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Melanoma Surgeons May Get Imaging Help

August 12, 2010
Written by: , Filed in: Interventional Radiology
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A new imaging technique could guide melanoma surgery, minimizing the amount of tissue that’s cut away while ensuring that every bit of the tumor is removed.

Two researchers at Washington University in St. Louis combined forces to create images of exceptional three-dimensional clarity. Lihong Wang, PhD, the Gene K. Beare Distinguished Professor of Biomedical Engineering, developed photoacoustic tomography (PAT) imaging. Younan Xia, PhD, the James M. McKelvey Professor of Biomedical Engineering, contributed a contrast agent.

Melanoma is a relatively rare skin cancer, but it accounts for about 75 percent of the skin cancer deaths. So it’s crucial that the initial surgery remove every bit of the tumor. Until now, no imaging technique has been able to precisely show a tumor’s boundaries during surgery. So surgeons err on the side of caution by cutting well beyond the tumor’s visible margins.

Dr. Wang’s new technique relies on the photoacoustic effect. The absorption of light heats a material, every so slightly, causing thermoelastic expansion. If the light is pulsed at the right frequency, the material will rapidly expand and contract, creating a sound wave.

Said Dr. Wang, as quoted in a Washington University news release:

We detect the sound signal outside the tissue, and from there on, it’s a mathematical problem. We use a computer to reconstruct an image. We’re essentially listening to a structure instead of looking at it.

PAT imaging seems to be safe as well. It uses photons with energies of only a couple of electron volts. X-rays have energies in the thousands of electron volts.

Dr. Xia’s contrast agent sharpens the image. He uses gold nanocages—infinitesimal, hollow gold cages that he tunes to absorb light strongly at a wavelength to which tissue is particularly transparent. The nanocages tend to accumulate in tumors anyway because the cells that line a tumor’s blood vessels are disorganized and leaky. But Dr. Xia makes sure they end up at the tumor by also attaching a hormone that binds to hormone receptors in the melanoma.

Dr. Wang and Xia reported on their research in the journal ACS Nano.

Related seminar: Interventional Radiology Review

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