Designer Lens Helps See the Big Picture

Quantitative phase images reveal more details than classical microscopy images. The new technique captures both bright-field images and phase images in a single measurement. (Source: KAUST)

Microscopes have been at the center of many of the most important advances in biology for many centuries. Now, KAUST researchers have shown how a standard microscope can be adapted to provide even more information. In its simplest form, micro­scopy creates an image of an object by measuring the intensity of light passing through it. This requires a sample that scatters and absorbs light in different ways. Many living cells, however, absorb very little visible light, meaning that there is only a small dif­ference between light and dark regions, known as the contrast. This makes it difficult to see the finer detail.

But the light passing through the sample changes not only its intensity, but also its phase: the relative timing of the peaks in the optical wave. “Phase-contrast micro­scopy converts phase into larger amplitude variations and hence allows the viewing of fine, detailed trans­parent structures,“ explains Congli Wang. Measuring the phase of light is trickier than measuring its intensity. Most phase-contrast micro­scopes must include a component that converts the phase change to a measurable intensity change. But this conversion is not precise; it only approximates the phase infor­mation.

Wang and his colleagues from the Visual Computing Center, under the supervision of Wolfgang Heidrich, a professor of computer science, have now developed a new method for quantitative phase and intensity imaging. Crucial to the perfor­mance of their microscope was an element known as a wavefront sensor. Wavefront sensors are custom-designed optical sensors that can encode the wavefront, or phase, information into inten­sity images.

The team designed an inno­vative high-resolution wavefront sensor, and the team members are now incorporating it into a commercial microscope to improve the per­formance of micro­scopy imaging. They then reconstructed the phase-contrast image using a computer algorithm they developed to numerically retrieved quanti­tative phase from an image pair: a cali­bration image obtained without the sample and a measurement image obtained with the sample in place.

This approach stream­lines several aspects of microscopy. While other methods have achieved quantitative phase imaging in the past, they have required expensive or compli­cated setups, specialized light sources or a long time to generate the image. “Our method allows snapshot acqui­sition of high-resolution ampli­tude bright-field and accurate quanti­tative phase images via affordable simple optics, common white-light source and fast compu­tations at video rates in real time,” says Heidrich. “It is the first time, to our knowledge, that all these advantages are combined into one technique.” (Source: KAUST)

Reference: C. Wang et al.: Quantitative Phase and Intensity Microscopy Using Snapshot White Light Wavefront Sensing, Sci. Rep. 9, 13795 (2019); DOI: 10.1038/s41598-019-50264-3

Link: Visual Computing Center, King Abdullah University of Science and Technology KAUST, Thuwal, Saudi Arabia

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