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28 results on '"Akbari, Najva"'

5. Field-portable pixel super-resolution colour microscope.

Author

Greenbaum, Alon, Akbari, Najva, Feizi, Alborz, Luo, Wei, and Ozcan, Aydogan

Subjects
Humans, Microscopy, Vaginal Smears, Equipment Design, Color, Cost-Benefit Analysis, Female, General Science & Technology
Abstract

Based on partially-coherent digital in-line holography, we report a field-portable microscope that can render lensfree colour images over a wide field-of-view of e.g., >20 mm(2). This computational holographic microscope weighs less than 145 grams with dimensions smaller than 17×6×5 cm, making it especially suitable for field settings and point-of-care use. In this lensfree imaging design, we merged a colorization algorithm with a source shifting based multi-height pixel super-resolution technique to mitigate 'rainbow' like colour artefacts that are typical in holographic imaging. This image processing scheme is based on transforming the colour components of an RGB image into YUV colour space, which separates colour information from brightness component of an image. The resolution of our super-resolution colour microscope was characterized using a USAF test chart to confirm sub-micron spatial resolution, even for reconstructions that employ multi-height phase recovery to handle dense and connected objects. To further demonstrate the performance of this colour microscope Papanicolaou (Pap) smears were also successfully imaged. This field-portable and wide-field computational colour microscope could be useful for tele-medicine applications in resource poor settings.

Published
2013

11. Radiofrequency Encoded Angular-Resolved Light Scattering

Author

Akbari, Najva

Subjects
Electrical engineering, Physics, Electromagnetics, Flow cytometry, Mie Scattering, Scattering
Abstract

Label-free classification of microstructures is a valuable approach in a variety of fields including cytometry and atmospheric science. The sensitive classification of microscopic cells and organisms is especially an important outstanding problem in biology. Flow cytometry is a routine method for cell classification. Current flow cytometers use light scattering at two fixed angles to infer information about size and internal complexity of cells at rates of more than 10,000 cells per second. However, this approach limits the precision and information that can be deduced by the cell population from the light scattering patterns. Capturing the full angular scattering spectrum of cells and particles would enable classification of cells with higher resolution and specificity. By capturing the angular dependence of scattering intensity we will be able to extract information about the scattering particle, hence providing a label-free method for particle classification. Current systems that provide angular scattering patterns do not have the throughput required to be implemented in state-of-the-art flow cytometers. Inverse scattering has been one of the more difficult problems to solve in electromagnetic wave interaction problems. Yet there have been many solutions obtained by analytical and computational modeling for various cases. The angular light scattering profile of particles is dependent on their morphological parameters, such as size, shape, and their internal structure. One of the most interesting applications of modeling these scattering profiles is in characterizing cells to identify abnormalities. Methods to take advantage of this angular dependent information have been demonstrated, however, these methods have various limitations such as low speed and precision. Here I present a new high throughput multi-angle resolved light scattering measurement technique that is able to capture the full angular scattering profile of particles in a single shot using a single detector. Termed Radiofrequency Encoded Angular-resolved Light Scattering (REALS), this technique uses one-to-one radiofrequency-to-angle mapping to measure angular dependence of light scattered from particles in a single shot using a photomultiplier tube. Using this technique it is possible to capture the continuous scattering profile over a wide dynamic range without mechanical scanning. This information allows us to characterize particle morphology and size with increased accuracy and high throughput, enabling label-free and high speed flow cytometry. As a proof of concept we distinguish the radius of tapered silica fiber over a range of radii.

Published
2015

16. Short-Wave Infrared Confocal Fluorescence Imaging of Deep Mouse Brain with a Superconducting Nanowire Single-Photon Detector

Author

Xia, Fei (author), Gevers, Monique (author), Fognini, Andreas (author), Mok, Aaron T. (author), Li, Bo (author), Akbari, Najva (author), Esmaeil Zadeh, I.Z. (author), Qin-Dregely, Y. (author), Xu, Chris (author), Xia, Fei (author), Gevers, Monique (author), Fognini, Andreas (author), Mok, Aaron T. (author), Li, Bo (author), Akbari, Najva (author), Esmaeil Zadeh, I.Z. (author), Qin-Dregely, Y. (author), and Xu, Chris (author)

