Mention "ultrasound" and most people likely will think of an image of a fetus in a mother's womb. But while providing peeks at the not-yet-born is one of ultrasound's most common applications, that's only a small part of the picture.
Ultrasound, also called sonography, is probably the most widely employed imaging tool in medicine today.
The technology uses high-frequency sound waves inaudible to humans to produce images from inside the body. A device called a transducer that is placed on the skin sends the sound waves into the body and records the echoes as they bounce back, thus defining the size, shape and mass of soft tissues and organs. This information is relayed to a computer that translates it into images on a monitor, allowing doctors to view, interpret and evaluate what's going on inside the patient.
Ultrasound testing is noninvasive, safe, painless for patients and capable of providing accurate images without the radiation that's part of X-rays and CT scans and the magnetic fields of MRIs. It is also far more portable and far less expensive than other imaging technologies. Not surprisingly, its use is growing exponentially.
"The use of ultrasound is probably expanding at a greater rate than ever," said Frederick Kremkau, Ph.D., director of the Program for Medical Ultrasound at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina. "It's often seemed to me that we were reaching the end of what ultrasound can do, but that's never happened."
Kremkau has a singular perspective on the evolution of medical sonography. Though he's not a physician - his doctorate is in electrical engineering - he has worked with ultrasound technology since the late 1960s and has led Wake Forest Baptist's pioneering ultrasound education program since 1985.
Kremkau also is the author of a textbook, "Sonography Principles and Instruments," that's in its ninth edition, a past president of the American Institute of Ultrasound in Medicine and a frequent lecturer on the subject.
For decades, sonography was employed in only a handful of medical specialties. But "over the years we've been able to get more and more information out of the instruments," Kremkau said, and today ultrasound is used across the spectrum of disciplines, from anesthesiology to urology.
Ultrasound's positive attributes apply to all patients, but they have special value with two specific populations in addition to pregnant women - children and the elderly.
"Ultrasound has no radiation risk and may be less intimidating than other imaging methods for some kids," said Milan Nadkarni, M.D., medical director of the Emergency Department at Wake Forest Baptist's Brenner Children's Hospital. "We use it a lot, and are looking to use it in more instances."
Referring to the type of ultrasound test used to capture images of the heart, Wake Forest Baptist cardiologist Win Pu, M.D., said, "Because of echocardiography's noninvasive nature it is particularly suitable for older adults, who often have increased risk of complications from invasive procedures and of kidney injury from the contrast die used in other imaging methods."
Ultrasound is not just a diagnostic tool. Its various applications include treating soft-tissue injuries, guiding physicians during needle biopsies and other procedures, breaking up kidney stones and delivering drugs to very precise areas.
That's not a bad medical record for something created for use on the high seas.
The sinking of the Titanic in 1912 and the outbreak of World War I two years later spurred demand for a way to detect icebergs and submarines. This led to the invention of systems that used high-frequency sound waves to indicate the size, location and movement of objects underwater - what we know as sonar.
In the following years many potential uses for ultrasound technology - military, nautical, industrial, scientific, medical -were explored. The first medical application, in the 1920s, was physical therapy, and in the '30s and '40s it was employed as a treatment for arthritis, eczema and other ailments.
Ultrasound was first used as a diagnostic tool in the 1940s, but with some serious shortcomings. The machines were cumbersome, the one-dimensional black-and-white images they produced were primitive and into the 1960s the patient had to be partially submerged in water for sonography to work.
But the pace of progress soon accelerated. A big step was the invention in the mid-'60s of a transducer that could be placed directly on the patient with the use of water-based gel that permitted the ultrasound waves to enter the body. Major developments since then have included two-dimensional imaging, grayscale imaging, Doppler technology (the same as seen on TV weather forecasts), color imaging, 3-D imaging, 4-D (motion in real time) imaging and, most recently, elastography (which can show the relative hardness or softness of tissue).
While ultrasound imaging has become more and more advanced with digital technology, the equipment has become more compact and more mobile. Portable ultrasound consoles have been around since the 1980s, but pocket-sized devices hit the market in the early 2000s and today there are ultrasound scanners that work with laptops, tablets and smart phones, adding telemedicine to ultrasound's capabilities.
This high-tech portability, Kremkau believes, is ultrasound's greatest asset.
"It's what we call point-of-care ultrasound, where it can be applied to a patient virtually anywhere - at the bedside, in the home, at the site of an accident, on the battlefield in warfare, any remote location," he said. "The smaller devices aren't going to replace the more sophisticated ones, but they're great for screening and triage, and they can send the data to a hospital for expert evaluation."
Could the hand-held ultrasound device become the 21st-century equivalent of the stethoscope? "I'm not a very good predictor," Kremkau said. "But I don't see why not."
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