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Validation of automated systems--system definition.

A Parenteral Drug Association (PDA) Committee on Software Validation was formed about three years ago to address some of the issues associated with validating automated systems, particularly where all, or part, of the automated system is supplied by outside vendors. A Technical Report that describes a process which emphasizes system definition, a comprehensive system specification, system qualification and ongoing evaluation will issue later this year. The concepts described in this document will be consistent with the PMA's System Development Life Cycle approach which is commonly used for computer system validation. The following article has been developed from the System Definition section of this PDA Technical Report.

Computer Systems

EMPIAR: the Electron Microscopy Public Image Archive.

Public archiving in structural biology is well established with the Protein Data Bank (PDB; wwPDB.org) catering for atomic models and the Electron Microscopy Data Bank (EMDB; emdb-empiar.org) for 3D reconstructions from cryo-EM experiments. Even before the recent rapid growth in cryo-EM, there was an expressed community need for a public archive of image data from cryo-EM experiments for validation, software development, testing and training. Concomitantly, the proliferation of 3D imaging techniques for cells, tissues and organisms using volume EM (vEM) and X-ray tomography (XT) led to calls from these communities to publicly archive such data as well. EMPIAR (empiar.org) was developed as a public archive for raw cryo-EM image data and for 3D reconstructions from vEM and XT experiments and now comprises over a thousand entries totalling over 2 petabytes of data. EMPIAR resources include a deposition system, entry pages, facilities to search, visualize and download datasets, and a REST API for programmatic access to entry metadata. The success of EMPIAR also poses significant challenges for the future in dealing with the very fast growth in the volume of data and in enhancing its reusability.

Imaging, Three-Dimensional

Validation of respiratory mechanics software in microprocessor-controlled ventilators.

BACKGROUND AND METHODS: Several microprocessor-controlled ventilators, available for clinical use, contain optional computer software programs capable of performing near-instantaneous determinations of airway resistance and lung compliance. This study was undertaken to determine the validity of the measurements for airway resistance and lung compliance obtained by the software packages on three microprocessor-controlled ventilators. Three ventilator models were studied. An artificial ventilator-patient circuit was constructed using a test lung and an endotracheal tube. Airway pressure and gas flow curves were recorded using conventional means. Static lung compliance and airway resistance were calculated using standard equations, while automated measurements were obtained from the ventilators. The following parameters were then varied to simulate a wide variety of clinical situations: tidal volume, peak inspiratory flow rate, respiratory rate, endotracheal tube, and test lung compliance. RESULTS: Automated measurements were highly correlated with values obtained manually (resistance: Puritan-Bennett 7200a r2 = .94, Bear 5 r2 = .98, Veolar r2 = .96; compliance: 7200a r2 = .93, Bear 5 r2 = .97, Veolar r2 = .97). Calculated limits of agreement between the two methods demonstrate that although not in absolute agreement, the software-determined values for airway resistance and lung compliance differed from the manually derived values in a ventilator-specific, predictable fashion. CONCLUSIONS: The correlation and agreement demonstrated between values of airway resistance and lung compliance measured by the respiratory mechanics software packages and those values derived manually suggest that these software packages may be useful for measuring trends, as well as responding to treatment in the clinical setting. These results apply only to the controlled, mechanical ventilation mode. Further studies are indicated to validate this software in patients capable of generating spontaneous breaths.

Airway Resistance

Validation of an adaptive software trigger and arrhythmia diagnostic algorithm.

The authors have developed an algorithm for the identification of arrhythmias using intracardiac atrial and ventricular leads. The algorithm is based on the rate of the depolarizations and a measure of the organization of electrical activity in each of the cardiac chambers. The most important requirement of the algorithm is to identify the occurrence of each cardiac event correctly. A robust amplitude-adaptive software trigger is developed, which accurately detects depolarizations in both chambers. With this reliable trigger the authors demonstrate the veracity of the arrhythmia identification algorithm.

Algorithms

Validating the knowledge base of a therapy planning system.

Validation of expert system knowledge bases has proved to be difficult. This paper presents a description of a system called ScriptGen that generates test data for validating the knowledge base of the ONCOCIN cancer therapy planning system. Because of the size and complexity of the ONCOCIN knowledge base, we require tools for automated validation. ScriptGen, which applies techniques developed in testing both traditional software and expert systems, uses a parallel model of the ONCOCIN knowledge base and its own inference engine to generate test cases. We derived the limits of the system from a study that seeded errors into an existing knowledge base.

