Showing papers on "Image resolution published in 1990"

Functional organization of primate visual cortex revealed by high resolution optical imaging

Abstract: A high spatial resolution optical imaging system was developed to visualize cerebral cortical activity in vivo. This method is based on activity-dependent intrinsic signals and does not use voltage-sensitive dyes. Images of the living monkey striate (VI) and extrastriate (V2) visual cortex, taken during visual stimulation, were analyzed to yield maps of the distribution of cells with various functional properties. The cytochrome oxidase--rich blobs of V1 and the stripes of V2 were imaged in the living brain. In V2, no ocular dominance organization was seen, while regions of poor orientation tuning colocalized to every other cytochrome oxidase stripe. The orientation tuning of other regions of V2 appeared organized as modules that are larger and more uniform than those in V1.

Optimization of particle image velocimeters. I, Double pulsed systems

Abstract: The spatial resolution, detection rate, accuracy and reliability of a particle image velocimeter (PIV) depend critically upon the careful selection of a number of parameters of the PIV system and the fluid motion. An analytical model and a Monte Carlo computer simulation have been developed to analyse the effects of experimental parameters and to optimize the system parameters. A set of six nondimensional parameters that are the most significant in optimizing PIV performance are identified. They are the data validation criterion, the particle image density, the relative in-plane image displacement, the relative out-of-plane displacement, a velocity gradient parameter, and the ratio of the mean image diameter to the interrogation spot diameter. These parameters are studied for the case of interrogation by autocorrelation analysis. By a single transformation, these results can be applied to interrogation by two-dimensional Fourier transform analysis of the Young's fringes.

Paint by numbers: abstract image representations

Abstract: Computer graphics research has concentrated on creating photo-realistic images of synthetic objects. These images communicate surface shading and curvature, as well as the depth relationships of objects in a scene. These renderings are traditionally represented by a rectangular array of pixels that tile the image plane.As an alternative to photo-realism, it is possible to create abstract images using an ordered collection of brush strokes. These abstract images filter and refine visual information before it is presented to the viewer. By controlling the color, shape, size, and orientation of individual brush strokes, impressionistic paintings of computer generated or photographic images can easily be created.

Analysis/synthesis techniques for subband image coding

Abstract: Analysis/synthesis systems designed for low bit rate image coding, their impact on overall system quality, and their computational complexity are discussed The investigation focuses on the design of analysis/synthesis systems for image coding and the perceptual impact of these systems at low bit rates Two objectives are emphasized in developing these systems: confining the total size of the subband images to be equal to the original image size, and designing the filters so that perceptual distortion is not introduced by the analysis/synthesis system Methods based on circular convolution and symmetric extensions are developed and discussed in detail The theory, design, and implementation of both recursive and nonrecursive filtering systems are discussed Methods are introduced which display advantages over conventional quadrature mirror filter based approaches >

Analysis of T2 limitations and off-resonance effects on spatial resolution and artifacts in echo-planar imaging

Abstract: Several aspects of blipped echo-planar imaging (EPI) are treated mathematically. An expression relating the necessary readout gradient strength and sampling time to the spatial resolution and readout duration is derived. It is shown how the net spatial resolution may be limited by the object's T2 characteristics and Bo field homogeneity, irrespective of the number of sampled points. Additionally, off-resonance effects result in a loss of spatial resolution and image distortion to a considerably greater degree than in conventional two-dimensional Fourier transform imaging. The extent of these effects is directly related to the time required to acquire the data matrix, and is therefore amplified when EPI is implemented on a standard commercial whole-body system which because of limited gradient performance uses necessarily longer sampling durations. Specific hardware modifications to a standard commercial imager are considered to allow successful EPI implementation. EPI image characteristics are compared quantitatively with those of conventional methods. © 1990 Academic Press, Inc.

Super resolution from image sequences

Abstract: An iterative algorithm to increase image resolution is described. Examples are shown for low-resolution gray-level pictures, with an increase of resolution clearly observed after only a few iterations. The same method can also be used for deblurring a single blurred image. The approach is based on the resemblance of the presented problem to the reconstruction of a 2-D object from its 1-D projections in computer-aided tomography. The algorithm performed well for both computer-simulated and real images and is shown, theoretically and practically, to converge quickly. The algorithm can be executed in parallel for faster hardware implementation. >

Introduction to image processing

Abstract: 1 The image as an analogue signal.- 2 Scanning of an image by an aperture.- 3 Extension of the aperture notion.- 4 Photographic images.- 5 Digitizing and reconstructing images.- 6 Basic techniques of digital image processing.- 7 Algebraic operations between images.- 8 Coloured images.- 9 Linear processing of signals and images.

