What you can expect

By Mayo Clinic Staff

During an ultrasound exam, you usually lie on an examination table. A small amount of gel is applied to your skin. The gel helps eliminate the formation of air pockets between the ultrasound and your body. During the exam, a technician trained in ultrasound imaging (sonographer) presses a small hand-held device (transducer), about the size of a bar of soap, against your skin over the area of your body being examined, moving from one area to another as necessary.

Based on the same principles as sonar, a technology used to detect underwater objects, the transducer generates and receives high-frequency sound waves that can't be heard by the human ear.

As the sonographer places the transducer on your skin, crystals inside the transducer emit pulses of sound waves that travel into your body. Your tissues, bones and body fluids reflect the sound waves and bounce them back to the transducer. The transducer then sends this information to a computer, which composes detailed images based on the patterns created by the sound waves.

Though the majority of ultrasound exams are performed with a transducer on your skin, some ultrasounds are done inside your body (invasive ultrasounds). For these exams, a specialized transducer is attached to a probe that's inserted into a natural opening in your body. Examples of these exams include:

  • Transesophageal echocardiogram. A small, specialized transducer is inserted into your esophagus to obtain images of the nearby heart. Such exams are typically performed with sedation.
  • Transrectal ultrasound. A small, specialized transducer is inserted into a man's rectum to view his prostate.
  • Transvaginal ultrasound. A small, specialized transducer is inserted into a woman's vagina to view her uterus and ovaries.

Ultrasound is usually a painless procedure. However, you may experience some mild discomfort as the sonographer guides the transducer over your body, especially if you're required to have a full bladder. A typical ultrasound exam takes from 30 minutes to an hour.

Feb. 23, 2012