Showing papers on "Image quality published in 1982"

Phase Retrieval And Diversity In Adaptive Optics

Abstract: Wavefront sensing by phase retrieval implies extraction of the Fourier transform of a complex signal based on observation of the modulus of the signal Only the image intensity from a system's focal plane array is required to estimate the phase aberrations These estimates are used to derive control signals to align (or to maintain alignment of) the optical system The concept can be used in both a predetection and postdetection mode In the former, the control system labors to keep the optics in a diffraction-limited mode all the time In the latter, the control system induces a phase or wavelength diversity that allows successive images to be restored to nearly diffraction-limited quality by postprocessing of the image This second mode is particularly interesting because it will reduce the design effort for both the optical system and the control system How the phase or wavelength diversity is achieved is not clear at this time If the method has utility, it provides an interesting challenge to designers of optical devices In this paper we describe the mathematics of the technique and show some computer simulations which involve both point sources and extended objects

Optimal short scan convolution reconstruction for fan beam CT

Abstract: The problem of using a divergent fan beam convolution reconstruction algorithm in conjunction with a minimal complete (180 degrees plus the fan angle) data set is reviewed. It is shown that by proper weighting of the initial data set, image quality essentially equivalent to the quality of reconstructions from 360 degrees data sets is obtained. The constraints on the weights are that the sum of the two weights corresponding to the same line-integral must equal one, in regions of no data the weights must equal zero, and the weights themselves as well as the gradient of the weights must be continuous over the full 360 degrees. After weighting the initial data with weights that satisfy these constraints, image reconstruction can be conveniently achieved by using the standard (hardwired if available) convolver and backprojector of the specific scanner.

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.

Picture Quality Prediction Based on a Visual Model

Abstract: Distortion measures are developed for the purpose of predicting the subjective quality of moving monochrome television pictures. The need for such measures is particularly recognized in the area of digital picture coding. Subjectively relevant distortion measures that mirror viewers' assessments of picture quality would make the task of designing and optimizing coding schemes considerably easier. The distortion measures are based on a spatiotemporal model of threshold vision that incorporates the filtering and masking processes. The visual filtering is carried out by parallel excitation and inhibition paths, each of which is separately linear but which combine in a nonlinear way to take account of the adaptation with background luminance. The masking is in the form of a point-by-point weighting of the filtered error based on the amount of spatial and temporal activity in the immediate surround. The processed error averaged over the picture is then used as a prediction of picture quality. Three Classes of distortion measure are considered: 1) the raw error measures that have been used in the past; 2) the filtered error measures where the filtering properties of vision are taken into account; and 3) the masked error measures where the masking processes are also included. It is shown that the filtered error measures are better predictors of picture quality than the raw error measures. The masked error measures lead to further improvements but only if local rather than global averaging procedures are used. It is postulated that this is because viewers tend to base their quality ratings on critical areas rather than on the whole picture.

Multi-function image processing system

Abstract: A system is provided which separates line image data from a complex background by analyzing both contrast and shape characteristics of the image data The system inherently provides image rotations and compression Image quality monitoring is also provided

Generalized holography and computational solutions to inverse source problems

Abstract: The inverse source problem for one- and two-dimensional coherently radiating sources is studied within the framework of generalized holographic imaging. It is shown that the image field produced from a generalized hologram of a one-dimensional source contains a complete description of the source. For such sources, structure larger than one-half wavelength is accurately imaged, whereas information on smaller scales can be obtained from a linear operator applied to the image field. The image fields of two-dimensional sources are shown to contain only partial information about these sources. It is shown, however, that perfect imaging is possible for the class of sources satisfying the homogeneous Helmholtz equation. This class is shown to be identical with the class of minimum energy sources recently encountered in connection with the inverse problem for three-dimensional sources. For noisy images there are serious practical limitations on source detail obtainable from any imaging system; the generalized hologram achieves near-ideal performance when the image is noisy.

A true three-dimensional reconstruction algorithm for the spherical positron emission tomograph

Abstract: A spherical detector configuration in truncated form, consisting of multiple layers of ring detector arrays, can substantially improve the reconstructed image quality in positron emission tomography since all inclined annihilation photon rays can now be used for reconstruction of the image. A new true three-dimensional reconstruction (TTR) algorithm suitable for spherical and quasi-spherical forms of detector arrays is presented. In this algorithm each set of two-dimensional projection data is filtered with a 2-D filter function appropriate to the angular orientations, then back-projected onto the object space in every direction. An example of statistical image quality improvement for this algorithm over the conventional two-dimensional algorithm using only intraplane rays is presented using computer simulation.

