In vivo laser Doppler holography of the human retina

The eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. Optical angiography in the retina requires sensitive measurements, which hinders conventional full-field laser Doppler imaging schemes. To overcome this limitation, we used digital holography to perform laser Doppler perfusion imaging of human retina with near-infrared light. Two imaging channels with a slow and a fast CMOS camera were used simultaneously for real-time narrowband measurements, and offline wideband measurements, respectively. The beat frequency spectrum of optical interferograms recorded with the fast (up to 75 kHz) CMOS camera was analyzed by short-time Fourier transformation. Power Doppler images drawn from the Doppler power spectrum density qualitatively revealed blood flow in retinal vessels over 512 × 512 pixels covering 2.4 × 2.4 mm² on the retina with a temporal resolution down to 1.6 ms. The sensitivity to lateral motion as well as the requirements in terms of sampling frequency are discussed.

Subsampled phase retrieval for temporal resolution enhancement in lensless on-chip holographic video

On-chip holographic video is a convenient way to monitor biological samples simultaneously at high spatial resolution and over a wide field-of-view. However, due to the limited readout rate of digital detector arrays, one often faces a tradeoff between the per-frame pixel count and frame rate of the captured video. In this report, we propose a subsampled phase retrieval (SPR) algorithm to overcome the spatial-temporal trade-off in holographic video. Compared to traditional phase retrieval approaches, our SPR algorithm uses over an order of magnitude less pixel measurements while maintaining suitable reconstruction quality. We use an on-chip holographic video setup with pixel sub-sampling to experimentally demonstrate a factor of 5.5 increase in sensor frame rate while monitoring the in vivo movement of Peranema microorganisms.

Automated Fourier space region-recognition filtering for off-axis digital holographic microscopy

Automated label-free quantitative imaging of biological samples can greatly benefit high throughput diseases diagnosis. Digital holographic microscopy (DHM) is a powerful quantitative label-free imaging tool that retrieves structural details of cellular samples non-invasively. In off-axis DHM, a proper spatial filtering window in Fourier space is crucial to the quality of reconstructed phase image. Here we describe a region-recognition approach that combines shape recognition with an iterative thresholding method to extracts the optimal shape of frequency components. The region recognition technique offers fully automated adaptive filtering that can operate with a variety of samples and imaging conditions. When imaging through optically scattering biological hydrogel matrix, the technique surpasses previous histogram thresholding techniques without requiring any manual intervention. Finally, we automate the extraction of the statistical difference of optical height between malaria parasite infected and uninfected red blood cells. The method described here paves way to greater autonomy in automated DHM imaging for imaging live cell in thick cell cultures.

Dynamics of cell and tissue growth acquired by means of extended field of view lensfree microscopy

In this paper, we discuss a new methodology based on lensfree imaging to perform wound healing assay with unprecedented statistics. Our video lensfree microscopy setup is a simple device featuring only a CMOS sensor and a semi coherent illumination system. Yet it is a powerful mean for the real-time monitoring of cultivated cells. It presents several key advantages, e.g. integration into standard incubator, compatibility with standard cell culture protocol, simplicity and ease of use. It can perform the follow-up in a large field of view (25 mm(2)) of several crucial parameters during the culture of cells i.e. their motility, their proliferation rate or their death. Consequently the setup can gather large statistics both in space and time. Here we uses this facility in the context of wound healing assay to perform label-free measurements of the velocities of the fronts of proliferation of the cell layer as a function of time by means of particle image velocimetry (PIV) processing. However, for such tissue growth experiments, the field of view of 25 mm(2) remains not sufficient and results can be biased depending on the position of the device with respect to the recipient of the cell culture. Hence, to conduct exhaustive wound healing assays, we propose to enlarge the field of view up to 10 cm(2) through a raster scan, by moving the source/sensor with respect to the Petri dish. We have performed acquisitions of wound healing assay (keratinocytes HaCaT) both in real-time (25 mm(2)) and in final point (10 cm(2)) to assess the combination of velocimetry measurements and final point wide field imaging. In the future, we aim at combining directly our extended field of view acquisitions (>10 cm(2)) with real time ability inside the incubator.

Biodynamic imaging of live porcine oocytes, zygotes and blastocysts for viability assessment in assisted reproductive technologies

The success of assisted reproductive technologies relies on accurate assessment of reproductive viability at successive stages of development for oocytes and embryos. The current scoring system used to select good-quality oocytes relies on morphologically observable traits and hence is indirect and subjective. Biodynamic imaging may provide an objective approach to oocyte and embryo assessment by measuring physiologically-relevant dynamics. Biodynamic imaging is a coherence-gated approach to 3D tissue imaging that uses digital holography to perform low-coherence speckle interferometry to capture dynamic light scattering from intracellular motions. The changes in intracellular activity during cumulus oocyte complex maturation, before and after in vitro fertilization, and the subsequent development of the zygote and blastocyst provide a new approach to the assessment of preimplant candidates.

Fully automated digital holographic processing for monitoring the dynamics of a vesicle suspension under shear flow

We investigate the dynamics of a vesicle suspension under shear flow between plates using DHM with a spatially reduced coherent source. Holograms are grabbed at a frequency of 24 frames/sec. The distribution of the vesicle suspension is obtained after numerical processing of the digital holograms sequence resulting in a 4D distribution. Obtaining this distribution is not straightforward and requires special processing to automate the analysis. We present an original method that fully automates the analysis and provides distributions that are further analyzed to extract physical properties of the fluid. Details of the numerical implementation, as well as sample experimental results are presented.

Tympanic membrane contour measurement with two source positions in digital holographic interferometry

The data acquisition from the shape of an object is a must to complete its quantitative displacement measurement analysis. Over the past years whole field of view optical non-invasive testing has been widely used in many areas, from industrial ones to, for instance, biomedical research topics. To measure the surface contour from the tympanic membrane (TM) of ex-vivo cats digital holographic interferometry (DHI) is used in combination with a two-illumination positions method: the shape is directly measured from the phase change between two source positions by means of a digital Fourier transform method. The TM shape data in conjunction with its displacement data renders a complete and accurate description of the TM deformation, a feature that no doubt will serve to better comprehend the hearing process. Acquiring knowledge from the tissue shape indicates a mechanical behavior and, indirectly, an alteration in the physiological structure due to middle ear diseases or damages in the tissue that can deteriorate sound transmission. The TM shape contour was successfully measured by using two source positions within DHI showing that the TM has a conical shape. Its maximum depth was found to be 2 mm, considering the umbo as the reference point with respect to the TM annulus plane, where the setup is arranged in such a manner that it is capable of measuring a height of up to 7 mm.