Medical imaging: Pin-sized probes
Published online 09 December 2009
The smallest optical probe to date could provide real-time images of living tissues inside the body
Fig. 1: A photograph of the optical coherence tomography (OCT) probe, just 4 mm in diameter, that could provide images of internal living tissue without causing damage.
© 2009 C. S. Premachandran
Medical biopsies are often carried out by removing parts of tissue for analysis, but this procedure can traumatize patients and is impossible in delicate areas such as the brain. For this reason, there is demand for new types of probe that could enter the body without causing damage and image cells in real time.
One of the most promising imaging techniques is called optical coherence tomography (OCT). C. S. Premachandran at the A*STAR Institute of Microelectronics in Singapore and co-workers have built the smallest OCT probe to date1, which could reveal the microstructure of living tissues and aid the diagnosis of cancers.
“The OCT method has both higher resolution and deeper penetration into tissue than other techniques such as ultrasound and confocal imaging,” explains Premachandran. “A conventional OCT system uses a hand-held probe 20 millimeters in diameter, which can be used for ex vivo and skin level imaging applications; but for in vivo imaging and optical biopsies, there is a clear need for miniaturized probes.”
OCT probes are simple in concept; they contain optic fibers that deliver light to the area of interest, and then collect the reflected light to build up an image. The main challenge is to make a probe that can view as much as possible with the minimum of movement.
To control the direction of their light beam and scan over a large area, Premachandran and co-workers built a ‘micromirror’ just 500 micrometers in size. Their mirror is supported by four springs that can be thermally activated to move the mirror around, rotating it up to 16°. The light is focused onto the mirror by a ‘graded-index’ lens, providing a large working distance despite the device's small size.
The researchers integrated their whole device into a silicon optical bench, which is transparent to infrared light. Overall, the probe is just four millimeters in diameter (Fig. 1).
“Our probe is slightly smaller than other probes reported in the literature,” says Premachandran. “We are now working to reduce the diameter further to three millimeters.” He and his co-workers also hope to develop 360° scanning so that the whole area surrounding the probe can be scanned and imaged.
“Currently we have only tested our probe by imaging onion tissue, so our next move is to do imaging on animal tissue and cancers. Finally we will try it in a live animal model and develop oral cancer applications for humans.”
The A*STAR affiliated authors in this highlight are from the Institute of Microelectronics
References
- Premachandran, C.S., Khairyanto, A., Sheng, K.C.W., Singh, J., Teo, J., Yingshun, X., Nanguang, C., Sheppard, C. & Olivo, M. Design, fabrication and assembly of an optical biosensor probe package for OCT (Optical Coherence Tomography) application. IEEE Transactions on Advanced Packaging 32, 417–422 (2009). | article
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