Researchers 'lase' a trail to early detection of breast tumors

By Aditi Risbud

A novel laser engineered to home in on tiny tumors may someday enhance early detection of cancers in breast, skin and other tissues, researchers report. Using a high-frequency laser to probe tissue biopsies from mice, a team of scientists at Stanford, the University of Neuchatel in Switzerland and the University of California-Davis has developed an experimental technology that ultimately may bring higher resolution and fewer risks than mammography and magnetic resonance imaging (MRI).

"If there's a safer, newer way of imaging that could combine the current technologies, it would be very promising for studying cancerous tissues," says Stanford research associate Seongsin Kim, who holds a doctorate in electrical engineering. "Considering research efforts have increased recently, I would expect the technology to come to market within the next five years."

Allison Kurian, a medical doctor who is an instructor in the Division of Oncology and conducts clinical research in hereditary breast cancer through the Stanford Cancer Genetics Clinic,says, "A new kind of imaging could give us a new tool for clinical studies and distinguishing between tumors and normal tissue."

Conventional imaging technologies for detecting breast tumors include mammography, which uses X-rays, and MRI, which uses strong magnetic fields. But neither of these techniques is ideal. Mammograms often miss smaller tumors and can expose women already at high risk for developing cancer to radiation. Conversely, MRI scans that detect alterations in tissue can produce false positives, leading to unnecessary biopsies.

In lasers, a higher frequency means smaller tumors can be detected, Kim says. Terahertz lasers are energetic enough to resolve features five times smaller than MRI and 50 times smaller than mammography. Data from the Centers for Disease Control and Prevention indicate screening to detect cancerous tumors—while they are still small—could prevent 16 percent of deaths associated with breast cancer in women over age 40.

This terahertz technology, says Kurian, "might fill a gap in imaging breast tissue for women who are at highest risk."

The type of laser used in this study, called a quantum cascade laser, allows researchers to tune the laser to a desired frequency. This lets scientists explore a range of medical applications, says Kim, including tumor detection.

In a typical laser, a crystal such as a ruby is used to provide a fixed output frequency. But in a quantum cascade laser, the crystal has been engineered to contain different layers of materials. In the case of the terahertz laser, each layer within a crystal of aluminum gallium arsenide is chemically distinct. The result is a laser that can emit light in a 'cascade' to allow unparalleled imaging capabilities while providing less exposure to radiation than mammography.

To test the laser's abilities, the researchers obtained 2-millimeter-thick pieces of liver, fat, muscle and tendon from mice and scanned the tissues for 30 minutes each with the laser. They also tested healthy and cancerous liver tissue from the mice. By measuring the difference between absorbed and transmitted power through these tissues, the researchers could distinguish features that differentiate healthy from cancerous tissues. Such 'differential absorption' provides higher contrast and resolution compared to optical imaging.

Eventually, says Kurian, "we want to get to the point where we have something that is feasible for medical imaging, such as a handheld device like [that used in] ultrasound." The scan speed for such a device would have to be improved for use in a medical setting, she says.

The study, titled "Biomedical terahertz imaging with a quantum cascade laser," appeared in the April 14 issue of Applied Physics Letters, and drew together engineers and doctors in a multidisciplinary collaborative effort. Stanford's Interdisciplinary Translational Research Program (ITRP) funded the study. ITRP is a joint effort of the Beckman Center for Molecular and Genetic Medicine, the [Medical] Dean's Office and the Virginia and D.K. Ludwig Fund for Cancer Research.

Stanford researchers Kim, visiting scholar Fariba Hatami and Electrical Engineering Professor James Harris teamed up with Kurian, Oncology and Genetics Professor James Ford and applied physics graduate student Douglas King. The technology for the cascade laser stemmed from previous research by co-authors Giacomo Scalari, Marcella Giovannini, Nicolas Hoyler and Jerome Faist at the University of Neuchatel, Switzerland. Faist invented the cascade laser with colleagues at Bell Laboratories in 1994. Co-author Geoff Harris at the University of California-Davis contributed to greater understanding of the tissue characteristics.

"We see women at the highest risk for cancer, so they are highly motivated and most in need of new technology," says Kurian. "It's an exciting new possibility."

Editor Note:

Science-writing intern Aditi Risbud wrote this release.

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