Microlenses for 3-D endoscopes

Oct 05, 2011

Modern endoscopic techniques enable doctors to perform surgery without major incisions. Certain interventions require instruments with special 3-D optics. Researchers have developed an image sensor that transmits perfect 3-D images from inside the human body thanks to the use of microlenses.

The surgeon carefully guides the endoscope through the patient’s nasal cavity to the operation zone. It is a delicate procedure for which the surgeon has to prepare in detail before commencing the actual intervention. Where are the blood vessels that need to be avoided, what is the exact location of the cancerous tissue, and to what depth must the surgeon cut through the brain tissue to expose the area of interest? The camera integrated in the slender endoscope tube enables the surgeon to see every detail in sharp 3-D resolution – almost as if he were actually inside the patient’s brain. The stereoscopic vision provided by a 3-D endoscope considerably simplifies the work of neurosurgeons and other specialists. They can navigate a safe path through the tissue without the risk of collateral damage, and the work can be accomplished faster.

The ability to see inside the patient’s body in perfect 3-D is the result of work by researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg and the project partners in the EU project "Minisurg". The CCD sensors available in the past only provided low-resolution images. Thanks to the researchers’ work, CMOS image sensors of the type commonly incorporated in single-lens-reflex (SLR) cameras can now be used in medical applications. “To make this possible, we developed special microlenses,” explains IMS project manager Dr. Sascha Weyers. The secret lies in the optical design of the CMOS sensors, in which a cylindrical microlens is placed in front of every two vertical lines of sensors in the pixel configuration. A superimposed lens captures the light falling on the microlenses, which focus it on the pixels. The special feature of this arrangement is that the lens has two apertures, “rather like the right and left eye” says Weyers. In other words: two beams of light are captured by the lenses – that arriving from the left passes through the “left eye” to be focused on the right-hand vertical line of sensors, and vice versa. The two light rays cross underneath the lens arrangement. As a result, the CMOS sensor receives two sets of image data that are processed separately in the same way that the brain processes images coming from the left and right eye. A software program splits the incoming data and processes each set separately. Depending on the capabilities of the display system, the surgeon either sees the 3-D directly on the screen or can see them when wearing polarized glasses.

It takes a special kind of microlens to ensure that the light rays are focused precisely on the sensor. In order to manufacture the lenses, the Fraunhofer engineers first had to calculate the optimum shape by means of simulations. To eliminate external factors, it had to be ensured that the lens was capable of clearly separating the right and left visual channels. In concrete terms this means ensuring that no more than five percent of the energy from one light ray is captured by the line of sensors serving the other channel – in signal transmission this is known as crosstalk.

The next task for the researchers was to adapt the conventional manufacturing process for microlenses to the requirements of the calculated lens shape. They also had to fulfill a number of requirements relating to the production of the miniature camera. They met the challenge, and the resulting chip is so small that it fits into a tube measuring no more than 7.5 millimeters in diameter. Together with the bundle of optical fibers that serves as the light source, the endoscope measures 10 millimeters in diameter – the perfect size for minimally invasive surgery.

Explore further: Blu-ray disc can be used to improve solar cell performance

add to favorites email to friend print save as pdf

Related Stories

Color sensors for better vision

Oct 05, 2009

CMOS image sensors in special cameras -- as used for driver assistance systems -- mostly only provide monochrome images and have a limited sensitivity to light. Thanks to a new production process these sensors ...

Cameras out of the salt shaker

Mar 11, 2011

There have been gloves and shavers for one-off use for a long time. In future, there will also be disposable endoscopes for minimally invasive operations on the human body. A new microcamera is what makes ...

UV-transparent coating for image sensors

Feb 08, 2011

Image sensors as used in cell phones are partially color-blind. This is because of their coating, which prevents UV light from passing through. CMOS chips have as a result not been suitable for spectroscopy ...

Writing patterns, logos and lettering in light

Oct 01, 2008

(PhysOrg.com) -- Logos and lettering can be written in light using freeform lenses. But how does the surface of the lens have to be structured in order to focus the light in the shape of a specific pattern? ...

Paper-Thin Compound-Eye Camera

Jul 09, 2004

The focal length of a lens means that a camera has to have a certain thickness - or so we might think. Insect eyes show that this need not be the case: A camera chip based on the compound-eye principle can be used for person ...

Recommended for you

Researcher explores drone-driven crop management

11 hours ago

A flock of pigeons flies over the soybean field where J. Craig Williams is standing. He reaches down and rips off a brown pod from one of the withered plants and splits it open. Grabbing a tiny bean between ...

Wireless electronic implants stop staph, then dissolve

Nov 24, 2014

Researchers at Tufts University, in collaboration with a team at the University of Illinois at Champaign-Urbana, have demonstrated a resorbable electronic implant that eliminated bacterial infection in mice ...

Scientist develops uncrackable code for nuclear weapons

Nov 24, 2014

Mark Hart, a scientist and engineer in Lawrence Livermore National Laboratory's (LLNL) Defense Technologies Division, has been awarded the 2015 Surety Transformation Initiative (STI) Award from the National ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.