Ultrasound (also termed sonography, ultrasonography, and Doppler study) is a non-invasive diagnostic medical technique that uses high frequency sound waves to produce images (sonogram) of the internal structures of the body. These sound waves are not detectable by human hearing.
Using an ultrasound machine (ultrasonography), a technician or doctor moves a device called a transducer (probe) over part of your body. The transducer emits sound waves which bounce off the internal tissues, and creates images from the waves that bounce back. Different densities of tissues, fluid, and air inside the body produce different images that can be interpreted by a physician, typically a radiologist (a physician who specializes in imaging technologies). Many studies are done by a trained technologist (sonographer) and then interpreted by a radiologist.
A two-dimensional (2D) is the most common type of ultrasound exam. These 3D and 4D ultrasounds are possible due to the advances in computerized analysis of sound waves at different angles. Three dimensional images are compiled from the sound waves coming back at different angles and the images are easier to understand and show more details. The difference between a 3D and 4D ultrasound is that the 4D is like a video showing motion of a 3 dimensional object.
Ultrasound can be used as a diagnostic or screening tool to confirm medical disorders or to assist in performing medical procedures. It is also used as a therapeutic tool in treating musculoskeletal problems, renal stones (kidney stones), and gallstones.
Ultrasound Diagnostic or Screening Uses
- Obstetrics: Pregnancy ultrasound (fetal ultrasound or baby ultrasound) is used to assess the progression of a fetus. It is used to find out the number of fetuses in the womb, the age of the fetus, the location of the placenta, the fetal position, movement, breathing and heart rates, and the amount of amniotic fluid in the uterus. Most women have at least one ultrasound during pregnancy. The exams can be done trans-vaginally (early in a pregnancy), but most are done trans-abdominally. 3D and 4D ultrasound have limited medical uses, such as when a specific problem is suspected. Currently 3D and 4D ultrasounds are popular for "keepsake" sonogram pictures of the baby in the womb. The best time for a 3D ultrasound for fetal photos is when the baby is about 26 weeks. The FDA warns against the use of ultrasound for nonmedical reasons. Although there has been no proof of risk, the long-term effects of these ultrasounds have not been studied. Doppler ultrasounds are used to measure blood flow and may be used if there is a suspicion that the fetus is not growing properly.
- Gynecology: Vaginal ultrasound, pelvic ultrasound, or transvaginal ultrasound is used to diagnose growths or tumors of the ovary, uterus, and Fallopian tubes. It can be used to assess non-pregnancy related issues as well:
- Cardiology: Echocardiography (heart ultrasound) is a common way to evaluate the overall function of the heart. It is used to evaluate the flow of blood through the chambers and valves of the heart. It also assesses the strength of the heart beat and the volume of blood pumped through. Doppler ultrasound echocardiography is often used for the following:
- Blood vessels: Ultrasound is useful in detecting problems with most of the larger blood vessels in the body. Using Doppler ultrasound technology, the flow of blood through the vessels can be observed and measured. Narrowing of vessels (stenosis) or widening of vessels (dilatation, also referred to as aneurysms) can be detected. Ultrasound testing of blood vessels includes:
- Abdominal structures: Abdominal ultrasound is used to evaluate the solid organs within the abdominal cavity, including the liver, gallbladder, pancreas, kidneys, and bladder.
- Renal ultrasound is used to evaluate the function and structure of the kidneys. Swelling around the kidney with blockage in the urinary tract can be seen with ultrasound, making abdominal ultrasound useful in detecting kidney stones.
- Liver ultrasound is used to find abnormalities in the liver tissue and ducts.
- Gallbladder ultrasound can screen for gallstones or an infected gallbladder.
- Appendix ultrasound is used in children or pregnant women, where it is necessary to avoid radiation from aCT scan (computerized tomography).
- Testicular ultrasound: Used to diagnose testicular torsion, epididymitis (testicle infection), and testicular masses.
- Neck ultrasound: The thyroid and parathyroid glands can be imaged to detect nodules, growths, and tumors.
- Breast ultrasound: Used to image the breasts and to guide biopsy of breast masses in order to evaluate for breast cancer.
- Knee ultrasound: Ultrasound can be used to evaluate the structures in the back of the knee to determine if a Baker's cyst is present.
- Eye ultrasound: An eye ultrasound is used to look at the back of the eye (retina). It is often used when a patient hascataracts that make looking into the eye difficult. The test may help diagnose retinal detachment. It can also assist in cataract surgery.
- Skin ultrasound: Ultrasound can be used to help find certain types of foreign bodies that may become lodged in the skin.
