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An ultrasound is an imaging test that uses high-frequency sound waves to produce images of structures in the body. An ultrasound works by bouncing sound waves off solid parts of the body.

Why an ultrasound is done

An ultrasound may be done to:

  • look at the size, location and structure of soft tissue organs
  • diagnose cancer
    • distinguish fluid-filled cysts from solid tumours
    • look for any abnormalities
      • Sound waves cannot penetrate through bone or air-filled structures, so ultrasound is not used to detect abnormalities in bone or lungs.
    • guide the doctor during a needle aspiration or biopsy
    • determine the stage (how deeply a tumour has penetrated the wall of an organ)
    • show how blood flows through vessels (Doppler ultrasound)
      • Ultrasound is helpful in assessing the extent or spread of certain tumours because blood flow is different in tumours than normal tissues.
  • help plan cancer treatment

How an ultrasound is done

An ultrasound is usually done as an outpatient procedure in a doctor’s office, clinic or hospital. The test usually takes 15–30 minutes, but may take longer.

  • Depending on the organ or structures being studied, special preparation may be needed for an ultrasound. Preparation may include:
    • fasting overnight
    • taking a laxative
    • having an enema
    • drinking a large amount of water just before the test so that the bladder is full
  • The person lies on an ultrasound table.
  • The ultrasound technologist places a special gel on the skin over the area to be examined.
    • The gel lubricates the skin and improves transmission of the sound waves.
    • The gel feels cool and slippery.
  • A microphone-like instrument, called a transducer (probe), is placed directly on the skin surface and moved across the area being examined.
    • For some types of ultrasound the transducer may be inserted into a body opening, such as the rectum (transrectal ultrasound) or the vagina (transvaginal ultrasound).
  • High-frequency sound waves from the transducer bounce off organs and tissues.
  • A computer analyzes the echoes created by the sound waves and displays images on a screen.
  • A radiologist (a doctor who specializes in using imaging techniques) may come to check the images and make sure no more are needed before the person leaves.
  • The technologist wipes off the gel after the ultrasound is done.
  • The person can usually resume normal activities after the test.

Potential side effects

There are no potential side effects associated with ultrasound. There is no pain involved during the test. Sometimes the pressure of the transducer on the body can be uncomfortable, particularly if it is placed on an area that is already sore.

What the results mean

The images created by ultrasound are caused by different echo patterns. An ultrasound can show:

  • fluid-filled cysts
  • solid tumours
  • cancer spread (metastasis)
  • whether cancer is affecting the structure or function of certain organs
  • cancer spread into blood vessels, particularly in the liver and pancreas (Doppler ultrasound)

An ultrasound cannot always tell the difference between a cancerous (malignant) tumour and a non-cancerous (benign) tumour.

What happens if a change or abnormality is found

The doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed.

Special considerations for children

Parents can stay with the child during the ultrasound. The child may bring a favourite toy, security item (blanket or pillow) or pacifier to help distract them and keep them calm.

Check with the doctor or nurse for special preparation instructions. Depending on the type of ultrasound, children may need to:

  • not eat or drink
  • drink but not empty the bladder

The preparation for an ultrasound depends on the age and experience of the child. Find out more age-specific information on helping children cope with tests and treatment.


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Nearly 1 in 2 Canadians is expected to be diagnosed with cancer in their lifetime.

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