Showing papers on "Image quality published in 1983"

The k-trajectory formulation of the NMR imaging process with applications in analysis and synthesis of imaging methods

Abstract: The fundamental operations of nuclear magnetic resonance (NMR) imaging can be formulated, for a large number of methods, as sampling the object distribution in the Fourier spatial-frequency domain, followed by processing the digitized data (often simply by Fourier transformation) to produce a digital image. In these methods, which include reconstruction from projections, Fourier imaging, spin-warp imaging, and echo-planar imaging, controllable gradient fields determine the points in the spatial-frequency domain which are sampled at any given time during the acquisition of data (the free induction decay, or FID). The detailed time dependence of the resulting trajectory of sample points (the k trajectory) determines the relative weight and accuracy with which image information at each spatial frequency is measured, establishing theoretical limitations on image quality achievable with a given imaging method. We demonstrate here that these considerations may be used to compare the theoretical capabilities of NMR imaging methods, and to derive new imaging methods with optimal theoretical imaging properties.

Beam Steering with Linear Arrays

Abstract: The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.

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.

Video-enhanced microscopy with a computer frame memory.

Abstract: SUMMARY Video-enhanced microscopy combined with the use of a computer frame memory extends considerably the useful range of our video enhanced contrast (AVEC) methods for polarizing, double-beam interference and differential interference contrast microscopy Increased visual contrast is achieved by two stages of amplifications: the first optical, by using high bias retardation settings, and the second electronic These steps are followed by a reduction of background brightness by means of a clamp voltage applied to a DC restoration circuit of the video camera One of the limitations of the AVEC method alone is the inevitable appearance under high gain conditions of a pattern of mottle due to inaccessible dirt and defects in the lenses even of high quality This limitation has been circumvented by storing the mottle pattern in the frame memory (frame store) and continuously subtracting it from each succeeding frame to clear the image A major gain in image quality has resulted In polarizing microscopy, the frame memory can be used also to subtract the image at one compensator setting from that at the equivalent setting of opposite sign, thus removing from the final image not only most of the mottle pattern but also the contrast due to the bright-field contrast In the polarizing microscope, these manipulations of the raw video image make it possible to observe and measure the birefringence of various organelles and elements such as microtubules, intermediate filaments and bundles of as few as a half dozen actin filaments Since scattered light is also removed from the image, features hidden from view in the unprocessed image become visible In differential interference microscopy, the AVEC method makes visible (ie detectable) many linear elements and particles that are an order of magnitude smaller than the resolution limit and not visible in the optical image Such features are inflated by diffraction, however, to Airy disk size

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

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.

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%.

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.

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.

Parathyroid scanning by computed tomography.

Abstract: Conventional parathyroid computed-tomographic scanning detected 51% (29/57) of tumors averaging 1.5 X 1.0 X 0.8 cm in size at surgery. Forty-six per cent (7/43) of the scans were uninterpretable due to shoulder-streak artifacts. Using a specially designed patient positioning device and a new imaging protocol involving dynamic scanning and the intravenous administration of a bolus of contrast material, 14 patients were scanned; 78% (18/23) of tumors averaging 1.4 X 1.0 X 0.8 cm in size were detected. All 14 scans were interpretable, and image quality was markedly improved.

Image restoration by transformation of signal-dependent noise to signal-independent noise.

Abstract: A transformation to convert signal-dependent noise corrupting an image to additive Gaussian signal-independent noise is derived in this paper. Wiener filtering techniques using a Markovian covariance model for the image signal are applied to the transformed data followed by an inverse transformation to restore the degraded image. An ad hoc technique using contrast manipulation to adaptively convert signal-dependent noise to signal-independent noise is also described. The results of the computer simulations designed to evaluate the performance of these techniques are also presented.

A compatible high-definition television system

Abstract: A compatible HDTV system with the potential of having significantly better picture quality than the present NTSC color TV system is proposed. It realizes an increase in horizontal and vertical resolution and has considerably less crosstalk between the composite signal components compared to the NTSC signal. The increased resolution will allow a display as large as present home projection televisions with a sharper-looking and more detailed image than is possible with the present NTSC system. Also, the elimination of crosstalk adds to picture quality. A large screen size together with improved image quality should provide the user with a feeling of realism and involvement. This system also allows the use of more detailed graphics and more text per page for new services such as teletext.

