doppler ultrasound can visualize the flow of blood through the heart by placing a probe on the chest or esophagus (transesophageal echocardiography or TEE).
In general, ultrasound is considered a safe method of investigation. There is no scientific evidence of harmful effects. In pregnancy, ultrasound is considered safe for the mother and unborn baby, though experts advise against using them without a medical reason, as this carries unnecessary financial costs and may lead to further unnecessary tests.
Ultrasound has an excellent safety record. It does not use the ionizing radiation of X-rays and computed tomography scans (CT scans), making it the best option for use during pregnancy. It produces realtime images demonstrating the movement of structures, which allows assessment of their function. It is a painless procedure, causing only minor discomfort at times. The equipment is relatively inexpensive and can be small and portable, ideal for bedside investigations. These are the main advantages of ultrasound scanning.
There are several disadvantages which can limit the use of ultrasound in some areas. Ultrasound waves cannot penetrate bone, therefore scanning the brain is not possible. Certain gas-containing areas, such as the intestine, do not deliver good ultrasound imaging results. Additionally, obesity can make it difficult to image structures deep in the body.
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