Spatial Resolution Requirements Research Articles

Spatial Resolution Requirements in Digital Radiography of Scaphoid Fractures

Spatial Resolution Requirements in Digital Radiography of Scaphoid Fractures

An investigation of the spatial resolution requirements for two-point correlation measurements using LDV

The spatial resolution requirements for accurate two-point correlation measurements at small separations are investigated. Practical guidelines in terms of characteristic measuring volume sizes and estimated Kolmogorov length scales are given. Sample measurements of two-point one-component longitudinal correlations on the centerline of a turbulent jet are presented.

Diagnostic usefulness of chest computed radiography--film versus cathode-ray tube images.

Seventy-one plain chest images obtained by computed radiography (CR) with an imaging plate were interpreted on film and two kinds of cathode-ray tube (CRT) monitors installed separately at two facilities (1,024 x 1,536 pixels, 8 bits, and 1,024 x 1,280 pixels, 10 bits) by 20 radiologists and four chest internists. The clinical categories of these 71 cases included pulmonary nodules and interstitial abnormalities. Image reading sessions were held over a total of 4 days, ie, 2 days and then another 2 days, 3 weeks later. Twenty-four observers formed four groups with six members each. Two groups read either films or CRT images at one of the two facilities. In the second experiment, 26 of 71 images were compressed at 10:1, 19 of 71 were compressed at 20:1, and 26 were not compressed. Analyses of the areas under the receiver-operating characteristic curves showed no significant differences in detection of pulmonary abnormalities between film and CRT. In detecting interstitial pulmonary abnormalities, film was more sensitive than CRT monitor. There were no significant differences in observers' performances between the two different kinds of CRT workstation. Subjective evaluation of image quality showed that images irreversibly compressed to the ratios of 10:1 and 20:1 were inferior to original images. Although further considerations are needed with regard to spatial resolution requirements, image processing, and image compression, the utilization of CR CRT image as a substitute for CR film image will be possible.

Telemammography: implementation issues.

Telemammography has the potential to improve access to centralized expertise for the interpretation of breast imaging studies. Digital mammography has more demanding spatial resolution requirements than other forms of medical imaging because of the need to detect microcalcifications, the fine details of lesion margins, and subtle architectural distortion. The resolution requirements for mammography have important implications for image acquisition and display technologies. The large size of the resulting image data sets places significant demands on local and wide area networks as well as storage media. Image data compression will be particularly important for telemammography to help make systems practical and affordable. This article describes how existing technologies can be adapted to implement telemammography systems in the near future.

A Large Area, High-Resolution a-Si:H Array for X-Ray Imaging

ABSTRACTThe development of a large area, high-resolution, a-Si:H x-ray imager is reported. The array has 1536×1920 pixels, a pixel pitch of 127μm, and an area of 19.5×24.4 cm2. Tne array is tailored to the high frame rate and high spatial resolution requirements of diagnostic x-ray imaging. The design of this array is presented and examples of x-ray images are illustrated. Initial Measurements of the sensor capacitance and pixel time constant properties are in good agreement with theoretical expectations. These results indicate that high-resolution arrays of this construction are capable of providing fluoroscopic images at rates of at least 30 frames per second.

Satellite remote sensing of surface energy balance: Success, failures, and unresolved issues in FIFE

The FIFE staff science group, consisting of the authors, developed and evaluated process models relating surface energy and mass flux, that is, surface rates, to boundary layer and surface biophysical characteristics, that is, surface states. In addition, we developed and evaluated remote sensing algorithms for inferring surface state characteristics. In this paper we report the results of our efforts. We also look in detail at the sensor and satellite platform requirements (spatial resolution and orbital requirements) as driven by surface energy balance dynamics and spatial variability. We examine also the scale invariance of the process models and remote sensing algorithms, that is, to what degree do the remotely sensed parameters and energy balance relations translate from the patch level where they were developed to the mesoscale level where they are required? Finally, we examine the atmospheric correction and calibration issues involved in extending the remotely sensed observations within a season and between years. From these investigations we conclude that (1) existing formulations for the radiation balance and latent heat components of the surface energy balance equation are valid at the patch level. (2) Many of the surface physiological characteristics that parameterize these formulations can be estimated using satellite remote sensing at both local and regional scales; a few important ones cannot. (3) The mathematical structures relating radiation and surface energy flux to remote sensing parameters are, for the most part, scale invariant over the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) study area. The conditions for scale invariance are derived. (4) The precision of satellite remote sensing estimates of surface reflectance, calibrated and corrected for atmospheric effects, is no worse than about 1% absolute. The errors may actually be smaller, but an upper bound of 1% results from sampling variance caused by differences among the satellite and ground sensors in spatial resolution, atmospheric effects, and calibration. (5) Afternoon cumulus in the study area required both the Landsat and the SPOT satellites for monitoring of the vegetation dynamics. This result implies the need for multiple polar orbiters, or geosynchronous satellites in an operational implementation. We found that canopy Fpar, the fraction of incident photosynthetically active radiation absorbed by a canopy, can be estimated with an error of about 10% using remote sensing, provided that regional variability in the reflectance of the canopy substrate is dealt with properly. We also found that spectral vegetation indices (VIs) respond primarily to the photosynthetically active radiation absorbed by the live or green component of the canopy as opposed to its necrotic or dead vegetation. This is of critical importance since radiation absorption by the live part of the canopy is the rate‐limiting process for photosynthesis and other key process rates such as evaporation. We found for the FIFE study area the surface moisture content at O to 10 cm to be another key rate‐limiting variable in photosynthesis and evaporation. At gravimetric soil moisture levels below 20%, photosynthesis and evaporation were strongly attenuated. Only microwave sensors have shown potential for satellite remote sensing of soil moisture and only in the top few centimeters. Hydrological models may also play a critical role in monitoring root zone soil moisture levels, but additional research is needed. From our review of the research of others in FIFE we conclude that downwelling shortwave radiation and surface albedo are also amenable to remote sensing. Unfortunately, from our research we also found that the remote estimation of surface temperature to useful accuracies is problematical; consequently, the use of thermal infrared measurements to infer sensible heat flux is probably not feasible to acceptable accuracies.

