Showing papers on "Image quality published in 1986"

Enhancement of Mammographic Features by Optimal Adaptive Neighborhood Image Processing

Abstract: X-ray mammography is the only breast cancer detection technique presently available with proven efficacy. Mammographic detection of early breast cancer requires optimal radiological or image processing techniques. We present an image processing approach based on adaptive neighborhood processing with a new set of contrast enhancement functions to enhance mammographic features. This procedure brings out the features in the image with little or no enhancement of the noise. We also find that adaptive neighborhoods with surrounds whose width is a constant difference from the center yield improved enhancement over adaptive neighborhoods with a constant ratio of surround to center neighborhood widths.

Optimal coherent image amplification by two-wave coupling in photorefractive BaTiO3

Abstract: Coherent image amplification by two-wave coupling in a crystal of photorefractive BaTiO3 is analyzed. This amplifier is optimized with respect to such operational characteristics as gain versus amplified image quality and space-bandwidth product. Experimental results that demonstrate coherent image amplification of 4000, space-bandwidth product of 1,000,000, and gray-level dynamic range of greater than 100 are presented.

Image rendering by adaptive refinement

Abstract: This paper describes techniques for improving the performance of image rendering on personal workstations by using CPU cycles going idle while the user is examining a static image on the screen. In that spirit, we believe that a renderer's work is never done. Our goal is to convey the most information to the user as early as possible, with image quality constantly improving with time. We do this by first generating a crude image rapidly and then adaptively refining it where necessary as long as the user does not change viewing parameters. The renderer operates in a succession of phases, first displaying only vertices of polygons, next polygon edges, then flat shading polygons, then shadowing polygons, then Gouraud shading polygons, then Phong shading polygons, and finally anti-aliasing. Performance is enhanced by each phase using results from previous phases and trimming the amount of data needed by the next phase. In this way, only a fraction of the pixels in an image may be Phong shaded while the rest may be Gouraud or flat shaded. Similarly anti-aliasing is performed only on pixels around which there is significant color change. The system features fast response to user intervention, encourages user intervention at any moment, and makes useful the idle cycles in a personal computer.

The field dependence of NMR imaging. II. Arguments concerning an optimal field strength.

Abstract: Some of the factors involved in the choice of field strength for NMR imaging are examined. The influences of relaxation times and chemical shift upon image quality and signal-to-noise ratio are highlighted, and power deposition is introduced as a significant factor which may limit the flexibility and information available at higher fields as long as 180 degrees echo pulses continue to be necessary. Chemical-shift imaging is examined and found wanting as a means of coping with chemical-shift artifacts, and the use of multiple echoes (albeit with research) in conjunction with multiple-slice techniques is advocated as representing an efficient data-gathering scheme which can improve image signal-to-noise ratio. With such use, a medium field strength (0.5-1 T) is presented as representing, for general purpose imaging of head and torso, the best current compromise when imaging time is of major importance, with the important caveat that new techniques may always invalidate this conclusion.

SPECT liver imaging using an iterative attenuation correction algorithm and an external flood source

Abstract: The results obtained from the inclusion of a new intrinsic attenuation correction algorithm into a protocol for SPECT liver imaging are presented in this study. A total of six patients were evaluated with this protocol. The new algorithm uses a transmission tomographic acquisition that is obtained before a standard emission tomograph, and requires the use of an external flood source. The transmission tomograph results in an attenuation image, or map, of the patient. The attenuation map then serves as input into the final intrinsic correction algorithm, that also uses data from a standard emission acquisition. The results of the six patients studied show that the algorithm can correct for attenuation effects without degrading image quality. In all the cases studied, the attenuation corrected images made the cases easier to interpret than did the images obtained without attenuation correction.

Respiratory effects in two-dimensional Fourier transform MR imaging.

Abstract: Respiratory and other regular motions during two-dimensional Fourier transform magnetic resonance imaging produce image artifacts consisting of local blurring and more or less regularly spaced "ghost" images propagating along the direction of the phase-encoding magnetic field gradient The patterns of these ghost artifacts can be understood in terms of the technique of image production and basic properties of the discrete Fourier transform This understanding permits, without respiratory gating, production of images of improved quality in body regions in which there is significant respiratory motion In particular, the ghosts can be maximally separated from the primary image by choosing intervals between phase-encoding gradient pulse increments that are equal to one-half the respiratory period; they can be minimally separated by choosing an interval equal to the respiratory period Increasing the number of signal averages between each phase-encoding increment decreases the intensity of the ghosts

Optical image quality and the cone mosaic

Abstract: Contrary to the orthodox view that optical image quality should "match" the photoreceptor grain, anatomical data from the eyes of various animals suggest that the image quality is significantly superior to the potential resolution of the cone mosaic in most retinal regions. A new theory is presented to explain the existence of this relation and to better appreciate eye design. It predicts that photoreceptors are potentially visible through the natural optics.