Continuous-slice PENN-PET: a positron tomograph with volume imaging capability.

Abstract: The PENN-PET scanner consists of six hexagonally arranged position-sensitive Nal(TI) detectors. This design offers high spatial resolution in all three dimensions, high sampling density along all three axes without scanner motion, a large axial acceptance angle, good energy resolution, and good timing resolution. This results in three-dimensional imaging capability with high sensitivity and low scatter and random backgrounds. The spatial resolution is 5.5 mm (FWHM) in all directions near the center. The true sensitivity, for a brain-sized object, is a maximum of 85 kcps/microCi/ml and the scatter fraction is a minimum of 10%, both depending on the lower level energy threshold. The scanner can handle up to 5 mCi in the field of view, at which point the randoms equal the true coincidences and the detectors reach their count rate limit. We have so far acquired [18F]FDG brain studies and cardiac studies, which show the applicability of our scanner for both brain and whole-body imaging. With the results to date, we feel that this design results in a simple yet high performance scanner which is applicable to many types of static and dynamic clinical studies.

Three-dimensional iterative reconstruction algorithms with attenuation and geometric point response correction

Abstract: A three-dimensional iterative reconstruction algorithm which incorporates models of the geometric point response in the projector-backprojector is presented for parallel, fan, and cone beam geometries. The algorithms have been tested on an IBM 3090-600S supercomputer. The iterative EM reconstruction algorithm is 50 times longer with geometric response and photon attenuation models than without modeling these physical effects. An improvement in image quality in the reconstruction of projection data collected from a single-photon-emission computed tomography (SPECT) imaging system has been observed. Significant improvements in image quality are obtained when the geometric point response and attenuation are appropriately compensated. It is observed that resolution is significantly improved with attenuation correction alone. Using phantom experiments, it is observed that the modeling of the spatial system response imposes a smoothing without loss of resolution. >

Deconvolution from wave-front sensing: a new technique for compensating turbulence-degraded images

Abstract: A new technique of high-resolution imaging through atmospheric turbulence is described. As in speckle interferometry, short-exposure images are recorded, but in addition the associated wave fronts are measured by a Hartmann–Shack wave-front sensor. The wave front is used to calculate the point-spread function. The object is then estimated from the correlation of images and point-spread functions by a deconvolution process. An experimental setup is described, and the first laboratory results, which prove the capabilities of the method, are presented. A signal-to-noise-ratio calculation, permitting a first comparison with the speckle interferometry, is also presented.

Performance characteristics of an eight-ring whole body PET scanner.

Abstract: The technical characteristics of the multislice whole-body positron emission tomographic scanner (model PC4096-15WB Scanditronix) and its performance parameters are described. Spatial resolution at the center of the field of view was found to be 4.9 mm in-plane and 4.6 mm (cross slices) and 6.0 mm (direct slices) in the axial direction. The sensitivity for true and scattered coincidences is approximately 5,000 cps for direct slices and 7,100 cps for cross slices. At an activity concentration of 37 kBq/ml the system deadtime was approximately 5%. By measuring a uniform phantom with a cold cylindrical insert (5.0 cm diameter), the scatter fraction was found to be approximately 5%. The mean global uniformity over all 15 slices was 6.5%, whereas the local uniformity was found to be 4.3%. No systematic nonuniformities were observed. Finally, various methods for attenuation correction (transmission scan, contour finding, ellipse) were utilized to test their effects on the resulting reconstructed images.

Application of computerized tomography to the investigation of ionospheric structures

Abstract: Ionospheric total electron content (TEC) measurements, obtained simultaneously at several locations, can be processed using computerized tomography (CT) algorithms to obtain two-dimensional images of ionospheric electron density. Using TEC data, computerized ionospheric tomography (CIT) reconstructs an image of the electron density structures in a vertical slice above the receiving stations. We successfully applied this technique to realistic simulations of ionospheric density variations over 16° of latitude and a height range of 50 to 1000 km. A method for approximating the peak height and scale height of the electron density profile will be discussed as well as a reconstruction technique based on the multiplicative algebraic reconstruction technique algorithm and a back projection based initial guess. The quality of reconstructions is considered for two geometries and image resolutions. In particular, the image of a mid-latitude trough with background horizontal density gradient and large-scale irregular structures has been reconstructed from TEC data generated from a model based on an incoherent scatter radar observation. The CT reconstructed image was compared with the original contour map obtained by the incoherent scatter radar. Good agreement has been achieved. The CIT technique has also been applied to a modeled ionosphere to calculate the range rate corrections for a Doppler-tracking radar.

