Showing papers on "Image resolution published in 1983"

An electronically collimated gamma camera for single photon emission computed tomography. Part I: Theoretical considerations and design criteria

Abstract: The detection and imaging characteristics of a new type of gamma camera for single photon emission computed tomography have been investigated. Unlike conventional gamma cameras which use mechanical collimation, the new gamma camera utilizes electronic collimation which is obtained from a sequential interaction of gamma radiation with a dual position-and-energy sensitive detection system. Coincident counting between the two detectors provides localization of activity upon a multitude of conical surfaces throughout the object, wherefrom the three-dimensional activity distribution can be reconstructed. Not only does electronic collimation provide simultaneous multiple views of the object, but a large gain in sensitivity is also indicated over a conventionally collimated gamma camera under conditions of similar spatial resolution. Detector optimization studies have been performed to design a prototype system comprising a 33 X 33 array of high-purity germanium detectors coupled to an uncollimated conventional scintillation camera. The cumulative signal-to-noise ratio in projection images obtained with this system is expected to be about a factor of 4 higher (sensitivity about a factor of 15 higher) than that obtained in a corresponding projection image with a conventional gamma camera for imaging a uniformly distributed Tc-99m source in a 20-cm-diam X 20-cm-tall cylinder. A similar gain is expected in the tomographic images.

A look at motion in the frequency domain

Abstract: A moving image can be specified by a contrast distribution, c(x,y,t), over the dimensions of space x,y, and time t. Alternatively, it can be specified by the distribution C(u,v,w) over spatial frequency u,v and temporal frequency w. The frequency representation of a moving image is shown to have a characteristic form. This permits two useful observations. The first is that the apparent smoothness of time-sampled moving images (apparent motion) can be explained by the filtering action of the human visual system. This leads to the following formula for the required update rate for time-sampled displays. W(c)=W(l)+ru(l) where w(c) is the required update rate in Hz, W(l) is the limit of human temporal resolution in Hz, r is the velocity of the moving image in degrees/sec, and u(l) is the limit of human spatial resolution in cycles/deg. The second observation is that it is possible to construct a linear sensor that responds to images moving in a particular direction. The sensor is derived and its properties are discussed.

High resolution tomographic imaging method

Abstract: A method for use with a computerized axial tomographic scanner (CAT) of providing an image of a sample that has spatial resolution in the axial direction that is smaller than the width of the X-ray beam of the CAT. The sample is scanned at a plurality of points in a plurality of cross sections that are separated by a distance that is less than the width of the X-ray beam of the CAT to determine the measured density function for each of the plurality of points. The measured density function is deconvolved with the beam width function for the CAT for each of the plurality of points to obtain the actual density function for the plurality of points. The actual density function is then used to generate an image of the sample that has a spatial resolution in the axial direction that is smaller than the width of the X-ray beam of the CAT.

An improved algorithm for reprojecting rays through pixel images

Abstract: It is often desired to calculate line integrals through a field of reconstructed CT density pixels for the purpose of improving CT image quality. Two algorithms widely published and discussed in the past are known to either degrade spatial resolution or generate errors in the results due to the discontinuous "square pixel" modeling of the reconstructed image. An algorithm is described, based on linear interpolation between pixels, which provides superior accuracy without unnecessary loss of resolution. It was tested on simulated data for a head section and on a narrow Gaussian density distribution. The experimental results demonstrated improved performance. The method is expected to prove useful for many types of post-reconstruction processing, including beam hardening, missing data, and noise supression algorithms.

High-speed three-dimensional X-ray computed tomography: The dynamic spatial reconstructor

