11 Jun 2007
A non-invasive laser scan offers a unique insight into the characteristic biochemistry of a developing skin cancer.
The new technique, developed by researchers at Duke University in the US, involves scanning the skin with multiple colors of laser light and then using the characteristic absorption of melanin and hemoglobin to assess the distribution of these two chemicals in the suspected area. "There is ample reason to believe that this method can distinguish between cancer and non-cancerous growths in humans," team leader Warren S Warren told optics.org.
The distributions of hemoglobin and melanin serve as early warning signs for skin cancer growth. But skin scatters light strongly, so simple microscopes cannot be used to locate those molecules except right at the surface. Laser methods such as two-photon fluorescence microscopy have been used to probe deeper, but both melanin and hemoglobin remain dark and inaccessible using these techniques. "To date, little headway has been made applying laser diagnostic methods to skin cancer detection, and the best clinical method remains simple visual examination to detect the development of melanomas," Warren noted.
"Our method involves "shaping" the laser pulses or pulse trains in order to extract the molecules' signatures, and detecting the backscattered light. We had previously demonstrated that this works on molecules in solution, but nobody has tried this approach before on skin tissues."
Melanomas characteristically have stronger absorption from melanin than from hemoglobin, and in animal studies the Duke team found they could easily pick up the signatures of both. Discriminating between them was achieved by scanning with multiple colors of light, either at the same time or in sequential scans depending on the sensitivity.
The new non-invasive laser method could enable doctors to see as much as a millimeter below the surface of the skin, which should be enough for a diagnosis. The laser powers involved are considerably less than a laser pointer, and limiting the pulses to femtosecond bursts ensures that the skin does not overheat while illuminated.
"Now we need to test a large number of different tissue samples, to differentiate exactly the differences between known human tumors and known benign lesions. A compact laser system based on the technique could be available to dermatologists within three years," said Warren.