Arthur F. Gmitro

Hopfield model associative memory with nonzero-diagonal terms in memory matrix.

The discrete-valued neural network proposed by Hopfield requires zero-diagonal terms in the memory matrix so that the net evolves toward a local minimum of an energy function. For a version of this model with bipolar nodes and positive terms along the diagonal, the net evolves so that only updates that lower the energy by a sufficient amount are accepted. For a net programmed as an outer-product associative content-addressable memory, the version with nonzero-diagonal elements performs nearly identically to one with zero-diagonal terms, and the dropping of the zero-diagonal requirement is advantageous for optical implementation.

In-Vivo Fluorescence Spectroscopy Of Normal And Atherosclerotic Arteries

Laser-induced fluorescence spectroscopy can discriminate atherosclerotic from normal arteries in-vitro and may thus potentially guide laser angioplasty. To evaluate the feasibility of laser-induced fluorescence spectroscopy in a living blood-filled arterial system we performed fiberoptic laser-induced fluorescence spectroscopy in a rabbit model of focal femoral atherosclerosis. A laser-induced fluorescence spectroscopy score was derived from stepwise linear regression analysis of in-vitro spectra to distinguish normal aorta (score>0) from atherosclerotic femoral artery (score<0). A 400 u silica fiber, coupled to a helium cadmium laser and optical multichannel analyzer, was inserted through a 5F catheter to induce and record in-vivo fluorescence from femoral and aortoiliac arteries. Arterial spectra could be recorded in all animals (n=10: 5 occlusions, 5 stenoses). Blood spectra were of low intensity and were easily distinguished from arterial spectra. The scores (mean ± SEM) for the in-vivo spectra were -0.69 ± 0.29 for artherosclerotic femoral, and +0.54 ±. 0.15 for normal aorta (p<.01; p=NS compared to in-vitro spectra). In-vitro, a fiber tip to tissue distance <50 u was necessary for adequate arterial LIFS in blood. At larger distances low intensity blood spectra were recorded (1/20 the intensity of tissue spectra). Thus, fiberoptic laser-induced fluorescence spectroscopy can be sucessfully performed in a blood filled artery provided the fiber tip is approximated to the tissue.

The spine in 3D: Computed tomographic reformation from 2D axial sections

A new program (3D83, General Electric) was used to reformat three-dimensional (3D) images from two-dimensional (2D) computed tomographic axial scans in 18 patients who had routine scans of the spine. The 3D spine images were extremely true to life and could be rotated around all three principle axes (constituting a movie), so that an illusion of head-motion parallax was created. The benefit of 3D reformation with this program is primarily for preoperative planning. It appears that 3D can also effectively determine the patency of foraminal stenosis by reformatting in hemisections. Currently this program is subject to several drawbacks that require user interaction and long reconstruction time. With further improvement, 3D reformation will find increasing clinical applicability.

Computed tomography videography: an electrooptical system for video-rate image reconstruction

A system for reconstruction of computed tomography (CT) images in a video frame time (1/30 sec) is described. The system implements the filtered backprojection algorithm using an electrooptic filtering technique, an optical backprojection, and a video detector. When coupled to a real-time system for acquiring projection data, the combined system realizes what we term CT videography.

CT Videography Using an Optical Computer for Image Reconstruction

Recent advances in the technology of data acquisition for Computed Tomography have made real-time acquisition a reality. Cardiac motion can now be essentially frozen. Real-time reconstruction is not currently available and so present systems act much like a movie camera (real-time acquisition followed by a relatively long reconstruction period and finally retrospective viewing). When coupled to a reconstruction system capable of real-time reconstruction of the motion image, CT videography becomes possible. This talk will present an optical computer capable of reconstructing an image in a video frame time (30 ms). The system implements the filtered back-projection algorithm using an acousto-optic convolver and an incoherent optical back-projector. System architecture and performance will be discussed. A comparison and discussion of other technologies for real-time reconstruction will also be presented.

TWO-DIMENSIONAL IMAGE PROCESSING BY ONE-DIMENSIONAL FILTERING OF PROJECTION DATA.

Two-Dimensional (2-D) inputs can be reduced to a set of 1-D functions by projection coding. Two-dimensional (2-D) operations can be implemented by the appropriate processing of these 1-D distributions. This paper discusses two possible projection coding methods and describes the operations and hardware necessary to measure the 1-D functions, process them, and reconstruct the desired 2-D distribution.

Evaluation of spectral discriminant functions for guidance of laser angioplasty

Development of a clinically acceptable laser angioplasty system has been hindered by the inability to adequately guide ablative laser radiation to atherosclerotic plaque. Low power laser-induced fluorescence spectroscopy is capable of discriminating normal and atherosclerotic arterial tissue. The purpose of this investigation was to develop and evaluate several spectral classification algorithms that would enable discrimination of atherosclerotic and normal arterial tissue by a computer controlled fluorescence guided laser angioplasty system.

Evaluation Of Spectral Discriminant Functions For Guidance Of Laser Angioplasty

Development of a clinically acceptable laser angioplasty system has been hindered by the inability to adequately guide ablative laser radiation to atherosclerotic plaque. Low power laser-induced fluorescence spectroscopy is capable of discriminating normal and atherosclerotic arterial tissue. The purpose of this investigation was to develop and evaluate several spectral classification algorithms that would enable discrimination of atherosclerotic and normal arterial tissue by a computer controlled fluorescence guided laser angioplasty system.

A Rapid Feature Extractor Based Upon Optically Gathered Projection Data

A typical computer vision system has an analog (i.e. TV camera) front end that delivers a two-dimensional image to digital hardware. Often, the initial computations consist of extraction of features from this image. We propose here an analog preprocessor that can directly deliver a variety of features or perform certain kinds of computations on the input image in a time comparable to the scan times of most TV systems. The system operates directly on projections (i.e. line integrals) of the two-dimensional image rather than the image itself. Two reasons for this are: (1) certain operations are performed more naturally in the projection space, (2) the projections can be processed as one-dimensional temporal signals; devices for these operations have significant advantages over two-dimensional spatial signal processors. We show implementations for performing the following operations: (1) features consisting of the image,Fourier power spectrum integrated along radial pie-wedge segments and concentric arcs. (2) Computation of the Hough transform for detecting line segments. (3) Computations of moments invariant to translation, rotation, and geometric scaling. (4) Computation of certain geometric features with similar invariance properties.