Instrument Quality Assurance: What Is Required

Robert E. Zimmerman

Joint Program in Nuclear Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, MA 02115 USA


Abstract

A successful, meaningful quality assurance program begins with the director of the nuclear medicine laboratory and propagates down the chain of responsibility to the technologist responsible for operation of individual instruments. Included in that chain are the director, physicist, chief technologist(s) and each of the technologists. Every person has a role in the process.

Written protocols for periodic evaluation and testing of the equipment must be followed. These protocols may include daily operational tests, weekly, monthly, quarterly and yearly performance tests and initial acceptance testing of new instruments.

Nuclear medicine instrumentation is changing rapidly and recommended testing intervals and required procedures are changing, also. As professionals we should be aware of these changes and be ready to adapt our protocols to the changing conditions.

There are many documents available on instrument quality assurance. The most valuable are listed and discussed in an annotated bibliography.

Components of a QA program

In most settings the director of the nuclear medicine clinic is ultimately responsible for the work performed in the clinic. This is often a physician trained in nuclear medicine but may be another professional competent to direct the operations. The director is responsible for instilling the quality assurance ethic, making sure it is an important aspect of the workday.

The nuclear medicine physicist is responsible for insuring that the instrument quality assurance protocols are designed appropriately and conducted correctly. He will perform periodic reviews (quarterly) of the results and will periodically (yearly) review protocols for appropriateness. This may be a part time position in many situations. Health physicists are normally not qualified to perform this role, without advanced training in nuclear medicine instrumentation.

The chief technologist in most nuclear medicine clinics is responsible for seeing that the routine quality assurance tests are performed, results evaluated and corrective action initiated when required. This will be accomplished in conjunction with the technologist staff. The physicist will interact with the staff frequently as problems occur and as they are corrected.

The Protocol Manual

The protocol manual for a nuclear medicine laboratory will contain the complete description of the clinical procedures and the technical or instrument quality assurance procedures.

The instrument quality assurance sections will contain detailed protocols that are performed on a regular basis for all the imaging instruments and non-imaging instruments. The instrument quality assurance protocols will be designed by the nuclear medicine physicist in conjunction with the chief technologist. These protocols will be amended as new equipment is purchased and as the
circumstances change within the lab e.g. if an old SPECT camera is used only for planar work.

Acceptance Testing

Each instrument that is purchased should undergo acceptance testing before being incorporated into the daily regime. The results of the acceptance tests will become the baseline values for the regular instrument quality assurance program for that instrument.

Tools

It is important to recognize that there will need to be a financial investment in an instrument quality assurance program. This investment is modest when compared to the value of the services performed for a patient. Listed below are the minimum tools that a modern nuclear medicine laboratory should have on hand. Full details of tools can be found in the documents listed in the bibliography, especially the IAEA TECDOC.

For dose calibrators:

At least two of the following:

  1. Co-57, 40-400 MBq or 1-10 mCi - for accuracy and constancy test
  2. Cs-137, 4-40 MBq or 0.1-1 mCi- for accuracy test
  3. Ba-133, 4-40 MBq or 0.1-1 mCi - for accuracy test
  4. Co-60, 2-20 MBq or 0.05-0.5 mCi - for accuracy test
  5. other long-lived sources of appropriate amount for testing accuracy.

All of these sources should be sealed and in solid form and calibrated to at least +/- 5% by a recognized calibration procedure traceable to a national calibration laboratory.

For well counters:

At least one of the following:

  1. Cs-137, 4-20 kBq or 0.1-0.5 uCi, for energy resolution measurements, constancy tests
  2. I-129, 4-20 kBq or 0.1-0.5 uCi, as an I-125 substitute.

