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A general algorithm for three-dimensional (3D) modeling of acoustic fields generated by phased array transducers and propagating in uniformly lossy media is introduced and illustrated also with the help of specific examples. Applications of the method are foreseen in the analysis and the design of transducers for echographic applications in order to evaluate and/or optimize their performances.
A method to model the left ventricular myocardium in thallium-201 Single Photon Emission Computed Tomography (SPECT) is presented. This method is based on the fitting of the morphological skeleton of the left ventricle to a truncated bullet. This automatic approach would provide a more reproducible visualization of the organ for clinical applications.
A system for constructing courseware in Radiology is described. It uses widely available, inexpensive hardware and software to produce material that is versatile and easy to use. The computer-naive student readily interacts with both text and images. We briefly describe the hardware, the software, the development process, and the different prototype applications developed at this time.
Smart instruments require on-line computers, special purpose hardware, or both. A pupillometer is described that relies only on a general purpose microcomputer with a frame grabber to process infrared video camera pictures of the human eye. An essential feature of the instrument is that a top-down model controls the image processing algorithms. The model generates regions of interest, ROIs, positioned from knowledge of anatomy and optics of the eye and information from previously analyzed frames. Within these adaptively controlled ROIs, fast, run-time algorithms automatically calculate local thresholds, area measurements, moments for centroid position information, and use pyramiding to shorten calculation time for large pupils. Outputs are precise measurements of pupil size and eye position in real time, with adequate bandwidth for most purposes.
Multimedia lives with images; medical images are born from digital imaging. A physician's multimedia workstation cannot exist without tools for manipulating images, performing measurements and, generally speaking, extracting and collecting pieces of information from the available data. Image analysis and computer vision constitute a wide and rapidly evolving field. This paper is intended as an introductory document for medical imaging researchers and practitioners wishing an overview of recent developments and trends. The major lines of activities in the domain are presented, under the common framework of a processing pipeline. After a presentation of the various stages of this pipeline, current subjects of research are indicated.
A special software package for interactive display and manipulation of medical images was developed at the University Hospital of Geneva, as part of a hospital wide Picture Archiving and Communication System (PACS). This software package, called Osiris, was especially designed to be easily usable and adaptable to the needs of noncomputer-oriented physicians. The Osiris software has been developed to allow the visualization of medical images obtained from any imaging modality. It provides generic manipulation tools, processing tools, and analysis tools more specific to clinical applications. This software, based on an object-oriented paradigm, is portable and extensible. Osiris is available on two different operating systems: the Unix X-11/OSF-Motif based workstations, and the Macintosh family.
Computer-assisted neurosurgery uses the latest technological advancements in imaging, computers, mechanics, and electronics to improve the accuracy and reduce the invasiveness and risk of neurosurgical procedures. We describe the Wayne State University, Detroit, Michigan, computer-assisted neurosurgical system with the emphasis on software and discuss the theory guiding the development of this system and its application in real-time position tracking systems. Our system consists of the Neurological Surgery Planning System (NSPS) software which we developed at our medical center and three types of position tracking systems: the Zamorano-Dujovny (Z-D) are digitizer for frame-based procedures, an articulated arm, and an infrared-based digitizer for frameless procedures. The NSPS software is designed to offer neurosurgeons a safe and accurate method to approach intracranial lesions by preoperatively planning a surgical trajectory. Software consisting of the most advanced technologies in computer vision, computer imaging/graphics, and stereotactic numeric analysis forms the core of the system. Capabilities for correlating data from imaging studies to facilitate image reconstruction, image mapping, and three-dimensional (3D) visualization of target volumes enable the neurosurgeon to simulate surgical procedures into a preoperative protocol to be used during surgery, both to follow the preplanned trajectory and to track the position of surgical instruments in real-time on the computer monitor. The tracking systems position and orient the surgical instruments relative to the patient's head. With these devices, the display of the surgical instruments together with the virtual images create an excellent intraoperative tool.
We demonstrate the feasibility and utility of using anatomical/vascular correlation in image-guided surgery, by interfacing a PC-based stereoscopic Digital Subtraction Angiography (DSA) analysis system to a three-dimensional (3D) image based surgical workstation that has been modified to allow presentation of stereoscopic images. Numerical values representing the position and angulation of a hand-held probe are transmitted to both systems simultaneously, enabling the probe to be visualized stereoscopically in both anatomical and vascular images during the surgical procedure. The integration of the patient's vascular and anatomical data in this way provides the surgeon with a complete overview of brain structures through which he is passing the electrode-guiding cannulas, enabling him to avoid critical vessels en route to the targets.
An improved method for computer-aided 3D reconstruction of neuroanatomical structures derived from intracranially fixed human brains is demonstrated. The embedded brains are cut into slices. The sliced surfaces are photographed. The outlines of the neuroanatomical structures are drawn onto transparencies which are scanned. The surfaces of the structures are 3D reconstructed with the triangulation method. The cortical structures of the human brain are complex, resulting in possible ambiguities for triangulation which must be solved interactively. These surface reconstructions allow for 3D visualization of the brain and its components comparable with intravital conditions found in clinical neuroimaging.
In this report, we describe a new application for three-dimensional computer image processing that can provide for improved depiction of anatomical structures on routine nonvolumetric magnetic resonance (MR) examinations. The technique can be applied to standard two-dimensional MR images of the brain, spine, musculoskeletal system, and body including those obtained with relatively thick slices and with an intersection gap. This report demonstrates use of the reformation technique to establish retrospectively the symmetry in bilateral structures that were displayed out of alignment due to suboptimal patient positioning or patient motion during image acquisition and to improve the depiction of anatomical structures that were oriented out of the plane of original image acquisition. This method can be performed interactively in near real time, requires no increase in patient examination time, and has potential application throughout the body.
