Gamma camera quality control

1. • Quality control (QC), which may be
defined as an established set of
ongoing measurements and analyses
designed to ensure that the
performance of instrument within a
predefined acceptable range
• QC is thus a critical component of routine
nuclear medicine practice
What is QC?

2. Gamma Camera QA
Procurement of Gamma camera
• Selection of the equipment
• Site selection
• Local power conditions
• Environmental conditions (temp,
humidity, dust)

3. Gamma camera
Performance parameters
• Uniformity
• Spatial resolution
• Spatial linearity
• Energy resolution
• Count rate performance (Max CR, CR (20% loss, t etc)
• System sensitivity
• Multiple window spatial registration
• Detector head shielding
• Crystal hydration
• Collimator evaluation
• Computer hardware (pixel size, timer, ADC linearity)
• Computer software
• Total performance
• SPECT

4. Order of Events in the Quality
Control of Gamma Camera
• Operational Checks
• Acceptance and Reference testing
• Periodic QC tests
– Daily, weekly, monthly, quarterly, annual

5. Quality Control
Standards:
– National Electrical Manufacturers
Association (NEMA NU-1 94)
– International Electromechanical
Commission (IEC 61675-2)
– International Atomic Energy Agency (IAEA
TECDOC 602)
– American Association of Physicists in
Medicine (AAPM No. 9)

6. Operational Checks
. Visual Inspection
Inspection of Table Top
Inspection of Limits of the System
Inspection of Security Systems
Inspection of Collimators
Inspection of Movements
. Check of Background Radiation

7. Acceptance and Reference
Testing(Planar&SPECT)
– Test of centering of PHA window settings
– Test of intrinsic flood-field uniformity
– Test of Intrinsic Count Rate
– Test of intrinsic flood-field uniformity for
radionuclides other than 99mTc
– Test of intrinsic spatial resolution

8. Acceptance and Reference
Testing(Planar&SPECT) contd..
– System Spatial Resolution
– Intrinsic Spatial Linearity
– Intrinsic Energy Resolution
– Maximum Count Rate
– Multiple Window Spatial Registration
– Detector Head Leakage

9. Acceptance and Reference
Testing(SPECT)
– Determination of pixel size
– Test of Center of Rotation
– Test of Tomographic Resolution in Air
– Test of Tomographic Resolution With
Scatter
– Test of Slice Thickness at Center of Slice

10. MINIMUM QC TESTS
– Visual Inspection
– Background Radiation Level
– Uniformity
– Photo Peak and Window Setting
– Intrinsic Spatial Resolution
– Intrinsic Spatial Linearity
– Multiple Window Spatial Registration
– Center of Rotation (Only For SPECT)
– Tomographic Resolution (Only For
SPECT)

11. • Flood field phantom
• Orthogonal hole transmission pattern
phantom
• Resolution and linearity phantom
• PLES bar phantom
• Step-wedge phantom
• Total performance phantom
• CT phantom
PHANTOMS REQUIRED FOR
GAMMA CAMERA QC

12. Background Radiation Levels
and Contamination
High Level Radiation may be due to:
– Radioactive patients in the Proximity of
System
– Unshielded Sources
– Radioactive Contamination on the Floor,
Wall, Collimators and Detector

13. Photo Peak and Window Setting
• Centering the peak
is essential
• Off peaking causes
imaging artifact
• What would
happen if you
imaged a patient
with peaking of
wrong isotope

14. Example of off-peaking
• Creation of lesions in the
liver
• Could this lead to an
inappropriate diagnosis?

15. INTRINSIC ENERGY RESOLUTION
– Intrinsic Energy Resolution is a
performance Characteristic of a
scintillation camera that describe
its ability to resolve two photons
with Different energy
– Intrinsic Energy Resolution shall be
measure as the ratio of the
photopeak FWHM to the photopeak
center energy given as a percentage

16. UNIFORMITY
Uniformity is the ability to produce a Uniform
Smooth image across the detector against a
Uniform Irradiation
– Intrinsic Uniformity (without collimator, Point source)
– Extrinsic Uniformity (with collimator , Flat source)
(appropriate radioisotopes are used for the purpose)

19. Intrinsic Uniformity Results
• Qualitative: Inspection
for variations in
brightness and density
• Quantitative: Integral
and diff. uniformity to
be computed for CFOV
(Central field of view)
and UFOV (Useful field
of view)
IU = 100 (Max - Min)
(Max + Min)
DU = 100 (High - Low)
(High + Low)

28. • Source and flood (dis water) are uniform
mixed.
• No air bubbles.
• No overfilling with liquid.
• No leakage of radioactive contents
Construction of flood source
phantom

29. • Co- 57 sheet sources have two major
drawbacks.
• expensive and need to be replaced
every 1-2 years.
• New Co-57 sheet sources usually
contain small amounts of Co-56 and
Co-58. These radionuclidic
contaminants have a shorter half-life