Antineoplastic Combined Chemotherapy Protocols

PRELOG: precedence logic inference software for blood donor deferral.

Blood collection facilities have recently witnessed a substantial increase in the complexity of tests used to detect infectious disease in donor populations, and there is a stringent regulatory effort by the Food and Drug Administration (FDA) to validate the software for managing this information. PRELOG is precedence-based inference software used to determine a donor's suitability for continued donations and whether the donation can be released for transfusion. PRELOG accepts ternary input for test results (positive, negative, or undetermined), and solves the logic rules sequentially, so that the rulebase can be validated in a concise and consistent manner.

Blood Banks

Evaluating and validating very large knowledge-based systems.

Most knowledge-based systems for use in medicine have been developed in response to specific problems such as the diagnosis of abdominal or chest pain in an accident and emergency department, or the diagnosis and treatment of meningitis. There is a role for a general decision support system capable of answering queries about any aspect of medicine, particularly in primary care. However, evaluating such a knowledge base requires more elaborate methodology than a simple iterative test and refine cycle. At the design stage an adequate knowledge base structure is required to allow focused modification of the knowledge base when errors are discovered. During the prolonged evaluation cycle the partially formed knowledge base must be tested with such techniques as validation checks for consistency and completeness and examination of characteristics of problem-solving procedures. Finally a variety of criteria that represent the performance, robustness, flexibility, predictability, validity, coverage, relevance and congruity of the knowledge base are needed for a full description of the system's worth. Two case studies from the Oxford System of Medicine project are provided as examples of this philosophy: validating specific medical facts and comparing two methods for aggregating reasoning for and against a decision option.

Artificial Intelligence

Exploring subjective vs. objective issues in the validation of computer-based critiquing advice.

Evaluation is an important part of the development of computer-based medical expert systems. Such evaluation may be particularly difficult when judging a critiquing system which responds to a proposed management strategy with a discussion of the advisability of that approach. DxCON is an expert system which produces a prose critique discussing the radiologic workup of obstructive jaundice. This paper describes DxCON, and its experimental validation by three independent judges. A central component of the validation involved allowing the judges to react to the system's advice in a quite flexible, unstructured fashion. This project provides a case study of how subjective issues impact both the design and implementation of a validation of a medical expert system whose output is explanatory prose.

Cholestasis

ANABEL: intelligent blood-gas analysis in the intensive care unit.

ANABEL (ANalysis of Acid-Base status by Evaluating Lisp) is a prototype medical intelligent decision-support system aiming to assist clinicians in an Intensive Care Unit environment with the interpretation of blood-gas measurements. Its architecture is based on the merging of representations for declarative (domain-descriptive) and procedural (problem-solving) medical knowledge. The system performs diagnosis in two stages (tentative and differential) by first evaluating elementary computational units of procedural knowledge (procedures) and then abstracting their symbolic outputs in generating text. Thus, a 'semantic trace' is built which reflects the system's line of reasoning in reaching its conclusion. This paper describes the design aspects, development and clinical validation of ANABEL.

Acid-Base Imbalance

Development and validation of HEPAR, an expert system for the diagnosis of disorders of the liver and biliary tract.

HEPAR is an expert system in the field of hepatology which can be used as a supportive tool in the diagnosis of disorders of the liver and biliary tract. The representation language employed in HEPAR consists of production rules with object-attribute-value triples. In the system, medical diagnosis is modelled according to the strategy which is clinically used in this field. The patient's disorder is assessed in two stages. In the first stage, available data from medical interview, physical examination and simple laboratory tests are used to determine whether the disorder is hepatocellular or biliary obstructive in nature, and whether benign or malignant features are present. In the second stage the system produces a subset of possible diagnoses out of a set of more than 80 disease categories, using additional data from supplementary tests. The results of the first stage classification cause considerable pruning of the search space. In this paper the structure, development process and approach followed in the validation of the HEPAR system are described. The results of a recent performance validation study using data from 181 consecutive patient cases are discussed.

Biliary Tract Diseases

Evaluation of clinical decision aids--more to think about.

