Wendy J. Plesniak

Advances in holographic video

We discuss recent developments in the MIT electronic holography display. These include the use of multiple galvanometric scanners as the horizontal scanning element, two 18-channel acousto-optic modulators (AOMs) working in tandem, and a bank of custom-designed high- bandwidth framebuffers. We also describe some recent progress on computational issues.

Reconfigurable image projection holograms

We introduce reconfigurable image projection RIP holo- grams and a method for computing RIP holograms of three-dimensional 3-D scenes. RIP holograms project one or more series of parallax views of a 3-D scene through one or more holographically reconstructed projection surfaces. Projection surfaces are defined at locations at which the hologram reconstructs a variable number of real or virtual images, called holographic primitives, which collectively compose the surface and constitute exit pupils for the view pixel information. RIP holograms are efficiently assembled by combining a sweep of 2-D parallax views of a scene with instances of one or more precomputed diffractive elements, which are permitted to overlap on the hologram, and which reconstruct the holographic primitives. The technique improves on the image quality of conventional stereograms while affording similar efficient computation: it incorporates realistic computer graphic rendering or high-quality optical capture of a scene, it eliminates some artifacts often present in conven- tional computed stereograms, and its basic multiply-and-accumulate op- erations are suitable for hardware implementation. The RIP approach offers flexible tuning of capture and projection together, according to the sampling requirements of the scene and the constraints of a given dis- play architecture.

Real-time holographic video images with commodity PC hardware

The MIT second-generation holographic video system is a real-time electro-holographic display. The system produces a single-color horizontal parallax only (HPO) holographic image. To reconstruct a three-dimensional image, the display uses a computed fringe pattern with an effective resolution of 256K samples wide by 144 lines high by 8 bits per sample. In this paper we first describe the implementation of a new computational subsystem for the display, replacing custom computing hardware with commodity PC graphics chips, and using OpenGL. We also report the implementation of stereogram computing techniques that employ the PC hardware acceleration to generate and update holographic images at rates of up to two frames per second. These innovations shrink the system’s physical footprint to fit on the table-top and mark the fastest rate at which full computation and update have been achieved on this system to date. Finally we present first results of implementing the Reconfigurable Image Projection (RIP) method of computing high-quality holograms on this new system.

Incremental update of computer-generated holograms

We describe the incremental computing method for making localized changes to a computer-generated hologram to rapidly modify the 3-D image it reconstructs. The method populates a scene with holo- graphic primitives, tracks scene-based changes, and updates the diffrac- tive contributions of only affected primitives. Changes are rapidly incor- porated into the hologram via simple arithmetic operations, and only affected regions of the hologram are updated at each simulation time step. The method can accommodate different holographic primitive rep- resentations, is designed to be suitable for hardware assistance, and is also compatible with computer-graphics-style techniques for smooth shading, texture mapping, and reflections.

Compact prototype one-step Ultragram printer

We describe a prototype reduced-size holographic stereogram printer capable of producing scalable, Ultragram-format hardcopy output. An analysis of the resolution requirements for high quality stereogram output with respect to the printing method and printer components is presented. A holographic optical element is combined with a pseudorandom band-limited diffuser to focus the spatially modulated object beam and provide Fourier-plane broadening, thus improving image quality. We analyze issues of image preparation time and integration of image rendering and exposure control to optimize system resource requirements.

Tangible holography: adding synthetic touch to 3D display

Just as we expect holographic technology to become a more pervasive and affordable instrument of information display, so too will high fidelity force-feedback devices. We describe a testbed system which uses both of these technologies to provide simultaneous, coincident visuo- haptic spatial display of a 3D scene. The system provides the user with a stylus to probe a geometric model that is also presented visually in full parallax. The haptics apparatus is a six degree-of-freedom mechanical device with servomotors providing active force display. This device is controlled by a free-running server that simulates static geometric models with tactile and bulk material properties, all under ongoing specification by a client program. The visual display is a full parallax edge-illuminated holographic stereogram with a wide angle of view. Both simulations, haptic and visual, represent the same scene. The haptic and visual displays are carefully scaled and aligned to provide coincident display, and together they permit the user to explore the models 3D shape, texture and compliance.

