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All
systems require the use of a high-count uniformity correction
flood. Most new systems, if not all, require the user to acquire
a 100 million-count correction flood. This correction is applied
to all images acquired, whether they be planar scans, dynamic
flow studies, or SPECT.
COLLIMATION OF THE IMAGING SYSTEM
The
careful selection of the appropriate collimator may be specific
to the organ system, the energy of the isotope, resolution requirements,
or the manufacturer of the camera. Because collimators are an
integral part of nuclear medicine imaging systems, the importance
of assessing collimator integrity is vital to the resultant
image quality.
Routine
extrinsic floods, daily, weekly and/or monthly, will provide
an assessment of collimator uniformity over time, allowing the
facility to observe and track subtle changes that may indicate
more serious problems. Early detection of image degradation
due to collimator non-uniformity will alert the user to call
service and address problems or issues, perhaps avoiding costly
shutdowns for significant repair later.
The
integrity of the collimator requires both external and internal
assessment. Externally the collimator is visually inspected
for dents, nicks, or other damage. The camera running into the
imaging table, a step stool, an object striking the surface
of the camera face, or improper alignment and mounting of the
collimator are just some of the causes of collimator compromise.
Internally,
temperature changes or power surges may cause the soft metal
construction of the septa and bonded lead foil sheets of the
collimator to be altered or separated, thus affecting the uniformity
of the imaging system. At least once a year a very high count
extrinsic flood, preferable 100 million counts, should be acquired
and reviewed by the technologist, RSO/Medical Director and service
engineer during a preventive maintenance visit to assure uniformity
of the entire gamma camera.
It
is important to remember that both intrinsic and extrinsic uniformity
flood images should be evaluated to assure the function of the
entire imaging system. The intrinsic flood assesses the uniformity
of the detector itself. Extrinsic floods allow evaluation of
the uniformity of the detector and the collimator in combination,
as used for patient studies.
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figure 2: QC MATRIX
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SPECT QC
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ICANL
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SNM |
ASNC |
Digirad
QC |
Siemens
Medical Solutions USA, Inc. c.cam |
Siemens
Medical Solutions USA, Inc. e.cam Signature Series
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Siemens
Medical Solutions USA, Inc. Symbia |
Philips
QC CardioMD |
Philips
QC Forte, Skylight, Precedence |
Routine
Uniformity Flood |
Daily
(prior to use) ~2-5M counts |
Daily |
Daily
1.5 - 4M counts* |
Daily
3M - 6M counts |
Daily
(prior to use) ~10M - 30M counts |
Daily
(prior to use) ~10M - 30M counts |
Daily
(prior to use) ~10M - 30M counts |
Daily
10M counts |
Daily
15M counts |
High
Count Flood (>30M cts) |
Monthly
calibration, or PMRII |
PMR;
typically >30M cts |
Up
to 100M counts per detector (interval not stated)
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As
needed (24M - 96M counts) |
Monthly
30M counts per detector |
Monthly
200M counts per detector |
Monthly
200M counts per detector |
Weekly
>30M counts |
Recalibrate
only when needed |
Sensitivity |
Weekly |
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Weekly
or Daily |
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|
|
|
Weekly |
Weekly |
Linearity
|
Weekly |
Weekly |
Weekly
(rotating quadrants weekly) |
None.
Crystal size defines intrinsic resolution |
Site
Preference |
Site
Preference |
Site
Preference |
Weekly |
Weekly |
Resolution |
Weekly |
Weekly |
Weekly
(rotating quadrants weekly) |
None.
Crystal linear array defines linearity |
Site
Preference |
Site
Preference |
Site
Preference |
Weekly |
Weekly |
Center
Of Rotation (COR) |
Monthly |
PMR |
Weekly
or Bi-monthly |
Weekly |
Weekly,
Check monthly acquisition |
Monthly |
Monthly |
Weekly |
Weekly |
Collimator
Integrity |
Annually |
Annually |
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Daily |
Installation,
if site damage suspected & Site Preference |
Installation,
if site damage suspected & Site Preference |
Installation,
if site damage suspected & Site Preference |
Weekly
(check for damage to septa and to locking mechanism)
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Weekly
(check for damage to septa and to locking mechanism)
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Preventive
Maintenance |
Every
6 months or PMR |
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Semi-annually |
Every
6 months |
Every
6 months |
Every
6 months |
Every
6 months |
Every
6 months |
Phantom
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Periodically,
High Count |
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N/A |
Site
Preference |
Site
Preference |
Site
Preference |
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NOTES:
*ASNC recommendation for Daily Uniformity Flood: 1.5M
- 4M counts depending on detector size for visual; 4500
counts/cm2 for quantitative uniformity; min 10K counts
for center of FOV; Integral Uniformity <5%, <3%
preferred; Differential Uniformity <5%.
**PMR: Per Manufacturer's Recommendation must be clearly
documented from the operator manual and included in
the QC manual if variance to required QC.
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In
2005, the ICANL compiled a QC matrix to identify the
QC for SPECT systems, by comparing guidelines from SNM, ASNC,
ICANL and several camera manufacturers (see figure 2: QC
Matrix, above). Throughout when a site preference is noted,
it is required that the site show formal documentation from
the specific manufacturer's operator manual with the recommended
standard QC for that system.
In
summary, applicant laboratories are encouraged to follow the
ICANL Standards when developing and evaluating their
quality control programs. Referencing the ASNC, SNM, NRC and
other published guidelines and examples is recommended in order
to establish best practice policies and procedures for the assessment
of all nuclear medicine equipment. By performing routine quality
control procedures, nuclear medicine laboratories are able to
demonstrate that they are capable of providing quality patient
care through expert imaging.
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