Phased array ultrasound imaging through planar tissue layers

Abstract: Conventional ultrasound imaging devices are designed based on the assumption of a homogeneous tissue medium of constant acoustic velocity = 1540 m/sec. However, the body consists of tissue layers of varying thicknesses and velocities which range from 1470 m/sec in fat to 3200 m/sec in skull bone. Refraction effects from these layers degrade ultrasound image quality. In this paper, pulse-echo ultrasound imaging is modeled as imaging an organ of interest through an intervening planar tissue layer, such as liver through fat in the abdomen or brain through skull bone in the adult head. Refraction effects from planar tissue layer interfaces are analyzed using Snell's law and measured using phantoms. We also introduce an on-line phased array correction technique based on planar tissue layers to restore ultrasound image quality. We conclude that fat/organ planar interfaces do not degrade image quality significantly. However, refraction effects at a skull/brain planar interface degrades resolution and target acquisition and introduces geometric distortion. Our plane layer phased array correction technique significantly improves image quality in phantoms through lucite aberrators and improves adult cephalic ultrasound image quality when used through the top of the adult skull. The correction technique is robust even in the presence of inaccurate estimates of skull thickness.

Compressed quantized image-data transmission technique suitable for use in teleconferencing

Abstract: A technique for transmitting compressed quantized image-data from a transmitter to a receiver over a limited bandwidth communication channel employs temporal differential pulse code modulation incorporating pyramid image processing spectrum analyzers and synthesizers. This technique permits the selective elimination by data-compression of only those portions of the original image information which contribute least to the perception of image quality by a viewer of a synthesized display image at the receiver.

Magnetic resonance imaging artifacts: mechanism and clinical significance.

Abstract: Many types of artifacts may occur in magnetic resonance imaging. These artifacts may be related to extrinsic factors such as patient motion or metallic artifacts; they may be due specifically to the MR system such as power gradient drop off and chemical shift artifacts; they may occur as a consequence of general image processing techniques, as in the case of truncation artifacts and aliasing. Change in patient position, pulse sequence, or other imaging variables may improve some artifacts. Although reduction of some artifacts may require a service engineer, the radiologist has the responsibility to recognize MR imaging problems. The radiologist's knowledge of MR imaging artifacts is important to the continued maintenance of high image quality and is essential if one is to avoid confusing artifactual appearances with pathology.

A Statistical Method For Adaptive Stochastic Sampling.

Abstract: Stochastic sampling is a good alternative to pure oversampling in terms of image quality. A method for adaptively controlling the number of required samples to the complexity of the picture is presented. The quality of the obtained picture can be controlled by two well-understandable parameters, these parameters define an error interval size and the probability that a pixel lies within it. The usefulness of the method is described by applying it to distributed ray-tracing.

Digital restoration of indium-111 and iodine-123 SPECT images with optimized Metz filters.

Abstract: A number of radiopharmaceuticals of great current clinical interest for imaging are labeled with radionuclides that emit medium- to high-energy photons either as their primary radiation, or in low abundance in addition to their primary radiation. The imaging characteristics of these radionuclides result in gamma camera image quality that is inferior to that of 99mTc images. Thus, in this investigation 111In and 123I contaminated with ∼4% 124I were chosen to test the hypothesis that a dramatic improvement in planar and SPECT images may be obtainable with digital image restoration. The count-dependent Metz filter is shown to be able to deconvolve the rapid drop at low spatial frequencies in the imaging system modulation transfer function (MTF) resulting from the acceptance of septal penetration and scatter in the camera window. Use of the Metz filter was found to result in improved spatial resolution as measured by both the full width at half maximum and full width at tenth maximum for both planar and SPECT studies. Two-dimensional, prereconstruction filtering with optimized Metz filters was also determined to improve image contrast, while decreasing the noise level for SPECT studies. A dramatic improvement in image quality was observed with the clinical application of this filter to SPECT imaging.

Respiration artifacts in MR imaging: reduction by breath holding.

Abstract: Respiratory motion commonly produces degradation of image quality on magnetic resonance scans of the upper abdomen due to artifacts produced in the direction of the phase encoding gradient. Such artifacts may be reduced, although not eliminated, on image sequences obtained with relatively short acquisition times by means of breath holding during the middle 20% of the sequence.