A maximum correlation method for image construction of IRAS survey data

Abstract: An algorithm is presented for the construction of images using linear array data with nonuniform scan coverage of object space and nonuniform detector responses. The algorithm achieves the maximum correlation between adjacent pixels, i.e., the smoothest image, consistent with the data and data uncertainties. For high spatial data density and signal-to-noise ratio, the achievable spatial resolution can exceed the diffraction limit of the optics. The capability of the algorithm is illustrated using 60-micron data from the region centered on the galaxy M101, obtained during the all-sky survey performed by the Infrared Astronomical Satellite. The 60-micron map produced has a resolution of about 36 arcsec and allows the identification of many H II regions by position and aperture photometry for the brighter ones. The achieved resolution is discussed in terms of the a priori estimate of the mean correlation length of the data, the directly measured FWHM in the final image, and the results of aperture photometry of M101 H II regions NGC 5447, 5455, 5461, 5462 and 5471.

First diffraction-limited astronomical images with adaptive optics

Abstract: An adaptive optics prototype system has been tested at the 1.52 m telescope of the Observatoire de Haute Provence, resulting in diffraction-limited images at near infrared wavelengths (2.2 to 5 microns). This paper presents the first results and a short analysis, which demonstrate the considerable gain in resolution and sensitivity achieved by this technique. Single stars, close binary stars, and a satellite have been resolved. In some cases another star several arcseconds apart has been used as reference for the wavefront sensing.

Confocal microscopy of the living eye.

Abstract: Confocal microscopy is an imaging paradigm that allows optical sectioning of almost any material with increased axial and lateral spatial resolution and better image contrast. We have applied this technology to the study of the living eye of cats, albino rabbits, and humans. The technique allows in vivo, noninvasive, real time images of the eye at magnifications (630x) which allow resolution of anatomical detail at the cellular level. In this paper we report details of our current instrument techniques and some of our results. The past development, present state-of-the-art, and projected future advances and applications of this novel microscopy are discussed. Preliminary observations are reported for all layers of the cornea, the limbus, and wound-healing responses in single animals.

High-resolution OCDR in dispersive waveguides

Abstract: In the analysis of integrated optical waveguide structures by coherence-domain reflectometry, spatial resolution may be seriously impaired by second order dispersion of the waveguides under test and by the presence of structures in the source spectrum An algorithm for evaluation of measured interferograms is presented to correct for these effects It is based on Fourier and wavenumber scale transformations

Signal-to-noise efficiency in magnetic resonance imaging

Abstract: The dependence of signal-to-noise ratio (SNR) on the analog filter, the sampling rate and the number and dimensions of voxels is derived for magnetic resonance imaging (MRI). It is shown that the object signal-to-noise ratio scales directly with the voxel volume and the square root of the number of voxels. Defining an efficiency figure of merit as the SNR divided by the square root of the imaging time, it is shown that efficiency is always improved when imaging with the lowest possible resolution (largest voxel dimensions) consistent with viewing the desired anatomical detail. The results directly imply the relative efficiency of 3-D (volume), 2-D (plane), 1-D (line) and 0-D (point) imaging techniques. It is shown that spatial averaging is an inefficient method of noise reduction in MRI. As long as voxel size is maintained constant, one can image as many pixels in the readout direction as desired with no loss in SNR; that is, the number of pixels in the readout direction has no effect on the image SNR. Further, multiple sampling of each phase encoding value (to improve SNR) has no advantage over increasing the number of pixels in the phase encoding direction while leaving the voxel size constant. Some experimental observations are given.

Environmental sensitivity index (ESI) mapping for oil spills using remote sensing and geographic information system technology

Abstract: The original environmental sensitivity index (ESI) mapping concept for oil spills was developed to assist spill-response coordinators in evaluating the potential impact of oil along a shoreline and the allocation of resources during and after a spill. This paper describes enhancements to the ESI concept which includes: (1) a planimclric basemap derived from SPOT multispectral and/or panchromatic data resampled to 10 × 10 m spatial resolution within ± 5 m root mean square error; (2) information for a shoreline ESI derived from a combination of visual and digital image processing techniques applied to remotely-sensed data; (3) information on oil-sensitive wildlife placed in a geographic information system (GIS) for rapid retrieval and querying; and (4) placing all access and protection information in the GIS and interfacing it with a relational database for rapid access and query. These enhancements to the ESI mapping concept make it more effective for developing contingency plans before an oil spill and ma...

