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How do ultrasound scans work?

An ultrasonic scan uses sound waves of high frequency to produce images of the body’s inside. Good for use during pregnancy.

Ultrasound scans, or sonography, are safe because, instead of radiation, they use sound waves or echos to create an image.

Ultrasound scans are used to determine fetal growth, and they can detect liver, heart, kidney or abdominal problems. Also, they can help with other forms of biopsy.

The created image is called a sonogram.

Important facts about ultrasound scans

  • Ultrasound scans are safe and widely used.
  • They are often used to check the progress of a pregnancy.
  • They are used for diagnosis or treatment.
  • No special preparation is normally necessary before an ultrasound scan.


Ultrasound scans are carried out by a sonographer.
Ultrasound scans are carried out by a sonographer.

The individual doing an ultrasound scan is called a sonograph, so radiologists, cardiologists, or other experts interpret the images.

Typically the sonographer carries a transducer, a handheld instrument, like a wand which is positioned on the skin of the patient.

Ultrasound is a sound moving through soft tissue and fluids, but it bounces backwards, or echoes, off denser surfaces. So it creates a image.

The term “ultrasound” refers to sound at a frequency which can not be heard by humans.

Typically the ultrasound for diagnostic uses varies between 2 and 18 megahertz (MHz).

Higher frequencies provide better images of quality, but are more readily absorbed by the skin and other tissues, so they can not penetrate as deeply as lower frequencies.

Higher frequencies penetrate deeper, but inferior in image quality.

How does it capture an image?

Ultrasound, for example, passes through blood in the heart cavity, but if it reaches a heart valve, it returns, or bounces back.

If there are no gallstones, it will pass straight into the gallbladder but if there are stones, it will bounce back from them.

The denser the target hits the scanner, the more it bounces back.

This bouncing back, or echo, gives its features to the ultrasonic picture. Increasing shades of grey represent increasing densities.

Ultrasound transducers

The transducer, or wand, is usually mounted on the patient’s body surface but certain kinds are mounted internally.

This will include photos which are simpler and more detailed.

Examples include:

  • an endovaginal transducer, for use in the vagina
  • an endorectal transducer, for use in the rectum
  • a transesophageal transducer, passed down the patient’s throat for use in the esophagus

Some very small transducers can be placed on a catheter’s end and inserted into the blood vessels to examine the blood vessel walls.


Ultrasound image
Ultrasound images are made from reflected sound, and a diagnosis can then be made.

Ultrasound is commonly used during procedures such as biopsies, for diagnosis, treatment and guidance.

It may be used to analyze internal organs including the liver and kidneys, the pancreas, the thyroid gland, the testes among ovaries, and others.

An ultrasonic scan will show whether a lump is a tumor. This may be cancerous, or a cyst overflowing with blood.

It can help to diagnose soft tissue disorders, muscles, blood vessels, tendons, and joints. A frozen shoulder, tennis elbow, carpal tunnel syndrome and others are examined.

Circulatory problems

Ultrasound Doppler can measure blood flow in a vessel or blood pressure. It can assess blood flow rate and any obstructions.

One example of Doppler ultrasound is an echocardiogram (ECG). It can be used to construct cardiovascular system images, and at different points to measure blood flow and cardiac tissue movement.

An ultrasound from Doppler can determine the function and condition of cardiac valve areas, any heart defects, valvular regurgitation, or blood leakage from valves, and it can demonstrate how well the heart pumps out blood.

It can also be used to:

  • examine the walls of blood vessels
  • check for DVT or an aneurysm
  • check fetal heart and heartbeat
  • evaluate for plaque buildup and clots
  • assess for blockages or narrowing of arteries

A carotid duplex is a type of carotid ultrasonography which may include an ultrasonic Doppler. This will demonstrate how blood cells pass through the arteries of the carotid.

Ultrasound in anesthesiology

Ultrasound is commonly used by anesthetists to direct a needle past nerves with anesthetic solutions.

An ultrasound can be performed in a doctor’s office, in an ambulatory clinic, or in a hospital.

Most scans take 20 to 60 minutes to complete. Usually, it’s not uncomfortable, and no noise.

No special planning is required in most cases, but patients may want to wear loose-fitting and comfortable clothing.

If the liver or gallbladder is affected, the patient can have to either run for several hours before the operation, or eat nothing.

The patient should drink plenty of water for a scan during pregnancy, and especially early pregnancy, and try to avoid urinating for some time before the test.

The scan provides a better image of the uterus when the bladder is full.

The scan normally takes place inside a hospital’s radiology department. The test is carried out by a doctor or a specially trained sonographer.

External ultrasound

The sonographer places a lubricating gel on the skin of the patient, and puts a transducer above the lubricated surface.

The transducer is placed over the body part which needs to be checked. Examples include ultrasonic tests of the heart of a patient or a fetus in the uterus.

The patient should not be feeling pain or discomfort. They are just going to feel the transducer over the skin.

The full bladder can cause slight discomfort during pregnancy.

Internal ultrasound

If it is appropriate to examine the internal reproductive organs or urinary system, the transducer can be positioned in a man’s rectum or in a woman’s vagina.

For example, an endoscope can be used to examine any portion of the digestive system, the esophagus, chest lymph nodes, or the stomach.

At the end of the endoscope, which was placed into the patient’s body, a light and an ultrasound tool was connected, normally through the mouth.

Patients are given drugs prior to the operation to reduce any discomfort.

Internal ultrasonic scans are less convenient than external ones, and the chance of internal bleeding is small.


Most types of ultrasound are noninvasive, and do not involve exposure to ionizing radiation. It’s believed the procedure is very healthy.

Nonetheless, unnecessary “keepsake” scans during pregnancy are not recommended because the long-term risks are not known. Ultrasound is recommended only when medically needed during pregnancy.

Anyone who’s allergic to latex will Inform their doctor not to use a latex-covered probe.

Chukwuebuka Martins

Chukwuebuka Martins is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.