Ultrasound is the ideal tool to examine children of all ages. It is fast, painless, uses no ionizing radiation, and does not require a baby to remain still for long periods. Real-time modes show movement of internal tissues and organs. Advanced ultrasound imaging techniques such as color Doppler, 4D ultrasound, harmonic imaging, and higher resolution, as well as the application of ultrasound contrast agents broaden the potential of ultrasound.
Pediatric [paediatric, Brit.] ultrasound can be used in all body regions and reduce the number of more invasive or radiating examinations that often additionally need sedation or intravenous iodinated contrast agents.

See also Fetal Ultrasound, Reflux Sonography, Ultrasound Safety, Abdominal Ultrasound and Pregnancy Ultrasound.

As far as ultrasound is concerned, 4D ultrasound (also referred to as live 3D ultrasound or 4B-mode) is the latest ultrasound technology - the fourth dimension means length, width, and depth over time. 4D Ultrasound takes 3D ultrasound images and adds the element of time to the progress so that a moving three-dimensional image is seen on the monitor. A 4D scan takes the same amounts of time as a 2D or 3D scan; the difference is the ultrasound equipment being used. One advantage of a 4D fetal ultrasound to a 2D-mode is that parents can see how their baby will generally look like. However, there are different opinions over the medical advantages.
To scan a 3D ultrasound image, the probe is swept over the maternal abdomen. A computer takes multiple images and renders the 3D picture. With 4D imaging, the computer takes the images as multiple pictures while the probe is hold still and a 3D image is simultaneously rendered in real time on a monitor.
In most cases, the standard 2D ultrasound is taken, and then the 3D/4D scan capability is added if an abnormality is detected or suspected. The 3D/4D sonogram is then focused on a specific area, to provide the details needed to assess and diagnose a suspected problem. A quick 4D scan of the face of the fetus may be performed at the end of a routine exam, providing the parents with a photo.
See also Obstetric and Gynecologic Ultrasound, Pregnancy Ultrasound, Fetal Ultrasound and Abdominal Ultrasound.

Higher frequencies are attenuated by tissue more than lower frequencies. This means that the higher the frequency the lower the depth of penetration but the greater the resolution.
Harmonic imaging allows the use of a lower frequency pulse to be picked up and sampled at the second harmonic (higher frequency) where the low frequency allows greater penetration and high frequency provides better resolution.

See also Skinline.

Perfluorochemicals are used as microbubble filling gases because of their low solubility in blood and high vapor pressure. Various types of perfluorochemical gases like perfluorocarbon, perfluorobutane, perfluoropropane, and perfluorohexane are used to substitute the air in microbubbles to improve the stability and plasma longevity of the agents. Perfluorocarbons are liquids at room temperature but gas at body temperature. The large molecules of perfluorocarbons have slow diffusion and solubility which increase the enhancement time of the ultrasound contrast agent as compared to air.

See also Filling Gas, and PESDA.

Periorbital Doppler is a continuous wave Doppler examination, determining the amplitude, flow direction, and compression effect of the frontal or supraorbital arteries in the periorbital region.

See also Acoustic Window, and Cerebrovascular Ultrasonography.