Limits to the resolution of elevation maps from stereo SAR images

Abstract: In Synthetic Aperture Radar (SAR) interferometry from a satellite, the altimetric information is obtained from the phase difference of two focused complex images gathered by the same sensor in two passes along parallel or crossing orbits. The altimetric resolution of such a system improves when the satellites displacement is increased in the cross-track direction. The maximum allowed displacement, limited by speckle noise, increases with the spatial resolution of the SAR image. Excluding the additive noise, we show that the achievable vertical resolution is better than the slant range resolution times the cosine of the off-nadir angle for about 99 per cent of the image points. As an example, an altimetric map of the Panamint Valley area is calculated using repeated passes of the Seasat satellite. The effect of the additive noise is visible when the cross-track distance of the two orbits is low.

Description of a simultaneous emission-transmission CT system

Abstract: We are designing an instrument which will perform correlated emission-transmission image acquisition, but which departs from previous systems by incorporating a low-power x-ray tube and generator, rather than a radionuclide source, for the transmission image. The system uses an array of high-purity germanium (HPGe) detectors and detector electronics with energy discrimination circuitry to separate x-rays (at 100 or 120 kVp) from higher energy gamma rays from the 99mTc or 123j radiopharmaceutical injected into the patient. The data acquisition electronics have time constants matching the charge collection time (50 ns) of the HPGe detectors to maximize count-rate capabilities (up to 1 million cps per detector element), while maintaining adequate energy resolution (approximately 10% FWHM). Each detector channel has two energy windows for simultaneous transmission-emission imaging or for dual-energy x-ray studies. A host computer provides system control as well as data acquisition, data correction, tomographic image reconstruction, image display, and data analysis. As a radionuclide imaging system, this instrument will function as a single-slice SPECT scanner with high-count rate capabilities and excellent energy resolution for imaging short-lived radionuclides, improved photopeak discrimination and scatter rejection, and simultaneous imaging of multiple radionuclides. The system also will generate radiographic images in either a tomographic or projection scanning mode, while dual-energy x-ray CT will provide material specific imaging. However, the novel and potentially powerful capabilities of this instrument would derive from its inherent correlation of functional information from SPECT with precise anatomic information from CT or the material-specific morphologic information from dual-energy x-ray CT. The simultaneously acquired radiographic images should relieve the deficiencies of poor statistics and limited spatial resolution commonly associated with SPECT systems. Dual-energy xray CT also can provide an energy-corrected and anatomically-correlated map of attenuation coefficients for more accurate quantitation of emission radionuclide data.

A color sequential optical offset image sampling system

Abstract: The system of the present invention increases the resolution (number of picture elements or pixels) of an image that may be formed from an image sensor without increasing the resolution of the sensor. The system operates upon a color image beam using a set of primary color filters (14), including at least two filters of the same color, with at least one of the filters being capable of displacing the color image beam by a distance equal to a fraction of the distance between adjacent photosensitive elements which form the image sensor. The color wheel (12) is rotated to sequentially place each filter of the set of primary filters into the color image beam. The array of photosensitive elements (22) forming the image sensor is positioned to receive the colored image beam which passes through each filter. Each photosensitive element produces signals indicative of the intensity of the color image beam components incident thereon. The signals produced by the photosensitive elements of the image sensor are stored for each filter positioned in the path of the color image beam. A composite image signal is formed from the stored signals by combining the signals such that the filter displaced pixels are interleaved with the non-displaced pixels. The resultant image therefore has a greater number of pixels, or higher resolution, than the image sensor.

Multichannel biomagnetic system for study of electrical activity in the brain and heart.

Abstract: The authors designed a multichannel system for noninvasive measurement of the extremely weak magnetic fields generated by the brain and the heart. It uses a flat array of 37 superconducting magnetic field-sensing coils connected to sophisticated superconducting quantum interference devices. To prevent interference from external electromagnetic fields, the system is operated inside a shielded room. Complete sets of coherent data, even from spontaneous events, can be recorded. System performance was evaluated with phantom measurements and evoked-response studies. A spatial resolution of a few millimeters and a temporal resolution of a millisecond were obtained. First results in patients with partial epilepsy and investigations of the cardiac conductive pathway indicate that biomagnetism is now ready for a systematic clinical evaluation. Interpretation of measurements was facilitated by highlighting biomagnetically localized electrical activity in three-dimensional digital magnetic resonance images.