A real-time, synthetic-aperture, digital acoustic imaging system

Abstract: We present recent results obtained with a 32-element real-time synthetic aperture acoustic imaging system. The system, which was described at last year’s Acoustic Imaging Conference, has been developed in two main directions. First, a comprehensive testing program has enabled us to diagnose and correct a number of sources of electronic error, and this, coupled with the addition of high quality grey scale display systems, has resulted in greatly improved image quality. Second, in recognizing the need for quantitative as well as qualitative interpretation of NDE images, we have developed a communication channel between the imaging system and a mini-computer. This facility allows us not only to process experimental data collected from the imaging system with greater sophistication than is possible using the real-time hardware alone but also enables us to obtain images synthesized from theoretical models generated in the computer and rapidly reconstructed in the imaging system. This is an extremely useful facility since it is possible to compare the experimental performance of the system directly with what would be expected theoretically.

Development Of A New Digital Radiographic Image Processing System

Abstract: A new digital radiographic image processing system has been developed. The important capabilities of this system include a large image format, high image quality, on-line operation for reading, processing, and writing, and a software package for various types of image processing. A non-linear filtering technique is introduced which improves contrast of radiographic image structure while maintaining low noise in low-density areas. Preliminary clinical results demonstrate the improvements in diagnostic image quality.

The Use of Computers for Image Processing in Nuclear Medicine

Abstract: A survey of various image processing techniques as applied to images in nuclear medicine is presented. These may be classified as procedures to improve detectability, to correct for distortion, to compress, to quantitate and to aid automation. On evaluation, although rather disappointing results from conventional image 'enhancing' techniques have been found, the use of various image 'transforming' procedures seems highly satisfactory and, in particular using array processors, of increasing importance in this field.

Endoscope with image correction means

Abstract: In an endoscope for displaying an image of an object on a monitor screen, a static induction transistor (SIT) image sensor having a number of light receiving elements is arranged at a light emitting side of an image guide bundle. In order to eliminate dead spots appearing in the displayed image due to broken fibers in the image guide bundle, pixel signals of light receiving elements corresponding to the dead spots are formed by interpolation with the aid of pixel signals derived from light receiving elements adjacent to the relevant light receiving elements to be interpolated. As an interpolation function, for example, an average of the pixel signals derived from the adjacent light receiving elements is used. The addresses of the light receiving elements corresponding to the dead spots are stored previously in a PROM during a manufacturing stage. In this manner, the interpolated image of the object having an excellent image quality can be displayed on the monitor.

Digital Imaging For Radiation Therapy Verification

Abstract: A linear diode array was used to scan a radiation field for pulsed high-energy x-ray imaging With a signal of about 50 picocoulombs of charge from each diode for each beam pulse, the signal to noise ratio for an image of an open field was 119 An image of a porcine femur in a wax phantom was obtained by scanning the transmitted radiation The resultant electronic image was superior in quality when compared to the standard radiotherapy port film The simplicity of the detector system has demonstrated the feasibility of constructing an electronic portal imaging system for clinical use

Plate making system for video picture

Abstract: PURPOSE:To perform easily and securely plate making of high quality by reproducing a desired picture signal from a master tape on the bais of a time code and correcting it, and then converting it into an R, G, and B signal and storing them for the plate making. CONSTITUTION:Time codes from a time code memory 37, an external memory 38, etc., are specified selectively through a console panel 50 and a desired picture signal recorded on the one-inch tape of a VTR32 together with a time code is reproduced. This reproduction output is corrected at the picture quality improving part 60 consisting of a time base corrector 61, noise reducer 62, detail corrector 63, etc., to obtain a high-quality picture signal, which is converted by an RGB decoder 52 into an R, G, and B color signal. Then, those color signals are corrected by a gradation correcting part 72 independently of one another and stored on a floppy disk 81, etc., and those storage contents are used to perform easily and securely the high-quality plate making on the basis of the color signals of high quality with excellent resolution without an image picking up a CRT video image by a TV camera.

The elimination of grids during intensified fluoroscopy and photofluoro spot imaging.

Abstract: Grids can significantly increase the contrast of diagnostic radiologic images, but they increase the dose to the patient and staff by a factor of two or more. Image quality with and without grids for fluoroscopic and photofluoro spot imaging of lower gastrointestinal studies has been examined. The authors show that dose reductions between one-third and one-half can be obtained with little or no degradation in contrast and diagnostic image quality if grids are not used for gastrointestinal examinations involving image intensifiers.

