How Ultrasound Imaging Works
Ultrasound, also called sonography, uses sound waves to develop ultrasound images of what’s going on inside the body. An instrument called a transducer emits high-frequency sound, inaudible to human ears, and then records the echoes as the sound waves bounce back to determine the size, shape, and consistency of soft tissues and organs.
This information is relayed in real time to produce images on a computer screen. Ultrasound technicians, or sonographers, have special training in how to perform the test. Then a radiologist or your doctor will interpret the ultrasound images. This technology can help diagnose and treat certain conditions.
Uses of Ultrasound Tests
Ultrasound imaging has many uses in medicine, from confirming and dating a pregnancy to diagnosing certain conditions and guiding doctors through precise medical procedures.
Pregnancy. Ultrasound images have many uses during pregnancy. Early on, they may be used to determine due dates, reveal the presence of twins or other multiples, and rule out ectopic pregnancies. They also are valuable screening tools in helping to detect potential problems, including some birth defects, placental issues, breech positioning, and others. Many expectant parents look forward to learning the sex of their babies via ultrasound midway through a pregnancy. And later in pregnancy, doctors can even use ultrasounds to estimate how large a baby is just before delivery.
Diagnostics. Doctors employ ultrasound imaging in diagnosing a wide variety of conditions affecting the organs and soft tissues of the body, including the heart and blood vessels, liver, gallbladder, spleen, pancreas, kidneys, bladder, uterus, ovaries, eyes, thyroid, and testicles. Ultrasounds do have some diagnostic limitations, however; sound waves do not transmit well through dense bone or parts of the body that may hold air or gas, such as the bowel.
Use during medical procedures. Ultrasound imaging can help doctors during procedures such as needle biopsies, which require the doctor to remove tissue from a very precise area inside the body for testing in a lab.
Therapeutic applications. Ultrasounds sometimes are used to detect and treat soft-tissue injuries.
Types of Ultrasound
Most ultrasounds are done using a transducer on the surface of the skin. Sometimes, however, doctors and technicians can get a better diagnostic image by inserting a special transducer into one of the body’s natural openings:
- In a transvaginal ultrasound, a transducer wand is placed in a woman’s vagina to get better images of her uterus and ovaries.
- A transrectal ultrasound is sometimes used in the diagnosis of prostate conditions.
- A transesophageal echocardiogram uses the transducer probe in the esophagus so that the sonographer can obtain clearer images of the heart.
Additionally, ultrasound technology has advanced to allow for different types of imaging:
- Doppler is a special type of ultrasound that creates images of blood flow through vessels.
- Bone sonography helps doctors diagnose osteoporosis.
- Echocardiograms are used to view the heart.
- 3D imaging adds another dimension to the ultrasound image, creating three-dimensional interpretations rather than the flat two-dimensional images that are made with traditional ultrasound.
- 4D ultrasounds show 3D images in motion.
Benefits of Ultrasound
Ultrasounds offer many advantages:
- They are generally painless and do not require needles, injections, or incisions.
- Patients aren’t exposed to ionizing radiation, making the procedure safer than diagnostic techniques such as X-rays and CT scans. In fact, there are no known harmful effects when used as directed by your health care provider.
- Ultrasound captures images of soft tissues that don’t show up well on X-rays.
- Ultrasounds are widely accessible and less expensive than other methods.
What to Expect During an Ultrasound
Depending on the type of ultrasound test you are having, your doctor may offer special instructions, such as not eating or drinking anything for a number of hours before the test. Or you may be advised to drink several glasses of water in the time leading up to the test and refrain from using the bathroom to ensure that your bladder is full.
You should wear comfortable clothing that is easy to remove or partially remove. In some cases, you may need to disrobe or wear a gown, but often an ultrasound technician can easily access the area of the body that is being screened without your having to take off your clothes.