Caltech Engineers Devise Method to Boost Conventional Microscope Into Billion-Pixel Imaging System

Posted on July 31, 2013

Engineers at the California Institute of Technology (Caltech) say they have devised a method to boost a conventional microscope into a billion-pixel imaging system. Using the new approach, the researchers were able to improve the resolution of a conventional 2X objective lens to the level of a 20X objective lens. The researchers say the improvements cost only about $200 to implement.

Changhuei Yang, professor of electrical engineering, bioengineering and medical engineering at Caltech, is senior author on the paper that describes the new imaging strategy, which was published here in Nature Phototonics.

Yang says, "In my view, what we've come up with is very exciting because it changes the way we tackle high-performance microscopy."

The physical limitations of microscope objectives are due to aberrations from their optical lenses. The Caltech scientists note that microscope makers tackle these limitations by using ever more complicated stacks of lens elements in microscope objectives to mitigate optical aberrations.

Guoan Zheng, lead author on the new paper and the initiator of this new microscopy approach, says, "We found a way to actually have the best of both worlds. We used a computational approach to bypass the limitations of the optics. The optical performance of the objective lens is rendered almost irrelevant, as we can improve the resolution and correct for aberrations computationally."

Zheng also says, ""One big advantage of this new approach is the hardware compatibility. You only need to add an LED array to an existing microscope. No other hardware modification is needed. The rest of the job is done by the computer."

The final images produced by the new system contain 100 times more information than those produced by conventional microscope platforms. The new system acquires about 150 low-resolution images of a sample. Each image corresponds to one LED element in the LED array. In the various images light coming in from known different directions illuminates the sample. A novel computational approach, called Fourier ptychographic microscopy (FPM), is then used to stitch together th low-resolution images to form the much higher-resolution result.

Yang explains that when we look at light from an object, we are only able to sense variations in intensity. But he says, light varies in terms of both its intensity and its phase, which is related to the angle at which light is traveling.

Yang says, "What this project has developed is a means of taking low-resolution images and managing to tease out both the intensity and the phase of the light field of the target sample. Using that information, you can actually correct for optical aberration issues that otherwise confound your ability to resolve objects well."

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