Sonar and Ultrasound

Widely used in healthcare to diagnose and treat patients, ultrasound is an innovative diagnostic tool that has helped save countless lives. It is cost effective compared to similar, but more expensive tests such as MRI’s (magnetic resonance imaging).

Unlike the societal norm fifty years ago, when patients did not question their physicians’ decision and frequently hesitated to discuss symptoms, people today take a very different approach to their own healthcare. Proactive and more knowledgeable than ever before, patients now create question lists for their doctors, actively seek natural remedies, and strive to create a ‘team’ effect with their physician. However, ask this same patient now receiving an ultrasound how ultrasound works and they may just shrug their shoulders.

The amazing technology behind ultrasound begins with understanding the concept of SONAR, sound navigation and ranging. Sonar is used by submarines to detect objects underwater such as torpedoes and mines. Bats, primarily blind, use sonar to navigate through the dark. Whales and dolphins also use sonar to negotiate the waters.

Sonar works as an echo does. If you stand at the entrance to a cave and yell, your voice carries as sound waves into the cave. Some of these sound waves will bounce off of walls deep in the cave and return back you as an echo. In sonar, the sound waves that would come back to you as an echo are measured for the time it took them to be reflected off the cave walls and returned. Because sound travels very quickly, sonar can measure these times to determine how far away an object is. Using sonar, ships and submarines are able to obtain the distance to an object, as well as determine a fair approximation of what the object even is. The difference in items such as a small marble or pellet can be detected by a whale from an amazing fifty feet away.

Ultrasound uses the same principle as sonar. High frequency sound waves, from one to five megahertz, are transmitted by the ultrasound machine into the body using a probe or transducer. The human ear can hear sounds that are within 20 to 20,000 hertz. Because ultrasound transmits sound waves that are higher, no sound can be heard during the testing.

The sound waves are sent out as pulses. The Ultrasound Technician can change the frequency as well as length of these pulses. They are directed using acoustics lens so they focus on the area of diagnostic study. Once the sound waves enter your body, they travel along until they encounter a boundary, such as an organ, that reflects (bounce) them back to the probe. Others continue until they too reach a boundary that will reflect them back.

As these sound waves come back to the probe, the times are sent to the ultrasound machine which begins to calculate distances. Each time a sound wave returns, the machine measures the distance between the probe itself and the object that sound wave bounced off of (such as an organ). Also, the amount of time it took that sound wave to return is measured.

These time measurements are so quick they are usually tabulated within millionths of a second. Science understands that sound waves travel through different substances at different times. Sound travels through your body’s tissues at a rate of 5,005 feet per second. Using this rate, as well as the collected distances from the probe to each boundary, the ultrasound machine can quickly calculate. This forms an image, two-dimensional, that is displayed on the screen.

The resulting images that are produced show a distinct difference between a healthy organ and one that has a mass, or has change its internal structure. Organs can be viewed to determine a size variance, if the general shape has changed, and even small areas of fluid collection. If a patient asks their physician to examine a lump, or mass, on their leg, the Physician can observe the general outward appearance, as well as palpate the mass. Any additional examination would most like involve an invasive procedure such as a needle biopsy or surgical removal. With ultrasound, however, the mass can be examined more deeply. The images can differentiate between a mass that is malignant (cancer) or a benign cyst or abscess. Tumors, inflammations, trauma, areas of fluid collection, and aneurysms can easily be viewed.

While small, the transducer probe of the ultrasound is one of the most important components of ultrasound.  Able to transmit and receive sound, transducers control the image resolution and can also control how deeply the sound waves travel, or penetrate, into your body. Each transducer, along with its components, contains the amazing technology known as the piezoelectric effect.

In 1880, Pierre and Jacques Curies discovered that when electric current is applied to quartz crystals they begin to rotate and quickly change their shape. This rapid shape change causes vibrations in the quartz crystals, which in turn produces sound waves. The sound waves travel outward from the vibrations. This effect is called the piezoelectric effect, or pressure electricity.

There are one or more quartz crystals in each ultrasound probe. These crystals, through the piezoelectric effect, allow the probes to make the sound waves needed for ultrasound. The Curies also discovered that when sound waves hit the crystals they produce electric current. This allows the transducer probes to both transmit and receive sound waves.  When the Ultrasound Technician adjusts or changes the length or frequency of the sound waves, these changes cause the electric current that hits the crystals to change, thereby altering the duration.

Another important component of ultrasound is the CPU, the central processing unit,   the intelligence of ultrasound. The CPU provides the electric currents to the transducer probe. The CPU contains a microprocessor and memory, as well as amplifiers. The CPU is where the transducer probe sends all of the collected times and measurements from the sound echoes. The CPU then calculates this raw data. Once the information is calculated, images are formed on the monitor screen, ultrasound images. The CPU also stores the completed calculations and images on disk.




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