A New Apparatus for Brain Imaging: Four-Head Rotating Gamma Camera Single-Photon Emission Computed Tomograph

Abstract: The development of a new rotating gamma camera SPECT device for imaging the brain was undertaken with the objective of achieving the highest full volume imaging spatial and temporal resolution performance. For this purpose, four rectangular gamma camera detectors were arranged as close to the head as possible, and united in a block to insure detector head registration and alignment as well as to enable rotation stability at high speeds. Phantom and clinical studies performed demonstrated 42 sequential, 4-mm thick transaxial images acquired in one scan and with sufficient volume to permit the entire cerebrum and cerebellum to be imaged with high sensitivity. The central field of view reconstructed spatial resolution measured 7.0 mm full width of half maximum utilizing the high-resolution collimator, and tomographic images of arbitrary planes including sagittal and coronal demonstrated equally high resolution. The high sensitivity and high speed rotational acquisition capability of the device permits dynamic SPECT studies to be carried out in the analysis of rapidly varying radiotracer concentrations.

Method and system for reproducing monochromatic and color images using ordered dither and error diffusion

Abstract: A method and system for color and monochromatic printing wherein ordered dither and error diffusion processes are combined to provide high quality printed images with good spatial resolution, good gray scale transitions, good low frequency and high frequency responses and a high computational speed. Using this process, gray scale numbers representative of a scanned image are summed for each super pixel of the scanned image and divided by a chosen gray level normalizing factor. This division operation is done to obtain a normalized ordered dither quotient number of drops (dots) to be printed in super pixels and to further obtain an error remainder number of dots to be dispersed to surrounding super pixels. The normalized ordered dither quotient number of dots are printed in pre-assigned individual pixels within printed super pixels, and the error remainder number of drops are diffused to other pre-assigned surrounding or adjacent super pixels. In this manner, a combination of ordered dither and error diffusion signal processing and printing is achieved to simultaneously take advantage of some of the best characteristics of both types of signal processing printing. In color printing, the above operation is carried out in each of a plurality of separate color planes, and all of the quotient information is retained and printed in a predetermined priority sequence for each color plane.

Dual density digital image system

Abstract: A data processing system stores and displays digital images, and includes a workstation having a document input scanner for digitizing document images at a first resolution, an image display unit for displaying digitized document images at a second resolution which is less than the first resolution and a printer for printing digitized document images at a third resolution greater than the second resolution. The system reduces communications traffic and assures fast access time on the network since the bulk of the traffic will utilize the smaller compressed data records required for the second resolution. However, these improvements in communication traffic and access time do not sacrifice the availability of high resolution compressed data records occasionally needed for printing and other high resolution operations.

Scanning tunneling microscopy on rough surfaces: Tip‐shape‐limited resolution

Abstract: This paper discusses the reliability of scanning tunneling microscopy (STM) images of mesoscopically rough surfaces. The specific structure of these images represents a convolution between the real surface topography and the shape of the tip. In order to interpret these images quantitatively, the line scans of steep and high steps can be used to obtain an image of the tip itself. This image shows tip radii ranging typically from 5 to 15 nm and cone angles of about 30° over a length of 80 nm, and can in turn be used to recognize the limits of STM resolution on a rough surface: High‐resolution transmission electron microscopy cross‐section images of Au island films on a Au‐Nb double layer are convoluted with the experimentally observed tip shape; the resulting line scans correspond very well with STM graphs of the same samples. Finally an overall criterion for the resolution of the STM on such surfaces is proposed.

A time-delay integration charge-coupled device camera for slot-scanned digital radiography.

Abstract: We have developed a low‐noise digital camera based on a 512×96 element CCD operating in the time‐delay integration mode. This camera has been combined with an x‐ray image intensifier to record radiographicimages produced by a scanning slot beam of radiation. This results in the rejection of a large fraction of scattered radiation, without a significant increase in x‐ray tube heat loading or image acquisition time. Here we describe the design of our CCDcamera and the results of our investigations of camera resolution, linearity, noise, and quantum efficiency. We have found that both the resolution limit (50 mm−1) and the dynamic range (2100) of this novel camera are greater than reported values for conventional video cameras. Applications of this system in digital angiography and mammography are discussed.