Coincident display using haptics and holographic video

In this paper, we describe the implementation of a novel system which enables a user to “carve” a simple free-standing electronic holographic image using a force-feedback device. The force-feedback (or haptic) device has a stylus which is held by the hand like an ordinary cutting tool. The 3D position of the stylus tip is reported by the device, and appropriate forces can be displayed to the hand as it interacts with 3D objects in the haptic workspace. The haptic workspace is spatially overlapped and registered with the holographic video display volume. Within the resulting coincident visuo-haptic workspace, a 3D synthetic cylinder is presented, spinning about its long axis, which a person can see, feel, and lathe with the stylus. This paper introduces the concept of coincident visuo-haptic display and describes the implementation of the lathe simulation. After situating the work in a research context, we present the details of system design and implementation, including the haptic and holographic modeling. Finally, we discuss the performance of this prototype system and future work.

High Throughput Tools to Access Images from Clinical Archives for Research

Historically, medical images collected in the course of clinical care have been difficult to access for secondary research studies. While there is a tremendous potential value in the large volume of studies contained in clinical image archives, Picture Archiving and Communication Systems (PACS) are designed to optimize clinical operations and workflow. Search capabilities in PACS are basic, limiting their use for population studies, and duplication of archives for research is costly. To address this need, we augment the Informatics for Integrating Biology and the Bedside (i2b2) open source software, providing investigators with the tools necessary to query and integrate medical record and clinical research data. Over 100 healthcare institutions have installed this suite of software tools that allows investigators to search medical record metadata including images for specific types of patients. In this report, we describe a new Medical Imaging Informatics Bench to Bedside (mi2b2) module (www.mi2b2.org), available now as an open source addition to the i2b2 software platform that allows medical imaging examinations collected during routine clinical care to be made available to translational investigators directly from their institution’s clinical PACS for research and educational use in compliance with the Health Insurance Portability and Accountability Act (HIPAA) Omnibus Rule. Access governance within the mi2b2 module is customizable per institution and PACS minimizing impact on clinical systems. Currently in active use at our institutions, this new technology has already been used to facilitate access to thousands of clinical MRI brain studies representing specific patient phenotypes for use in research.

Haptic holography: a primitive computational plastic

We describe our work on haptic holography, a combination of computational modeling and multimodal spatial display, which allows a person to see, feel, and interact with three-dimensional freestanding holographic images of material surfaces. In this paper, we combine various holographic displays with a force-feedback device to render multimodal images with programmatically prescribed material properties and behavior. After a brief overview of related work which situates visual display within the manual workspace, we describe our holo-haptic approach and survey three implementations, Touch, Lathe, and Poke, each named for the primitive functional affordance it offers. In Touch, static holographic images of simple geometric scenes are reconstructed in front of the hologram plane, and coregistered with a force model of the same geometry. These images can be visually inspected and haptically explored using a handheld interface. In Lathe, a holo-haptic image can be reshaped by haptic interaction in a dynamic but constrained manner. Finally in Poke, using a new technique for updating interference-modeled holographic fringe patterns, we render a holo-haptic image that permits more flexible interactive reshaping of its reconstructed surface. We situate this work within the context of related research and describe the strengths, shortcomings, and implications of our approach.

Holographic video display of time-series volumetric medical data

We describe an animated electro-holographic visualization of brain lesions due to the progression of multiple sclerosis. A research case study is used which documents the expression of visible brain lesions in a series of magnetic resonance imaging (MRI) volumes collected over the interval of one year. Some of the salient information resident within this data is described, and the motivation for using a dynamic spatial display to explore its spatial and temporal characteristics is stated. We provide a brief overview of spatial displays in medical imaging applications, and then describe our experimental visualization pipeline, from the processing of MRI datasets, through model construction, computer graphic rendering, and hologram encoding. The utility, strengths and shortcomings of the electro-holographic visualization are described and future improvements are suggested.