FEATURE MEMS
Hamamatsu MEMS mirrors are sold to system integrators, or incorporated into the company’s own devices
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scanning system,’ Scholles added. The IPMS team is currently searching for
direct commercialisation of the device and is in talks with endoscope manufacturers. Meanwhile, at the end of this year, scientists
from Stony Brook University (SUNY) in New York, USA anticipate that their latest miniature handheld microscope will be ready for first- in-human studies. The microscope, which is also being incorporated into an endoscope, uses dual-axis confocal microscopy – a modified version of confocal microscopy that provides clearer images with better contrast. The device works in a comparable fashion to the Fraunhofer system, and employs a MEMs mirror to deflect a focused laser beam, transmitted via an optical fibre, into the tissue. As the MEMS mirror tilts in two dimensions, the system is able to scan the position of the beam and recreate an image in a point-by- point fashion.
One application the scientists are aiming for is the detection of oral cancer at an earlier stage, and they are hoping to approach the gold standard of pathology, according to Dr Liu at Stony Brook: ‘We are trying to see cells and sub-cellular structures on a microscopic level, in order to approach the gold standard
22 ELECTRO OPTICS l MARCH 2014
of pathology. Instead of taking tissues out and placing them under a large microscope, we’ve decided to shrink down the microscope and bring it directly to the tissue.’ To image over a range of depths, one possible strategy is to use a MEMS mirror to deflect the laser beam further into the tissue. One aspect the SUNY team has been working on is a suitable way to move the MEMS chip to give the laser beam more penetration. ‘The MEMS mirror provides you with the tilting that scans a horizontal plane in the tissue,’ Liu described. ‘If you want to image deeper, which is in the vertical direction, you need to move the MEMS mirror forwards and backwards.’ To move the mirror, the team is using piezo actuators that are able to shift the MEMS component forwards or backwards by a couple of hundred microns. ‘So, the MEMS mirror is mounted on another stage that doesn’t use MEMS technology, but piezo technology, to push the MEMS mirror,’ said Liu. ‘We’ve also used small motors to do this.’
One application
the scientists are aiming for is the detection of oral cancer at an earlier stage
One shortcoming with microscopy as an imaging technique is that it is not able to measure beyond a depth of half a millimetre into tissue. But as the majority of cancers originate at epithelial surfaces, micro- endoscopes are well suited for their diagnosis. However, achieving a higher level of depth would provide more diagnostic information to the doctor, such as if the cancer has spread to underlying tissues. ‘One thing the clinicians would like to see is the depth of invasion,’ said Liu. ‘If the cancer has invaded into the deeper
parts of the tissue it means that the cancer has metastasised to other parts of the body. We, and others, are working on innovative strategies to increase the image depth of these microscopes.’
Unlike Fraunhofer, which is producing the MEMS scanning mirror, the SUNY team has chosen to outsource from a commercial company in order to shorten the time to market. ‘We deliberately chose to use a commercial mirror from a start-up company in
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Hamamatsu Photonics
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