Reliability and Medical Devices

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Reliability and Medical Devices

• Prof. Monique Frize, P. Eng., O.C.
• ELG5123/94.526
• February 2003

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Content

• Definitions and terms (Hardware)
• Quality quality assurance (products)
• Software terms and definitions
• Approaches to improve quality safety

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Terms and Definitions

• Medical device Instrument, machine, implant, in
  vitro reagent, apparatus, contrivance, implement,
  including part, component or accessory intended
  for application in diagnosis, or in treatment,
  cure, mitigation or prevention of disease or
  intended to affect the structure or any function
  of the body.

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Terms and Definitions

• Reliability The probability that an item will
  carry out its function satisfactorily for the
  stated period when used according to the
  specified conditions.

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Terms and Definitions

• Maintainability Probability that a failed item
  will be repaired or restored to its satisfactory
  operational condition.
• Maintenance Measures appropriate for retaining
  an item in, or repairing/restoring it to, a
  stated state, ensuring that physical assets
  continue to meet their stated missions.

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Terms and Definitions

• Risk The chance, degree of probability of loss,
  damage, harm, or injury.

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One Definition of QUALITY

• Conformance to requirements.
• More later..

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Other Important Definitions

• Safety Conservation of human life and its
  effectiveness, and the prevention of damage to
  items as per operational requirements.

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Other Important Definitions

• Human error Failure to carry out a required task
  (or the performance of a prohibited action) that
  could result in disruption of scheduled
  operations or damage to equipment or property.

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Other Important Definitions

• Failure Inability to operate an item within the
  stated guidelines.
• Mean time between failures (MTBF) Exponentially
  distributed times between failures, the sum of
  the operating time of given items over the total
  number of malfunctions or failures.

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Issues on Quality (Control)

• Definition Quality is the totality of features
  or characteristics of an item that influence its
  ability to meet requirements of users (or of its
  intended use).

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Quality Assurance (Control)

• Definition Planned and orderly sequence of all
  actions appropriate to provide satisfactory
  confidence that the product conforms to specified
  technical requirements. (Products)
• OR Bench testing before a product is released
  and/or distributed to clients. Meet specs?
  Endurance tests?

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Quality Assurance (Control)

• Inspection Process of examining, measuring,
  testing, or otherwise making comparisons of the
  item with the specified requirements.

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Quality Management (products)

• Definition Totality of functions concerned with
  the evaluation and achievement of quality.
• Quality system Organisational set-up,
  responsibilities, resources, processes, for
  implementing quality management.

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Other Concepts (Quality)

• Quality measure Quantitative measure of
  characteristics and features of an item or
  service.
• Relative quality Degree of excellence of an item
  or service.

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Other Concepts (Quality)

• Quality policy Managements set goals and
  approach in achieving quality.
• Total quality Business philosophy that involves
  all individuals for continuously improving an
  organisations performance with respect to
  quality.

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Other Concepts (Quality)

• Quality function deployment Systematic and
  structured technique to highlight customer
  requirements, translate them into a realisable
  item or service parameters, and guide or direct
  the process of implementation in a manner that
  brings about a competitive advantage.

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Software Terms and Definitions

• Definition Computer programs, procedures, rules,
  and relevant documentation (in contrast to
  hardware or physical equipment)
• Medical device software Under the US Food, Drug,
  and Cosmetic Act, any software that satisfies the
  definition of a medical device is considered a
  device to which all relevant FDA medical device
  statutory and regulatory provisions are
  applicable.

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More Sofware Definitions ...

• Software error Conceptual, syntactic, or
  clerical discrepancy that results in one or more
  faults in the software.
• Debugging Process of correcting and isolating
  errors.
• Software testing This is to determine (through
  testing) if a program satisfies specified
  requirements.

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Software Testing

• Error testing Ensuring the device performs
  correctly in abnormal situations (internal parts
  failure, power surges or outages,
  incomprehensible values generated by peripheral
  devices.

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Software Testing

• Safety testing Focus test efforts on conditions
  potentially harmful to patient or user.

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Software Testing

• Functional testing Direct test efforts on what
  the device is supposed to do.
• This is the heart of traditional validation and
  verification procedures. Exhaustive testing

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Software Testing

• White-box testing Employed when it is required
  to verify the internal functioning of the device
  software. This allows the tester to look inside
  the device and develop tests to discover weak
  spots in the internal logic of the program.

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Software Testing

• Free-form testing Used whenno formal test plan
  can find each important software bug. This test
  subjects the device to additional stress on top
  of the formal approaches listed previously.
• Test the device in unconventional and unexpected
  ways to attempt to provoke a failure.

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More Sofware Definitions ...

• Software quality Totality of characteristics and
  features of a software item that determines its
  capability to meet specified requirements or
  conform to specifications.
• Software reliability Probability a given
  software will operate for a specified time
  interval, without an error, when used within the
  framework or designed conditions stated.

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Comparisons (hardware VS software)

• Hardware
  Software
• parts degrade no
  degradation parts
• processes governed physics not physics
• failure modes different
  
• interfaces physical
  interfaces conceptual
• fewer paths (cause failures) more distinct
  paths
• less sensitive to small errors very
  sensitive

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Error Prevention

• Observing workers and performing audits after
  incidents or accidents (OR)
• Train and educate
• Try to design devices fool-proof
• Labels and warnings may help
• Guards or special lock mechanisms, etc...

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Main Source

• Medical Device Reliability and Associated Areas.
  B.S. Dhillon,CRC Press, 2000.