Abstract: Most X-ray CT scanners require a few seconds to produce a single two-dimensional (2-D) image of a cross section of the body. The accuracy of full three-dimensional (3-D) images of the body synthesized from a contiguous set of 2-D images produced by sequential CT scanning of adjacent body slices is limited by 1) slice-to-slice registration (positioning of patient); 2) slice thickness; and 3) motion, both voluntary and involuntary, which occurs during the total time required to scan all slices. Therefore, this method is inadequate for true dynamic 3-D imaging of moving organs like the heart, lungs, and circulation. To circumvent these problems, the Dynamic Spatial Reconstructor (DSR) was designed by the Biodynamics Research Unit at the Mayo Clinic to provide synchronous volume imaging, that is stop-action (1/100 s), high-repetition rate (up to 60/s), simultaneous scanning of many parallel thin cross sections (up to 240, each 0.45 mm thick, 0.9 mm apart) spanning the entire anatomic extent of the bodily organ(s)of interest. These capabilities are achieved by using multiple X-ray sources and multiple 2-D fluoroscopic video camera assemblies on a continually rotating gantry. Desired tradeoffs between temporal, spatial, and density resolution can be achieved by retrospective selection and processing of appropriate subsets of the total data recorded during a continuous DSR scan sequence.

Performance evaluation of a positron tomograph designed for brain imaging.

Abstract: The NeuroECAT, a multiplane positron tomograph for imaging the brain, was characterized in terms of both quantitative performance and image quality. The tomograph has four modes of operation, defined by the placement of interplane septa and shadow shields. Each mode was fully characterized by measurement of image resolution, axial resolution, resolution uniformity, scatter, accidentals, and deadtime. Each measurement was performed with scattering media simulating the human head, and resolutions were obtained from images processed with reconstruction techniques actually used in patient imaging. The results for the most frequent mode of operation are: image resolution 9.8 +/- 0.2 mm (FWHM), axial resolution 12.4 +/- 0.4 mm, and scatter 8.1% +/- 0.6. At a count rate of 10,000 cps per image plane, accidentals are 9% and the deadtime 3%. Accidentals are measured and subtracted in hardware, and corrections for deadtime loss are calculated from the on-line measurement of triple-coincidence events. Scatter is estimated from the scan data and subtracted in software. Image quality is demonstrated by phantom studies and by the patient images obtained with (F-18) fluorodeoxyglucose and carbon-11 monoxide. The FDG images show clear delineation of the convolutions of the cortical ribbon, internal gray nuclei, internal and external capsules, and othermore » substructures of the brain. The carbon monoxide images, in addition to visualizing the large vessels, clearly show the blood volumes of the cortex, the Sylvian fissure, and the circle of Willis.« less

Remote thermal imaging with 0.7‐μm spatial resolution using temperature‐dependent fluorescent thin flims

Abstract: We have applied the recently developed technique of fluorescent thermal imaging to measure the surface temperature profile of a test sample with unprecedented temperature and spatial resolution. A particularly simple temperature profile was produced by passing an electrical current through a long, unresolvably thin metal stripe on a glass substrate. The sample was coated with a fluorescent thin film whose fluorescence efficiency decreases with increasing temperature. Digital processing of the fluorescence image produces a quantitative surface temperature map with simultaneous temperature and spatial resolutions of 0.08 °C and 0.7 μm, respectively. This spatial resolution approaches for the first time the dimensions of state‐of‐the‐art integrated circuits. Extension of this technique into the nanosecond time domain will allow new advances in the fields of photothermal microscopy, integrated circuit diagnostics, and thermal transport measurements.

Accuracy of measurement of star images on a pixel array

Abstract: Algorithms are developed for predicting the accuracy with which the brightness of a star can be determined from its image on a digital detector array, as a function of the brightness of the background. The assumption is made that a known profile is being fitted by least squares. The two profiles used correspond to ST images and to ground-based observations. The first result is an approximate rule of thumb for equivalent noise area. More rigorous results are then given in tabular form. The size of the pixels, relative to the image size, is taken into account. Astronometric accuracy is also discussed briefly; the error, relative to image size, is very similar to the photometric error relative to brightness.

Image sharpening for mixed spatial and spectral resolution satellite systems

Abstract: Two methods of image sharpening (reconstruction) are compared. The first, a spatial filtering technique, extrapolates edge information from a high spatial resolution panchromatic band at 10 meters and adds it to the low spatial resolution narrow spectral bands. The second method, a color normalizing technique, is based on the ability to separate image hue and brightness components in spectral data. Using both techniques, multispectral images are sharpened from 30, 50, 70, and 90 meter resolutions. Error rates are calculated for the two methods and all sharpened resolutions. The results indicate that the color normalizing method is superior to the spatial filtering technique.