Ultrasound Procedural Uses
- Ultrasound-guided needle biopsy: Ultrasound helps medical professionals guide needles into specific areas of the body to extract cells for laboratory testing.
- Ultrasound-guided needle aspiration: Ultrasound may be used to guide a needle into pockets of fluid accumulated in the body that need to be drained (for example, an abscess, pleural effusions, or ascites).
- Ultrasound-assisted intravenous access: When an intravenous (IV) line is required and veins are difficult to access, ultrasound may be used to assist in finding larger veins in the neck, chest wall, or groin.
Ultrasound Therapeutic Uses
Extracorporeal shock wave lithotripsy (ESWL) is a form of ultrasound used to break up kidney and gallbladder stones. In many cases, the patient is given some sedation or pain medication as the high intensity waves needed to fracture the stones can cause discomfort.
A few physicians use HIFU (high intensity focused ultrasound) to treat cancer, while others use ultrasound for targeted drug delivery, hemostasis or thrombolysis. However, these techniques are not widely available and are still being evaluated for efficacy.
Ultrasound is often used to treat musculoskeletal injuries, and is frequently used to treat sports injuries. For example, plantar fasciitis and tendinitis are commonly treated using therapeutic ultrasound. It is believed to help reduce inflammation and increase blood flow to affected areas. However, there is little evidence that tissue therapeutic ultrasound is effective. More study is needed.
During the Ultrasound
For the most part, ultrasound is considered a painless, non-invasive diagnostic tool. The procedure usually takes from 30 minutes to an hour.
Most ultrasound scans can be performed with the transducer placed atop the skin, with the sound waves aimed at the organ or body part being tested. The patient is usually placed in a comfortable position that provides the ultrasound technician (sonographer) access to the part of the body being tested.
The area being studied is covered with a small amount of gel to eliminate air pockets between the transducer and the skin. The sonographer moves the transducer across the body part being studied to obtain images.
You may feel pressure as the transducer is moved over an area, and if the area is sensitive, you may feel pain, but the waves from the transducer do not cause this pain.
If Doppler ultrasound is used, you may hear pulse-like "whooshing" sounds that change in pitch as the blood flow is monitored.
Some exams are considered "invasive ultrasounds," where the transducer is attached to a probe and inserted into a natural opening in the body. These exams may cause some discomfort or pain due to the sensitivity of the tissue being touched by the probe, but not by the ultrasound waves.
- Transesophageal echocardiogram: The transducer is inserted into the esophagus to obtain images of the heart.
- Transrectal ultrasound: The transducer is inserted into a man's rectum to view the prostate.
- Transvaginal ultrasound: The transducer is inserted into a woman's vagina to view the uterus and ovaries.
After the Ultrasound
Once the ultrasound procedure is complete, gel will be wiped off your skin and you should be able to resume your normal activities immediately in most cases or within a few hours if a more invasive study is done.
According to the Food and Drug Administration, ultrasound has an excellent safety record since it was put into regular use more than 30 years ago.
It avoids the use of radiation that is common in other diagnostic procedures by using harmless sound waves to produce images.
By using ultrasound technology to assist in other procedures, you may also reduce the risk and increase the effectiveness of those other procedures.
Specialized high intensity ultrasound waves such as those used for ESWL and HIFU have the ability to cause discomfort and potentially serious damage to tissue nearby the area of treatment. These risks are minimized by good control of wave intensity exposure timing and focus techniques.
Currently, 3D and 4D ultrasound is being used to allow parents and their families to see a three-dimensional image of their child while still in the womb. The cost of these ultrasounds is around $200. However, the risks to the fetus is currently under debate. The FDA and several medical organizations, such as the American Institute of Ultrasound in Medicine (AIUM), have come out against “entertainment” sonograms, citing potential health hazards with non-medically justified ultrasound energy and possible misinterpretation of sonograms by patients and unskilled personnel. The ultrasound heats up tissue and this increase in temperature has also been cited as a potential risk. The FDA considers it illegal for anyone to promote, sell, or lease ultrasound equipment for the purpose of making keepsake fetal videos, particularly if there is no medical prescription.
An ultrasound technician will usually perform the procedure. Images are usually available immediately from the scan but they need to be interpreted by a radiologist.
The radiologist's report is given to the physician who ordered the ultrasound, who will then discuss the results with you.
There are limitations to ultrasound that may affect the results. Ultrasound is not the recommended procedure for:
- Bowel or organs obscured by the bowel: Air and gas can disrupt the ultrasonic waves.
- Obese patients: The more tissue the sound waves have to pass through, the weaker the signal and the more distorted the image becomes.
- Internal structure of bones or certain joints: Ultrasound cannot penetrate bone.