Abstract

Optical microscopy is a valuable tool for in vivo monitoring of biological structures and functions because of its noninvasiveness. However, imaging deep into biological tissues is challenging due to the scattering and absorption of light. Previous research has shown that the two optimal wavelength windows for high-resolution deep mouse brain imaging are around 1300 and 1700 nm. However, one-photon fluorescence imaging in the wavelength region has been highly challenging due to the poor detection efficiency of currently available detectors. To fully utilize this wavelength advantage, we demonstrated here one-photon confocal fluorescence imaging of deep mouse brains with an excitation wavelength of 1310 nm and an emission wavelength within the 1700 nm window. Fluorescence emission at 1700 nm was detected by a custom-built superconducting nanowire single-photon detector (SNSPD) optimized for detection between 1600 nm and 2000 nm with low detection noise and high detection efficiency. With the PEGylated quantum dots and SNSPD both positioned at the optimal imaging window for deep tissue penetration, we demonstrated in vivo one-photon confocal fluorescence imaging at approximately 1.7 mm below the surface of the mouse brain, through the entire cortical column and into the hippocampus region with a low-cost continuous-wave laser source and low excitation power. We further discussed the significance of the staining inhomogeneity in determining the depth limit of one-photon confocal fluorescence imaging. Our work may motivate the further development of long wavelength fluorescent probes, and inspire innovations in high-efficiency, high-gain, and low-noise long wavelength detectors for biological imaging., ImPhys/Optics, BUS/Quantum Delft

Published
2021
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20. Imaging deeper than the transport mean free path with multiphoton microscopy

Author

Akbari, Najva, Rebec, Mihailo R, Xia, Fei, and Xu, Chris

Abstract

Multiphoton fluorescence microscopy enables deep in vivo imaging by using long excitation wavelengths to increase the penetration depth of ballistic photons and nonlinear excitation to suppress the out-of-focus fluorescence. However, the imaging depth of multiphoton microscopy is limited by tissue scattering and absorption. This fundamental depth limit for two-photon microscopy has been studied theoretically and experimentally. Long wavelength three-photon fluorescence microscopy was developed to image beyond the depth limit of two-photon microscopy and has achieved unprecedented in vivo imaging depth. Here we extend the theoretical framework for characterizing the depth limit of two-photon microscopy to three-photon microscopy. We further verify the theoretical predictions with experimental results from tissue phantoms. We demonstrate experimentally that high spatial resolution diffraction-limited imaging at a depth of 10 scattering mean free paths, which is nearly twice the transport mean free path, is possible with multiphoton microscopy. Our results indicate that the depth limit of three-photon microscopy is significantly beyond what has been achieved in biological tissues so far, and further technological development is required to reach the full potential of three-photon microscopy.

Published
2022

28. Label-free multiphoton imaging reveals volumetric shifts across development in sensory-related brain regions of a miniature transparent vertebrate.

Author

Tatarsky RL, Akbari N, Wang K, Xu C, and Bass AH

Abstract

Animals integrate information from different sensory modalities as they mature and perform increasingly complex behaviors. This may parallel differential investment in specific brain regions depending on the demands of changing sensory inputs. To investigate developmental changes in the volume of canonical sensory integration brain regions, we used third harmonic generation imaging for morphometric analysis of forebrain and midbrain regions from 5 to 90 days post fertilization (dpf) in Danionella dracula , a transparent, miniature teleost fish whose brain is optically accessible throughout its lifespan. Relative to whole brain volume, increased volume or investment in telencephalon, a higher order sensory integration center, and torus longitudinalis (TL), a midbrain visuomotor integration center, is relatively consistent from 5 to 30 dpf, until it increases at 60 dpf, followed by another increase at 90 dpf, as animals reach adulthood. In contrast, investment in midbrain optic tectum (TeO), a retinal-recipient target, progressively decreases from 30-90 dpf, whereas investment is relatively consistent across all stages for the midbrain torus semicircularis (TS), a secondary auditory and mechanosensory lateral line center, and the olfactory bulb (OB), a direct target of the olfactory epithelium. In sum, increased investment in higher order integration centers (telencephalon, TL) occurs as juveniles reach adulthood and exhibit more complex cognitive tasks, whereas investment in modality-dominant regions occurs in earlier stages (TeO) or is relatively consistent across development (TS, OB). Complete optical access throughout Danionella 's lifespan provides a unique opportunity to investigate how changing brain structure over development correlates with changes in connectivity, microcircuitry, or behavior.

Published
2024
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