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Ultrasound FAQs

How does the procedure work?

Ultrasound imaging is based on the same principles involved in the sonar used by bats or ships at sea. As the sound passes through the body, echoes are produced that can be used to identify how far away an object is, how large it is, its shape and its consistency (fluid, solid or mixed). The ultrasound transducer functions as both a generator of sound (like a speaker) and a detector (like a microphone). When the transducer is pressed against the skin it directs inaudible, high-frequency sound waves into the body. As the sound echoes from the body’s fluids and tissues the transducer records the strength and character of the reflected waves. These echoes are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. The "live" images of the examination are usually recorded on videotape but one or more frames of the moving picture may be "frozen" to capture a still image.


Why do I have to have a full bladder for a pelvic ultrasound?

A distended bladder acts as a "window" through which the sound waves travel and allows the sonographer to visualize the pelvic organs. A distended bladder also displaces bowel, which can prevent visualization of the pelvic organs.


Why do I have to fast for an abdominal ultrasound?

Fasting reduces the amount of air in the stomach and intestines which can interfere with visualization of the abdominal organs. It also ensures that the gallbladder will be distended so it can be thoroughly evaluated.


Can you tell me the sex of my baby?

If the baby is in a good position for the sonographer to see the genital region, the baby's sex can be determined. The sex can be determined as early as 14 to 16 weeks, although it may not be clearly visible until 20 to 22 weeks.


What are the benefits of ultrasound?

  • Ultrasound imaging offers these benefits:
  • Provides a simple, painless and noninvasive imaging method for viewing structures within the body
  • Uses no ionizing radiation (x-rays) and is the preferred image modality for diagnosis and monitoring of pregnant women and their unborn infants
  • Produces real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies
  • Visualizes structure, movement and live function in the body's organs and blood vessels


What are the limitations of ultrasound imaging?

Ultrasound has difficulty penetrating bone and therefore can only see the outer surface of bony structures and not what lies within. For visualization of bone, other imaging modalities such as magnetic resonance imaging (MRI) may be selected. Because ultrasound waves do not pass through air, an evaluation of the stomach, small intestine and large intestine may be limited. Intestinal gas may also prevent visualization of deeper structures such as the pancreas and aorta. Obese patients are also more difficult to image because tissue attenuates (weakens) the sound waves as they pass deeper into the body. Therefore, there are times where additional testing such as CT or MRI may be required to fully evaluate a condition.