Your child should be dressed in comfortable, loose-fitting clothing for an ultrasound exam. Other preparation depends on the type of examination. For some scans, you will be instructed to withhold food and drink for as many as 12 hours before your child’s appointment. For others, you may be asked to have your child drink up to six glasses of water two hours prior to the exam and avoid urinating, so that his or her bladder is full when the scan begins. Sedation is rarely needed for ultrasound examinations.

Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships at sea and fish detectors. As a controlled sound bounces against objects, its echoing waves can be used to identify how far away the object is, how large it is, and how uniform it is.

The ultrasound transducer functions as both a loudspeaker to create the sounds and a microphone to record them. When the transducer is pressed against the skin, it directs a stream of inaudible, high-frequency sound waves into the body. As the sound waves echo from the body’s fluids and tissues, the sensitive microphone in the transducer records the strength and location of the reflected waves. With Doppler ultrasound the microphone captures and records tiny changes in the sound wave’s pitch and direction. These signature waves are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. Still frames of the moving picture are frozen to capture a series of images.

Ultrasound imaging of the abdomen is painless, fast and easy. Your child will lie on his or her back on an examining table. The radiologist or sonographer will spread warm gel on the skin, then press and move the transducer firmly against the body to capture the desired images. There may be varying degrees of discomfort from pressure as the radiologist or sonographer guides the transducer over the abdomen, especially if the child has a full bladder. The examination usually takes less than 30 minutes.

Benefits

• Ultrasound provides real-time imaging, making it a good tool for quick evaluation of potentially emergent conditions such as appendicitis.
• Ultrasound equipment is much less intimidating to young children than the large equipment used in other types of imaging, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans.
• Ultrasound scanning does not require a child to lie perfectly still in order to capture a useful image.
• Ultrasound imaging is a painless, low-cost and non-invasive examination.
• Ultrasound is widely available and easy to use.
• Ultrasound does not expose children to ionizing radiation.

Risks

For standard diagnostic ultrasound there are no known harmful effects to humans.