What are Ultrasound Probes Used For?

The ultrasound transducer, also known as an ultrasound probe, is the key element or the central focus in any ultrasound system. The transducer probe is what is responsible for making the sound waves and receiving the echoes. If you can picture the ultrasound machine as representing a human being: the ultrasound probe is the mouth and the ears. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the ultrasound probe, there are one or more quartz crystals ─ called piezoelectric crystals. In ultrasound equipment, a piezoelectric ultrasound transducer converts electrical energy into extremely rapid mechanical vibrations—so fast, in fact, that it makes sounds, but ones too high-pitched for our ears to hear.

The ultrasound probe is generally placed directly on the patient's body and moved over the area to be viewed. Since water is a good conductor for sound waves, a water-based gel is usually placed on the patient's skin to help facilitate movement of the ultrasound waves. For example, patients undergoing obstetric ultrasound are usually asked to arrive for the test with a full bladder.

The ultrasound probe also has a sound-absorbing substance to eliminate reverse reflections from the probe itself, and an acoustic lens to help focus the sound waves that are produced. Ultrasound probes come in many shapes and sizes, and the shape of the ultrasound transducer determines its field of view, and the frequency of sound waves that are produced determines how deep the sound waves penetrate, as well as the resolution of the image.

Ultrasound probes may contain one or more crystal elements. For example, in multiple-element ultrasound probes, each crystal has its own circuit. Multiple-element ultrasound transducers have the advantage that the ultrasound beam can be directed simply by changing the timing in which each element gets pulsed. The quartz crystals in the ultrasound probe change shape and emit ultrasonic waves when they are stimulated with an electrical current. These sound waves bounce back from the body and hit the quartz crystals, which then produce an electrical current that the probe sends to the computer. Variations in the current help the computer "see" shapes and masses inside the body. “Steering” the beam is especially important for cardiac ultrasound.

In addition to ultrasound probes that can be moved across the surface of the body, some ultrasound probes are designed to be inserted through a variety of openings of the body (vagina, rectum, esophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach). Getting closer to the organ allows for more detailed views, for more precision diagnoses.

While the most universal use of ultrasound transducers is still visualizing the growing fetus in a pregnancy, there are other medical applications, as well. Ultrasound probes can be used to examine the heart, thyroid gland and blood flow in veins and arteries. In cancer patients, ultrasound transducers may be used to diagnose the disease or to guide biopsies or other procedures. The use of diagnostic ultrasound probes is considered safe, with no known undesirable effects.