The complexity of transactions: a means for assessing interoperability.

Interoperability seems to be a major focal point of the activities within the Informatics Society in general, and the Medical Informatics society in particular. In both Europe and the USA standardization efforts are pursued in order to enable interoperability. However, even if the technical requirements are met, interoperability is sometimes not feasible because the message exchange needed is too complex. This complexity is influenced by at least three factors: the volume of the data to be exchanged, the functionality of the information exchange, and the communication standard adopted.

ROC assessment of compressed wrist radiographs.

The aim of this paper is to validate a compression scheme applied on a medical image database of digitized wrist radiographs. The compression scheme adapts itself to local statistical properties of the images. The diagnostic quality of the reconstructed images is evaluated using a ROC protocol involving five medical experts. The results of this evaluation enable us to validate the compression scheme on this database with a compression ratio of 40 (0.2 bits per pixel).

Statistical comparison of ROC curves from multiple readers.

Receiver operating characteristic (ROC) analysis is the commonly accepted method for comparing diagnostic imaging systems. In general, ROC studies are designed in such a way that multiple readers read the same images and each image is presented by means of two different imaging systems. Statistical methods for the comparison of the ROC curves from one reader have been developed, but extension of these methods to multiple readers is not straightforward. A new method of analysis is presented for the comparison of ROC curves from multiple readers. This method includes a non-parametric estimation of the variances and covariances between the various areas under the curves. The method described is more appropriate than the paired t test, because it also takes the case-sample variation into account.

Conventional film-screen versus computed storage phosphor radiography. Simulated miliary lung disease in an anthropomorphic phantom.

RATIONALE AND OBJECTIVES: In this experimental study, the authors examined whether laser printed hardcopies from digital storage phosphor radiographs yield diagnostic performance equal to conventional film-screen radiographs in the detection of simulated miliary disease, using a standardized object. METHODS: A commercially available anthropomorphic chest phantom was used for radiographic evaluation. Miliary disease was simulated by superimposing one to four sheets of millet seeds on the lungs, resembling a miliary disease pattern with varying degrees of detectability. An observer study (receiver-operating characteristic) with eight radiologists was conducted to compare the reader performance using hardcopies of computed storage phosphor radiography versus the conventional film-screen system, optimized for chest x-rays. The digitally generated images were presented as a double-image hardcopy, with a conventionally adopted version and an edge enhanced image version. RESULTS: When analyzed separately, one out of the eight observers performed slightly better using the conventional films. When treated as a group, analysis of the areas under the receiver-operating characteristic curves demonstrated no significant difference in reader performance for each of the systems under investigation (t = 0.286). The Wilcoxon test could not prove a statistical difference. CONCLUSION: Storage phosphor technology is a method that yields equal diagnostic performance as conventional film in evaluating miliary disease of the chest.

Remote expert consultation for MRI procedures by means of teleradiology.

From April 1992 to January 1993, radiology expert opinion for MRI procedures was offered by means of teleradiology. The experiment was carried out in addition to an existing service of a mobile MRI unit. MRI images were sent by means of teleradiology via regular telephone lines from the mobile MRI unit to an academic hospital, which served as expert consultation centre. During this period, 43 requests for expert opinions were performed. This article describes the clinical effects of these expert opinions, and the technical and organisational requirements to perform teleradiology in daily clinical practice.

HIPIN--a generic HIS/RIS-PACS interface based on clinical radiodiagnostic procedures.

Within the EurIPACS HIPIN topic a generic HIS/RIS-PACS interface will be designed, implemented and evaluated. It is generally agreed that integration with the HIS/RIS is essential for the acceptance of PACS in a clinical environment. An interface between HIS/RIS and PACS allows more efficient usage of both systems, better integration of data, better consistency checking on shared data and better security and error handling. Also the PACS performance is improved by using HIS/RIS information to steer the image migration within the PACS. In this paper the functional specifications of the interface are described. These specifications are based on descriptions of clinical radiodiagnostic procedures. The generic interface consists of a common part, and of site specific adapters. The common part is identical for all incarnations and performs message scheduling, processing and logging. The adapters are specific for each communication standard, e.g. ACR-NEMA or HL7, and for each hospital. The interface will be implemented at the radiology department of the Philipps University Hospital in Marburg (Germany) and at the orthopaedic and neuroradiology departments of the hospital of the Free University in Brussels (Belgium).

Methodology for the evaluation of diagnostic image quality.

This paper explains the theoretical backgrounds of various methods for the evaluation of diagnostic image quality. It introduces the Receiver Operating Characteristics (ROC) methodology. The major prerequisites, some important features of the experimental set-up and of the data analysis of an ROC study are explained. Dedicated software packages to support ROC studies are introduced. A possible method on how to relate image quality and cost-effectiveness is presented. Finally some current problems of the ROC method and possible improvements are discussed.

An analysis of the costs of a hospital-wide Picture Archiving and Communication System with the software package CAPACITY.