For probe systems:

At least one of the following:

  1. Co-57, 400-2000 kBq or 10-50 uCi for low energy calibration and constancy tests
  2. Cs-137, 400-2000 kBq or 10-50 uCi for low energy calibration and constancy tests

For gamma cameras:

All of the following:

  1. Co-57, 400-2000 kBq or 10-50 uCi point or "button" sources
  2. Co-57, 200- 400 MBq or 5-10 mCi flood source
  3. fillable flood source that is verified to be uniform
  4. planar performance phantom (thyroid or liver, typically)
  5. resolution pattern: quadrant bar, hole pattern or other
  6. method of routinely making line sources
  7. method of routinely making point sources
  8. mask for the UFOV of the camera
  9. SPECT performance phantom. This phantom should provide for testing SPECT uniformity, SPECT reconstructed resolution and SPECT reconstructed contrast.

Optional - these tools can often be borrowed from the manufacturer:

  1. NEMA resolution pattern
  2. Dead time scatter phantom for extrinsic dead time measurements
  3. copper sheets and source holders for intrinsic dead time measurements

    Software for performance evaluation is often available from the manufacturer, sometimes permanently or more often on loan and useable only under supervision of the service person.

For display:

  1. A means of generating a test pattern to check the full range of luminance and contrast (e.g. SMPTE test pattern suitable for computer displays)


Annotated Bibliography

Quality control of nuclear medicine instruments 1991IAEA-TECDOC-602, May 1991INIS Clearinghouse (for microfiche copy)orNuclear Medicine SectionDivision of Life SciencesInternational Atomic Energy AgencyWagramerstrasse 5P.O. Box 100A-1400 Vienna, Austriahttp://www.iaea.or.at

This is the latest in a series of quality control documents for nuclear medicine produced by the IAEA. Most significant aspect of this book is the detailed protocols for all nuclear medicine instruments. This book has been widely distributed throughout the world, especially in developing countries. Knowledgeable physicists and technologists can adapt the protocols in this book to their local situation.

Performance Measurements of Scintillation CamerasNEMA Standards Publication No. NU 1-1994National Electrical Manufacturers Association2101 L Street, N.W.Washington. DC 20037 USAhttp://www.nema.org/medical/index.htmhttp://www.nema.org/medical/temp/ medstd.htm#nuclear

This is the 1994 version of the NEMA protocols for testing and specifying gamma camera performance and incorporates some SPECT tests. This is most useful as an educational document and a source book for designing one's own protocols for gamma camera testing. It cannot be over emphasized that many of the tests specified in this document cannot be successfully run in the users hands without considerable support from the manufacturer. Even then, certain tests are very difficult to conduct except under factory conditions. The NEMA protocols are not sufficient. A number of important tests are not described here and are not specified by the manufacturer.

Characteristics and Test Methods for Anger Type Gamma CamerasIEC Technical Publication 789 (1990)International Electrotechnical CommissionPO Box 1311211 Geneva 20, Switzerland. http://www.iec.ch

I have no personal knowledge of this document but it is recognized to be a very good reference in the area of gamma camera QA.

Scintillation Camera Acceptance Testing and Performance EvaluationAAPM report No. 61980

This document contains basic planar camera acceptance testing protocols and is an excellent place to begin learning about these important protocols. Computer-aided Scintillation Camera Acceptance TestingAAPM report No 91981

This extended report No. 6 to cameras with computer. Unfortunately software described in this report has not become readily availiable

Rotating Scintillation Camera SPECT Acceptance Testing and Quality ControlAAPM report No 221987

This extended the AAPM report series to SPECT cameras.

American Association of Physicists in MedicineOne Physics Ellipse College Park, MD 20740-3846 USA(301)209-3350; FAX (301) 209-0862; Membership (301) 209-3386 http://aapm.org/pubs/booklets/booklets.html

Available on order from American Institute of Physics, c/o AIDCPO Box 20Williston, VT 05495 (800-488-2665)

Hospital Physicists' Association47 Belgrave SquareLondon SW1X 8QX United Kingdom

HPA has had a number of documents available on testing of nuclear medicine instrumentation.

zimmer@bwh.harvard.edu Robert E. ZimmermanHarvard Medical SchoolJoint Program in Nuclear Medicine

Brigham & Women's HospitalRadiology Department75 Francis St.Boston MA 02115