The application of matched filtering to x-ray exposure reduction in digital subtraction angiography: clinical results.

Abstract: This new digital fluorography processing method of matched filtering generates a set of images that have been acquired at continuous video-frame rates (30 per second) over the temporal extent of the bolus (10 seconds), and it combines them to produce the equivalent of a single digital subtraction angiography (DSA) image. Because of the extensive temporal averaging used, the method can provide substantial x-ray exposure reduction per run as compared with conventional techniques for an equivalent signal-to-noise ratio in the final image. The matched filtering technique was compared with conventional pulsed (one per second) DSA images of both extracranial and intracranial arteries, and the results are presented. Matched filtered images provided image quality that was equivalent to that of conventional DSA images at about one-fourth the patient exposure per run for both carotid artery and cerebral vessel studies. Despite long integration times, patient motion irretrievably corrupted image quality in only two ...

Quantitative Models of Image Quality

Abstract: Fourteen image quality metrics were evaluated for hard-copy and soft-copy displays of digital images degraded by various levels of noise and blur. All quality metrics were formulated to include the displayed modulation spectrum of the image. The statistical analyses suggested that several of the metrics correlated strongly with performance, and, thus, support the proposed utility of image-dependent quality measures. An MTFA-type metric was shown to correlate highest with the average performance scores across noise and blur conditions.

Digital scanned projection radiography: optimization of image characteristics.

Abstract: Fast interactive programs for the investigation of the effects of different processing methods were developed in an attempt to optimize the diagnostic value of digital scanned projection radiography (SPR) data. Filters from two classes of functions with varied frequency characteristics were evaluated. Arbitrary combinations of filtered and unfiltered images were generated. Speed was achieved by implementing the filtering as a convolution operation with standard computed tomography hardware (20 sec/image). The criteria for the choice of the reconstruction parameters are discussed. The clinical results show that suppressing the low-frequency content of the image, as in smoothing, low-pass filtering, and subtracting the background from the original image, optimizes the diagnostic value of SPR images.

Data compression in digital angiography using the Fourier transform.

Abstract: While digital techniques in radiology develop rapidly, problems arise with archival storage and communication of image data. This paper reports on experiments concerning data reduction of digital image sequences of the heart and the brain. The time‐intensity curves corresponding to every picture element are subjected to the Fourier transform and reconstructed from a number of coefficients smaller than the original number of images. The reconstruction error is assessed by visual inspection and by determining the mean‐square deviation of the original and the reconstructed curve. It is shown that compression factors between 5 and 10 may be achieved without loss of diagnostic information. It is furthermore demonstrated that storage of the images in the form of Fourier coefficients leads to advantages in fast retrieval, enhancement of morphology, and possibility of further quantitative analysis.

Image transmission through a turbulent medium using a point reflector and four-wave mixing. 2: Characteristics of the system.

Abstract: The characteristics of the one-way image transmission system presented in Part 1 are investigated in detail [ Appl. Opt.22, 2192 ( 1983)]. First, a general expression of the expectation of the transmitted image is derived for turbulence that may be typical in image transmission in the horizontal direction. Then, with the help of numerical examples, the image quality is discussed in terms of the point spread function for both thin layer and uniformly distributed turbulence. It is shown that the image transmission system is effective especially where turbulence exists relatively close to the transmission plane.

Investigations of the Influence of Hologram Aberrations on the Light Intensity Distribution in the Image Plane

Abstract: The aim in this paper is to analyse, for the examples chosen, the influence of particular aberrations of the point-object hologram on the light intensity distribution in the plane which is assumed to be the image plane. The numerical method used for calculating the light intensity at any image point is that presented in an earlier paper. The calculations have been carried out for three cases of holographic imaging. The recording and reconstruction geometry has been chosen so that it was possible to examine the influence of the particular aberration on the image quality. The calculated energy distribution in the aberration spots is consistent with those resulting from using third-order aberration theory as well as from ‘ray-tracing’ calculations.