Spatial resolution and count density requirements in brain SPECT imaging

A set of simulations has been performed to investigate the spatial resolution and count density requirements for brain SPECT imaging. Projections were drawn from a matrix representation of the Hoffman brain phantom. These projections were convolved with realistic point spread functions and Poisson noise was added to simulate a wide range of imaging situations normalized to a fixed imaging time. The projections were optimally smoothed with a Wiener filter and were reconstructed with a ramp filter. The quality of the reconstructed images was determined objectively from the normalized mean square between the simulated data and the true distribution. This ranking was validated against the preferences of a group of trained observers. The results from this study indicate that the optimal choice of spatial resolution (collimation) depends on the available count density.

Quantitative assessment of digitized portal images: effect of sampling frequency on observer performance.

To investigate spatial resolution requirements for digitized portal images in radiation therapy, observer performance tests were performed. One hundred twenty portal images were digitized with sampling frequencies of 0.700, 0.350, and 0.175 mm for observation. Receiver operating characteristic analysis was used to determine the acceptable sampling frequency for clinical portal images. The detectability of setup errors was significantly better on the original images than on the digitized images with sampling frequencies of 0.700 mm (P = .005) and 0.350 (P = .046). Some clinical disadvantages might accrue with the use of a sampling frequency of 0.350 mm or larger.

Improved Resolution Backscatter Coefficient Imaging

This paper reports the extension of a method for imaging acoustic backscatter coefficients that allows for greater spatial resolution in the resulting images. This is done by using a broad-band excitation pulse and short-duration time gates in the analysis. The images produced had better spatial resolution than the previously reported technique [Ultrasonic Imaging 10, 121-138]. Furthermore, the pixel values were based upon quantitatively accurate backscatter coefficients at given spatial locations. The paper also discusses the additional computational requirements of greater spatial resolution and proposes a least-squares fit to a smoothly varying set of sparse data to generate the data points in between.

Improved resolution backscatter coefficient imaging

This paper reports the extension of a method for imaging acoustic backscatter coefficients that allows for greater spatial resolution in the resulting images. This is done by using a broad-band excitation pulse and short-duration time gates in the analysis. The images produced had better spatial resolution than the previously reported technique [Ultrasonic Imaging 10, 121–138]. Furthermore, the pixel values were based upon quantitatively accurate backscatter coefficients at given spatial locations. The paper also discusses the additional computational requirements of greater spatial resolution and proposes a least-squares fit to a smoothly varying set of sparse data to generate the data points in between.

Requirements for Static and Dynamic Spatial Resolution in Advanced Television Systems: A Psychophysical Evaluation

Requirements for Static and Dynamic Spatial Resolution in Advanced Television Systems: A Psychophysical Evaluation

Precision Ion Milling of Layered, Multi-Element TEM Specimens with High Specimen Preparation Spatial Resolution

It is now a requirement in the semiconductor industry to prepare TEM specimens of pre-specified regions with a specimen preparation resolution exceeding 100nm. In other words, given the coordinates x, y, z of the location desired for TEM analysis, the TEM specimen preparation procedure must yield a thin TEM specimen containing the point x, y, z plus or minus 100nm. Preparation of failure analysis specimens in other fields of endeavor, such as: metallurgical, ceramic, composite material laboratories etc., have specimen preparation spatial resolution requirements below one micron in some cases with the likelihood that greater precision will be required in the future.

