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, your doctor may ask you 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.
An ultrasound scanner consists of a console containing a computer and electronics, a video display screen and a transducer that is used to scan the body. The transducer is a small, hand-held device about the size of a bar of soap, attached to the scanner by a cord. The radiologist or sonographer spreads a lubricating gel on the child’s abdomen in the area being examined, and then presses the transducer firmly against the skin to obtain images.
The ultrasound image is immediately visible on a nearby screen that looks much like a computer or television monitor. The radiologist or sonographer watches this screen during an examination; often, the patient is able to see it as well.
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. The live images of the examination can be recorded on videotape. In addition, still frames of the moving picture are usually frozen to capture a series of images.
Your child is positioned on an examination table, and then a clear gel is applied to the abdomen to help the transducer make secure contact with the skin. The sound waves produced by the transducer cannot penetrate air, so the gel helps to eliminate air pockets between the transducer and the skin. The sonographer or radiologist presses the transducer firmly against the skin and sweeps it back and forth to image the area of interest.
When the examination is complete, you and your child may be asked to wait while the ultrasound images are reviewed, either on film or on a TV monitor. Often, the sonographer or radiologist is able to review the ultrasound images in real time as they are acquired, and your child can be released immediately.
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.
A radiologist, who is a physician experienced in ultrasound and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to your paediatrician or primary care physician. Your physician’s office will tell you how to obtain the results. New technology also allows for distribution of diagnostic reports and referral images over the Internet at some facilities.