Medical Metrology

Design Qualification, Installation Qualification, Operational Qualification, and Performance Qualification, (DQ)/IQ/OQ/PQ, refers to verification protocols that confirm, through review and testing, that manufacturing equipment fulfills written, legal obligations requiring conformance to acquisition specifications. These protocols are powerful quality control tools often involved in ISO regimens.

(DQ)/IQ/OQ/PQ has become a hot topic with the FDA. This is because of occasional problems with pharmaceutical product quality traced to the malperformance of manufacturing equipment and systems and/or to the performance of their controlling software. Part of the remedy, it is thought, is implementation of (DQ)/IQ/OQ/PQ.

Accordingly, the practice of (DQ)/IQ/OQ/PQ has recently taken hold among medical device manufacturers who today operate in an ever more demanding regulatory environment.

Overview
Herein, (DQ) or (Design Qualification), indicated in parentheses, is to designate it as a newer – and generally considered optional – addition to the process. However, it is becoming common as a precursor to equipment selection. (DQ) is usually the vendor’s responsibility and intended to ensure that the equipment’s design, if executed, will satisfy the end user’s detailed and specified requirements.

IQ – is to confirm proper equipment was installed with all required components, received with all required documentation, and that it meets stated specifications as installed.

OQ – confirms that equipment operates as intended in terms of the equipment manufacturer’s own expectations. The OQ check involves running through a standard operating procedure (SOP) for each state of the equipment to ensure it performs per the manufacturer’s own design intent.

PQ – makes sure, from the end users perspective, that the equipment’s final output is as specified by the end user across the entire range of required throughput.
 

Practical Terms
To provide an example of the (DQ)/IQ/OQ/PQ protocols in action, consider the implementation of a new dimensional metrology system intended to measure and inspect the manufacturing of a part for incorporation into a medical device:

Mitutoyo QuickVision Vision Measuring System

(DQ) – (Design Qualification) as pertaining to metrology equipment

• Not as standard as the other elements of the protocol, but becoming more common as a precursor to equipment selection.
• In some cases, the end user might contact a series of metrology equipment manufacturers to define operational and functional specifications of equivalent systems, useful to justify the final equipment choice.
• (DQ) items of interest may include:
  • Metrology equipment descriptions and brochures
  • Accuracy specifications
  • Indices of throughput
  • Manufacturer’s recommended installation layout
  • Utilities requirements
  • Environmental requirements

IQ – Installation Qualification as pertaining to metrology equipment

IQ items of interest may include:

• Metrology equipment received with inventory checklist (from the manufacturer)
• Equipment inspected upon receipt, verifying undamaged condition.
• Equipment is unpacked (the party unpacking may depend on who in stalls – manufacturer, certified trained representative, or end user)
• Prior to actual installation, ensure all utilities and environmen- tal requirements are ready
• Use of metrology equipment manufacturer’s set-up procedure

OQ – Operational Qualification as pertaining to metrology equipment

A description of OQ – Operational Qualification, is made clearer when expressed in terms of the implementation of an actual piece of metrology equipment. Therefore, the following descriptions of OQ and PQ relate to a medical device manufacturer’s implementation of a vision measurement system.

Unlike contact measuring systems, which determine workpiece geometry by utilizing a probe that displaces when physically contacting a feature’s surface, vision systems are non-contact. Instead, they work by capturing images of workpiece features and then analyzing the feature images to determine their dimensional characteristics. Vision system components include a camera, a processor, image analysis software, lighting, and often, networking capability.

The key activity of an OQ on vision measurement equipment involves the installer (whether the manufacturer or a manufacturer’s authorized representative) performing certified machine calibration tests. A table of certified procedures used typically by Mitutoyo America Corp. for calibration of vision metrology equipment accompanies the equipment. Each test is performed multiple times on the manufacturer’s own gage artifacts, see below. These artifacts are required to be traceable, in an unbroken chain of comparisons (together with associated measurement uncertainties) to a known standard. (See Traceability sidebar.)

A general list of items of interest to an OQ check of metrology equipment includes:

• Installer (or factory-authorized representative) is to perform calibration procedure and confirm that equipment operation was properly tested
• Reviews of calibration documentation, traceability, and calibration interval are with end user
• The end user receives a detailed accounting of results
• There is a review of preventive maintenance and procedures covering consumables and spare parts
• Review also occurs for vendor contacts for service, calibration, and parts
• There is review for software installation and functionality
• Review of operator training

Mitutoyo QuickVision system measures a calibration gage artifact.

PQ – Performance Qualification as pertaining to metrology equipment

The final check in the series, PQ verifies that the equipment is capable of satisfactorily measuring the end user’s actual workpieces, as they will be manufactured. This typically is a pass/fail test sometimes referred to as a buy off.

In the case of metrology systems, the PQ typically takes the form of a statistical Gage R&R (Gage Repeatability & Reproducibility) test. The Gage R&R measures the amount of variability induced in measurements by the measurement system itself, and compares it to the total variability observed to determine the viability of the measurement system.

Two key measures of a Gage R&R are:

1) Repeatability – An indication of the ability of a single piece of metrology equipment to provide consistent results taking into account variation induced to measurements attributable a single person, measuring the same part specimen, over multiple trials.

2) Reproducibility – An indication of the ability of a single piece of metrology equipment to provide consistent results. Reproducibility takes into account variation induced to measurements attributable to multiple operators, measuring multiple replicate part specimens (each specimen of the same design), over multiple trials.

The time, effort, and cost of a Gage R&R can add up geometrically. It is not uncommon for three operators to be involved, each operator testing ten identical parts ten times each (for a total of 300 trial measurements). There are no universal criteria for minimal sample size and number of trials for performing a Gage R&R. Those are up to the responsible quality managers who must assess risk depending upon the nature of the measurements.
 

Mitutoyo America Corp.
Aurora, IL
mitutoyo.com