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Our goal at UiT is to advance the frontiers of label-free optical imaging by developing next-generation systems in Quantitative Phase Microscopy (QPM) and Optical Diffraction Tomography (ODT), aimed at enabling high-sensitivity, high-resolution observation of biological systems across a range of temporal and spatial scales.
Leadership
Dr. Azeem Ahmad
Dr. Azeem Ahmad
Principal Investigator
(FRIPRO Young Talents)
Research Interests
Quantitative Phase Microscopy, Optical Diffraction Tomography, Optical Nanoscopy, Acoustic Microscopy and Tomography, Photoacoustic Microscopy
Advancing Label-Free Imaging for Thick and Scattering Biological Samples
Advancing Label-Free Imaging for Thick and Scattering Biological Samples
Our mission is to develop cutting-edge label-free quantitative microscopy and tomography platforms that overcome the limitations of conventional imaging in thick, scattering biological tissues.
Traditional optical imaging techniques struggle to deliver high-resolution insights in such complex environments due to multiple light scattering, signal degradation, and limited imaging depth. To address these challenges, we are engineering innovative solutions that harness:
Quantitative Phase Microscopy (QPM) for extracting intrinsic optical properties without staining
Optical Diffraction Tomography (ODT) to reconstruct 3D refractive index maps at sub-cellular resolution
Advanced computational methods to suppress scattering artifacts and recover high-fidelity structural information
By integrating novel optical designs with robust reconstruction algorithms, we aim to transform how researchers visualize and understand biological processes deep within native tissue environments, without the need for dyes, labels, or destructive preparation methods.
Our platforms are tailored for applications in neuroscience and organoid research, enabling dynamic and high-content imaging of life as it unfolds in three dimensions.
Challenges with imaging thick and scattering samples
Challenges with imaging thick and scattering samples
Imaging thick biological tissues remains a formidable challenge due to multiple scattering of light, which severely degrades image quality. As light propagates through a turbid medium, such as tissue, scattering events randomize both its direction and phase, resulting in:
Formation of incoherent background due to diffuse light
Loss of XYZ spatial resolution
Limited imaging and penetration depth
Reduced signal-to-noise ratio
Traditional microscopy techniques struggle under these conditions, producing blurred images with poor contrast, as shown in the adjacent figure where diffuse light dominates the field of view.
Figure Caption: Illustration of the challenges in imaging thick and scattering tissue samples. As light propagates through the sample, multiple scattering events distort the wavefront, resulting in diffuse light and an incoherent background in the images.
Figure Caption:
Comparison of blurred and sharp images of the same cell. The left panel shows a blurred image caused by multiple light scattering, resulting in loss of structural detail. The right panel displays a sharp image where the cell membrane and nucleus are clearly resolved, illustrating the importance of scattering compensation techniques for accurate cellular imaging.
Label-free microscopy and Tomography
Label-free microscopy and Tomography
Quantitative Phase Microscopy (QPM) and Optical Diffraction Tomography (ODT) are advanced imaging techniques widely used in biology and materials science for label-free, high-resolution imaging of transparent specimens like cells, tissues, or thin films.
Quantitative Phase Microscopy (QPM)
Quantitative Phase Microscopy (QPM) is a powerful, label-free imaging technique that enables non-contact, non-invasive visualization and measurement of transparent biological specimens such as cells and tissue sections. Unlike traditional brightfield or fluorescence microscopy, QPM does not require any staining or labeling, making it particularly well-suited for long-term imaging of living samples. The core principle of QPM lies in detecting the optical phase shift that occurs as light passes through a specimen. This phase shift arises from variations in refractive index and thickness across the sample.
By measuring the phase delay at each point in the field of view, QPM generates quantitative phase maps that reflect the sample’s optical path length. These maps provide valuable information about cellular dry mass distribution, morphology, and dynamics. In live cell imaging, QPM can be used to monitor cell growth, division, migration, and response to drugs over time, without perturbing the native cellular environment. For tissue imaging, QPM offers high-contrast visualization of unstained thin sections, allowing the study of microstructural and pathological changes at subcellular resolution.
A major advantage of QPM is its ability to combine high sensitivity to nanoscale features with full-field quantitative data acquisition. This enables precise assessment of cellular and tissue-level changes that are often missed by qualitative imaging methods. Overall, QPM provides a unique platform for quantitative, dynamic, and label-free imaging, contributing valuable insights into cell biology, tissue pathology, and biomedical research.
Optical Diffraction Tomography (ODT)
Optical Diffraction Tomography (ODT) is a label-free, quantitative imaging technique that enables three-dimensional (3D) reconstruction of the refractive index (RI) distribution within transparent or semi-transparent biological samples such as single cells, organoids, and thin tissues. It extends the capabilities of conventional phase microscopy by combining multiple angle-resolved measurements and solving an inverse scattering problem to recover volumetric information. Unlike fluorescence microscopy, which relies on external labeling, ODT leverages the intrinsic optical properties of biological specimens, making it highly suitable for live-cell and long-term imaging.
The working principle of ODT is based on illuminating the sample from different angles with coherent or partially coherent light. As the light interacts with the sample, it experiences phase shifts and diffraction due to the spatial variation in refractive index. These altered wavefronts are captured using a phase-sensitive imaging technique such as interferometry or digital holography. For each angle of illumination, a complex field image, containing both amplitude and phase, is recorded. These measurements collectively sample the object’s 3D Fourier space, allowing for numerical reconstruction of the internal refractive index distribution.
The reconstruction process relies on models derived from optical scattering theory. For weakly scattering samples, simplified approximations like the Born or Rytov models are sufficient. For more complex or thicker samples, more advanced solvers such as beam propagation methods, multi-slice models, or full-wave inversion techniques are used. The result is a high-resolution 3D map of the refractive index, which reflects the morphology and internal composition of the sample in a quantitative manner.
ODT offers several advantages: it is non-invasive, does not require staining, and provides sub-cellular resolution, typically around 200 nanometers laterally and about 1 micron axially. This makes it a valuable tool for studying dynamic biological processes, including cell growth, mitosis, membrane dynamics, and drug response. In tissue and organoid imaging, ODT enables the visualization of internal structures and pathological changes without the need for chemical processing.
In short, ODT bridges the gap between two-dimensional phase imaging and volumetric analysis, offering a powerful, label-free method for quantitative 3D imaging of live and fixed biological samples.
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