Optics of photorefraction: orthogonal and isotropic methods

Abstract: Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.

Fast count-dependent digital filtering of nuclear medicine images: concise communication.

Abstract: The formulation of an "optimal" filter for improving the quality of digitally recorded nuclear medicine images is reported in this paper. The method forms a Metz filter for each image based upon the total number of counts in the image, which in turn determines the average noise level. The parameters of the filter were optimized for a set of simulated images using the minimization of the mean-square error as the criterion. The speed of the image formation results from the use of an array processor. In a study of localization receiver operating characteristics (LROC) using the Alderson liver phantom, a significant improvement in tumor localization was found in images filtered with this technique, compared with the original digital images and those filtered by the nine-point binomial smoothing algorithm. The technique has been found useful for the filtering of static and dynamic studies as well as the two-dimensional pre-reconstruction filtering of images from single photon emission computerized tomography.

Spatial resolution of remotely sensed imagery A review paper

Abstract: An important system-performance parameter for remote-sensing systems is the spatial resolution. This term has an imprecise meaning and there are a multitude of different definitions. In this paper, the most important definitions are reviewed and consideration is given to the factors which influence the resolution of a given system. It is concluded that no single definition of spatial resolution can be applied to all systems, nor can spatial resolution alone be used to measure the significant information content of image data.

Evaluation of the spatial resolution of a CT scanner by direct analysis of the edge response function.

Abstract: A new approach to the measurement of the spatial resolution of a computed tomography (CT) scanner system is presented. The method is based on a direct least-squares fit of an analytical expression to a set of data obtained from a CT image of the interface between two materials. The implementation of the method in connection with the G. E. RTPLAN computer configuration is described. The method has been applied in determining the resolution of an EMI-7070 scanner and it is shown that the assumption of uniformity of the system resolution across the CT image is fulfilled within the accuracy of the present method. The reproducibility of the method has been estimated from a series of spatial resolution determinations performed on ten images taken with identical scan parameters. The standard deviation of this series was 3.2%.

Quantitative image reconstruction with weighted backprojection for single photon emission computed tomography.

Abstract: A new method of image reconstruction for single photon emission computed tomography is presented. The method is basically a filtered backprojection with some modifications. The algorithm consists of three steps: normalization of observed projections, modified convolution operation, and weighted backprojection. The weighting function for backprojection is determined to provide perfect attenuation compensation for a uniform attenuation medium and to keep the statistical noise in the reconstructed image low. The relative contributions of two conjugate projections to the image can be controlled by the reconstruction parameters, enabling improvement of the signal-to-noise ratio and spatial resolution at off-center area compared with the conventional averaging method of two conjugate projections. Simulation studies indicated that the method provides a satisfactory image for an extended source of 99mTc (mu = 0.15 cm-1) having a diameter of up to approximately 35 cm. A myocardium phantom is adequately reconstructed from a 180 approximately 225 degrees angle scan. The effect of nonuniform attenuation medium surrounding the source region can be corrected. This paper presents the mathematical basis of the procedure, the evaluation of the statistical noise, and some illustrative computer simulations.

Comparison of Several Techniques to Obtain Multiple-Look SAR Imagery

Abstract: Synthetic aperture radar imagery is contaminated by coherent speckle noise. In order to improve interpretability, multiple-look images are usually generated. In this paper, we examine the performance of several classes of techniques to generate such multiple-look imagery. The detailed impulse responses and the signal-to-speckle noise ratios obtained by the various techniques are presented. It is found that by using several types of image domain filters, the signal-to-speckle noise ratio can be improved over the conventional discrete mixed-integrator while keeping the equivalent rectangular resolution constant.

