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How Does an Ultrasound Work?


Have you ever had an ultrasound and wondered how they work? Here is what you need to know about the non-invasive test that can give your doctor a clear picture of what is happening inside your body.

Many people associated ultrasounds with pregnancy, as many OB/GYN doctors use ultrasound to examine the babies inside pregnant women. Doctors also use ultrasound to help diagnose the cause of a patient’s pain, swelling or other symptoms. Ultrasound can help doctors find the source of infection, guide a doctor’s hand during biopsies, provide valuable information in the diagnosis of heart conditions and even assess damage after a heart attack.

Ultrasound is safe, non-invasive, and does not use dangerous radiation like old-fashioned x-rays. The ultrasound procedure requires little to no preparation and can be done at nearly any time.

But, how exactly does the ultrasound machine work? 

How Ultrasound Works

Ultrasounds work by bouncing sound waves off an object and listening for the sound wave to return. Measuring these bouncing sound waves can help create an image of what the object looks like, as sound waves bouncing on nearby aspects of the object return faster than do those sound waves bouncing on faraway features of the item. Various returning sound waves can have different pitches and directions too, depending on if the sound wave bounced off the curve of an internal organ, the density of fluid or thick tissue.

Ultrasound imaging uses the same sonar principles used by bats, ships and fishermen. Ultrasound imaging in medicine focuses on detecting changes in the appearance, size, shape or contour of patients’ organs, tissues and vessels, or used to detect tumors or other abnormal masses.

During a medical ultrasound examination, the ultrasound technician uses a handheld transducer to both send sound waves into the body and to receive the echoing sound waves. When the technician presses the transducer against the skin, the device sends tiny pulses of inaudible, high-frequency sound waves into the patient’s body. These transducers produce sound waves at frequencies well above the threshold of human hearing at 20KHz and higher; most transducers used today operate at much higher frequencies in the megahertz (MHz) range.

These sound waves bounce off internal organs, tissues and fluids to return to the transducer, which records tiny changes in the returning sound’s pitch and direction. A computer measures and displays the signature waves to create a real-time picture on a monitor. The technician will capture one or more frames of the moving pictures as still images. Technicians may also save short video loops of the images.

Doppler ultrasound is a special application of the ultrasound technique. Doppler measures the speed and direction of blood cells as they move through blood vessels. Like the changing pitch of a train’s whistle as the locomotive passes, movement of blood cells changes the pitch of the reflected sound waves. Scientists refer to this the Doppler Effect. A computer collects and processes the sounds to color pictures and graphs that represent the flow of blood through the blood vessels.

There are two main types of medical ultrasounds: diagnostic ultrasound and therapeutic ultrasound. Diagnostic ultrasounds help doctors diagnose patients by producing images of internal fluids, tissues and organs. Therapeutic ultrasounds use the power of sound energy to interact with body tissues in a way that modifies or destroys the tissue. Ultrasound specialists use therapeutic ultrasounds to move or push tissue, heat tissue, dissolve blood clots or deliver drugs to specific locations within a patient’s body. Ultrasound professionals can also use therapeutic ultrasounds with very high-intensity beams to destroy diseased or abnormal tissues, such as tumors, without the need for surgery. 

History of Ultrasound

While ultrasound is an advanced medical technology today, its roots go all the way back to 1794, when physiologist Lazzaro Spallanzani was the first person to study echolocation among bats. This echolocation, which is the use of sound waves to locate objects, is the basis of ultrasound physics.

In 1877, brothers Jacques and Pierre Currie discover piezoelectricity, in which they used probes to emit and receive sound waves. In 1915, the sinking of the Titanic inspired physicist Paul Langevin to invent a device that could detect objects at the bottom of the sea. He eventually invented the hydrophone, now recognized as the world’s transducer.

Doctors began to use ultrasound, also known as sonography, as a form of physical therapy in the 1920s through the 1940s. Neurologist Karl Dussik started using ultrasound for medical diagnosis in hopes of detecting brain tumors in 1942. Doctors then started using ultrasound for a wide variety of uses, such as for detecting gallstones and breast tumors.

They started using ultrasound in OB/GYN, cardiology, and other fields through the next few decades. Other advances include handheld transducers, Doppler, three-dimensional (3D) imaging, and use during other procedures.

Today’s ultrasound technology is safe, effective and highly useful in the diagnosis and treatment of many diseases. For more information on how ultrasound works, talk with your ultrasound professional. 

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