Ultrasound, or sonography, is an imaging technique introduced into medicine in the 1960s, based on sonar, a technique which sends sound waves through water and uses the returning echoes to characterize submerged objects. Ultrasound makes use of the same theory, instead using high frequency sound waves which are inaudible to the human ear. These ultrasound waves are transmitted into the body, and the way in which they "echo" back is recorded and displayed as a real-time visual image. When an ultrasound is taken, a hand-held transmitter is placed directly on the body in the area to be imaged. In addition, special sonographic gel is applied, serving to both lubricate and aid in transmission of the sound waves.

Ultrasound is often used to examine soft tissues in the body, which are not well visualized on traditional x-ray techniques. This includes internal organs, such as the heart, liver, gallbladder, spleen, pancreas, kidneys, and bladder. Ultrasound has also been used to examine the brain in newborns, transmitting through the "soft spot" on the top of the head called the anterior fontanelle. It is also an imaging modality often used for prenatal imaging, to determine the condition of pregnant women and their fetuses (obstetric ultrasound).

An obvious advantage of ultrasound is that the body is not exposed to ionizing radiation, as in traditional x-rays. For this reason, ultrasound is considered safe for pregnant women when other imaging techniques might put the baby at risk. In addition, as mentioned above, ultrasound images are "real-time," meaning that the sonographer conducting the exam can make adjustments as the exam is taking place to ensure the best visualization of the structures of interest. In prenatal imaging, the sonographer can determine how the fetus is positioned and is then able to move the transmitter to visualize specific fetal organs. This real-time image is also useful in visualizing motion, which is important in examining the heart (as in an echocardiogram) to evaluate heart function. Finally, the fact that the image is immediately available allows for faster interpretation and diagnosis.

On the other hand, ultrasounds are limited in the area of the body which can be visualized at one time, which can be especially limiting in visualizing deeper structures in patients who are particularly obese. Images produced by ultrasound are also notoriously difficult to decipher, as the images produced are small cross-sections, usually with very little in the way of anatomic reference points. This difficulty can be lessened if the physician interpreting the image is present during the exam to observe where the transmitter is placed externally on the patient's body.

Recently, ultrasound has been combined with Doppler technology, allowing visualization of directional fluid flow. This has been used to evaluate blood flow through the heart in echocardiograms. This technique is also often employed in visualizing vascular structures, especially in the field of vascular surgery. Ultrasound has also been used for guidance in placing drains and catheters in the field of interventional radiology.

*The images shown here are some of the best in Dr. Terry Angtuaco's collection throughout her career. Not all ultrasounds are this clear; many ultrasound images are fuzzy. Although these images show the fetal face clearly, with prenatal ultrasound, the baby is sometimes looking away such that the sonographer is unable to get a view of the face.

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