Data compression method for graphics images

Abstract: Graphic images are generally considered to be those images comprised of text and/or drawings. Data compression of graphics images is desired whenever a fast image transmission speed is desired in a limited band width channel. It is also used for storage of a large number of images in a limited capacity storage system. A high compression ratio is achieved by thresholding the graphics image to a bilevel black-white image at one bit per pixel and then employing a second data compression on the black-white image. At low resolution, bilevel images have poor quality at edges and a quality improvement is needed. The data compression apparatus and method disclosed separates the graphics image into at least first and second bit planes identifies edge pixels from the first bit plane indicating a black/white change, locates the edge pixels and generates at least a single bit for each edge pixel indicating whether the edge pixel has a maximum intensity value such as black or white or an intermediate gray intensity value. Intermediate values are not allowed except at edge pixels which enhances both quality and compressibility of the resulting graphics image.

Digital Processing for Improvement of Ultrasonic Abdominal Images

Abstract: Digital processing that increases resolution by spatial deconvolution and histogram-based amplitude mapping has been used to improve ultrasonic abdominal image quality. The processing was applied to pulse-echo ultrasound data obtained from clinical imaging instrumentation modified to permit digital recording of signals in either RF or video forms for subsequent off-line analysis. Spatial deconvolution was accomplished both along the axis and across the width of the ultrasonic beam. Axial deconvolution was carried out on RF data with a point spread function derived from the echo of a wire target. Lateral deconvolution was performed on the video envelope placed in a matrix by an inverse filter with parameters that adjust themselves to the spatial frequency content of the image being processed. Resultant image amplitudes were mapped into a hyperbolic distribution to increase image contrast for improved demonstration of low amplitudes. The combination of processing produced resolution improvements to show boundaries more sharply and contrast changes to demonstrate more detail in the images.

Using Pyramids to Define Local Thresholds for Blob Detection

Abstract: A method of detecting blobs in images is described. The method involves building a succession of lower resolution images and looking for spots in these images. A spot in a low resolution image corresponds to a distinguished compact region in a known position in the original image. Further, it is possible to calculate thresholds in the low resolution image, using very simple methods, and to apply those thresholds to the region of the original image corresponding to the spot. Examples are shown in which variations of the technique are applied to several images.

Method of increasing the image resolution of a transmitting mask and improved masks for performing the method

Abstract: A mask (21) for use in photolithography with incident light which is at least partially coherent has a layer or zone of a transparent material (26) at every other transmitting region (24, 25) of the mask. The transparent material has an index of refraction n and a thickness d such that (n-1) d=Φλ where λ is the wave length of the incident light, and Φ is a fraction between 1/4 and 3/4. Graph (a) shows the amplitude of the electric vector of the emergent light at the mask and graph (b) that vector at the image plane. Graph (c) shows the light intensity at the image plane.

Image Design: Generation of a Prescribed Image at the Output of a Band-Limited System

Abstract: Image design involves determining the object distribution which produces a prescribed image at the output of a given imaging system. We solve the problem of generating two parallel lines at the output of an imaging system that is modeled by a linear band-limited system foliowed by a point nonlinearity of the hardlimiting type. It is shown that a solution always exists whatever the system's bandwidth. In principle, infinite two-line resolution is achievable. In practice, resolution much higher than the conventional resolution of the imaging system is possible.

The Information Content of Synthetic Aperture Radar Images of Terrain

Abstract: A statistical model is developed that portrays an imaging radar as a noisy communication channel with multiplicative noise, and the model is used to evaluate the average amount of information that can be extracted about a target from its radar image. The average information content is also used to define a measure of radiometric resolution for radar images. It is shown that the information content and the resolution capabilities of an imaging radar reach a limit beyond which an increase in scene dynamic range does not improve the information content or the resolution. This limitation results from the multiplicative nature of the noise introduced in the imaging process.

The Effects of Surface Mapping Corrections with Synthetic-Aperture Focusing Techniques on Ultrasonic Imaging

Abstract: Image processing to improve the resolution of ultrasonic imaging systems requires an accurate knowledge of the geometry and properties of the media through which the ultrasound travels. This is particularly true when a method such as the synthetic-aperture focusing technique (SAFT) is used. For SAFT to function properly, it is necessary to know accurately the path traveled by the ultrasound from transducer to target and back again. A form of SAFT imaging is described in which the imaging routine also constructs a map of the target surface. This map is then used to calculate accurately the propagation history of the ultrasound for the SAFT processing. The resolution and positional accuracy of unprocessed images, unmapped SAFT images, and surface mapped SAFT images are compared. All but the surface mapping images show significant errors in positional accuracy for relatively small surface deviations. The surface mapping correction, however, brings the imaging accuracy back to within the limits of the mechanical experimental error. A more severely distorted surface destroys the phase relationships required for processing unless the surface variations are accounted for. In addition, results achieved with a flat ultrasonic transducer suggest significant simplifications that may ease field implementation of SAFT systems.

