New Scan 'Sees' Tumors Deep Inside Body

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Wednesday, April 2, 2008; 12:00 AM

WEDNESDAY, April 2 (HealthDay News) -- Stanford University researchers have developed a new imaging system that illuminates tumors deep inside the body and lets doctors view details 1,000 times smaller than previously possible.

Raman spectroscopy uses tiny nanoparticles injected into the body to serve as beacons for lasers, according to a description the method published in this week's online issue of theProceedings of the National Academy of Sciences.

When a laser beam outside the body hits them, the specialized particles emit signals that can be converted into a visible indicator of their location in the body. These strong, long-lived signals can simultaneously transmit information about multiple molecular targets.

"Usually we can measure one or two things at a time," senior author Dr. Sanjiv Sam Gambhir, a professor of radiology at Stanford's School of Medicine, said in a prepared statement. "With this, we can now likely see 10, 20, 30 things at once."

The new system utilizes the Raman effect, which occurs when light is shined on an object. The light causes roughly one in 10 million photons to bounce off the object's molecules with an increase or decrease in energy, called Raman scattering. This forms a unique measurable pattern, called a spectral fingerprint, for each type of molecule.

The Stanford research team tested the system on mice, injecting them with various engineered Raman nanoparticles and then viewing the anesthetized mice under a special microscope where they were exposed to laser light. The nanoparticles, for example, would be "tagged" with different pieces of proteins that sought out different tumor molecules.

In these experiments, the team spotted targets 1,000 times smaller than what is viewable with the most precise fluorescence imaging available. Since the Raman effect lasts indefinitely, as long as the particles stay in the body they can work as signals.

Because of these findings, the technique could be useful during tumor surgery on humans by aiding in the removal of even the most microscopic bits of cancerous tissue, the researchers said.

Gambhir's lab is further studying these Raman nanoparticles, including optimizing their size and dosage and evaluating possible toxicity. A clinical trial using gold nanoparticles in humans in conjunction with a colonoscopy to indicate early-stage colorectal cancer is being planned.

More information

The U.S. National Library of Medicine and the National Institutes of Health has more about diagnostic imaging techniques.

SOURCE: Stanford University Medical Center, news release, March 31, 2008



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