30. • Distortion of the sheet source ,
• presence of air bubbles inside the
source,
• poor mixing of the isotope within the
source,
Refillable sources
disadvantage

37. Spatial Resolution
• Spatial Resolution is a performance
characteristic of a scintillation camera
that describes its ability to resolve two
separate point or line source of radiation
as separate entities
–Intrinsic Spatial Resolution (without collimator)
» FWHM 3.5 - 4.5 mm FWTM 6.5 - 9 mm
–System Spatial Resolution (with collimator)
Acceptance and annual test

38. Intrinsic resolution

39. Intrinsic resolution
Analysis

40. • Four quadrant bar phantom
• Acquire intrinsically
• Large matrix 512x512)/zoom
• 5 million counts
Intrinsic resolution
Alternative method

42. System resolution
• Measured as FWHM,
FWTM
• With and without scatter
• Values are 4.5-10 mm
• Collimator is determining
factor

43. Spatial Resolution (line source on the face of the
collimator) FWHM = 4.34 mm

44. Spatial Resolution (line source at 11cm from the face of the
collimator)
FWHM = 9.47 mm

45. Intrinsic spatial Linearity
• Spatial Linearity is a performance
characteristic of a scintillation camera that
describe the amount of Spatial distortion
of image with respect to the object
spatial Linearity describes the degree of
linearity in the image of a linear object

48. Spatial Linearity and
Resolution
• NEMA linearity
phantom (slit mask
in contact with
crystal exposed with
a point source at a
distance)

49. Spatial Linearity and
Resolution
Quadrant bar and Resolution
phantoms

50. Spatial Linearity and
Resolution
• Qualitative: Inspection of
distortions in the lines and
visualization of patterns in
all quadrants
• Quantitative: Calculation
of absolute and differential
linearity and FWHM and
FHTM values

52. Multiple Window Spatial
Registration
• Collimated Gallium-67
sources are used at
central point, four
points on the X-axis
and four points on the
Y axis
• Perform acquisitions
for the 93, 184 and 300
keV energy windows
• Displacement of count
centroids from each
peak is computed and
maximum is retained
as MWSR in mm

57. Count Rate Performance
• Performed to ensure that the time to
process an event is sufficient to
maintain spatial resolution and
uniformity in clinical images
acquired at high-count rates

65. System planar sensitivity
• Acceptance test
• Values are expressed as
cps/mCi
• Typical values 150-350
cps/mCi
• Multiple head within 5%

66. Collimator evaluation
• Hole angulation
• Image of a point source placed at about 10
feet in front of detector
• Images of parallel line sources in X and Y
directions at various distances from
collimator
• COR off set values for three different radii
of rotation

67. Collimator hole angulation
• Collimator affects the
image quality
• Reconstruction algorithm
assumes that all channels are
perpendicular
• one degree channel tilt
produces 3.5 mm error during
backprojection at 20 cm

68. Collimator Damage
• Image on the right
indicates damage
to the collimator
septa
• Image on the left
shows the effects
of septa damage
on a diagnostic
study

69. HEAD Shield Leakage
• Determination of the
penetration of the head
shielding by sources
placed 10 cm away from
the detector housing and
reported as a leakage in
counts/ min/ MBq or count
rate with respect to the
reference point on the
collimator

70. SPECT Quality Control
• SPECT uniformity
• Uniformity and sensitivity at different angles
• SPECT resolution in air and water
• COR offset values for different collimators
and their configurations
• Total performance

74. SPECT Resolution in air (NEMA)

75. SPECT Resolution (NEMA Phantom)

76. SPECT Resolution (NEMA Phantom)

77. SPECT Resolution with Scatter( NEMA Phantom)

78. TOMOGRAPHIC RESOLUTION
• Three transverse slices should be reconstruct by
ramp filter
• For each of the three points calculate LSF
• For each of the three points calculate FWHM and
FWTM
• Those value must not exceed two times the
Planar spatial resolution

80. TOMOGRAPHIC RESOLUTION
Tomographic Spatial Resolution is a
performance characteristic of a
scintillation camera that describes its
ability to resolve two separate point or
line source of radiation as separate
entities in tomographic mode

81. Recommended frequency of
QC tests
Daily
Visual Inspection, Background Level Check
,Qualitative/quantitative Uniformity Check ,Photo Peak Check
Weekly
Quantitative Uniformity Check
Montly
Center of Rotation, Intrinsic Uniformity, Extrinsic Uniformity
After major service or half yearly/annually
Spatial Resolution ,Spatial Linearity ,MWSR ,SPECT Resolution

82. Quality control report
• It is imperative that the QC result and setting
are recorded and available at the site
• The proper record keeping greatly facilitates
detection of gradual deterioration of
performance over an extended period of time
• A baseline set of QC result should be recorded
after installation and acceptance testing to serve
as a reference for the life of the equipment