While the patient’s history and physical examination are the building blocks of making a medical diagnosis, the ability to peer inside the body can be a powerful tool. Ultrasound is an imaging technique that provides that ability to medical practitioners.
What is an ultrasound?
Ultrasound produces sound waves that are beamed into the body causing return echoes that are recorded to “visualize” structures beneath the skin. The ability to measure different echoes reflected from a variety of tissues allows a shadow picture to be constructed. The technology is especially accurate at seeing the interface between solid and fluid filled spaces. These are actually the same principles that allow SONAR on boats to see the bottom of the ocean.
What is ultrasonography?
Ultrasonography is body imaging using ultrasound in medical diagnosis. A skilled ultrasound technician is able to see inside the body using ultrasonography to answer questions that may be asked by the medical practitioner caring for the patient. Usually, a radiologist will oversee the ultrasound test and report on the results, but other types of physicians may use ultrasound as a diagnostic tool. For example, obstetricians use ultrasound to assess the fetus during pregnancy. Surgeons and emergency physicians use ultrasound at the bedside to assess abdominal pain or other concerns.
A transducer, or probe, is used to project and receive the sound waves and the return signals. A gel is wiped onto the patient’s skin so that the sound waves are not distorted as they cross through the skin. Using their understanding of human anatomy and the machine, the technician can evaluate specific structures and try to answer the question asked by the patient’s physician. This may take a fair amount of time and require the probe to be repositioned and pointed in different directions. As well, the technician may need to vary the amount of pressure used to push the probe into the skin. The goal will be to “paint” a shadow picture of the inner organ that the health care practitioner has asked to be visualized.
The physics of sound can place limits on the test. The quality of the picture depends on many factors.
- Sound waves cannot penetrate deeply, and an obese patient may be imaged poorly.
- Ultrasound does poorly when gas is present between the probe and the target organ. Should the intestine be distended with bowel gas, organs behind it may not be easily seen. Similarly, ultrasound works poorly in the chest, where the lungs are filled with air.
- Ultrasound does not penetrate bone easily.
- The accuracy of the test is very much operator dependent. This means that the key to a good test is the ultrasound technician.
Ultrasound can be enhanced by using Doppler technology which can measure whether an object is moving towards or away from the probe. This can allow the technician to measure blood flow in organs such as the heart or liver, or within specific blood vessels.
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