Scatter correction algorithm for digitally acquired radiographs: theory and results

Abstract: A scatter correction algorithm for digitally acquired radiographs (SCADAR) is presented. SCADAR requires the acquisition of two digital images, taken at different object-to-detector distances. These two images are digitally magnification compensated, and subtracted. The primary component in the resulting difference image delta is mathematically eliminated, and hence the delta image is used as a measure of the local contribution of scattered radiation. A gray scale transformation is used to transform the delta image to a scattered component image, which is then smoothed by Fourier filtering, using a matched filter to increase the signal-to-noise ratio. The smoothed scatter image is then subtracted from its corresponding original image, resulting in the corrected SCADAR image. Implementation of SCADAR can result in a large increase in image contrast, and a significant reduction in shading due to scattered radiation effects. The mathematical derivation of the algorithm is developed, and experimental verification is given for some of the principles used. Using experimental images acquired from scattering phantoms, the results of SCADAR on various image parameters such as contrast and detail signal-to-noise ratio are discussed.

An X-ray examination apparatus with a locally divided auxiliary detector

Abstract: Incorporated in an X-ray examination apparatus is a detector array 32 for the detection of the image-carrying beam 10, which array is set up in such a manner that image information from substantially the entire output screen of an X-ray image-intensifier tube incorporated in the apparatus can be detected. The detector array is used for brightness control and for adaptation of the quantities influencing the image quality, in which process use can be made of a measured field which can be programmed to be selected, to be positioned and to be set and in which process spatial image information can also be used by the matrix form of the detector.

Progressive Coding and Transmission of Digital Diagnostic Pictures

Abstract: In radiology, as a result of the increased utilization of digital imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), over a third of the images produced in a typical radiology department are currently in digital form, and this percentage is steadily increasing. Image compression provides a means for the economical storage and efficient transmission of these diagnostic pictures. The level of coding distortion that can be accepted for clinical diagnosis purposes is not yet well-defined. In this paper we introduce some constraints on the design of existing transform codes in order to achieve progressive image transmission efficiently. The design constraints allow the image quality to be asymptotically improved such that the proper clinical diagnoses are always possible. The modified transform code outperforms simple spatial-domain codes by providing higher quality of the intermediately reconstructed images. The improvement is 10 dB for a compression factor of 256:1, and it is as high as 17.5 dB for a factor of 8:1. A novel progressive quantization scheme is developed for optimal progressive transmission of transformed diagnostic images. Combined with a discrete cosine transform, the new approach delivers intermediately reconstructed images of comparable quality twice as fast as the more usual zig-zag sampled approach. The quantization procedure is suitable for hardware implementation.

Digital beam attenuator technique for compensated chest radiography.

Abstract: The feasibility of producing patient-specific beam attenuators for chest radiography has been investigated using an anthropomorphic phantom and a human volunteer. A low-dose test exposure is digitized, processed, and used to print a small cerium filter, which is placed in the x-ray beam near the collimator. The final radiograph is recorded on film. The technique results in relatively uniform film exposure, so that structures in all regions of the chest are simultaneously displayed with optimal film contrast. The equalized exposure improves image quality in the normally underpenetrated regions and reduces the role of cross-scatter from the lungs. The image is analogous to optical or computer-processed unsharp masking techniques, but the processing is accomplished in the x-ray beam and results in an improved exposure distribution, giving advantages that cannot be achieved with image processing techniques alone.

Beyond Signal-Detection Theory

Abstract: Assessment of image quality is an important and long-standing problem. To the user of a medical imaging system, it is important to be able to determine the expected performance of the system in various clinical applications. For the system designer, it is important to know how alteration of various design parameters influences performance.

The observation, calculation, and possible forecasting of astronomical seeing

Abstract: The possibility of forecasting seeing quality from routine meteorological data used as input to a numerical model of the boundary layer is discussed after demonstrating examples of reasonably good agreement between observed and calculated seeing on three nights when observed image diameter did not exceed 2 arc sec. Under poor seeing conditions (5 arc sec) agreement was not achieved. The comparisons were made between optical measurements by the Anglo-Australian Observatory and calculations based on temperature soundings from an aircraft and an empirical relationship for estimating dome seeing effects. It is argued that even limited seeing forecasts would assist in optimizing the observing schedules of highly utilized telescopes. A numerical model appears useful to predict C2N profiles of the atmosphere but cannot handle dome seeing effects, which often constitute a significant contribution to overall image quality.