Concept Of The Diagnostic Image Workstation

Abstract: The term Image Workstation refers to the image display and processing systems of a PACSwhich are located within a diagnostic imaging department. They shall give access to pic- tures and data according to the work routines. thus beino the interface between a PACS andits users. The paper will describe the role of the diagnostic image workstation. Evidentlycritical but most important will be all functions concerning image handling and display be-cause of the principal differences between a physical image ('hard image') and a displayedimage ('soft image'). The paper will therefore be focussed on the evaluation of requiredimage functions and their general technical solution.The diagnostic workstation - the user's window to a PACSPACS have been discussed at length in terms of key technologies, archiving and communi-cation functions, network topologies etc., in a word, the technical designers perspective.It was the basic objective, however, that a PACS shall assist medical professionals to per-form their work with pictures more efficient and more convenient. Logically, we should alsolook at a PACS from the user's perspective.Rasically, the user will not see much more on his desk than an interactive display. Thiswill be his 'window' to the PACS. Through this window he will look at the PACS as a collec-tion of stores for images and related data, and resources which will guide him to the in-formation desired for his actual work,

Quality Assurance in a National Breast Screening Study

Abstract: In order to provide quality assurance for the National Breast Screening Study currently underway in Canada, a mailed survey package was designed which allows for the monitoring of i) the exposure for the "average" craniocaudad view, ii) beam quality, iii) speed, contrast, and fog parameters of the film processing, and iv) the overall image quality. As well, measurements were made of depth-dose curves to a breast phantom for a number of techniques so that mean glandular dose to the breast could be estimated from entrance exposures. To measure the duration of the x-ray exposure, a device which uses a photodiode to detect scattered radiation from the breast was designed and has been used to check consistency of phototiming and x-ray output. At one centre, the average skin exposure for the craniocaudad view was 295 mR. The range was 150 - 800 mR, due to differences in tissue density and distribution, breast thickness and compression. The mean glandular dose was estimated to be 66 mrad. For the intercomparison of imaging at the centres, identical lucite phantoms have been constructed and distributed which require an exposure time similar to that of the "average" breast. An aluminum step wedge built up of 15 sheets of 0.4mm Al is used to obtain "sensitometric" curves for the mailed survey. Some of the factors responsible for the variation in patient dose and image quality in the study are discussed.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Assessment of Radiological Image Quality by Redundancy : Subject Contrast

Abstract: The relationship between the subject contrast and the total image performance of a radiograph can be assessed by a single number. In this study, the radiological image quality containing object information in two screen-film systems was assessed by the redundancy, C(Y). The quantity C(Y) in the LTII-QS system has a lower value at low subject contrast but a higher value at high subject contrast, compared with the LHII-RX system. The value of C(Y) is affected more by the radiographic mottle of the system at low subject contrast and more by the MTF of the system at high subject contrast.

Restoration of bilinearly distorted images: II. Bayesian method

Abstract: Bayesian estimation methods are applied to the problem of restoring a distorted noisy image. The distortion system is assumed bilinear, i.e., quadratic and with nonzero spread. Noise is Gaussian, additive, and signal independent. An algorithm for determining the maximum a posteriori probability restored image is determined by using the steepest-ascent method. Results are applied to one- and two-dimensional images in a partially coherent diffraction-limited system, and the effect of coherence and noise on image restorability is assessed.

Led array head

Abstract: PURPOSE:To eliminate the lowering in image quality caused by the adhesion of toner to a light emitting part or an image forming element by preventing the penetration of toner or paper dust into a space where LED and the image forming element are opposed, by blocking said space form the open air by using a deformable seal member. CONSTITUTION:A large number of LEDs 17 are linearily arranged to a base board 18 comprising ceramic and a heat dissipating plate 19 is adhered to said base board 18. An image forming element 21 such as a SELFOC lens held by a holding member 20 is provided so as to be opposed to the aforementioned LEDs 17 to constitute an LED array head 5. In this case, an adjustment means 30 for adjusting the distance between the base board 18 and the holding member 20 such as a nut is provided and a deformable seal member (for example, comprising rubber of foamed urethane) 27 surrounding the space 32 between the LEDs 17 and a coupling element 21 is interposed between the base board 18 and the holding member 20. By this mechanism, the distance of a light emitting part and the image forming element 21 is adjusted to enable the optimum adjustment of a focal point. USE:An LED printer using electrophotographic system.

