1. QC And NEMA In The Nuclear Arena
Gamma Cameras

2. Floods – Uniformity Testing
Types of floods
Co57
Impregnated plastic
Old source vs. the new source
Refillable flood
Adding the Tc99m
Mixing and spilling
It will bow if its too big
Point source at least 5 diameters away from the surface
Key Points
Setting the peak
How many millions of counts?
Size of the detector
Complete daily
Amount of activity

3. Corrected Vs. Uncorrected
Setting your correction matrix
Depends on SPECT
30 M vs. 120 M vs. the size of the head
Do one for each radiopharmaceutical
Correction will either subtract or add counts
Take un/corrected flood and bars
Correction for each PMT is no more than 10%
Acquire at least once or month or when needed

4. Intrinsic Uniformity Determine Integral and Differential Uniformity
Remove collimator place a 3mm Pb “ring” around the UFOV (example next side)
Set 20% window 99mTc with source (~200 μCi) 5 UFOV away
Set matrix at 64 x 64 to collect no more than 20,000 cps
Acquisition - center pixels must collect 4000counts/pixe; (~16 M count flood)
Complete a 9 pt smooth and calculate the following

5. Calculations

6. What are we looking at?
Integral uniformity looks at maximum deviation for both CFOV and the UFOV
Differential uniformity looks at the maximum change of counts over a range of any 5 pixels in every column and row
Excessive changes in any of the numbers is an indication non-uniformity problems
Time to call service guy!

7. Flood Sources Co57 Flood Source Rectangular or Circular 5 to 20 mCi
Non-uniformity at <1.0%
No mixing required – reduces
radiation exposure
Expensive since it must be
repurchased based on Co57 decay
Refillable Flood Phantom
Rectangular or Circular
Different sizes to fit a specific type of detector
Inject mCi amount of Tc99m
and mix in the water filled container
Concerns
Mixing can get messy
Radiation exposure when mixing
Air bubble will distort the image

8. Typical Bars – Four Quadrant
Multiple types of phantoms are available to match the size of the detector
Bars contain Pb embedded in plastic.
Bars attenuate the gamma radiation being emitted from the flood source
Bars vary in size within each quadrant
Is usually done with the collimator on
Known as an extrinsic bar
Tests system resolution
Imaging system should resolve between the 3rd and 4th smallest quadrant
Smallest bars are 2 mm, however, it depends on the type of 4 quadrant bar
purchased

9. Setting Up The Bar Phantom
Comments
How would imagine resolution be effected by LEHS vs. LEHR collimation?
How does increased counts effect image resolution?
How often is this procedure done on the imaging system?
Why are the bars rotated every time this procedure is done?

10. Other Types of Bar Phantoms
BHR Test Pattern
Lead plate that is 3.2 mm thick
is placed between 2 sheets of
Plastic
Orthogonal-holes are then drilled
in an array pattern
Emission source can be extrinsic
or intrinsic (intrinsic usually done)
Clearly defines system resolution
Over the entire camera
Linearity also identified
PLES (Equally Spaced Parallel-Bar)
Phantom
Checks linearity and resolution
Phantom is placed with flood source
on top (just like the Bar and Flood)
5 mm and 3 mm bars are available
Linearity is the key
X and Y axis- linearity is tested
Looking for a straight line
Lines should not be wavy

11. BHR Phantom Results
Example of a BHR phantom with 2.5 cm orthogonal-holes

12. More On Bars Do weekly and rotate each week How many counts?
Size of detector
Increased counts improves resolution
Collimation
Changes in resolution can be seen and identifies a loss of system resolution
Intrinsic or extrinsic?

13. Systems Uniformity/Linearity/Resolution
Uncorrected Flood
And Bars
4000k/image
Corrected Flood
And Bars
4000k/image

14. Edge Packing Intrinsic flood uses a mask on top of the crystal to
eliminate this artifact
Extrinsic flood may show this artifact

15. Setting The Peak Centering the peak is essential
Off peaking causes imaging artifact
What would happen if you imaged a patient with Co57 with Tc99m on board?

16. Example Of Being Off-Peak
Creation of lesions in the liver
Could this lead to an inappropriate diagnosis?

17. Distance And Resolution
These images show the effect
of distance on image resolution
Surface vs. 1 inch
2 inch vs. 3 inches
What conclusion can you make
when it comes to imaging a
patient?
Does count density also add to
this issue?

18. Problem With A PMT What causes this artifact?
How do both image sets differ?
How might this effect the a patient’s diagnosis?

19. Problems With Liquid Filled Floods
Image on the left shows a flood that was note mixed completely
Image on the right shows an air bubble in the flood

20. 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

21. More Issues Inappropriate X/Y coordinates set on the a formatter
Cracked crystal

22. Types Of Bars
A – Parallel-line equal-space (PLES) phantom: Small lead bars
Test Camera’s spatial resolution. Two transmission images are
Taken at right angles. Consider the Moire pattern
B – Four quadrant bar phantom: Show wholes of equal size.
The smallest bars can go down to 2 mm in size.
C – Orthogonal-hole (OH) phantom
Comes in different sizes (0.64 cm, 0.48 cm, and 0.32 cm
Diameter spaced at 1 cm, 0.96 cm, and 0.64 cm respectively.
Matching the lower end of system resolution is important.

23. Results Of Excessive Activity
Activity from the source should never exceed 20k/second
The image on the left shows the results of excessive activity
The image on the right is the same, however, the activity has been reduced to less than 20k per second

24. Intrinsic Uniformity
With a point source collect 64 x 64 flood where the center pixel receives a minimum of 4000 cts (16 million count flood)
Filter with a 9 point smooth
Integral uniformity is the maximum pixel deviation
Differential uniformity max change of cts over range of any 5 pixels in all rows and in all columns

25. Key Points
Identifies the amount of nonuniformity with all areas of the flood
Variations between un/corrected should be no greater than 15%
Should be done weekly to determine when the camera needs a PM
“Measles” occur when water gets into the crystal
Floods should be done with the collimator on to see if there are any defects in it
A crystals may crack when there is change of 8 degrees F
Room temperature should range between 40 and 110 degrees F

26. Measles Image is off-peak
Loss of the hermetic seal causes water to enter and dissolve the crystal

27. System Sensitivity
Is a parameter of camera’s ability to efficiently detect the incident gamma with the collimator on
Changes in sensitivity result from
Nonuniformities in the crystal
Decreased energy resolution
Incorrect collimation
Improper setting of the PHA
Recording the time it takes to collect a Co57 flood corrected for decay will identify any change in system sensitivity

28. System Spatial Resolution
Is defined as camera’s ability to accurately determine the original location of a gamma ray on an X-Y plan with collimation

29. Moiré Pattern
When a bar phantom is not lined (oriented) up septa in collimator this patter will occur
Bars travel at angle to the line of wholes (septa) in the collimator
This can be further seen on the next two slides

30. Moiré Continued Moiré seen on bar Images Bands represent
the bars and the
holes represent
the septa
Images across
From each other
Identify the pat-
tern

31. Moiré Continued
This shows a different moiré pattern because of the change
In rotation of the bars to the collimator septa

32. Instrumentation and QC
Consider the following procedures that involve QC and instrumentation
Uniformity Matrix
Floods and Bars
Other types of Bars - what is there purpose?
Linearity
Off peak or on peak
Effects of Distance on image resolution
Count density
PMT artifacts
Crystal artifacts
Collimator artifacts
Flood field artifacts

33. QC On The Dose Calibrator
Constancy
Accuracy
Linearity
Geometry
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