SCINTILLATION CAMERA QC AND ACCREDITATION
AAPM NATIONAL MEETING-SALT LAKE CITY, UT
7/23/01
L. Stephen Graham, Ph.D., FACR
VA Greater Los Angeles Healthcare System/UCLA School of Medicine
I. INTRODUCTION
A. Primary focus will be on the ACR program of accreditation
B. Elements of the program from the medical physics standpoint
1. Acceptance tests by qualified medical physicist (not covered in this presentation)
a. Less than 5% of cameras meet all specifications and perform properly
b. When the camera is “accepted” (passes acceptance tests), a complete set of quality
control tests should be done to provide a benchmark for subsequent tests
2. Quality control tests performed by technologists (reviewed each year) – summary only
a. Intrinsic or system uniformity – each day of use
b. Intrinsic or system spatial resolution – each week
c. Center of rotation (detector registration) – as recommended by physicist
3. Facility performance tests (annual) by qualified medical physicist
4. Phantom images that must be submitted for ACR accreditation
a. Planar only systems
b. SPECT systems
II. QUALITY ASSURANCE/PERFORMANCE TESTS BY MEDICAL PHYSICIST
A. Elements of planar quality assurance program
1. “Peaking”
a. Principle: Analyzer window selects that will be used to produce the image
1) The width of the pulse height analyzer window determines the amount of
unscattered and scattered photons (15% to 20%)
b. Procedure: Verify that the window is symmetrically positioned on the photopeak
(the part of the spectrum where the unscattered photons fall) and is of proper
width
2. Sensitivity
a. Principle: Measure the counts per minute per microcurie
b. Methods
1) Use low activity Co-57 point source (intrinsic) on detector
2) Use Tc-99m point source (intrinsic) at a fixed distance
3) Tc-99m in flask (systgem) or Co-57 flood (system)
c. Analysis: Compare to benchmark values
3. Flood Uniformity
a. Test methods
1) Intrinsic (collimator off) – point source at five maximum dimensions
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2) System (collimator on) - liquid filled (Tc-99m) or solid (Co-57) floods
Flood Source
Collimator
Detector
b. Procedure: Collect at least 1.25M counts (small field), 2.5M counts (large field),
or 4M counts (large rectangular field) for visual analysis or at least 10M to 15M
counts for computer analysis
c. Analysis
1) Visual analysis: Carefully evaluate the images for uniformity
2) Computer analysis: Compute integral and differential uniformity if at least 10M
to 15M counts are acquired
3) Compare with benchmark images for same acquisition parameters
d. Performance parameters recommended by American Society of Nuclear Cardiology
(ASNC)
1) Integral uniformity: < 5% (standard); < 3% (preferred)
2) Differential uniformity: < 5% (standard); < 3% (preferred)
e. Additional tests
1) Off-peak images – reveal poor PM tube balance, crystal hydration, cracked
crystal, uncorrected uniformity, electronic problems, etc.
2) Intrinsic or system uniformity with nuclides other than Tc-99m that are
commonly used
4. Spatial Resolution and Linearity
a. Test methods (same number of counts as for “flood” image)
1) Intrinsic resolution/linearity with resolution test pattern
2) System resolution/linearity with resolution test pattern (low energy collimators
only)
b. Analysis
1) Note the smallest bars or holes that are resolved and estimate FWHM
2) Inspect image for linearity
3) Compare with benchmark images
c. Performance parameters recommended by ASNC: Intrinsic resolution (detector
only) FWHM: < 6 mm (standard) ; < 4 mm (preferred)
4. Energy resolution
a. Principle: energy resolution is a measure of the system’s accuracy in determining
the energy of a photon
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b. Procedure: Follow vendor’s protocol using their software (not available on some
systems)
c. Analysis: Compare measured number to benchmark tests
5. Count rate performance
a. Methods
1) Use Tc-99m two source method to measure and calculate “dead time”
2) Measure Tc-99m maximum count rate
b. Analysis: Compare to benchmark tests
6. Additional tests
a. Multiple window spatial registration - Checks for change of image size as a
function of photon energy (can produce a loss of spatial resolution and contrast in
clinical studies if not properly calibrated)
1) Method: Use Ga-67 at a distance (intrinsic) with a bar pattern on the detector
2) Analysis: Inspect the image for phase shifts
b. Check of collimator uniformity - test individual collimators (except the pinhole) for
physical damage
c. Display system (camera and computer) - check for artifacts and loss of spatial
resolution and contrast using resolution test pattern images in multiple positions
(examine film and/or screen)
B. Tomographic (SPECT) quality assurance
1. Verify that calibrations are current
a. Center of rotation calibration - mandatory
1) Note that this is a calibration or check, not a test of performance
a) On some SPECT systems periodic checks are performed and actual
calibration is only done when needed
2) Principle: Determines the geometrical relationship between the electronic
center of the detector and the center of the computer matrix
a) A small loss of calibration produces a loss of spatial resolution in the
tomographic images; a large error corrupts the image
b) The maximum acceptable uncorrected error is 0.25 to 0.5 pixel
3) Procedure: Vendor's instructions must be carefully followed
a) In some systems the COR calibration must be done for each collimator,
matrix size, and zoom that is used for SPECT studies; in many systems a
COR calibration is only needed for each collimator
b) If a procedure is available, the detector registration (alignment for multiple
head systems) should also be checked
4) Analysis: Carefully review the output provided by the vendor
5) Correction for any mismatch is automatically applied during acquisition of the
projection images or during reconstruction
6) Frequency: The general consensus is that calibration or a calibration check
should be done each week, or at the very least, once each month
a) When the system is first installed, COR calibrations should be done more
frequently (weekly) until a pattern of stability has been established.