The molecular structure, electrostatic potentials and dynamics of imipramine, chlorimipramine, amitriptyline and nortriptyline were examined by computer graphics, molecular mechanical energy calculations and molecular dynamics simulations, using the AMBER all atom force field. Starting coordinates for amitriptyline and nortriptyline were generated by model building from the crystal structure of imipramine. The structures were refined by molecular mechanical energy minimization, and used as starting points for molecular dynamics simulations in vacuo and in aqueous solution. The simulations demonstrated considerable flexibility of the molecules, both in the side chain and in the ring system, where the angle between the phenyl rings varied between 90 degrees and 168 degrees. The most frequently observed conformations of imipramine, chlorimipramine and nortriptyline during the simulations had the side chain folded above one of the phenyl rings, while amitriptyline showed both folded and extended side chain conformations during the simulations. The results may provide increased understanding of the molecular recognition and specificity of tricyclic antidepressant drugs in interaction with neurotransmitter receptor molecules.
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Medical applications for virtual reality (VR) technologies are just beginning to emerge. These include VR surgical simulators, telepresence surgery, complex medical database visualization, and rehabilitation. These applications are mediated through the computer interface and embody VR as an integral part of a paradigm shift in the field of medicine. The Green Telepresence Surgery System consists of two components, the surgical workstation and the remote worksite. At the remote site there is a 3-D camera system and responsive manipulators with sensory input. At the workstation there is a 3-D monitor and dexterous handles with force feedback. The VR surgical simulator is a stylized recreation of the human abdomen with several essential organs. Using a head-mounted display and DataGlove, a person can learn anatomy from a new perspective by 'flying' inside and around the organs, or can practice surgical procedures with a scalpel and clamps. Database visualization creates 3-D images of complex medical data for new perspectives in analysis. VR applications in rehabilitation medicine permit impaired individuals to perform tasks not otherwise available to them, allow accurate assessment and therapy for their disabilities, and help architects understand their critical needs in public or personal space. And to support these advanced technologies, the operating room and hospital of the future will be first designed and tested in virtual reality, bringing together the full power of the digital physician.
Virtual reality comprises the computer-based generation of realistic three-dimensional visual, auditory, and tactile environments in which a user can explore and interact with virtual objects. Although traditionally used for input devices to virtual worlds, the instrumented glove and sensor technologies of virtual reality may provide a dramatic new method for the measurement and amplification of human motion. This paper discusses some potential uses of virtual reality technology to support and augment routine activities for people who have physical disabilities. We present two different but related applications of this technology.
A virtual model of a knee joint with muscles, ligaments and bones has been developed. This model includes realistic 3-D surface deformation and tissue stiffnesses. Tissue and bone deformation (palpation) produces real time force feedback to the user hand wearing a DataGlove and Rutgers Master. Collision detection algorithms determine when and where the virtual hand palpates the surface model. This user interaction with the muscles and bones of a human knee model may be used as a training and planning tool for knee surgery.
This guide provides a bibliography of many of the most noteworthy contributions to the emerging literature about virtual reality in medicine, along with listings of the most relevant conferences and resources for researchers. This is an abridged version of a continuously updated comprehensive document which is available on-line to the research community.
The glutathione post-activated neocarzinostatin chromophore (NCSi-glu)-DNA complex was studied in detail by 2-D NMR spectroscopy. The complex is a model for understanding the sequence specific cleavage of DNA by the native neocarzinostatin chromophore (NCS chrom), a highly potent enediyne antitumor agent. NMR spectral analysis is presented for the free NCSi-glu, the free DNA duplex and the NCSi-glu-DNA complex. In addition to the previously reported structural details of the complex (Gao, X.; Stassinopoulos, A.; Rice, J. S.; Goldberg, I. H. Biochemistry 1995, 34, 40), we demonstrate that the binding of NCSi-glu in minor groove results in a patch of negatively charged surface covering the otherwise relatively neutral minor groove. The formation of the complex is largely driven by hydrophobic forces and the solvation of the polar surface of the complex. Comparison of the conformations of NCSi-glu and DNA duplex in their free and bound form reveals an induced mutual fit of DNA and NCSi-glu upon complex formation. The reduced NCS chrom represents a DNA binding motif for sequence specific recognition of DNA via intercalation and minor groove interactions.
RATIONALE AND OBJECTIVES: This article proposes the use of a disembodied autonomous actor for navigation support within complex virtual medical objects reconstructed from Computed Tomography or Magnetic Resonance Imaging. Such objects are often maze-like, and users risk getting lost within them during Virtual Reality sessions. Therefore, users need paths for guided fly-throughs when performing non-invasive diagnostic tasks. MATERIALS AND METHODS: We present a synthetic vision-based actor capable of finding collision-free paths from a given position to a goal point in environments containing loops and impasses. When navigating, the actor voxelizes the virtual environment and searches for collision-free paths in voxel space by using a back tracking search algorithm. Automata and rules control its search behaviour. The resulting paths can be used in dedicated virtual endoscopy applications. RESULTS: Our path search method has been tested within a variety of tubular virtual anatomical structures in 3D such as aortas, colons, or blood vessels of the brain. The actor finds paths within reasonable time limits, even when considering complex anatomical surface models. CONCLUSION: The method may be used as a valuable tool for assisting virtual endoscopic diagnostic and screening activities in the near future.