Computer-simulated lung nodules in digital chest radiographs for detection studies.

Computer simulations of lung nodules overcome many shortcomings of creating radiographs using anthropomorphic nodule phantoms for lung nodule detection studies, but these algorithms can be cumbersome and involved. A simple, fast, and flexible computer program to simulate lung nodules in digital chest radiographs for detection studies is reported. To verify the realism of the simulated nodules, a psychophysical study and a statistical study were conducted. In the psychophysical study, six radiologists and four nonradiologists were asked to distinguish between 17 real lung nodules and 17 computer-simulated lung nodules shown in eight radiographs. The results show that the computer-simulated lung nodules are indistinguishable visually from real lung nodules. Using parameters from the Rose model of vision, results show that the simulated and real nodules are the same statistically. Thus, besides visual validity, statistical analysis in confirming the validity of the simulated lung nodules is included.

Evaluation of the ACR-NEMA standard for communications in digital radiology.

An implementation and evaluation of a prototype multivendor communications system which complies with the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) standard for communications in digital radiology is discussed. The system allows communications between interfaces from different manufacturers within a networked environment. The implementation includes network software compatible with the International Standards Organization's Open Systems Interconnect standard. The experience of the implementation effort and the evaluation of the system provide the basis for a critique of the ACR-NEMA standard. It is concluded that the ACR-NEMA standard is not well suited for application to the networked environment of picture archiving and communications systems. Two possible solutions are recommended for this problem. The first is a major revision of the existing standard. The second is the development of a family of network communications standards for digital radiology.

Design and testing of artifact-suppressed adaptive histogram equalization: a contrast-enhancement technique for display of digital chest radiographs.

One of the goals of our research in the field of digital radiography has been to develop contrast-enhancement algorithms for eventual use in the display of chest images on video devices with the aim of preserving the diagnostic information presently available with film, some of which would normally be lost because of the smaller dynamic range of video monitors. The ASAHE algorithm discussed in this article has been tested by investigating observer performance in a difficult detection task involving phantoms and simulated lung nodules, using film as the output medium. The results of the experiment showed that the algorithm is successful in providing contrast-enhanced, natural-looking chest images while maintaining diagnostic information. The algorithm did not effect an increase in nodule detectability, but this was not unexpected because film is a medium capable of displaying a wide range of gray levels. It is sufficient at this stage to show that there is no degradation in observer performance. Future tests will evaluate the performance of the ASAHE algorithm in preparing chest images for video display.

Standardization of network addressing in picture archiving and communications systems utilizing the ISO OSI protocols.

The establishment of a communications network requires the definition of addressing schemes to identify systems attached to the network. When it is anticipated that such a network will interconnect to, or communicate with, other similar networks it is beneficial to define standardized addressing schemes. This paper discusses the need for the standardization of network service access point (NSAP) addresses in picture archiving and communications systems (PACS) which use the open systems interconnect (OSI) communications protocols. Possible methods for establishing the necessary hierarchy of address registration authorities are discussed, along with the corresponding address formats.

Correlelogram stereo display: computer simulations.

Computer simulations are presented of a correlelogram stereo-display screen. First, an underlying physical model of the correlelogram is developed. A program for generating stereo pairs is then described. Next, the calculation of the layer transmissions for the correlelogram is discussed. Finally, several synthesized image pairs are presented.

Tomosynthesis and computer tomography: a continuous description with examples.

A continuous, as opposed to sampled, mathematical description applicable to 3-D image reconstruction from 2-D projections is applied to three examples. These examples are computer tomography, tomosynthesis, and coded-source tomosynthesis. The effects of various projection filtering procedures on reconstructed image quality are discussed for each example.

Magnitude-coupled phase quantization.

A method is described for minimizing Fourier-domain phase-quantization noise in the image reconstructed from a computer-generated hologram. This method uses manipulation of the hologram magnitude to counteract the deleterious effects of phase quantization.

Deterministic diffusers for holography.

We present here a new family of diffusers suitable for use in holography. We first exhibit a method for obtaining mathematical descriptions of diffusers that give nearly uniform amplitude at the hologram before insertion of an object. From these diffusers we select a few that redundantly map information into the hologram. Finally, we present a method of comparing the performance of different diffusers using a computer simulation technique that has a simple experimental analog.

Volume holograms constructed from computer-generated masks.

A new type of hologram that combines computer-generated holograms with volume holograms is described. This hologram allows arbitrary selection of the location and color of a computer-generated image when white light illumination is used. Potential applications include optical information processing, holographic optical elements, multicolor displays, and lens testing. Calculations are made to determine the range of wavelengths possible for image reconstruction. Experimental results are given and discussed.

Phase quantization in holograms-depth effects.

A three-dimensional holographic image is deteriorated due to quantization of the phase in the hologram. As in two-dimensional Fourier holograms, the deterioration is exhibited as a superposition of false images. However, in the three-dimensional case, the false images fall at depth positions other than the plane of the image to which they correspond. If far out of focus, these false images are harmless.

Simplified production of spatial inverse filters.

A logarithmic nonlinearity in the transmittance-versus-exposure curve of a photographic material can greatly simplify holographic fabrication of inverse filters. We present here two filter-production methods utilizing this non-linearity, which produce relatively high-dynamic-range inverse filters. Confirming computer simulations and coherent-optical experiments are presented.

Multispectral size-averaged incoherent spatial filtering.

A method of 2-D size-averaged incoherent recognition filtering is described. White light input illumination is used to multiplex chromatically a continuum of inputs differing in their spatial Fourier spectral magnifications. A two-grating dichromated-gelatin lateral-dispersion compensating device is inserted to correct chromatic dispersion introduced by a computer-generated hologram filter. The resulting registered recognition patterns are added to form a single effective filter size-averaged recognition peak. Using high efficiency compensating gratings and a bleached binary hologram allow the use of a relatively low-power light source.

Finite-length line-spread function.

In this paper we derive a formula for calculating the point-spread function (PSF) of a rotationally symmetric imaging system from measurements along a line through the image of an arbitrary separable input object. An important special case of this formula is when the input object is a finite-length slit. The set of measurements in this case is called the finite-length line-spread function (FLSF). The FLSF differs from the infinite-length line-spread function (LSF) only in the assumed finite length of the line that is input into the system. This difference between the FLSF and the LSF becomes important for imaging systems for which the PSF is large in extent and in which the isoplanatic patch is relatively small. The usual LSF-to-PSF conversion formulas cannot be applied accurately to such systems.

Linear estimation theory applied to the reconstruction of a 3-D vector current distribution.

Linear estimation theory incorporating statistical a priori knowledge is applied to the inverse problem of reconstructing a static 3-D vector source field from another 3-D vector measurement field. The motivation for this development is to reconstruct 3-D electric current distributions from a set of magnetic measurements. Such a capability would be useful for the clinical determination of neural currents, for example. A simulation is presented to demonstrate the reconstruction of a class of simple nonbiological source objects, and to show the dependence of these reconstructions on the data taking configuration and the statistical a priori knowledge that is incorporated into the reconstruction process.