Design and Implementation of Digital Tomographic Filters

Abstract: A technique is proposed which allows the selective filtering of conventional radiographs in order to obtain depth-dependent information by utilizing the depth-dependent information contained therein. This technique, referred to as tomographic filtering or tomographic filtration process (TFP), takes advantage of the finite size of the X-ray source, so that after processing, the image of a particular layer is improved while the others are not. This paper starts with a brief review of technique and then concentrates on the design and implementation of digital tomographic filters. Examples are shown, including images of simulated radiographs processed with such filters. Evaluations of the performance of these filters show that the image quality cannot be as good as that of standard tomography or multiprojection reconstruction techniques; nevertheless they represent an improvement over conventional radiology, and highlight additional depth-dependent information contained in radiographs. This paper concludes with suggestions for further research in this area.

Method and device for processing image

Abstract: PURPOSE:To reduce computing speed of image restructure by determining an ending period for calculation while evaluating repeatedly in each calculation the image improved serially by repeated calculation, and obtain a good quality image. CONSTITUTION:A computer 2 performs image reconfiguration projection data collected in a data collecting division 1, and controls the entire equipment. The restructured image is displayed on an image display device 3, and the image and computed results are stored in a storage device 4. Parameters are inputted by an inputting device 5. The computer 2 performs image reconfiguration with serial approximation, during which time the period for finishing calculation is determined while serially evaluating in every repeated calculation the image serially improved in image quality by repeated calculation.

Arrangement for producing visual images recorded on a disk of film

Abstract: An arrangement for producing visual images recorded on a disk of film includes an imaging system having a solid-state image sensor, which can take a first position where it picks up the whole area of the disk of film, and a second position where it picks up a single frame of image recorded on the disk. A control unit, which is operative in response to manual instructions provided from a keyboard, causes the image sensor to be in its first position during an entire area display mode so that the entire area of the disk will be displayed on a display screen. In an individual frame display mode, the control unit causes the image sensor to be in the second position, in response to a desired frame being designated by the keyboard, so as to display the designated frame on the monitor screen. Video signals developed from the image sensor may be under image processings, such as negative-to-positive inversion, corrections of color balance, and image quality including gradation and tone, in response to information recorded on the disk of film.

Gray scale image thresholding method

Abstract: A method is described for reducing the amount of data that must be transmitted over a telecommunications link in order to generate an acceptable video image of a bilevel document at a remote monitor. Document data is captured at 8 bits/pel with a conventional video freeze-frame system. The captured data is normalized to eliminate variations due to camera settings, room lighting levels and the like. A table lookup process is used to threshold the data to 4 bits/pel with different single pel values being assigned to pels having normalized normalized values above or below set threshold values. The number of intermediate gray scale ranges is reduced. The thresholding process provides log strings of constant pel values while suppressing small nonuniformities in the document's background. The resultant data is opti­ mized for run length compression and the image quality is improved. At the receiver, a second table lookup process is used to define playback values. To provide optimum contrast between characters and background, the table lookup values at the receiver may be different from those used in the compression process.

Digital substraction angiography in the evaluation of intracranial and extracranial vascular disease

Abstract: Digital subtraction angiography (DSA) is a method of visualizing the vessels of the body with the intravenous injection of contrast material. Improvements in computers, television systems, and image intensifiers have contributed to the increased image quality of DSA. With DSA, the vessels such as the carotid bifurcations and the intracranial vasculature can be visualized with a 2–3% concentration of contrast material, while with conventional angiography, the concentration of contrast in vessels is 40–50%. Using IV DSA, visualization of the carotid bifurcations is of good or excellent quality 85% of the time. In a high percentage of these cases, IV DSA replaces conventional angiography, although for imaging of the intracranial vessels, IV DSA is not as good as conventional angiography. In most tumor patients, however, conventional intracranial angiography is not needed because IV DSA combined with computed tomography gives sufficient information.