Design constraints in computed tomography: A theoretical review

Abstract: The mathematical coupling of various types of measurement errors to image artifacts in conventional computed tomography geometries is derived. Primarily treated are errors which occur at a fixed radius, simple harmonic error fluctuations, and random errors. The results can be used to establish a quantitative relationship between desired image quality and design tolerances on various components of the computed tomographyscanner.

Effects Of Primary Mirror Segmentation On Telescope Image Quality

Abstract: A number of designs for future astronomical telescopes call for large primary mirrors that are mosaics of smaller mirrors. We describe here a study of some characteristics of the images expected from a telescope with a primary mirror composed of 36 hexagonal segments. Various effects caused by the segmentation and imperfections in the segment fabrication and control have been analyzed using physical optics. The diffraction-limited image distribution from the segmentation geometry of the primary is derived, and the diffraction spikes are shown to be similar to those caused by secondary support struts in existing telescopes. A general relation between surface quality and image quality is given, and the implications for surface quality tolerances are discussed. The optical effects of segment phasing errors are derived, showing that at least for visible light observations the phasing is unimportant. For observations at 10 μm near diffraction-limited perfor-mance can be achieved with a 10 meter aperture requiring that the segments be phased correctly at this wavelength.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Experimental Results of Computerized Ultrasound Echo Tomography

Abstract: In a series of experiments on test objects and excised organs we investigated the influence of several physical effects on image quality in the procedure of computerized ultrasound echo tomography. The main results are the following: 1. High resolution of less than one wavelength is demonstrated with simple test objects. This resolution is independent of direction and constant over the whole image plane. 2. Image distortions by interference of waves, well known from B-scans, are strongly reduced. 3. The sensitivity and dynamic range are high and are shown at objects with high contrast. 4. Images of excised organs have essentially better quality than conventional B-scans.

Dome Induced Image Motion

Abstract: "Local seeing" effects degrade image quality with conventional impaired performance of mirror alignment systems. Essential to the design of advanced technology telescopes such as the National New Technology Telescope (NNTT) is a knowledge of these dome-induced image motion effects. Characterization of the turbulent, small scale thermal disturbances had been achieved with differential microthermal sensors able to detect millidegree centigrade thermal gradients with a bandwidth of 100 Hertz. Image degradation associated with dome microthermal activity is shown for sub-arcsecond images. Thermal spectra prepared with Fourier transforms from 0.02 to 65 Hertz show increases in thermal activity as the dome is opened. Relative motion of star pairs as a function of field separation is studied using a CID camera system. Light intensity profiles and centroids are recorded along an axis passing through the two separated stars. The relative motion for the binary star γ Andromeda is presented as image motion correlation spectra from .03 to 15 Hertz.

Evaluation of polychromatic image quality by means of transfer function

Abstract: The polychromatic optical transfer function requires a considerable amount of time for measurement and calculation, which reduces the possibilities of its being applied to the evaluation of opto-photographic systems As a simplification the authors have suggested defining the polychromatic modulation transfer function (PMTF) as a relation of contrasts for sinusoidal tests of several spatial frequencies measured by means of a microdensitometer whose spectral chromatic response is analogous to the human eye Criteria of quality were defined based on the PMTF and in order to study their efficiency in the evaluation of the image quality of colour opto-photographic systems the orders given by the criteria and by the eight observers were compared over a group of images corresponding to different conditions of aberrations The criterion which gave the best evaluation of image quality was the integral of the product of the PMTF by the transfer function of the eye and by the weight function f( nu )= nu

Multiparameter Optimization Of Mammography

Abstract: Analytical expressions have been written for image quality in mammography. A multiparameter optimization has been conducted to find the mammography system requiring the lowest patient dose for a given image quality. The optimization is subject to constraints imposed by technology such as; power limits on tube focal spots, absorption efficiency related to detector resolution and others. The optimization permits system geometry, kVp, filtration, detector resolution, focal spot size and grid characteristics to vary simultaneously and self consistently subject to an exposure time constraint. Significant dose reductions compared to current mammography systems have been found without assuming radical technological advances.

The influence of modulation transfer function shape on computed tomographic image quality.

