__FORCETOC__ Quantitative phase contrast microscopy or quantitative phase imaging are the collective names for a group of microscopy methods that quantify the

phase shift In physics and mathematics, the phase (symbol φ or ϕ) of a wave or other periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is expressed in such a s ...

that occurs when light waves pass through a more optically dense object. Translucent objects, like a living human cell, absorb and scatter small amounts of light. This makes translucent objects much easier to observe in ordinary light microscopes. Such objects do, however, induce a phase shift that can be observed using a phase contrast microscope. Conventional phase contrast microscopy and related methods, such as

differential interference contrast microscopy Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast (NIC) or Nomarski microscopy, is an optical microscopy technique used to enhance the contrast in unstained, transparent samples. DIC works on the ...

, visualize phase shifts by transforming phase shift gradients into intensity variations. These intensity variations are mixed with other intensity variations, making it difficult to extract quantitative information. Quantitative phase contrast methods are distinguished from conventional phase contrast methods in that they create a second so-called ''phase shift image'' or ''phase image'', independent of the intensity ( bright field) image.

Phase unwrapping Instantaneous phase and frequency are important concepts in signal processing that occur in the context of the representation and analysis of time-varying functions. The instantaneous phase (also known as local phase or simply phase) of a ''compl ...

methods are generally applied to the phase shift image to give absolute phase shift values in each pixel, as exemplified by Figure 1. Phase shift image of cells in 3D

The principal methods for measuring and visualizing phase shifts include ptychography and various types of holographic microscopy methods such as

digital holographic microscopy Digital holographic microscopy (DHM) is digital holography applied to microscopy. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front ...

, holographic interference microscopy and digital in-line holographic microscopy. Common to these methods is that an

interference pattern In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater amplitude (constructive int ...

(

hologram Holography is a technique that allows a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interf ...

) is recorded by a digital

image sensor An image sensor or imager is a sensor that detects and conveys information used to form an image. It does so by converting the variable attenuation of light waves (as they refraction, pass through or reflection (physics), reflect off objects) into s ...

. From the recorded interference pattern, the intensity and the phase shift image is numerically created by a computer

algorithm In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algo ...

. Quantitative phase contrast microscopy is primarily used to observe unstained living cells. Measuring the phase delay images of biological cells provides quantitative information about the morphology and drymass of individual cells. These features can be analyzed with image analysis software, which has led to the development of non-invasive live cell imaging and automated

cell culture Cell culture or tissue culture is the process by which cell (biology), cells are grown under controlled conditions, generally outside of their natural environment. After cells of interest have been Cell isolation, isolated from living tissue, ...

analysis systems based on quantitative phase contrast microscopy.published under CC BY 4.0 licensing
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Phase shift time-lapse microscopy video of a triploid cell division

Cell identification with computational 3D holographic microscopy
{{Optical microscopy Microscopy Cell imaging Microbiology techniques Optical microscopy

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