Physicians learned long ago that they could uncover clues about what was going on beneath the skin just by feeling and listening. Medicine took a giant step forward in the 18th century when physicians discovered that they could estimate the size of major organs by tapping on the body (“percussion”). By the 19th century, physicians were associating specific heart sounds with problems observed at autopsy; using body temperature to diagnose and monitor the progress of diseases; and taking accurate blood pressure measurements.
Gathering the data was less than half the battle. Making sense of the observations proved to be the bigger challenge. It didn’t take long to find that “normal” measurements vary widely from individual to individual. Desperately needed were data from the broader population and reliable standards for statistical analysis. To wit, it was important that physicians buy into the idea of regularly collecting and sharing key data. And there had to be a balance: gather the data, use the data—but never forget its limitations.
One simple data gathering technique, tapping on the body, evolved way beyond what its pioneers are likely to have imagined. Ultrasound imaging is the high-tech version of percussion. Employing the same principle that bats use to navigate, ultrasound scanners emit high frequency sound waves to create echoes that let us visualize structures within the body and study their motion. Ultrasound imaging is fast, non-invasive, and does not employ ionizing radiation. And it doubles as a therapeutic technology with applications range from cleaning teeth to breaking up kidney stones.
Today’s ultrasound scanners exploit a discovery made by Pierre and Jacques Curie in 1880. The Curie brothers discovered that mechanical stress causes some materials to generate small electric currents. One of their professors, Gabriel Lippmann, demonstrated the reverse—applying electric currents to the same materials distorts their shapes.
What began as a scientific curiosity evolved by World War I into a technology for detecting icebergs and enemy submarines. Though medical researchers experimented with ultrasound in the years following World War II, it wasn’t until cardiologist Harvey Feigenbaum showed how the technology could be used to diagnose specific heart problems in the 1960s that the technology began to gain traction in the clinic. (It’s also now famous for providing millions of expectant parents the first images of their unborn children.)
Ultrasound continues to demonstrate unique advantages. Ultrasound is less expensive than CT or MRI; near ideal for 4D (3D plus motion) studies; and as a screening tool lends itself to workflow automation. An emerging application, strain imaging, could provide information about the structural integrity of living tissues that can’t be obtained by other means. Strain imaging distinguishes and quantifies tissues in terms of stiffness and softness. In essence, strain imaging shows how each spot of tissue moves and could be used to gauge the overall health of specific types of tissue such as heart muscle.
In that case, ultrasound will not only tell us how well our hearts are performing, but how long they might last.
The evolution of medical diagnostic ultrasound traces back two-hundred and fifty years to when physicians started using percussion. Tap on the body and listen to the sound. A few pioneers working in the 1940s and 50s, beleaguered with doubt, thought that ultrasound echoes from inside the body just might turn out to be clinically useful. Decades later, buoyed by advances in electronics, ultrasound emerged as a key diagnostic tool.
Next time: Repair or Replace? Part I
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