Quantitative topographic analysis of fractal surfaces by scanning tunneling microscopy

The applicability of models based on fractal geometry to length scales of nanometers is confirmed by Fourier analysis of scanning tunneling microscopy images of a sputter deposited gold film, a copper fatigue fracture surface, and a single crystal silicon fracture surface. Surfaces are characterized in terms of fractal geometry with a Fourier profile analysis, the calculations yielding fractal dimensions with high precision. Fractal models are shown to apply at length scales to 12 Å, at which point the STM tip geometry influences the information. Directionality and spatial variation of the topographic structures are measured. For the directions investigated, the gold and silicon appeared isotropic, while the copper fracture surface exhibited large differences in structure. The influences of noise in the images and of intrinsic mathematical scatter in the calculations are tested with profiles generated from fractal Brownian motion and the Weierstrass-Mandelbrot function. Accurate estimates of the fractal dimension of surfaces from STM data result only when images consist of at least 1000–2000 points per line and 1/f-type noise has amplitudes two orders of magnitude lower than the image signal. Analysis of computer generated ideal profiles from the Weierstrass-Mandelbrot function and fractional Brownian motion also illustrates that the Fourier analysis is useful only in determining the local fractal dimension. This requirement of high spatial resolution (vertical information density) is met by STM data. The fact that fractal models can be used at lengths as small as nanometers implies that continued topographic structural analyses may be used to study atomistic processes such as those occurring during fracture of elastic solids.

Nondisplaced fractures: spatial resolution requirements for detection with digital skeletal imaging.

Fifty-six radiographs of nondisplaced or minimally displaced fractures of the extremities and an equal number of studies with normal findings were selected and digitized to produce spatial resolution varying from 5.75 to 0.72 line pairs per millimeter (1p/mm), corresponding to pixel sizes ranging from 0.08 to 0.64 mm. The conventional and digitized images were evaluated by 10 radiologists, who gave their decision confidence on a graded scale. Receiver operating characteristic analyses were performed from these data to compare the digital images with the conventional radiographs. There was a progressive improvement in observer performance as the pixel size decreased. A pixel size greater than 0.16 mm (2.88 1p/mm) resulted in a significant loss of diagnostic accuracy in comparison with conventional radiographs. Specific fractures in which a larger pixel size adversely affected the evaluation included torus injuries, corner fractures in child abuse, minimal avulsion injuries, and fractures that demonstrated only trabecular disruption.

Spatial resolution requirements for digitizing dental radiographs

A study was performed to determine the appropriate spatial resolution for digitizing and transmitting dental radiographs with the KODAK EKTASCAN, a computer-based digital enhancement and transmission system Periapical, bitewing, and panoramic radiographs were digitized in three formats representing varying spatial resolution parameters. Eight viewers used a 5-point rating scale to evaluate the detectability of periapical pathosis on the periapical images, of proximal surface caries on the bitewing images, and of various bony abnormalities on the panoramic images. Receiver operating characteristic curves were generated, and the results of the periapical, bitewing and panoramic experiments were presented as trapezoidal and maximum likelihood receiver operating characteristic curve areas. The results of this study indicate that digital images of dental radiographs provide adequate diagnostic accuracy for evaluating the presence of periapical pathosis, proximal surface caries, and specified bony abnormalities. The digitization parameters established for the KODAK EKTASCAN provide a guide for digitizing dental radiographs on other commercially available digital image-processing system.

Methods of measuring myocardial blood flow in humans

T HE DEVELOPMENT OF cardiac catheterization, begun by Forssmann and Cournand in the 1930s and 194Os, opened cardiac hemodynamic investigations to clinical investigators studying pathologic states in humans, thus removing the necessity of relying entirely on information obtained from animal experimentation. Despite the early development of clinical methods for measuring pressure in cardiac chambers and great vessels, and total flow emanating from the heart, techniques for quantitating flow to selected organs have been slow to develop. This has been particularly true for coronary blood flow measurements in humans. Over the past several decades, advances in measurement technologies have allowed physiologists to obtain a sophisticated understanding of regulation of coronary blood flow in animals. However, most of these techniques, developed and used for animal investigations, have not been directly transferable to human patients. Until relatively recently, only global left ventricular perfusion could be measured in conscious humans. The spatial resolution of commonly used techniques to measure myocardial flow in humans was crude, and the temporal resolution poor. These unsophisticated approaches contrast strikingly with the elegant methods available for animal studies, which allow perfusion in the myocardium to be measured with a spatial resolution in microns’ and a temporal resolution in milliseconds.* The necessity of relying on global coronary flow for estimates of regional perfusion is particularly inappropriate for the myocardium, since regional heterogeneity in perfusion is the rule in atherosclerotic coronary artery disease, and not infrequent in other pathologic states. The requirements for spatial resolution of perfusion in the myocardium are doubly demanding, since in addition to sophisticated lateral edge detection, an ideal measurement technique should be able to detect transmural differences in perfusion. The requirements for temporal resolution of perfusion in the myocardium are also stringent, since metabolic and neurogenic factors can alter coronary flow over a wide range with very short time constants. It is not surprising that because of the severe restraints imposed by the nature of the target organ, no one technique approaches that which would be considered ideal. Such an ideal method for measuring coronary blood flow in humans would allow detailed spatial resolution, have a rapid frequency response, allowing it to detect phasic changes in flow, and be minimally invasive. Unfortunately, no such ideal method presently exists. The purpose of this review is to evaluate those techniques that are in present use for measuring myocardial blood flow in humans. Newer techniques under active investigation will also be briefly examined. Emphasized in this discussion will be those techniques with which the authors have the greatest personal experience. The advantages and limitations of each technique will be compared to a theoretic ideal agent. The methodologies will be grouped into the following categories: electromagnetic flow meters, diffus-

