Ultrasound uses rhythmic pulses of high-frequency sound waves to form images. The principle is similar to the echolocation used by such animal species as bats and dolphins, and to the SONAR technology used in submarines.
First, a probe connected to the device sends high-frequency sound pulses into the human body. (The pulses are in the 1 to 5 megahertz range.) The sound waves travel until they reach a boundary between different tissues, such as that between soft tissue and bone.
Some of the sound waves echo back. Others continue on until they hit another boundary and get echoed back. The probe picks up the sound waves and transmits them to the machine. A computer in the machine calculates the distance each wave has traveled by the timing of the sound wave’s return. This is usually some millionths of a second, involving millions of sound waves!
Every ultrasound machine consists of the same basic parts.
- Transducer Probe and Pulse Controls
- Keyboard, Cursor, and Display
- Disk Storage Drive
The transducer probe is the most important part of the device. It makes and receives the millions of sound waves at the heart of the machine’s capabilities. A piezoelectric quartz crystal in the probe vibrates when electrified, producing ultrasonic waves. Meanwhile, a sound absorbing substance eliminates feedback from the probe, while an acoustic lens concentrates the waves.
There are many kinds of transducer probe that serve many different diagnostic functions. The frequency of the sound waves determines how deeply they insinuate themselves into the body and how sharp the resulting image is, while the shape of the probe determines the image scope.
There are multiple-element probes with more than one crystal that can be ‘steered’ across the body surface. Those are useful for heart imaging. There are also differently shaped probes that can be inserted into various body cavities, including the mouth, rectum, or vagina, and thus get closer to whatever internal organ requires imaging for a clearer view.
Three Dimensional and Doppler Ultrasound
3D ultrasound works in a way similar to a CAT scan or an MRI. A series of 2D images are taken of some part of the patient’s body, and then specialized software compiles them into a three-dimensional image. 3D ultrasound can be used to detect tumors and to create images of fetuses and of blood flow.
Doppler ultrasound takes advantage of the Doppler effect, according to which sounds become lower-frequency as they move away from an observer and higher-frequency as they move toward an observer. It is ideal for measuring the blood flow rate through the major arteries and heart.
Ultrasound in Action
There are no substantiated dangers resulting from these devices. On the contrary, ultrasound has many uses in medicine. For instance, in emergency rooms, it has gained currency as a rapid diagnostic tool.
In obstetrics and gynecology, it is used to check on the development of a pregnancy. It can show the size, position, and sex of the fetus, its growth rate, and the position of organs and tissues crucial to the pregnancy. Many other important factors can be checked, as well.
Ultrasound can be used in urology to examine the kidneys for kidney stones and abnormal blood flow, and also to check for prostate cancer. It assists cardiologists by imaging abnormal structures or functions within the heart and measuring the rate of blood flow into and out of the heart.
What an Ultrasound Exam is Like
The patient follows a technician into a room where there is an ultrasound device and removes either all of their clothes or those over the area being examined. The technician will drape a cloth over all areas of the body not being examined.
The technician will then apply a mineral oil jelly to the skin over the area being examined. This eliminates any air molecules obstructing the probe’s view and helps the sound waves enter the body.
After covering the probe with a plastic cover, the ultrasonographer will either run the probe over the skin or, depending on the nature of the exam, insert the probe into the patient’s body. The patient may be asked to move to facilitate the examination.
After the exam, the images will be stored on disk. The patient will then be given a towelette to clean off the jelly and allowed to clean up and get dressed. The patient might receive a printout of the images.