Imaging technique could speed cancer detection

Session attendees at the
AACR Annual Meeting 2012
Credit: AACR/Phil McCarten

CHICAGO—A new imaging technique relies on light and sound to create detailed, color pictures of tumors deep inside the body.

The technology, called photoacoustic tomography (PAT), may eventually help physicians diagnose cancer earlier and more precisely monitor the effects of cancer treatment, according to Lihong V. Wang, PhD, of Washington University in St. Louis, Missouri.

Dr Wang described PAT imaging at the AACR Annual Meeting 2012 and in a paper recently published in Science.

“This technology is potentially a game changer, both in how we monitor cancer and in how soon we know it’s there,” Dr Wang said.

He noted that clinical trials of PAT are still in the planning stages, but studies in animal models have shown promise. PAT was able to easily penetrate the body tissue to show tumors at depths never before possible.

PAT imaging works by converting light absorbed by soft tissues in the body into sound waves, which easily penetrate tissues. The tissue to be imaged is then irradiated by a nanosecond-pulsed laser at an optical wavelength.

Absorption of light by molecules beneath the surface creates a thermally induced pressure jump that launches sound waves. These sound waves are measured by ultrasound receivers at the body’s surface and reassembled to create what is, in effect, a photograph.

PAT images have a much higher contrast than X-ray images, Dr Wang said, because there are many highly colored molecules in the body that naturally serve as contrast agents. For instance, hemoglobin changes color as it gains or loses oxygen. And DNA, in its condensed form in the cell nucleus, is darker than the cell cytoplasm.

With a little help from organic dyes or genes engineered to express colorful products, PAT can also image tissues, such as lymph nodes, that would otherwise blend in with their surroundings.

Dr Wang is now working to evaluate PAT for 4 uses: monitoring early response to chemotherapy; identifying the sentinel lymph nodes for breast cancer staging; imaging melanomas; and imaging the gastrointestinal tract.

“Every issue of every top journal publishes exciting lab discoveries, but only a tiny fraction of them are ever translated into clinical practice,” Dr Wang said. “My hope is that photoacoustic tomography can help translate microscopic lab discoveries into macroscopic clinical practice.”

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