Within the scope of the Dutch PACS project, the costs of a hospital wide PACS in the Utrecht University Hospital were estimated, with the help of the software package CAPACITY. The cost analysis was based on the most recent specifications of the costs of the equipment, on extrapolations, and on the experience acquired with a PACS prototype in the Utrecht University Hospital. Savings due to a possible reduction in the length of stay, or due to logistic improvements were not taken into account. The results indicate that the extra costs of a hospital wide PACS would amount to 3.2% of the total hospital budget. By taking into account the expected price movements, it is predicted that a hospital wide PACS may allow enough savings to pay itself back, when installed near the turn of the century. The result of this cost analysis depends on a large number of assumptions. Therefore two sensitivity analyses are carried out, i.e., concerning the number of workstations required and concerning the organizational impact of PACS.

Medical imaging workstation: a software environment.

In a study to set up an experimental simple imaging workstation with facilities for image input, storage, presentation and manipulation, BAZIS developed a software package called FRACTALS (Filmless Radiology And Computerized Task Analysis Lab Software). The investment in the development of effective software for digital radiological workstations is of great importance in picture archiving and communication systems (PACS) research. General purpose workstations are becoming less expensive and more powerful. They are an important tool for performing radiological research and developing an adequate human interface. The software should provide the tools and flexibility for modifications that turn out to be required for interaction with the radiologists. The software package FRACTALS is presented in this paper and its applications and future developments are discussed.

Diagnostic evaluation of a PACS subsystem using mammographs. An ROC analysis.

The objective of this study was to compare the diagnostic accuracy of digitized mammographs with the original conventional films. The criterion was the detectability of small calcifications in the female breast. Four skilled radiologists read 100 films, conventional as well as digitized. The results were analysed using ROC methodology, and showed much lower diagnostic accuracy of digitized images (average AUC 0.67) compared to conventional films (average AUC 0.89). One of the problems with digitized images was to recognize and ignore film artifacts, which were hard to discriminate from small calcifications. The experiment was prepared, carried out and analysed with the FEASIBLE software package.

FEASIBLE (I): The PC software package for feature evaluation and system inspection by logged experiments.

FEASIBLE is an MS-DOS software package which can be used for the evaluation of: Picture Archiving and Communication System (PACS) components; diagnostic image quality; and image manipulation and representation techniques. The FEASIBLE software allows the user to design any psychophysical study in detail in the fields mentioned above, to execute an arbitrary number of sessions and to statistically analyse the results by way of the Receiver Operating Characteristic (ROC) technique. FEASIBLE consists basically of three modules: DESIGN, which allows the user to set up an experiment; EXECUTION, which allows the user to execute the experimental sessions based on the design entered in the DESIGN module and stored in the program's database; and, STATISTICS, which allows various statistical analyses on the data collected during the psychophysical sessions (including the calculation of ROC curves and related parameters) and can provide a graphical presentation of the results. FEASIBLE has been designed to support experts and those who have little knowledge of psychophysical experiments. This paper discusses the background, structure and possibilities of the FEASIBLE package at this point (version 1.2, May 1988).

FEASIBLE (II): Its use in an actual PACS evaluation study.

The software package FEASIBLE is a tool for carrying out observer performance studies. The structure, background and possibilities of the program are described in paper I of this series. Observer performance studies can be used to evaluate the diagnostic quality of Picture Archiving and Communication System (PACS) components. This paper summarizes the general features of such an evaluation. It states the specific characteristics of a diagnostic evaluation of a prototype PACS. The examples of the use of FEASIBLE presented here originate from the study that has recently been conducted within the Dutch PACS project, a cooperation between the BAZIS project IMAGIS (IMAGe Information System), the Utrecht University Hospital and Philips Medical Systems. Furthermore, this paper demonstrates how FEASIBLE is used to carry out an observer performance study. It is shown step-by-step how experiments on the evaluation of PACS components can be executed in an easy, reliable and quick way, by means of the FEASIBLE package.

Background of the demonstrated IMAGIS activities and future expectations.

In The Netherlands a national PACS development programme has been started, supported by the Dutch Society of Radiology and funded by the Dutch Department of Health because of the national character of the project. Three main partners are cooperating in this development: the Utrecht University Hospital (AZU), BAZIS and Philips International (Product Division Medical Systems), with the Delft University of Technology as the main BAZIS subcontractor. The non-profit foundation BAZIS, developing and supporting the ZIS Hospital Information System (in use in some 30 Dutch hospitals, over 15,000 acute beds), initiated its current IMAGe Information System (IMAGIS) projects in 1984. The activities were later integrated into the Dutch PACS project started in 1986. The final goal of the project is to achieve a PACS which is fully integrated with already existing hospital information systems (HIS). The development and operation of a HIS-PACS include many aspects of technical and clinical. The current efforts of BAZIS are concentrated on three main issues: diagnostic image quality evaluation (e.g. effects of data compression); modelling, software simulation and technology assessment of a prototype PACS (both general and detailed aspects); and coupling and integration of PACS and HIS (e.g. the BAZIS ZIS). Philips, Hamburg, is supplying equipment, particularly prototype components. A systematic clinical evaluation will take place at the Utrecht University Hospital.2+ We outline the background of the intermediate results as demonstrated during the 6th EuroPACS Conference:the psychophysical software package for Feature Evaluation And System Inspection By Logged Experiments (FEASIBLE); the modelling and simulation software package for Medical Image Representation, Archiving and Communication, Learned by Extensive Simulation (MIRACLES); and first results of the coupling experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Collicular involvement in a saccadic colour discrimination task.

