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CLEO news: Wednesday

17 Jun 2002

A holographic imaging system gives the first visual "fly-through" of living tumors just under the skin.

David Nolte and colleagues from Purdue University, US, have developed an optical imaging system that allows clinicians to "fly-through" near-surface tumors in real time.

The team says that the system, which can image to a depth of 1 mm, is ideal for applications in dermatology and endoscopy.

In the scheme, a laser fires 100 fs probe pulses into the skin. The pulses weakly reflect from varying depths below the surface and are compared to a coherent reference pulse which, thanks a time-of-flight measurement, originates from a known depth.

A hologram then rejects unwanted, incoherent light leaving only the useful, image-bearing signal. Only a fraction of a nanowatt of optical power is required to write the hologram.

"Our approach uses a holographic film that acts as a coherence filter," said Nolte. "Placed in front of a CCD camera, it provides direct images without the need for reconstruction."

A joystick controlling the depth of the reference pulse allows the clinician to explore the tumor. For example, to probe deeper into the tumor, the clinician simply pushes the joystick forward. The reflected pulses are then compared to this new reference and new depth information is written onto the hologram.

"Because this [scheme] uses short-coherence light, it is depth gated making it possible to fly-through scattering tissue as a succession of cross-sections in real-time," said Nolte.

The team has tested its system on rat osteogenic sarcoma tumors in vitro and has successfully reconstructed the cross-sections into a 3D model of the tumor. It now hopes to find a commercial partner and reduce the size of the system. If all goes well clinical trials could start within the next five years.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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