Validation and clinical testing of medical decision aids is a hot topic at present. We state a few main points which, in our opinion, have not received the attention they deserve. Our main concerns have to do with the statistical design and analysis of field evaluation studies; with long-term effects; and with the interplay between medicine and the software industry. The points represent our reaction to a recent symposium on the topic, published in this special issue. We take the opportunity to supplement the papers at hand in various ways and, where we see a risk of misconceptions or poor practice becoming cemented, try to point out the proper course.

Decision Making, Computer-Assisted

The evaluation of clinical decision support systems: what is necessary versus what is interesting.

The evaluation of clinical decision support systems has long been recognized as an important part of the overall field of medical computing, as well as a complex and varied field in its own right. There are a number of purposes for which such an evaluation might be performed. This paper focuses on one of those purposes, the assurance of safety when preparing to release the system for general use. The assurance of safety involves two major stages: (1) a comprehensive validation of the system's knowledge and advice, and (2) a period of use which exposes the system's advice and interface to the clinical environment.

Decision Making, Computer-Assisted

Development of a computer application for headache diagnosis: the Headache Diagnostic System.

A computer-assisted decision support system for headache classification and diagnosis is presented. The system provides: structured headache data collection, automated data quality control and management, and automated headache classification. The system is based upon headache classification and diagnostic criteria recently developed by the International Headache Society. Development, logical structure and validation of the system are discussed. The system is shown to provide a general improvement in headache classification reliability and has utility for validation and improvement of present headache classification criteria.

Adult

Automated recognition of corrupted arterial waveforms using neural network techniques.

A data acquisition system that automatically discards corrupted or undesirable signals would save untold hours of drudgery for researchers. Continuous recording of variables to provide detailed behavior patterns generates huge amounts of raw data. Unfortunately waveforms usually require visual inspection for isolating desired behavior or validating signal integrity. This tedious and time-consuming step can potentially be eliminated using a novel computer science technique. We have trained a simulated neural network to recognize corrupted arterial pressure waveforms. Our system can now evaluate the validity of the arterial waveform without human intervention with an average false positive error rate of 2.2% and an average false negative error rate of 12.6%.

Artifacts

Cellular viability in human tumor micro-organ cultures: in situ quantitation by image processing.

At present, cytotoxicity measurements using the fluorescent cytoprint assay are based on achieving complete cell death in cultures of drug-sensitive tumors. Thus, the usefulness of the assay would be extended if partial effects of chemotherapeutic drugs could be quantified. In this study, we addressed the issue by developing and validating a thresholding algorithm for automatic image processing that can be used to quantify the areas occupied by viable (i.e., fluorescent) micro-organs in the culture.

Drug Screening Assays, Antitumor

Validation of the medical expert system PNEUMON-IA.

The present study validates the expert system PNEUMON-IA. The aim of PNEUMON-IA is assessing the etiology of community-acquired pneumonias from clinical, radiological, and laboratory data obtained at the onset of the disease. Validation was performed using data from medical records of 76 patients with proven clinical diagnosis of pneumonia. The etiological diagnoses provided by PNEUMON-IA were compared to those established by five specialists unrelated to the development of the expert system. For each etiological possibility, both PNEUMON-IA and the experts provided a causal possibility, expressed as a linguistic label (i.e., "almost impossible"). Linguistic labels were then converted to numeric values. In the majority of cases, an etiological diagnosis was unavailable to be used as a gold standard. To overcome this limitation, distances between arrays of etiological possibilities given by specialists and by PNEUMON-IA were considered as an agreement measure between diagnoses. Cluster analysis based on those distances was used to classify PNEUMON-IA among experts. Results showed the same differences between specialists and PNEUMON-IA as among the specialists themselves. The method used to validate PNEUMON-IA could prove useful to assess the performance of expert systems in fields where no gold standard is available.

Adolescent

[Bacterio-expert: an integrated system for assisting in the validation of antibiotic sensitivity tests. Retrospective application in 4053 Staphylococcus].

Bacterio-expert is a simple expert system for assisting in the validation of antibiotic sensitivity testing. This system is incorporated in a data acquisition and editing program for bacteriologic test (Bacterio program written in Turbo-Pascal for personal computer users by the same authors). The principles of this system are explained and results with 4,053 antibiotic sensitivity tests on Staphylococcus aureus isolates are reported. Approximately 10% of tests required corrections.

Anti-Bacterial Agents