Medical imaging struggles to read dark skin. Researchers say they’ve found a way to make it easier

By Kaitlyn Schwanemann, CNN

(CNN) — Traditional medical imaging – used to diagnose, monitor or treat certain medical conditions – has long struggled to get clear pictures of patients with dark skin, according to experts.

Researchers say they have found a way to improve medical imaging, a process through which physicians can observe the inside of the body, regardless of skin tone.

The new findings were published in the October edition of the journal Photoacoustics. The team tested the forearms of 18 volunteers, with skin tones ranging from light to dark. They found that a distortion of the photoacoustic signal that makes the imaging more difficult to read, called clutter, increased with darkness of skin.

“When you have darker skin, you have more melanin. And melanin is actually one of the optical absorbers that we inherently have within our body,” Muyinatu Bell, an author of the study and director and founder of the Photoacoustic and Ultrasonics Systems Engineering (PULSE) Lab at JHU, told CNN. In other words, the amount of melanin content in the skin could be associated with more clutter.

“The skin essentially acts as a transmitter of sound, but it’s not the same type of focused sound that we get and we want with ultrasound, it’s everywhere diffused and creates a lot of confusion,” Bell said. “And so, this scattering of the sound that’s caused by the melanin absorption is worse and worse with the higher melanin concentration.”

Changing a technique

The study – a collaboration with researchers in Brazil who had previously used one of Bell’s algorithms – found that signal-to-noise ratio, a scientific measure that compares signal with background noise, improved for all skin tones when the researchers used a technique called “short-lag spatial coherence beamforming” while performing medical imaging. That technique, originally used for ultrasounds, can be applied to photoacoustic imaging.

The technique involves a combination of light and ultrasound technology, forming a new medical imaging modality, Theo Pavan, an author of the study and associate professor with the department of physics at University of São Paulo in Brazil, told CNN.

“We really verified that it was much less sensitive to the skin color in terms of the quality of the image that you can get compared to the conventional methods that … is more commonly used by the community,” Pavan said.

The study is “the first to objectively assess skin tone and to both qualitatively and quantitatively demonstrate that skin” photoacoustic signal “and clutter artifacts increase with epidermal melanin content,” the researchers wrote.

The applications of photoacoustic technology vary, but with the researchers’ new developments, it may help diagnose health issues more accurately and equitably.

“Right now, it’s increasing the application of the breast imaging,” and the next step would be to “increase the image quality overall,” said Guilherme Fernandes, an author of the study and a Ph.D. candidate in physics applied to medicine and biology at USP.

Broader rethinking in health care

The researchers’ work could also mean advancements for equity in health care at large.

“In our scientific technology, there is a bias in terms of developing these products, for things that work well in lighter-skinned people,” said Dr. Camara Jones, a family physician, epidemiologist and former president of the American Public Health Association, who was not involved in the new study.

“The biggest problem is that we use a thing we call race, as a risk factor — as a health risk factor. And so race is the social and interpretation of how people look in a race-conscious society. Race is not biology,” Jones explained. “We’ve mapped the human genome. We know there’s no basis in the human genome for racial sub-speciation.”

This study isn’t the first to find skin color biases in medical technology. Medical equipment that leverages infrared sensing has also been found to not work as well on darker skin, since skin tone can interfere with the reflection of light.

Many devices that were in frequent use during the Covid-19 pandemic, such as pulse oximeters and forehead thermometers, involve emitting and capturing light to make a measurement. But if that device isn’t calibrated for darker skin, the pigmentation could affect how the light is absorbed and how the infrared technology works.

Bell said her research can hopefully pave a way to eliminating discrimination in health care and inspire others to develop technology that helps everyone, regardless of their skin tone.

“I believe that with the ability to show that we can devise and develop technology — that doesn’t just work for one small subset of the population but works for a wider range of the population. This is very inspiring for not only my group, but for groups around the world to start thinking in this direction when designing technology. Does it serve the wider population?” Bell said.

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– CNN’s Jacqueline Howard contributed to this report.