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New Toy: Photoacoustic Tomography’s Promise

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Photoacoustic tomography potentially can catch cancer in its nascent stages, find early signs of other diseases, precisely guide sentinel node biopsies, and otherwise expand the uses of imaging—all without harmful radiation.

Lihong V. Wang, PhD, describes the state of the photoacoustic tomography art in the March 23 issue of Science. Dr. Wang is the Gene K. Beare Distinguished Professor of Biomechanical Engineering for the School of Engineering & Applied Science at Washington University in St. Louis.

Light photons can penetrate about 7 centimeters of soft tissue, but their reflections are so scattered that they’re useless for imaging. Photoacoustic tomography, however, uses laser-generated light pulses to cause subsurface molecules to generate sound waves in the process of absorbing the light. Sound waves don’t scatter nearly as much as light.

Reading the sound waves creates a color photograph of structures beneath the surface of the skin. The light pulses do not produce ionizing radiation or, as far as we know, anything else that damages the body.

Dr. Wang and his team are developing clinical and research applications for the new technology. A Washington University news release quotes him as saying:

My hope is that photoacoustic tomography, which has consistent contrast over all length scales, can help translate the microscopic lab discoveries to macroscopic clinical practice.

Here are some of the things the team is working on:

  • Revealing cancer at its earliest stages. Photoacoustic tomography can show excessive (hypermetabolic) use of oxygen by tissues. “Because hypermetabolism is a quintessential hallmark of cancer,” Dr. Wang said, “photoacoustic imaging may allow cancer to be detected at the earliest stage without using a foreign contrast agent.”
  • Exactly targeting sentinel node biopsies. Current radioactive tracer techniques give only a rough idea of the node’s location. Photoacoustic tomography provides such clear images when an optical dye is injected that it should allow a needle to be guided directly to the sentinel lymph node. A clinical trial is under way.
  • Detecting the oxygen saturation of hemoglobin. Most diseases create abnormalities in oxygen metabolism, so being able to noninvasively read oxygen saturation without the use of a radioactive tracer holds great diagnostic promise.

Dr. Wang sees his team as a bridge in developing the technology:

We’re really just tool builders who are going to help other scientists make the revolutionary discoveries in biology and medicine. At least that’s my hope.

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