David Abookasis

Computer-generated holograms of three-dimensional objects synthesized from their multiple angular viewpoints

Synthesizing computer-generated holograms (CGHs) of a general three-dimensional (3D) object is usually a heavy computational task. We propose and demonstrate a new algorithm for computing CGHs of 3D objects. In our scheme, many different angular projections of computer-designed 3D objects are numerically processed to yield a single two-dimensional complex matrix. This matrix is equivalent to the complex amplitude of a wave front on the rear focal plane of a spherical lens when the object is located near the front focal point and illuminated by a plane wave. Therefore the computed matrix can be used as a CGH after it is encoded to a real positive-valued transparency. When such CGH is illuminated by a plane wave, a 3D real image of the objects is constructed. The number of computer operations are equivalent to those of a two-dimensional Fourier CGH. Computer and optical constructions of 3D objects, both of which show the feasibility of the proposed approach, are described.

Computer-generated holograms of three-dimensional realistic objects recorded without wave interference

We propose a method of synthesizing computer-generated holograms of real-life three-dimensional (3-D) objects. An ordinary digital camera illuminated by incoherent white light records several projections of the 3-D object from different points of view. The recorded data are numerically processed to yield a two-dimensional complex function, which is then encoded as a computer-generated hologram. When this hologram is illuminated by a plane wave, a 3-D real image of the object is reconstructed.

Imaging cortical absorption, scattering, and hemodynamic response during ischemic stroke using spatially modulated near-infrared illumination

We describe a technique that uses spatially modulated near-infrared (NIR) illumination to detect and map changes in both optical properties (absorption and reduced scattering parameters) and tissue composition (oxy- and deoxyhemoglobin, total hemoglobin, and oxygen saturation) during acute ischemic injury in the rat barrel cortex. Cerebral ischemia is induced using an open vascular occlusion technique of the middle cerebral artery (MCA). Diffuse reflected NIR light (680 to 980 nm) from the left parietal somatosensory cortex is detected by a CCD camera before and after MCA occlusion. Monte Carlo simulations are used to analyze the spatial frequency dependence of the reflected light to predict spatiotemporal changes in the distribution of tissue absorption and scattering properties in the brain. Experimental results from seven rats show a 17+/-4.7% increase in tissue concentration of deoxyhemoglobin and a 45+/-3.1, 23+/-5.4, and 21+/-2.2% decrease in oxyhemoglobin, total hemoglobin concentration and cerebral tissue oxygen saturation levels, respectively, 45 min following induction of cerebral ischemia. An ischemic index (I(isch)=ctHHbctO(2)Hb) reveals an average of more then twofold contrast after MCAo. The wavelength-dependence of the reduced scattering (i.e., scatter power) decreased by 35+/-10.3% after MCA occlusion. Compared to conventional CCD-based intrinsic signal optical imaging (ISOI), the use of structured illumination and model-based analysis allows for generation of separate maps of light absorption and scattering properties as well as tissue hemoglobin concentration. This potentially provides a powerful approach for quantitative monitoring and imaging of neurophysiology and metabolism with high spatiotemporal resolution.

Security optical systems based on a joint transform correlator with significant output images

An improved optical security system based on correlation between two phase-only computer generated masks is proposed. The two phase masks are placed together at the input plane of a joint transform correlator. A priori known output image is obtained in the system output only if one mask is the right key for the other mask. In addition to a simple verification, our security system is capable of identifying the type of an input mask according to the corresponding output image that it generates. The two phase masks are designed using an iterative optimization algorithm with constraints in the input and output domains. Computer simulations are presented with the resultant images formed by the two phase-only elements.

Three types of computer-generated hologram synthesized from multiple angular viewpoints of a three-dimensional scene

We describe various techniques to synthesize three types of computer-generated hologram (CGH): the Fresnel-Fourier CGH, the Fresnel CGH, and the image CGH. These holograms are synthesized by fusing multiple perspective views of a computer-generated scene. An initial hologram is generated in the computer as a Fourier hologram. Then it can be converted to either a Fresnel or an image hologram by computing the desired wave propagation and imitating an interference process of optical holography. By illuminating the CGH, a 3D image of the objects is constructed. Computer simulations and experimental results underline the performance of the suggested techniques.

Seeing through biological tissues using the fly eye principle

During the past decade, optical imaging through scattering medium has proved to be a powerful technique for many applications. It is especially effective in medical diagnostic, since it is safe, noninvasive and low-cost compared with the conventional radiation techniques. Based on a similar principle of the flys visual system, we show a novel method of optical imaging through scattering medium. An image of bones hidden between two biological tissues (chicken breast) is recovered from many noisy speckle pictures obtained on the output of a multi-channeled optical imaging system. The operation of multiple imaging is achieved using a microlens array. Each lens from the array projects a different speckled image on a digital camera. The set of speckled images from the entire array are first shifted to a common center and then accumulated to a single average picture in which the concealed object is exposed.

Watermarks encrypted in a concealogram and deciphered by a modified joint-transform correlator

We describe an electro-optical method of deciphering a watermark from a recently invented encoded image termed a concealogram. The watermark is revealed as a result of spatial correlation between two concealograms, one containing the watermark and the other containing the deciphering key. The two are placed side by side on the input plane of a modified joint-transform correlator. When the input plane is illuminated by a plane wave, the watermark image is reconstructed on part of the correlators output plane. The key function deciphers the concealed watermark from the visible picture only when the two specific concealograms are matched. To illustrate the systems performance, both simulation and experimental results are presented.

Performance comparison of iterative algorithms for generating digital correlation holograms used in optical security systems

An optical security system based on a correlation between two separate binary computer-generated holograms has been developed and experimentally tested. The two holograms are designed using two different iterative algorithms: the projection- onto constrained sets algorithm and the direct binary search (DBS) algorithm. By placing the ready-to-use holograms on a modified joint transform correlator input plane, an output image is constructed as a result of a spatial correlation between the two functions coded by the holograms. Both simulation and experimental results are presented to demonstrate the systems performance. While we concentrate mainly on the DBS algorithm, we also compare the performance of both algorithms.

Using NIR spatial illumination for detection and mapping chromophore changes during cerebral edema

We used spatially modulated near-infrared (NIR) light to detect and map chromophore changes during cerebral edema in the rat neocortex. Cerebral edema was induced by intraperitoneal injections of free water (35% of body weight). Intracranial pressure (ICP) was measured with an optical fiber based Fabry-Perot interferometer sensor inserted into the parenchyma of the right frontal lobe during water administration. Increase in ICP from a baseline value of 10 cm-water to 145 cm-water was observed. Following induction of cerebral edema, there was a 26±1.7% increase in tissue concentration of deoxyhemoglobin and a 47±4.7%, 17±3% and 37±3.7% decrease in oxyhemoglobin, total hemoglobin concentration and cerebral tissue oxygen saturation levels, respectively. To the best of our knowledge, this is the first report describing the use of NIR spatial modulation of light for detecting and mapping changes in tissue concentrations of physiologic chromophores over time in response to cerebral edema.

Measuring and Mapping Optical Properties and Chromophore Changes During Brain Injury in the Near-Infrared Spectral Range Using Spatial Modulation of Light: Initial Results

In this paper we describe the use of spatially modulated light projection for quantifying changes in chromophores during acute ischemic injury in the rat barrel cortex. The approach we use is based on spatial modulation of white light projected onto the brain by commercial projector. The reflected light is acquired on a CCD camera, which is then processed in the computer to obtain the concentration and distribution of chromophores through steady-state diffusion model. Experimental results from permanent stroke model underline the performance of the suggested techniques.