Scanning recording type printing method and apparatus for realizing the same

Abstract: A scanning recording type printing method, by which a pixel recroding pulse signal (S) is produced by comparing a comparison data signal (DB), which is formed by repeating an up counting operation and a down counting operation for every pixel, which is the smallest unit region of an image, with a depth data signal (DA) for one scanning line and the location of each of net points of at least one color printed within a pixel is controlled by the pixel recording pulse signal (S) so that worsening of the image quality in a high precision fine image printing can be reduced.

Frequency and Spatial Compounding Techniques for Improved Ultrasonic Imaging

Abstract: One of the key limitations in ultrasonic imaging results from clutter signals corresponding to a large number of coherent, unresolved and randomly distributed reflectors located around the desired target. The backscattered echoes from such reflectors can severely deteriorate the image quality to the point of concealing the desired target. This fundamental problem which exists in many imaging and detection problems cannot be eliminated by conventional noise reduction techniques such as time averaging. However, in recent years clutter suppression has been achieved in A-scan applications using some novel frequency and spatial compounding techniques, where the clutter signals are decorrelated by shifting the transmitted frequency or the transducer position, respectively, prior to processing. In the work presented, these techniques are extended to imaging applications and evaluated using experimental data obtained from large grained samples. The experimental results indicate that the frequency and spatial compounding techniques are capable of improving the image quality beyond the conventional averaging techniques.

Digital data transmission method

Abstract: A method for transmitting digital video signals wherein spectral values are sorted according to magnitude and leading zeros are suppressed. In this way, the average word per pixel length can be reduced to about 1 bit, with image quality remaining acceptable.

Real-time image enhancement in NMR

Abstract: Clinical NMR motion picture (movie) images can be produced routinely in real-time by ultra-high-speed echo-planar imaging (EPI). The single-short image quality depends on both pixel resolution and signal-to-noise ratio (S/N), both factors being intertradeable. If image S/N is sacrificed rather than resolution, it is shown that S/N may be greatly enhanced subsequently without vitiating spatial resolution or foregoing real motional effects when the object motion is periodic. This is achieved by a Fourier filtering process. Experimental results are presented which demonstrate the technique for a normal functioning heart.

Evaluation of ion microscopic spatial resolution and image quality

Abstract: : This study of factors that influence image quality in the ion microscope will motivate modification of the existing configuration in order to improve the lateral resolution and the absolute sensitivity. The micro-test patterns provide an absolute scale of image evaluation and thus are used to characterize the imaging capabilities of the SIMS analyzer. The efforts anticipate the decreasing dimensions of the next generation of submicron structures. Additional keywords: spectroscopy; analytical chemistry. (Author)

Improvement of Lesion Detection in Scintigraphic Images by SVD Techniques for Resolution Recovery

Abstract: The properties of singular value decomposition (SVD) are used to implement an SVD spatial domain pseudoinverse restoration filter. This type of filter is attractive for poor imaging conditions (low spatial resolution, high image noise) and is thus appealing for nuclear medicine images. The method might offer some advantages over more traditional frequency domain filter techniques since the restoration is performed on a local rather than global basis. High-contrast thyroid phantom images collected at different count densities and low-contrast liver phantom images were processed with the SVD filter. Restored images yielded improved spatial resolution, lesion contrast, and signal-to-noise ratio. The SVD pseudoinverse restoration filter implemented as an interactive process permits the operator to terminate filtering at a stage where the visually "best" image is obtained compared to the original data. Processed images suggest that the technique may have potential for improving lesion detection in nuclear medicine.

On the parameters of human visual performance: an investigation of the benefits of antialiasing

Abstract: A two-part experiment was conducted to investigate the effects of aliasing artifacts and screen resolution on a simple visual recognition task. The results indicate that in many cases far less realism may be necessary in synthetic computer-generated imagery than is often assumed in the literature. The first part of the experiment comprised a subjective rating of image quality, the second part measured task effectiveness of image quality. In the second part subjects were asked to discriminate between images of two types of objects built from cubes, similar to objects used in experiments involving mental rotation.At higher resolutions the elimination of aliasing artifacts did not significantly improve subjects' performance. At intermediate and low resolutions, comparable to what might be used for iconic menus, the reduction in aliasing artifacts resulted in improved performance. The subjective ratings indicate that for both high and low resolution the elimination of aliasing artifacts does not improve “quality,” whereas images rendered at intermediate resolutions are significantly degraded by aliasing artifacts to the extent that antialiasing improves the subjective rating.An interpretation of these results is given in the context of an ongoing research program aimed at identifying the parameters of real-time human performance for graphics workstations.