Solid state image sensor

Abstract: A high-resolution image sensor uses integrated arrays of photosensitive elements in connection with a lens system which projects, onto the arrays, an erect, unmagnified, unreversed real image of the object being sensed (such as a line of a document). The arrays are staggered in two or more rows so that a single, large integrated array need not be used, yet the entire width of the document line can be covered by photosensitive elements while a 1:1 ratio is maintained between object size and image size. The real image is produced on the two or more rows of arrays by two or more optical systems which have a large depth-of-focus to allow for some variation in object distance. The sensor has a high image quality and is capable of detecting color.

Sea ice motion measurements from Seasat SAR images

Abstract: Data from the Seasat synthetic aperture radar (SAR) experiment are analyzed in order to determine the accuracy of this information for mapping the distribution of sea ice and its motion. Data from observations of sea ice in the Beaufort Sea from seven sequential orbits of the satellite were selected to study the capabilities and limitations of spaceborne radar application to sea-ice mapping. Results show that there is no difficulty in identifying homologue ice features on sequential radar images and the accuracy is entirely controlled by the accuracy of the orbit data and the geometric calibration of the sensor. Conventional radargrammetric methods are found to serve well for satellite radar ice mapping, while ground control points can be used to calibrate the ice location and motion measurements in the cases where orbit data and sensor calibration are lacking. The ice motion was determined to be approximately 6.4 + or - 0.5 km/day. In addition, the accuracy of pixel location was found over land areas. The use of one control point in 10,000 sq km produced an accuracy of about + or 150 m, while with a higher density of control points (7 in 1000 sq km) the location accuracy improves to the image resolution of + or - 25 m. This is found to be applicable for both optical and digital data.

Solid-state color TV camera image size control

Abstract: The apparent size of the image produced by a clocked solid-state television imager is controlled by the read clock rate. In a camera using such an imager the clock rate is adjusted to provide an effect similar to zoom. Where a plurality of imagers are used in a color camera, differential control of the clock rate as between the imagers allows compensation for lens chromatic aberration thereby providing for correction of misregistration. In the case where the optical system includes a variable focal length such as a zoom lens, the zoom control is coupled to the size clock control for compensating for the differences in optical power for different colors. The size adjustment may result in a second-order centering error. The centering error is reduced by a scheme for changing the time at which the read clock is gated to the imager in dependence upon the clock rate.

SPECT Resolution and Uniformity Improvements by Noncircular Orbit

Abstract: A noncircular orbit implemented by a combination of rotational and translational motions in single photon emission computed tomography improves significantly the image resolution and uniformity. The former is realized by closer access on the detector to the object at each projection angle, and the latter by suppression of ring artifacts through the shifts in the distance between the centers of detector and object. This has been demonstrated by comparing the SPECT images for an elliptical orbit of 40 cm x 30 cm with the equivalent circular orbit of 40 cm diameter, performed by SPECT system with a high resolution collimator. Resolution FWHM improvements were 1.5 to 2.5 mm. Lesion contrast improved by a factor of 2.8 for a nonradioactive rod of 6 mm diam. In phantom images, the elliptical orbit showed better definition of lesion shape, sharper edge response, and clearly increased detectability. Translational motion reduced ring artifacts, particularly near the image center.

Confocal surface acoustic wave microscopy

Abstract: When the scanning acoustic microscope is used in a defocussed mode to measure surface acoustic wave properties, circular surface wave fronts are generated on the specimen which propagate to a diffraction‐limited focus. Thus, high resolution surface wave images are simply formed and a wide range of established nondestructive testing techniques become available to the acoustic microscope. Images obtained in the reflection mode are presented which demonstrate the unexpectedly high spatial resolution.