b. High count flood image (intrinsic and/or system) for uniformity correction –
mandatory on most systems
1) Principle: Small non-uniformities in the detector or collimator can produce
artifacts in the reconstructed images
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a) A 5% error on the axis-of-rotation (the imaginary line around which the
detector(s) rotate) can produce a 35% artifact
2) Procedure: Acquire 30M (64 x 64 matrix) or 120M (128 x 128 matrix) count
image that will be used to correct for nonuniformity
3) Methods: Fillable flood (optional); Co-57 sheet source (standard)
4) Analysis: Carefully review clinical images for “ring” artifacts or other abnormal
patterns
5) Frequency: Weekly to monthly, once reliability is established
c. Pixel size calibration
1) Principle: Changes in pixel dimensions can distort reoriented images of the
heart and affect clinical studies in which attenuation correction is used
2) Frequency: Every six months
2. Phantom
a. Principle: Tomography of an object with known features provides an overall
evaluation of uniformity, spatial resolution, and contrast
b. Procedure: Fill the phantom with Tc-99m or Tl-201 and acquire a tomographic
study using total of ˜ 30M counts
c. Analysis: Carefully review the images for artifacts (rings, hot and cold spots not
associated with known structures), verify that resolution agrees with the
benchmark images and that the contrast is satisfactory
1) Quantification is optional
d. Frequency: General recommendation is each quarter or every six months and after
major service that might affect SPECT studies and after installation of new
software
1) Archived clinical studies may also be useful for checking new software
3. Patient motion detection
a. Summed projections - best for detecting vertical (along the table) motion
b. Sineogram - best for detecting horizontal (across the table) motion
c. Cine - can be used for detecting all types of motion
III. PHANTOM IMAGES FOR ACR ACCREDITATION
A. Planar systems (examples will be presented)
1. Intrinsic or system uniformity (Tc-99m or Co-57 and Tl-201 or Ga-67)
2. Intrinsic or system spatial resolution (Tc-99m or Co-57 and Tl-201 or Ga-67)
B. SPECT systems (examples will be presented)
1. Intrinsic or system uniformity as for planar systems
2. Planar spatial resolution by imaging ACR-approved SPECT phantom placed directly
on collimator (Tc-99m and Tl-201 or Ga-67)
3. Tomographic study with ACR-approved phantom (Tc-99m and Tl-201 or Ga-67)
C. Evaluation of the applications – General description
1. Clinical and phantom images for each camera are randomly submitted to a random
panel of physicians and medical physicists
2. The final report includes special assessments and recommendations
3. Three year accreditation is given to successful applicants
4. A certificate and machine label are provided for each approved camera specific to the
type of exams that can be performed
D. Evaluation of phantom images
1. ACR Phantom is based on a phantom that is commonly used
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2. All images are scored using one of five terms – excellent, good, satisfactory, marginal,
and fail (extensive descriptors are used for each term)
3. Intrinsic and system uniformity variations in image intensity due to incorrect balance of
the PM tubes, as well as CRT or video and/or formatter artifacts are considered
4. The type of resolution pattern is considered in the evaluation
E. On-site reviews of accredited facilities
1. Random on-site surveys may be performed during the accreditation period to validate
consistent quality
2. Sites are notified a few days in advance
3. Survey team includes physicians and physics reviewers and an ACR staff person
F. Future additions
1. Development of a fourth module on PET imaging is in process
2. Phantom is a modification of the phantom for module 2 that includes “hot” cylinders
IV. SUMMARY AND CONCLUSION
A. Acceptance tests are required/recommended by JCAHO and professional organizations
and is important for identifying problems and verifying proper operation
B. A comprehensive QC program documents the current state of the camera and identifies
loss of performance and should be reviewed annually or more frequently
C. NM accreditation demonstrates to payers and regulatory agencies, and referring
physicians, that the facility provides high quality health care
D. Immediate and long-term benefit is patient confidence and peer recognition
E. Medical physicists play an important role in this process
References
AAPM/RSNA 1994 Physics Tutorial for Residents: Cross-sectional Imaging: Emission
Tomography, Audiovisual Slide Set with Annotation. Radiological Society of North America,
Chicago, IL, 1994.
Garcia EV (ed): Imaging Guidelines for Nuclear Cardiology Procedures, Part 1. J Nucl Cardiol
3:G1-G46, 1996
Graham, L.S.: Quality control for SPECT systems. Radiographics 15:1471-1481, 1995.
Graham, L.S. and Muehllehner, G.: Anger Scintillation Camera. In Sandler et al. (eds):
Diagnostic Nuclear Medicine, 3rd edition, pp. 81-92. Williams & Wilkins, Baltimore, MD, 1996.
Graham, L.S.: Scintillation camera imaging performance and quality control. In Henkin, R. et al.
(eds): Nuclear Medicine: Principles and Practices, pp. 125-146. Mosby-Year Book St. Louis,
MO, 1996.
Nichols KJ, Galt JR. Quality control for SPECT imaging. In DePuey EG, Berman DS, Garcia
EV, (eds). Cardiac SPECT imaging. New York: Raven Press, Ltd., 1995:21-47.
AAPMSLC701.HAN
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