The effect of photoreceptor coupling and synapse nonlinearity on signal:noise ratio in early visual processing.

Electrical coupling of vertebrate photoreceptors is well known to improve the signal: noise ratio in the photoreceptor layer for large-area stimuli. For example, if N photoreceptors are perfectly coupled to each other, the signal: noise ratio is improved for stimuli illuminating more than a number M = square root of N of the receptors but is made worse for small-area stimuli illuminating less than M of the N receptors. Using the model of Lamb & Simon (J. Physiol., Lond. 263, 257 (1976], which treats the photoreceptor layer as a square array of cells, each coupled through a resistive gap junction to the four cells around it, we show that the signal:noise ratio for small-area stimuli is much greater than would be expected from a model in which receptors are assumed to be perfectly coupled. Contrary to predictions made assuming perfect coupling, receptor coupling should not prevent rods from detecting single photons, but whether the single photon signal can be detected at the bipolar cell level depends on how signals are read out of the receptor layer. The signal:noise ratio in bipolar cells postsynaptic to the photo-receptor layer is determined partly by synaptic convergence and nonlinearity in synaptic transmission from receptors. If the synaptic gain decreases with light-induced receptor hyperpolarization, as is found experimentally, then receptor coupling can improve the postsynaptic signal:noise ratio for stimuli illuminating only one receptor, even though coupling decreases the presynaptic signal:noise ratio for such stimuli. Moreover, increasing the number of coupled receptors projecting to a bipolar cell can improve the signal:noise ratio for localized stimuli if the synapse is sufficiently nonlinear (although, for the degree of nonlinearity seen in lower vertebrates, synaptic convergence makes the ratio worse for the single photon event). The fact that receptor coupling and synaptic convergence can, under some circumstances, improve the signal:noise ratio in bipolar cells suggests a principle of retinal design that may compete with the requirements of high spatial resolution.

Spatial resolution requirements in the fabrication of branching optical waveguides

A multimode optical waveguide trunk that branches into several single-mode waveguides, all of different cross sections, can route each of the modes of the trunk into a different output channel. Such branching waveguides (branches) are important in splitting and recombining optical signals in guided-wave optoelectronic devices. In practical optical waveguide branches, however, the channel separation is not achieved continuously, but rather by discrete increases in the distance between the branching channels. We show that this finite resolution in the pattern of branching waveguides may give rise to an increased intermode crosstalk, which severely deteriorates the mode routing features of these devices. This increased crosstalk arises from constructive interference of the scatterings which occur at the discontinuities along the branch. Our analysis provides design guidelines for minimizing this intermode crosstalk.

Microtomography Detector Design: It's Not Just Resolution

The design of an x-ray detector suitable for use in tomography must be optimized for the intended application. Recently, we have developed microtomography applications that require resolution of -1 micron in three spatial dimensions and -1% statistical accuracy in the reconstruction of attenuation coefficients for each cubic micron volume element in a .1 cubic mm specimen. X-ray detector design for these applications must take into account much more than just the demanding micron spatial resolution requirement. The detector must be optimized to take into account the physical properties of the specimen to be measured, the characteristics of the x-ray beam available to probe the specimen, signal to noise ratios needed in the reconstructed image and requirements of the data processing algorithm. In addition, the detector design should be sufficiently flexible to allow significant variation in the kinds of specimens that can be examined.

Spatial and photometric resolution and calibration requirements for cell image analysis instruments

Digital imaging systems intended for use in quantitative cell image analysis must meet stringent requirements on both photometric and spatial resolution to support the type of investigations currently ongoing in the biomedical research community. There must be a match between the optics (microscope), the image sensor (camera), the image digitization and storage hardware, and the algorithms for quantitative analysis of the digitized images. Applicable theory from the fields of optics, electronics, statistics, and signal processing allows development of workable rules for designing such a balance.