Abstract: The influence of modulation transfer function (MTF) shape on computed tomographic (CT) image quality was studied by computer simulation of a recently proposed x-ray detector with a nonuniform, shaped response to radiation. The shaped detector, while maintaining a high value of limiting spatial resolution, was shown to depress MTF and signal-to-noise ratio values at moderate spatial frequencies. This led to a significant loss of sharpness on noise-free images. Despite a superior radiation dose capture efficiency in the shaped detector, the MTF suppression was shown to produce inferior visibility of 1.0-mm objects in an image with typical CT noise. The significance for clinical imaging of the MTF suppression was demonstrated using a scan of a human head. The implication is that better methods than those currently used are needed for evaluating CT image quality.

Coherence requirements for partially coherent optical processing.

Abstract: The mutual intensity function for a partially coherent light is used to develop an expression for the output intensity distribution for a broadband optical information processor. The coherence requirement for smeared image deblurring and image subtraction is then determined using the intensity distribution. We also quantitatively show the dependence of coherence criteria on the spectral bandwidth, the source size, deblurring width, spatial frequency, and the separation of input object transparencies.

The effect of a television digital noise reduction device on fluoroscopic image quality and dose rate.

Abstract: In conventional fluoroscopy, the current, and therefore the dose rate, is usually determined by the level at which the radiologist visualizes a just tolerable amount of photon "mottle" on the video monitor. In this study, digital processing of the analogue video image reduced noise and generated a television image at half the usual exposure rate. The technique uses frame delay to compare an incoming frame with the preceding output frame. A first-order recursive filter implemented under a motion-detection scheme operates on the image of a point-by-point basis. This effective motion detection algorithm permits noise suppression without creating noticeable lag in moving structures. Eight radiologists evaluated images of vesicoureteral reflux in the pig for noise, contrast, resolution, and general image quality on a five-point preferential scale. They rated the digitally processed fluoroscopy images equivalent in diagnostic value to unprocessed images.

Image techniques for multiplanar computed tomography.

Abstract: Hardware and software options of the GE 8800 CT scanner were analyzed with respect to their effect on image quality for multiplanar images. Phantom studies were undertaken to demonstrate the effect of collimation, thick pixel reconstruction, and interpolation of both high- and low-contrast multiplanar images. Noise and spatial resolution were measured. Thick pixel reconstruction was found to be most useful in aiding in the delineation of low-contrast lesion boundaries. In addition, this option permits use of lower techniques, thus speeding data acquisition and reducing patient dose. Clinical examples are included.

Image transfer method and apparatus

Abstract: An image quality enhancement scheme is disclosed wherein the image information associated with each line of an image source is transferred to one line of an image receiving medium a plurality of times, the quality of the image information transferred to one line of the image receiving medium gradually improving following each subsequent transfer. A fiber optic cathode ray tube (CRT) transfers the image information to the image receiving medium. An electron beam generator in the CRT traces a plurality of scan lines on the inner faceplate of the CRT. The image receiving medium scrolls across the face of the CRT in synchronism with the trace of each of the scan lines on the inner faceplate thereof. The image information associated with each line of the image source is transferred to the one line of the image receiving medium via the trace of each of the plurality of scan lines. Consequently, following each such transfer via the trace of each corresponding scan line, the quality of the image recorded on said one line of the image receiving medium is gradually improved.

Optimization Of Short Scan Convolution Reconstruction In Fan Beam CT

Abstract: The problem of image reconstruction using a minimal complete set of projection measurements in conjunction with a standard divergent reconstruction algorithm is reviewed. It is shown that by optimally weighting the projection measurements, unimpaired image quality can be obtained. Boundary conditions are developed which minimize boundary discontinuities and resulting streaks in the final image. A simple application of calculus of variations is used to find a set of weights which satisfy the boundary conditions and which minimize second order changes in the weights. Image quality comparable to reconstruction from a full 360° data set is obtained using these weights.

Theoretical Prediction of X-Ray CT Image Quality Using Contrast-Detail Diagrams

Abstract: A theoretical model is developed to calculate contrast-detail diagrams(CDD) that can be used to express the image quality of an X-ray computerized tomography (CT) system. Using the model, CDDs are calculated for third and fourth generation scanners. The quantitative relations between the CT system characteristics and the consequent image quality are presented by means of calculated results.

The influence of picture element size on the quality of clinical radionuclide images

Abstract: The effect of picture element (pixel) size on image quality is investigated. Asked simply to state their preference for clinical images displayed with different pixel sizes, observers preferred those with the smallest pixel. Specific perceptual tasks, however, such as abnormality detection, are found to be insensitive to changes in pixel size up to a limit. Interpolation is found to have no effect on perceptual tasks, but 'random interpolation' produced a more pleasing image than simple linear interpolation.