Ultrasound (sonography)

What is it?

According to NIBIB: diagnostic ultrasound is a non-invasive technique for imaging inside the body. The probe produces the waves and detects their returning echoes, and the machine calculates the distance to tissue boundaries from the speed of sound and the time the echo takes to return.

According to MedlinePlus: "an imaging test that uses sound waves to create pictures (also called a sonogram) of organs, tissues and structures inside the body".

NIBIB notes that there is also a therapeutic type that does not produce images but acts on tissue; this page covers diagnostic imaging.

Why is it done?

According to MedlinePlus, it is used to monitor the health and growth of the foetus during pregnancy, to diagnose the causes of many conditions especially those affecting soft tissues such as organs and blood vessels, and to guide some biopsies by showing where the abnormal area is and guiding the needle.

According to the NHS, it examines symptoms such as pain and lumps, monitors conditions such as thyroid problems, and helps during procedures. NIBIB lists applications in the heart, blood vessels, thyroid, breast, abdomen and muscles, and Doppler imaging, which measures the speed and direction of blood flow, such as assessing blockage of the carotid arteries by plaques.

The FDA lists uses including abdominal, breast and foetal scans, echocardiography, Doppler blood-flow studies and guided biopsies.

Preparation

According to the NHS, you may be asked to drink several glasses of water without urinating so the bladder is full, and to remove jewellery from the area being scanned; the centre should give you instructions before the appointment. MedlinePlus says preparation varies depending on the part being examined.

The exact instructions (fasting, bladder filling) vary by scan; follow what your centre sends you.

How is it done?

According to MedlinePlus and the NHS, you lie on the bed and gel is placed on the skin, then the sonographer moves the probe over the area; the waves bounce off structures in the body and the machine turns them into images on the screen. NIBIB notes that the gel prevents air pockets forming between the probe and the skin, because they obstruct the passage of the waves.

The scan may be external, with the probe on the skin, or internal, with a tube-shaped probe placed in the vagina or rectum or attached to an endoscope for deeper images. According to the NHS, you can ask to insert the probe yourself in an internal scan, and you can ask for the scan to be stopped at any time.

According to the NHS, the scan takes about 10 to 45 minutes and may take longer. The lights may be dimmed to make the screen easier to see. NIBIB notes that the images may be two-, three- or four-dimensional (four-dimensional being moving 3D).

Understanding the result

According to the NHS, the result may be given at the end of the appointment, or may take a few weeks and then be sent to the referring doctor; this describes the UK hospital system. Your doctor will explain what the report means in your case.

Risks and side effects

According to the NHS: "The sound waves used in the scan are safe and the scan does not use any radiation"; some discomfort may occur with the internal probe and you can ask to stop at any time. According to MedlinePlus: there are no known risks and it does not use ionising radiation.

NIBIB notes that diagnostic scanning is considered generally safe, but the waves can cause biological effects under certain conditions, which is why the FDA has set operating limits, and it urges against casual use. The FDA states that the technology has had an excellent safety record for more than 20 years, that the energy may slightly heat tissue and produce tiny gas bubbles, and that the long-term consequences are still unknown, so the ALARA principle is observed.

Pregnancy: MedlinePlus and the FDA note that ultrasound is the preferred imaging method during pregnancy because it does not use ionising radiation, and the FDA warns that non-medical "keepsake" videos are discouraged and that over-the-counter foetal heartbeat monitors should be used by trained professionals. This does not mean postponing medically required scans, but having them done by a professional.

The source pages did not list warning signs that would call for contacting the doctor after this scan, so there are no source-based alerts here for the period after it.

Limits of the test

According to NIBIB: "Ultrasound is not good for imaging bone or air-containing tissue such as the lungs", with exceptions in certain circumstances where fluid is present.

Common questions