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Methods and Procedures for Improving Reliability of Medical Equipment

There are many methods and procedures used for improving medical equipment reliability. Some of these are presented below.

Parts Count Method

This method is used for predicting equipment/system failure during the bid proposal and early design stages [18]. The method requires information on three areas shown in Figure 9.1.

The parts count method calculates the equipment/system failure rate under the single-use environment by using the following equation [18]:

Areas of information required by the parts count method

FIGURE 9.1 Areas of information required by the parts count method.


Xe is the equipment/system failure rate expressed in failures/106 hours, к is the number of different generic part/component classifications.

Qj is the generic part quantity for classification j.

Agp is the generic part failure rate expressed in failures/106 hours.

Qa, is the generic component quality factor.

The values of ?.„p and Oyp are tabulated in Ref. [18], and additional information on this method is available in Refs. [18,19].

Failure Mode and Effect Analysis (FMEA)

This method is widely used for evaluating design at the early stage from the reliability aspect. This criterion is extremely useful for identifying the need for and the effects of design change. The method requires the listing of all possible failure modes of each and every component/part on paper and their effect on the listed subsystems, etc. FMEA is known as failure modes, effects, and criticality analysis (FMECA) when criticalities or priorities are assigned to failure mode effects.

Some of the FMEA’s important characteristics are as follows [20]:

  • • It is an effective tool for identifying weak spots in system design and indicate areas where further or detailed analysis is required.
  • • By examining failure effects of all components/parts, the entire system is screened completely.
  • • It is an upward approach that begins at the detailed level.

Additional information on this method is available in Chapter 4 and in Refs. [20,21].

General Approach

This is a 13-step approach developed by Bio-Optronics for producing reliable and safe medical devices [22]. The approach steps are as follows [22]: [1]

  • • Step 9: Conduct Laboratory and field test on the modified version of the product/device.
  • • Step 10: Build pilot units for performing necessary tests.
  • • Step 11: Ask impartial experts for testing pilot units under the field use environments.
  • • Step 12: Release the product/device design for production.
  • • Step 13: Study the product/device field performance and support with appropriate product/device maintenance.

Fault Tree Analysis (FTA)

FTA starts by identifying an undesirable event, called the top event, associated with a system under consideration [23]. Fault events which could cause the top event’s occurrence are generated and connected by logic operators such as OR and AND. The OR gate provides a TRUE (failure) output when only one or more of its inputs are true (failures). In contrast, the AND gate provides a TRUE (failed) output when all its inputs are TRUE (failures). All in all, the construction of the fault tree proceeds by generation of fault events in a successive manner until the fault events need not be developed any further.

Additional information on FTA is available in Chapter 4 and in Refs. [23,24].

Markov Method

This method is a very general approach and it can generally handle more cases than any other technique or method. It can be utilized in situations when the parts/ components are independent as well as for systems/equipment involving dependent failure and repair modes.

This method proceeds by the enumeration of system states. The state probabilities are calculated, and the steady-state reliability measures can be computed by utilizing the frequency balancing method [25]. Additional information on the method is available in Chapter 4 and in Refs. [26,27].

  • [1] Step 1: Conduct analysis of existing medical problems. • Step 2: Develop a product concept for determining a solution to a specificmedical-associated problem. • Step 3: Evaluate all possible environments under which the medical deviceunder consideration is functioning. • Step 4: Evaluate all possible individuals expected to operate the product/deviceunder consideration. • Step 5: Construct a prototype. • Step 6: Test the prototype under laboratory environment. • Step 7: Test the prototype under the actual field use environment. • Step 8: Make appropriate changes to the product/device design to satisfy fieldrequirements.
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