Safety-critical Medical Systems Research Articles

A Fault-Based Testing Approach in Safety Critical Medical Systems

The advent of technology has opened unprecedented opportunities in health care delivery system as the demand for intelligent and knowledge-based systems has increased as modern medical practices become more knowledge-intensive. As a result of this, there is greater need to investigate the pervasiveness of software faults in Safety critical medical systems for proper diagnosis. The sheer volume of code in these systems creates significant concerns about the quality of the software. The rate of untimely deaths nowadays is alarming partly due to the medical device used to carry out the diagnosis process. A safety-critical medical (SCM) system is a complex system in which the malfunctioning of software could result in death, injury of the patient or damage to the environment. The malfunctioning of the software could be as a result of the inadequacy in software testing due to test suit problem or oracle problem. Testing a SCM system poses great challenges to software testers. One of these challenges is the need to generate a limited number of test cases of a given regression test suite in a manner that does not compromise its defect detection ability. This paper presents a novel five-stage fault-based testing procedure for SCM, a model-based approach to generate test cases for differential diagnosis of Tuberculosis. We used Prime Path Coverage and Edge-Pair Coverage as coverage criteria to ensure maximum coverage to identify feasible paths. We analyzed the proposed testing procedure with the help of three metrics consisting of Fault Detection Density, Fault Detection Effectiveness and Mutation Adequacy Score. We evaluated the effectiveness of our testing procedure by running the suggested test cases on a sample historical data of tuberculosis patients. The experimental results show that our developed testing procedure has some advantages such as creating mutant graphs and Fuzzy Cognitive Map Engine while resolving the problem of eliminating infeasible test cases for effective decision making.

Illustrating the AADL error modeling annex (v.2) using a simple safety-critical medical device

Developing and certifying safety-critical and highly reliable systems almost always includes significant emphasis on hazard analysis and risk assessment. There have been substantial improvements in automation and formalization of other aspects of critical system engineering including model-driven development, analysis of source code and models, and verification techniques. However, hazard analysis and risk assessment are still largely manual and informal activities, tool support is limited (which for both development and auditing, increases time and effort and reduces accuracy and correctness), and artifacts are not integrated with architectural descriptions, system interfaces, high-level behavioral descriptions or code. The Error Model annex of the Architecture Analysis and Design Language (AADL) provides formal and automated support for a variety of forms of hazard analysis and risk assessment activities. Specifically, it enables engineers to formally specify errors, error propagation, error mitigation -- using annotations that are integrated with formal architecture and behavioral descriptions written in AADL. Plug-ins to the Open-Source AADL Tool Environment (OSATE) process these annotations to provide various forms of (semi)-automated support for reliability predication and tasks necessary to support common hazard analysis and risk assessment techniques such as Failure Modes and Effects Analysis (FMEA), Fault Tree Analysis (FTA), and Functional Hazard Analysis (FHA). In this paper, we illustrate basic aspects of Error Modeling in AADL using a simple safety-critical medical system -- an infant incubator called "Isolette". We summarize standard tasks involved in FMEA and FTA, we illustrate the principal steps involved in AADL Error Modeling for the Isolette, and we describe how those steps relate to FMEA and FTA. We give a brief survey of emerging automated analysis tools implemented as plug-ins to the AADL OSATE environment that process error modeling annotations. We believe this introduction to Error Modeling in AADL can expose engineers of high-integrity systems to techniques and tools that can provide a more rigorous, automated, and integrated approach to important risk management activities.

Constructing a Model-Based Software Monitor for the Insulin Pump Behavior

Modern medical systems undertaking the task of surveillance of patients are safety-critical systems steered by software. Such systems will bring man's life into hazard if they fail to meet patients' requirements; so, adequate reliability of the algorithms and computations used by software of such systems is a matter of concern. The environment of a medical safety-critical system consisting of a patient has safety requirements that should be satisfied by the system. A safety requirement is the one that if it is violated, the system environment will be subject to severe risk. An effective method to verify the algorithms and computations used by software of such systems against safety requirements is to keep the software under surveillance at run-time. This paper aims to present a model-based method to construct a run-time monitor for a safety-critical medical system called Continuous Infusion Insulin Pump (CIIP).

A case study on applying formal methods to medical devices: computer-aided resuscitation algorithm

The design and functional complexity of medical devices have increased during the past 50 years, evolving from the use of a metronome circuit for the initial cardiac pacemaker to functions that include electrocardiogram analysis, laser surgery, and intravenous delivery systems that adjust dosage based on patient feedback. As device functionality becomes more intricate, concerns arise regarding efficacy, safety, and reliability. It thus becomes imperative to adopt a standard or methodology to ensure that the possibility of any defect or malfunction in these devices is minimized. It is with these facts in view that regulatory bodies are interested in investigating mechanisms to certify safety-crictical medical devices. These organizations advocate the use of formal methods techniques to evaluate safety-critical medical systems. However, the use of formal methods is keenly debated, with most manufacturers claiming that they are arduous and time consuming.In this paper we describe our experience in analyzing the requirements documents for the computer-aided resuscitation algorithm (CARA) designed by the Resuscitative Unit of the Walter Reed Army Institute of Research (WRAIR). We present our observations from two different angles – that of a nonbeliever in formal methods and that of a practitioner of formal methods. For the former we catalog the effort required by a novice user of formal methods tools to carry out an analysis of the requirements documents. For the latter we address issues related to choice of designs, errors in discovered requirements, and the tool support available for analyzing requirements .