We have recorded the neural activity of single superior colliculus (SC) neurons in monkeys engaged in a saccadic target/nontarget discrimination task based on a colour cue. Since correct execution of this task probably depends on cortical signal processing, our experiments are of interest for getting a better insight in the problem of how cortical and subcortical signals, relevant for the visual guidance of saccades, are combined. The experiments were designed to distinguish between two extreme possibilities: The crucial cortical signal affects the saccadic system at or above the level of the SC movement-related cells (serial hypothesis); The colour-based target information bypasses the motor colliculus and affects the saccadic system at a level more downstream (bypass hypothesis). Under conditions where the saccadic system had to select a green target stimulus and to ignore the red nontarget spot, the saccade-related activity in SC visuomotor neurons remained as tightly coupled to the metrics of the saccade as it was in a simple spot-detection task. Since the saccade-related activity of these cells appeared to be based on colour information, we conclude that our data corroborate the serial hypothesis. The initial activity after stimulus onset appeared to be colour nonopponent in all neurons. In some cells the neural activity was quantitatively slightly different for the green target and the red nontarget. Since these minor differences were colour rather than motor response dependent, they were probably not part of the target-selection process. These data suggest the possibility that the decision as to which saccade should be made was largely imposed upon the SC visuomotor cells by an external source. We discuss various possibilities for the origin of the putative intervening signal which orders a saccade by causing a burst in the appropriate SC visuomotor neurons.

Visuomotor fields of the superior colliculus: a quantitative model.

Electrophysiological and electrical stimulation studies in the monkey have disclosed that both the retinal surface and the metrics of saccades are topographically represented in the superior colliculus. This mapping of sensory and motor space onto the colliculus is nonhomogeneous in that the central region is over-represented in both the visual and the motor map. Single unit studies have revealed that visual receptive fields of collicular neurons are typically quite large and are characterized by a skewed (asymmetrical) sensitivity profile. Analyses by McIlwain [J. Neurophysiol. 38, 219-230 (1975)] in the cat have suggested that this skewness property reflects mainly the spatial distortion inherent in the afferent mapping. In this paper we describe a quantitative model, based on a logarithmic mapping function combined with a Gaussian connectivity function in the colliculus, which can account for the extent and the shape of collicular receptive fields. Collicular neurons in the deeper layers have movement-related bursts of activity for saccades in a limited amplitude and direction range related to their location in the collicular map. These movement fields, like visual receptive fields, may be quite extensive and typically have a skewed profile. In our model, an efferent-mapping function is defined, which relates the locus of a population of recruited cells to the metrics of the ensuing saccade. The parameters of this function, which was taken to be identical with the afferent mapping function, were estimated from Robinson's [Vision Res. 12, 1795-1808 (1972)] electrical stimulation data. Based on the assumption that the population-activity profile resembles a two-dimensional Gaussian function, the shape and the size of movement fields can then be described with just 2 or 3 free parameters. Electrophysiological data recorded from a small sample of collicular visuomotor neurons were used to illustrate the procedure, which we designed to enable application of our model to the experimental data. The best fit was obtained when the mapping function was slightly anisotropic. Suggestions on how the model could be improved and extended are offered in the Discussion.

Latency dependence of colour-based target vs nontarget discrimination by the saccadic system.

First saccade responses to sudden presentations of a target/nontarget stimulus consisting of green and red spots of light have been investigated. This paradigm, which avoids certain ambiguities present in earlier experiments with identical double stimuli, leads to remarkably similar conclusions. We found, again, that the saccadic system had short-latency compromising responses (averaging response mode) when the stimulus pair had a modest direction difference (delta phi). When delta phi was enlarged, first saccades were either directed near the green or the red spot (bistable response mode). In a second series of experiments different instructions, emphasizing either speed or accuracy of response, have been given to investigate the relation between saccade accuracy and latency. It appears that, independent of instruction, there is a fixed relation between saccade metrics and latency. The only way to avoid errors, such as averaging responses, is to delay the saccade. Hypothetical mechanisms underlying this relation are discussed against recent neurophysiological studies.

Metrics of saccade responses to visual double stimuli: two different modes.

Earlier studies using visual double stimuli along the horizontal axis have revealed a strong averaging tendency in the saccadic system. This study shows averaging also for equally eccentric double stimuli with a modest difference in direction (delta phi = 30 deg). When the difference is enlarged (delta phi = 90 deg) the response pattern becomes bistable; i.e. the eye jumps near either one or the other stimulus. This bistable response mode is reflected also in saccade amplitude when double stimuli along the horizontal axis have a large difference in eccentricity. It is concluded that the saccadic system response mode to double stimuli depends on interstimulus spacing. Furthermore, both types of response can be shown to exist with double stimuli confined to one visual half-field.