Equipment and Quality Control

Question 1

Summarise how you would test ‘Whole body system uniformity’

Answer 1

• LEGP Collimator
• Use a uniform flood source such as Co-57 sheet
• Acquire static and whole-body images:
  256x1024 WB = With source in centre of FOV
  256x256 STATIC = Same distance as WB
  REPEAT FOR EACH DETECTOR
• Extract matrix from images and convert both to 64x64 to conserve counts
• Analyse global (Integral) and local (differential) uniformity using the NEMA protocol
• Suggested Frequency: Acceptance testing and after major component replacement

Question 2

Summarise how you would test Planar Intrinsic Uniformity of a Gamma Camera

Answer 2

• NO Collimator
• Use a point source of Tc-99m; 20-50 MBq in 1mL (Count rate < 20 kcps)
  
  • Acquire 30M Counts
  • Source must be at a distance of approx 5.5x
    FOV
• Acquire static and whole-body images:
  256x1024 WB = With source in centre of FOV
  256x256 STATIC = Same distance as WB
  REPEAT FOR EACH DETECTOR
• Analyse global (Integral) and local (differential) uniformity using the NEMA protocol
• Suggested Frequency: Daily

Question 3

Summarise how you would test Planar Intrinsic Resolution of a Gamma Camera

Answer 3

• NO Collimator
• Use a point source of Tc-99m; 200 MBq in 1mL
  
  • Source must be at a distance of approx. 5x
    FOV
  • Use transmission slit phantom which is
    placed directly on crystal
• Acquire images with phantom in both the x- and y-directions with respect to the camera head
• Analyse by drawing several 25mm wide profiles across the line peaks and calculate the FWHM & FWTM of each line
• Suggested Frequency: At acceptance and then
  annually

Question 4

Summarise how you would test Planar Extrinsic Resolution of a Gamma Camera

Answer 4

• All available Collimators
• Line sources of Tc-99m; 200 MBq
  
  • Activity entered into capillary tubes
  • PLES phantom
• Acquire images with ‘phantom’ source in both the x- and y-directions with respect to the camera head
• Analyse by drawing several 25mm wide profiles across the line peaks and calculate the FWHM & FWTM of each line
• In NHST perform with 180mm perspect scatter material in two orientations:
  
  • 30/Phantom/180 & 10/Phantom/170
• Suggested Frequency: At acceptance and then
  annually

Question 5

Summarise how you would test Whole Body Resolution of a Gamma Camera

Answer 5

• LEGP
• Line sources of Tc-99m; 500 MBq in 1mL
  
  • Activity entered into capillary tubes
  • PLES phantom
• Acquire images with ‘phantom’ source in both the x- and y-directions with respect to the camera head
• Analyse by drawing several 25mm wide profiles across the line peaks and calculate the FWHM & FWTM of each line
• 150mm of scatter between detector and capillaries
• Compare static and WB results
• Suggested Frequency: At acceptance and after
  major component replacement

Question 6

Summarise how you would test Whole Body Count Rate Variation of a Gamma Camera

Answer 6

• LEGP
• Point sources of Tc-99m; 100 MBq in 2L
  
  • Activity entered into capillary tubes
  • PLES phantom
• Acquire WB images with point source attached
  to centre of collimator face
• Convert to smaller matrix to increase counts
  and obtain profiles avoiding the ramp regions
• Determine the Mean, SD and CoV from the
  pixels in the profile
• Suggested Frequency: At acceptance and
  Quarterly

Question 7

Summarise how you would test Whole Body Exposure Time Correction of a Gamma Camera

Answer 7

• LEGP
• Uniform flood source using sheet of Co-57
• Acquire WB flood with sheet placed directly on detector
  
  • REPEAT FOR EACH DETECTOR
• Convert to smaller matrix to increase counts
  and obtain profiles in x- and y- directions
  avoiding the ramp regions or edges
• Determine the Mean, SD and CoV from the
  pixels in the profile
• Suggested Frequency: At acceptance and
  Monthly

Question 8

What is the clinical purpose of QA or WB imaging?

Answer 8

WB imaging involves the MOVEMENT of either the patient bed or the camera head
- This introduces new sources of error

For the production of good clinical images, the movement must be both UNIFORM and SMOOTH

They complement those of planar imaging and so can be performed less frequently

Question 9

Summarise how you would test Planar Extrinsic Uniformity of a Gamma Camera

Answer 9

• All available
• Uniform flood source using sheet of Co-57
• Acquire for 30M counts
• Analyse global (Integral) and local (differential) uniformity using the NEMA protocol
• Suggested Frequency: Weekly & After a service

Question 10

Summarise what tests you would do during acceptance testing of a new PET-CT scanner

Answer 10

1. Spatial Resolution
2. Sensitivity
3. Scatter Fraction
4. Count Rate Performance
5. Noise Equivalent Count Rate
6. Image Quality

Question 11

What corrections need to be applied to a gamma camera image to give a correct image?

Answer 11

1. Energy correction
2. Linearity
3. Uniformity