Ultrasounds how do they work

In this edition of How Stuff Works , we will look at how ultrasound works, what type of ultrasound techniques are available and what each technique can be used for. What is Ultrasound? Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen:. Photo courtesy Karim and Nancy Nice Ultrasound image of a growing fetus approximately 12 weeks old inside a mother's uterus.

This is a side view of the baby, showing right to left the head, neck, torso and legs. In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.

Photo courtesy Dynamic Imaging Limited Ultrasound machine with various transducer probes. Transducer Probe The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. 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 In the probe, there are one or more quartz crystals called piezoelectric crystals.

When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents.

Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves. Transducer probes come in many shapes and sizes, as shown in the photo above. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image.

Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasounc beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound see Basic Principles of Ultrasound for details on transducers.

For a scan during pregnancy, and especially early pregnancy, the patient should drink plenty of water and try to avoid urinating for some time before the test. The scan usually takes place in the radiology department of a hospital. A doctor or a specially-trained sonographer will carry out the test. The transducer is moved over the part of the body that needs to be examined.

The patient should not feel discomfort or pain. They will just feel the transducer over the skin. If the internal reproductive organs or urinary system need to be evaluated, the transducer may be placed in the rectum for a man or in the vagina for a woman. To evaluate some part of the digestive system, for example, the esophagus, the chest lymph nodes, or the stomach, an endoscope may be used. Internal ultrasound scans are less comfortable than external ones, and there is a slight risk of internal bleeding.

Most types of ultrasound are noninvasive, and they involve no ionizing radiation exposure. The procedure is believed to be very safe. Ultrasound during pregnancy is recommended only when medically needed. Anyone who is allergic to latex should inform their doctor so that they will not use a latex-covered probe. Platelet-rich plasma therapy is a controversial treatment that is growing in popularity in sports science and dermatology. Learn more. People with certain conditions or who have undergone chemotherapy or radiation may require a stem cell transplant.

They can use a person's own stem…. An intravenous IV injection is a fast and accurate way of administering a medication. Learn more about IV injections here. Learn more about its uses and how it compares with saline solution here. A BNP test is a type of blood test that doctors sometimes use to help diagnose heart failure. Read on to find out more. How do ultrasound scans work? You will need to ask your doctor or the ultrasound department if you need to do any special preparation before your scan.

If you are having an upper abdomen ultrasound, you will need to lie down on an examination table or bed. The ultrasound technologist, known as a sonographer, will place some gel onto your skin to provide better contact between your body and the ultrasound probe.

They will then place the hand-held probe on your skin above the area of your body, organ or tissue that is being studied. The two-dimensional or sometimes three-dimensional pictures are shown instantly on a monitor. Other types of ultrasound may need a slightly different procedure. For example, a woman undergoing an investigation of her pelvis may have a transvaginal scan, which involves inserting a special ultrasound probe into the vagina rather than or as well as scanning through the front of the pelvis.

An ultrasound scan usually takes around 20 to 40 minutes, depending on the type of examination. After the procedure, the sonographer will give you paper towels or something similar to wipe off the gel. You can then get dressed.

The results of the ultrasound scan are usually sent to your doctor, so you will have to make a follow-up appointment with them to get the results.

Most ultrasound scans are non-invasive and the procedure does not involve the use of ionising radiation such as x-rays. Ultrasound scans for pregnant women are now considered routine in Australia. Most people can go about their normal business once they have finished the ultrasound examination. Treatment — if any — depends on the reason for your scan. For example, fibroids detected during a scan may be surgically removed myomectomy , shrunk with medications or simply monitored.

Other conditions detected by an ultrasound scan, such as abdominal masses, may need further tests or exploratory surgery. This page has been produced in consultation with and approved by:.

Allergy testing is used to find which substances provoke an allergic reaction.