About this Research Topic
The non-invasive nature of optical imaging enables researchers to study a wide variety of materials under conditions approaching, or similar to, their "natural" environment. However, traditional imaging measures only intensity falling on a detector, which does not contain information about thickness or refractive index variations in materials. This can present a problem for imaging of transparent objects, or objects which otherwise present weak variations in intensity, such as cells in visible light microscopy, or soft tissue in x-ray imaging. This topic concentrates specifically on the techniques and applications of quantitative phase imaging methods. These methods enable small differences in thickness or optical density of materials to be measured, producing high contrast images for materials which produce poor contrast using traditional methods. Additionally, by determining quantitative phase, if the refractive index is known, the material thickness can be quantified, enabling 3D imaging.
Techniques of phase imaging include the design of both imaging hardware and software. Since phase is not directly measurable, phase imaging systems rely on optical system design that can render phase as intensity contrast at the detector. And in almost all cases, this intensity contrast is not directly proportional to the phase, and therefore post-processing of the image is required to reconstruct phase. In many cases, software and hardware design can inform each other to produce an optimized phase imaging system.
Prominent applications of phase imaging include visible light microscopy, where live biological specimens can be studied both in-vitro and in-vivo, providing a unique insight into the dynamic processes occurring in live organisms. Many phase imaging modalities, such as digital holographic microscopy and optical tomography, have been successfully applied to image a variety of microstructures, materials, and biological systems. In x-ray imaging, refractive index variations are orders of magnitude larger than attenuation coefficient variations for soft tissue at clinical energies, and thus phase imaging can enable the production of higher contrast images, improving the diagnostic capability of x-ray systems. This is particularly relevant to cancer screening, although x-ray phase imaging methods are generally suitable for non-destructive imaging of low density materials, which can be useful in security screening and industrial inspection.
Keywords: phase imaging, computational imaging, 3D imaging, real time imaging, live cells, soft tissues
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