Quantitative phase imaging (QPI) is an advanced imaging technique used in microscopy to measure and analyze the optical phase information of transparent specimens. Unlike traditional brightfield microscopy, which relies on the absorption of light, QPI directly captures and quantifies the phase changes induced by a specimen as light passes through it. This enables the visualization of transparent structures and provides valuable quantitative information about biological and non-biological samples.
Key features and concepts related to Quantitative phase imaging:
Phase contrast imaging: QPI enhances the contrast of transparent samples by measuring the phase shift of light passing through different parts of the specimen. This is particularly useful for visualizing unstained biological specimens, such as live cells, where traditional staining may interfere with natural processes.
Interference and phase retrieval: QPI typically involves the interference of a reference wave with the wave transmitted through the specimen. The resulting interference pattern contains information about the phase changes induced by the specimen. Computational methods are then employed to retrieve the quantitative phase information from the interference pattern.
Label-free imaging: QPI is a label-free imaging technique, meaning that it does not require the use of contrast agents or stains. This is advantageous for studying live cells and other dynamic biological processes without introducing exogenous substances.
High sensitivity: QPI is highly sensitive to changes in refractive index, allowing for the detection of subtle variations in cell morphology, thickness, and density. This sensitivity makes it valuable for studying cellular dynamics, including cell division and migration.
Applications in biomedical research: QPI finds applications in various fields, including cell biology, neuroscience, and medicine. It enables researchers to study cellular processes and diseases at a level of detail that may not be achievable with traditional imaging methods.
Holographic microscopy: Holographic techniques, such as digital holography, are often used in QPI to record and reconstruct three-dimensional information about the specimen. This adds depth and spatial information to the quantitative phase data.
Tomographic imaging: Some QPI methods can be extended to perform tomographic imaging, allowing for the three-dimensional reconstruction of specimens. This is particularly valuable in understanding complex structures and interactions within biological samples.