Reasoning of Safety-Critical Medical Devices using Formal Methods.

Abstract

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 medical bookkeeping, electrocardiogram analysis, laser surgery, and intravenous delivery systems that adjust dosages 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 the regulatory bodies are interested in investigating mechanisms by which to certify such medical devices. These organizations believe that the rigorous employment of formal mathematical models can achieve significant software quality over current practice, and advocate the use of formal methods to evaluate safety-critical medical systems. The use of formal methods is keenly debated though, with most manufacturers claiming that they are arduous and time-consuming.

In this thesis, titled 'Reasoning of Safety-Critical Medical Devices using Formal Methods', we evaluate the feasibility of formal method techniques for medical devices. More specifically, we discuss our experiences in modeling and verification of the specifications for a typical medical system called the Computer Aided Resuscitation Algorithm (CARA) using two formal methods based tools, UPPAAL and Spin.

We find that the use of UPPAAL and Spin for the analysis of the CARA system yields several anomalies and inconsistencies, hitherto undetected. The results from the two tools are found to be in accordance, and the effort involved comparable to conventional techniques. Based on our results, we conclude that formal methods provide a feasible and effective means for reasoning of safety-critical medical devices.