We introduce a lock-in method to increase the phase contrast in incoherent Differential Phase Contrast (DPC) imaging. The use of a smart pixel detector with in-pixel signal demodulation, paired with synchronized illumination, provides the basis of a bit-efficient approach to DPC. The experiments show an increased sensitivity by a factor of 8, for equivalent standard DPC measurements; single-shot sensitivity of 0.7 mrad at a frame rate of 1400 fps is demonstrated. This new approach may open the way for the use of incoherent phase microscopy in biological applications where extreme phase sensitivity and millisecond response time is required.
We introduce a lock-in method to increase the phase contrast in incoherent Differential Phase Contrast (DPC) imaging. The use of a smart pixel detector with in-pixel signal demodulation, paired with synchronized illumination, provides the basis of a bit-efficient approach to DPC. The experiments show an increased sensitivity by a factor of 8, for equivalent standard DPC measurements; single-shot sensitivity of 0.7 mrad at a frame rate of 1400 fps is demonstrated. This new approach may open the way for the use of incoherent phase microscopy in biological applications where extreme phase sensitivity and millisecond response time is required.
The phase sensitivity limit of Differential Phase Contrast (DPC) with partially coherent light is analyzed in details. The main optical parameters, such as the shape of illumination and the numerical aperture of the objective, together with the noise of the camera used to determine the minimum phase that can be detected. We found that a priori information about the sample can be used to fine-tune these parameters to increase phase contrast. We propose a simple algorithm to predict phase sensitivity of a DPC setup, which can be performed before the setup is built. Experiments confirm the theoretical findings.
The retina is composed of several transparent layers of neuronal and glial cells active during the vision process. Several studies showed that their structure and density is impacted by numerous eye diseases, such as macular degeneration, glaucoma and retinis pigmentosa. Quantifying such small morphological changes in retinal cells at different depths is of considerable interest to understand the root cause of the diseases as well as to follow the efficacy of new therapeutic approaches.
A widespread method to observe the retina ex-vivo at the cellular level is fluorescent confocal microscopy. However, a different imaging technique than fluorescence is required for in-vivo imaging in humans. We have shown that by using a combination of oblique illumination of the retina through the sclera, a phase image of the different layers can be generated and quantified.
Purpose: Retinal diseases are the major cause of blindness in industrialized countries. A forecast reported that an estimated number of 196 million people will be affected by age related macular degeneration by 2020. While tremendous effort is made to develop novel therapeutic strategies to rescue retinal neurons and retinal pigment epithelium (RPE), optimal means to evaluate the effects of such treatments and diagnose the disease are still missing.
Methods: We developed an imaging modality, called transscleral optical phase imaging (TOPI), which is able to resolve the individual human RPE cells in-vivo with the help of adaptive optics. The technology is based on oblique flood illumination and provides cellular resolution. The resulting 16 Hz-imaging speed, 5.7° × 5.7° field of view system allows for the visualization and the quantification of RPE cells within 2 seconds. Thanks to the approval from the ethic committee (CER-VD N°2017-00976), we conducted a study on 7 healthy human participants, with different skin pigmentations, 3 men and 4 women having an average age of 26 years. In all subjects, the RPE cell layer could be imaged and cell density could be quantified.
Results: We show the RPE density and area analysis for 7 healthy subjects. The results of the analyses show comparable values to those found in the literature.
Conclusion: The results of the study on healthy subjects demonstrate that TOPI is able to image and quantify in-vivo the human RPE cells, within a time frame of a few seconds (typically 2 seconds). The next step is to transfer the technique into a clinical environment.
Vision process is ruled by several cells layers of the retina. Before reaching the photoreceptors, light entering the eye has to pass through a few hundreds of micrometers thick layer of ganglion and neurons cells. Macular degeneration is a non-curable disease of themacula occurring with age. This disease can be diagnosed at an early stage by imaging neuronal cells in the retina and observing their death chronically. These cells are phase objects locatedon a background that presents an absorption pattern and so difficult to see with standard imagingtechniques in vivo. Phase imaging methods usually need the illumination system to be on the opposite side of the sample with respect to theimaging system. This is a constraintand a challenge for phase imaging in-vivo. Recently, the possibility of performing phase contrast imaging from one side using properties of scattering media has been shown. This phase contrast imaging is based on the back illumination generated by the sample itself.
Here, we present a reflection phase imaging technique based on oblique back-illumination. The oblique back-illumination creates a dark field image of the sample. Generating asymmetric oblique illumination allows obtaining differential phase contrast image, which in turn can be processed to recover a quantitative phase image. In the case of the eye, a transcleral illumination can generate oblique incident light on the retina and the choroidal layer.The back reflected light is then collected by the eye lens to produce dark field image.
We show experimental results of retinal phase imagesin ex vivo samples of human and pig retina.
In-vivo imaging of the eye’s fundus is widely used to study eye’s health. State of the art Adaptive Optics devices can resolve features up to a lateral resolution of 1.5 um. This resolution is still above what is needed to observe sub-cellular structures such as cone cells (1-1.25 um diameter). This limit in resolution is due to the small numerical aperture of the eye when the pupil is fully dilated (max 0.24).
In our work, we overcome this limit using a non-standard illumination scheme. A laser beam is shined on the lateral choroid layer, whose scattered light is illuminating the eye’s fundus. Thanks to a Spatial Light Modulator the scattered light from the choroid layer can be manipulated to produce a scanning focus spot on the fundus. The intensity of the reflected light from the fundus is collected from the pupil and used for reconstructing the image.
Optical phase conjugation is a technique that could find many applications in medical imaging and industry. However, state of the art techniques are limited in speed, portability and efficiency. Especially for digital optical phase conjugation, the electronic delays for image readout on a camera and addressing a spatial light modulator make this technique unpractical for phase conjugation in biological medium. Furthermore, the calibration of such a system is a very complex and expensive task. Thus, we propose integrating on the same device a camera and a liquid crystals spatial light modulator to achieve phase control thanks to in-pixel processing of a photodiode signal.
We present a CMOS light detector-actuator array, in which every pixel combines a spatial light modulator and a photodiode. It will be used in medical imaging based on acousto-optical coherence tomography with a digital holographic detection scheme. Our architecture is able to measure an interference pattern between a scattered beam transmitted through a scattering media and a reference beam. The array of 16 μm pixels pitch has a frame rate of several kfps, which makes this sensor compliant with the correlation time of light in biological tissues. In-pixel analog processing of the interference pattern allows controlling the polarization of a stacked light modulator and thus, to control the phase of the reflected beam. This reflected beam can then be focused on a region of interest, i.e. for therapy. The stacking of a photosensitive element with a spatial light modulator on the same chip brings a significant robustness over the state of the art such as perfect optical matching and reduced delay in controlling light.
In a context of embedded video surveillance, stand alone leftbehind image sensors are used to detect events with
high level of confidence, but also with a very low power consumption. Using a steady camera, motion detection
algorithms based on background estimation to find regions in movement are simple to implement and computationally
efficient. To reduce power consumption, the background is estimated using a down sampled image formed
of macropixels. In order to extend the class of moving objects to be detected, we propose an original mixed
mode architecture developed thanks to an algorithm architecture co-design methodology. This programmable
architecture is composed of a vector of SIMD processors. A basic RISC architecture was optimized in order to
implement motion detection algorithms with a dedicated set of 42 instructions. Definition of delta modulation as
a calculation primitive has allowed to implement algorithms in a very compact way. Thereby, a 1920x1080@25fps
CMOS image sensor performing integrated motion detection is proposed with a power estimation of 1.8 mW.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.