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Shalin Mehta

Graduate Student, NUS Graduate School for Integrative Sciences & Engineering (NGS)

Optical Bioimaging Lab,

Div. of Bioengineering, National University of Singapore, Block-E3A, #7-10, 7 Engineering Drive 1, Singapore 117574.

Phone: (+65) 90694182.

email: shalin (dot) mehta (at) gmail (dot) com

Career profile at LinkedIn

I am a PhD student at National University of Singapore (NUS) researching optical imaging methods that allow measurement of specimen morphology without label. I am excited about modeling of image formation (forward problem of imaging) in systems that use large illumination apertures, subsequent retrieval of specimen morphology from the images (inverse problem of imaging), and applications. These phase imaging methods are particularly applicable to study of fast cellular processes such as mitosis (cell division). I am advised by Prof. Colin Sheppard and collaborate with biologists, particularly at Liver Cancer Functional Genomics Lab of Prof. Caroline Lee.

Publications:

Following is the published/presented work with links in reverse chronological order. The accompanying pragraph is either an abstract or a note.

Peer-reviewed journal

  • “Phase-space representation of partially coherent imaging systems using the Cohen class distribution”, Shalin. B Mehta and Colin. J.R Sheppard, In review
  • “Quantitative phase-gradient imaging at high resolution with asymmetric illumination-based differential phase contrast,” Shalin. B Mehta and Colin. J.R Sheppard, Optics Letters, vol. 34, no. 13 (2009), pp. 1924-1926.

    Abstract: We describe a full-field phase-gradient imaging method: asymmetric illumination-based differential phase contrast (AIDPC). Imaging properties of AIDPC are evaluated using the phase-gradient transfer-function approach and elucidated with experimental images of an optical fiber and a histochemical preparation of a skeletal muscle section. In comparison with full-field differential interference contrast, AIDPC does not require phase shifting for quantitative imaging of phase gradient, provides artifact-free images of birefringent specimens, requires shorter camera exposure, and has larger depth of focus. It is amenable to transfer-function engineering, simultaneous fluorescence imaging, and automated live cell imaging.

  • “Partially coherent image formation in differential interference contrast (DIC) microscope,” Shalin B. Mehta and Colin J.R. Sheppard, Opt. Express, vol. 16, no. 24 (2008), pp. 19462-19479.

    Abstract:Some different image formation models have been proposed for Nomarski’s differential interference contrast (DIC) microscope. However, the nature of coherence of illumination in DIC, of key importance in image formation, remains to be elucidated. We present a partially coherent image formation model for DIC and demonstrate that DIC microscope images the coherent difference of shifted replicas of the specimen; but imaging of the each component is partially coherent. Partially coherent transfer functions are presented for various DIC configurations. Plots of these transfer functions and experimental images provide quantitative comparison among various DIC configurations and elucidate their imaging properties. Approximations for weak or slowly varying specimens are also given. These improved models should be of great value in designing phase retrieval algorithms for DIC.

Conference presentations (abstract/paper available)

  • “Linear Phase-Gradient Imaging with Asymmetric Illumination Based Differential Phase Contrast (AIDPC),” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, Novel Techniques in Microscopy, April 2009, OSA Technical Digest, p. NTuA5.

    Abstract: This paper demonstrates how one could engineer the transfer function of AIDPC, a novel optical thickness (phase) gradient measurement method suitable for live cell imaging, for linear imaging of the specimen phase-gradient.

  • “Quantitative phase retrieval in the partially coherent Differential Interference Contrast (DIC) microscope,” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, Focus on Microscopy, April 2009.

    An approach of calibrating parameters of the DIC microscope is presented. Analysis of phase-shifting DIC algorithm (used for retrieval of linear phase-gradient) is presented for partially coherent illumination. We note that the retrieved gradient wraps if the amount of shear exceeds a bound prescribed by the numerical apertures of the condenser and the objective.

  • Shalin B. Mehta and Colin J.R. Sheppard, “Full-field phase-gradient contrast methods for label-free quantitative imaging of cellular morphology: AIDPC and DIC,” Poster presentation, Focus on Microscopy, April 2009.

    Using images of several biological samples, this presentation explained properties of AIDPC and DIC relevant to biological microscopy.

  • “Asymmetric illumination based differential phase contrast (AI-DPC) for full-field transmission imaging of phase information in biological specimens,” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, Focus on Microscopy, April 2008.

    This was the first presentation about AIDPC.

Other presentations

If something catches your interest, I will be happy to email the slides.

  • “Full-field phase-gradient contrast methods for label-free quantitative imaging of cellular morphology: AIDPC and DIC,” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, 1st NGS (NUS graduate school for integrative sciences & engineering) Symposium, Singapore, Feb 2009.

    Best oral presentation award. The same work was presented at Focus on Microscopy, April 2009 as a poster.

  • “Quantitative imaging with Differential Interference Contrast (DIC) microscope – Role of coherence of illumination,” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, GPBE/NUS- Tohoku Graduate Student Conference in Bioengineering, Singapore, Dec 2008.

    Presentation about work reported in the 2008 paper on DIC published in Optics Express. Best oral presentation award.

  • “Phase imaging with oblique illumination,” Shalin B. Mehta and Colin J.R. Sheppard, Oral presentation, 10th Optics Within Life Sciences Conference, Singapore, Jul. 2008.
  • “Comparison of phase imaging methods based on optical processing at back focal plane,” Shalin B. Mehta, Colin J.R. Sheppard, and Caroline G.L. Lee, Invited presentation, Bioengineering seminar series, Singapore, Feb. 08.

    Explained how a common thread of signal-processing-at-the-back focal-plane runs through all contrast mechanisms designed for imaging of the phase information.

  • “Quantitative 3D and time-lapse imaging to investigate causative role of FAT10 in mitotic dysregulation,” Shalin B. Mehta, Jianwei Ren, Caroline G.L. Lee, and Colin J.R. Sheppard, Oral presentation, Graduate Student Symposium in Biological and Chemical Engineering, Singapore, Sep. 2007.

    About the second lab rotation carried out at Liver Cancer Functional Genomics Lab of Dr. Caroline Lee.

  • “Towards 3D quantification of hESC cultures by confocal microscopy,” Shalin B. Mehta, Lucky A.K. Kosasih, Andre Choo, Steve Oh, Ivan Reading, and Colin J.R. Sheppard, 5th ISSCR Annual Meeting, Cairns, Australia, Jun. 2007.

    From the first lab rotation carried out at Bioprocessing Technology Institute (BTI) with Dr. Steve Oh and Dr. Ivan Reading.

Also:

  • Reviewer for Optics Express.
  • Vice president at OSA NUS student chapter since two years

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