Jacob Beutel

The image quality characteristics of a novel ultra-high-resolution film/screen system

A film/screen system is described where the light emission of the intensifying screen is in the ultraviolet (UV), which is more efficiently absorbed by the film, and hence print-through is virtually eliminated. In addition, because of significantly higher UV absorption within the screen, the modulation transfer function is superior to that of conventional systems based on visible light. Thus the overall UV film/screen system has superior imaging efficiency and quality, as measured by the detective quantum efficiency and the noise equivalent quantum efficiency to those of conventional systems. These imaging characteristics of the novel systems are described and are compared with those of some conventional systems.

Application of neural networks to computer-aided pathology detection in mammography

Digitized mammograms are used as input to a system of feedforward neural networks for determining the presence of clusters of microcalcifications. Rather than presenting the locations of detected suspected pathologies on the digital image itself, the intent is to produce a transparent overlay marking these possible pathologies for later diagnosis by the radiologist. Current results indicate that this method will in general be more efficient than human observers in locating low contrast objects and clusters of small microcalcifications (down to 50 micron diameter).

Image quality characteristics of a novel film/screen system for mammography

The characteristics of a novel, very high resolution film/screen system for mammography are compared with those of a conventional film/screen system for mammography. The image quality characteristics of these systems are measured in terms of Wiener spectra, MTF and sensitometry. These parameters then determine the signal-to-noise (SNR) transfer properties of these systems in terms of the contrast transfer function (CTF), the detective quantum efficiency (DQE) and the noise equivalent quantum efficiency (NEQ). Furthermore, the SNR transfer characteristics are modeled and rationalized by means of the light scattering properties of the intensifying screens and the scintillation spectra of the phosphor. The new system displays superior SNR properties ascribable to its x-ray absorption attributes and the light scattering properties of the phosphor coating.

Determination of x-ray phosphor scintillation spectra

A fast, unique method for determining phosphor scintillation spectra by means of an electronic apparatus is described. A major advantage is that all of the controls are digital. This includes coincidence timing to determine whether an x-ray absorption event has occurred as well as control of the time window during which the number of light photons emitted in response to an x-ray absorption event is counted, and storage of the photon count itself. The apparatus and its logic are described in detail. The scintillation spectra and the resulting calculated Swank coefficient values of several phosphors obtained with this apparatus are presented as examples.

Comparison of digital Wiener-spectrum calculation methods for screen-film evaluation

Based on theoretical considerations and simulations of correlated stochastic noise-like fluctuations Shaw and Rabanni have predicted that the calculation of noise power spectra via the physical autocorrelation function may offer significant signal to noise ratio advantage over more conventional methods. In this paper noise power spectra of actual film-screen systems calculated by the standard direct Fourier transform method are compared with those obtained via the autocorrection function. We confirm that noise power spectra derived from the autocorrelation function are less sensitive to non-stochastic perturbations in the data and thus provide a more accurate representation of the noise characteristics of film-screen systems. This is of great importance when attempting to relate measurements to mechanistic models of the screen and film imaging parameters.

Image-quality characteristics of a film-screen system for chest radiology based on ultravision technology

As reported in an earlier paper, the characteristics of a film/screen system for chest radiology based on Du Ponts Ultra-VisionTM technology were initially designed by means of a digital model of the radiation transfer process. This film/screen system has now been made and its image quality characteristics are described and compared with model predictions.

Novel dry medical recording system

The properties of a novel dry medical recording system are presented in this paper. This system, developed through a cooperative effort between Sterling Diagnostic Imaging and Tektronix Corporation, is based on offset phase change solid inkjet technology and renders very stable, diagnostic quality medical images. A new technique of combining microdroplets of ink to construct grayscale is used and in most cases for a given gray level several possible combinations arise. Although these redundancies provide equivalent optical density, the resulting noise can vary considerably and criteria used to minimize the noise are reviewed.

Statistical processes limiting the noise of a screen-film system

In the present contribution we have investigated the nature and role of the probability distribution function governing the fluctuations in image density about a mean level, and especially the relationship of this distribution to the Wiener spectrum associated with image noise. Experimental measurements are shown confirming that, at a given mean density level, the probability distribution function is independent of exposure statistics regardless of whether the film is exposed to uncorrelated light photons or to correlated light via an intensifying screen. We therefore conclude that differences in the associated Wiener spectrum are entirely attributable to changes in the extent of the autocorrelation interval and not due to changes in the shape or extent of the probability distribution function.

Image quality characteristics of a high-speed film-screen system based on Ultra-Vision technology

A 600-speed system based on Ultra-VisionTM technology has been designed. Since the undoped yttrium tantalate phosphore used in other Ultra-VisionTM screens is incapable of achieving the required speed with existing films it was necessary to admix a small fraction of lanthanum oxybromide which is a more efficient x-ray to light converter and which emits both visible (approximately 470 nm) and UV (approximately 370 nm) light. The image quality performance of the resulting system approaches that of conventional 400-speed film/screen systems. These image quality characteristics are described and compared with those of conventional 600-speed and 400-speed systems.

New correlation method for measuring texture noise in x-ray screens

A new method to measure the texture (structure) noise produced by x-ray screens has been developed. Different films are exposed with the same screen and are scanned in registration. The numerical correlation of the two sets of pixel data then contains only the texture noise component. This is a powerful technique allowing texture noise to be measured quantitatively in the presence of the quantum noise and film grain noise background. Our results support the generally accepted belief that texture noise is small compared with quantum and film grain noise. There are advantages to visualizing texture noise behavior in Cartesian space (as correlation functions) as well as in frequency space (as noise power spectra). Some examples of structure noise correlations and the corresponding spectra are presented.