Lorad FFDM QC Procedures
for Medical Physicist
Tao Wu, Ph.D.
Hologic, Inc.
Lorad Selenia FFDM
Tests Following Lorad QC Manual
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Collimation Assessment
Artifact Evaluation
System Resolution
Phantom Image Quality Evaluation
Automatic Exposure Control Function Performance
Automatic Exposure Control Reproducibility
Signal-To-Noise and Contrast-To-Noise
Measurements
• Softcopy Workstation QC
Acquisition Workstation
Software
OS Login
Medical Physicist
username: phys
password: phys
Detector Warm-Up
After logging in OS, a dialog showing detector
warm-up status appears
If the system has been running - Dismiss
If the system has been shut down - Wait for 30-40 min
(or dismiss it and start with tests in which detector is not
involved, e.g. HVL, tube output)
Application Login
Username:Andrea
Password: Andrea
Turn Off Auto-decompression
Send Images to Output Devices
Send Images to Output Devices
Send Images to Output Devices
Non-Imaging Mode
Create a New Patient Account
Select “No Output”
Create a New Patient Account
Create a New Patient Account
Selenia QC Tests
Tests Following Lorad QC Manual
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•
•
•
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Collimation Assessment
Artifact Evaluation
System Resolution
Phantom Image Quality Evaluation
Automatic Exposure Control Function Performance
Signal-To-Noise and Contrast-To-Noise
Measurements
• Softcopy Workstation QC
Order of Testing
• Artifact Evaluation
• Phantom Image Quality Evaluation
• SNR and CNR Measurements
• AEC Function Performance
• Other Tests
Artifact Evaluation
Evaluation of detector, x-ray tube, filter etc
–
4 cm thick acrylic block
–
No compression paddle
–
Four flat field images
Mo/Mo, contact mode, LFS with grid
Mo/Rh, contact mode, LFS with grid
Mo/Mo, mag mode, SFS without grid
Mo/Rh, mag mode, SFS without grid
–
Review the images on acquisition workstation monitor
Window width = 500, Level = 350
Artifact Evaluation
Artifact Evaluation
Artifact Evaluation
Evaluation of Printer
– Select a computer-generated flat-field image
– Print the image and evaluate it
– Repeat the test for each printer
If a printer is connected to multiple Selenia
systems, it only needs to be tested once from
one Selenia.
Artifact Evaluation
Phantom Image Quality Evaluation
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ACR phantom with acrylic disc
AEC position 2
Print film
Measure film densities
- Background density > 1.20, with control limit ± 0.20
- Density difference over the acrylic disk > 0.40, with
control limit ± 0.05
• Phantom scoring (hard copy and softcopy station)
• 5 fibers, 4 speck groups, 4 masses
Phantom Image Quality Evaluation
SNR and CNR Measurements
SNR and CNR Measurements
• SNR ≥ 40
• Establish the reference CNR value during
the acceptance test
• CNR should stay within ±15% of the
reference
Automatic Exposure Control (AEC)
• AEC modes
Auto-Filter:
Auto-kV:
Auto-Time:
filter, kVp, mAs all automatically determined
filter manually selected
kVp and mAs automatically determined
filter and kVp manual selected
mAs automatically determined
• AEC Method
- Filter and kVp are determined by breast thickness (in AutoFilter and Auto-kV modes)
- A pre-exposure is used to determine mAs
• AEC positions
Auto-AEC (The densest tissue gets enough exposure)
Seven manual positions (marked on compression paddle)
AEC Function Performance
1. Performance at different thickness and
imaging modes
2. Performance at different compensation
levels
AEC Function Performance
1. Performance at different thickness and
imaging modes
– Acrylic or BR-12 blocks
– AEC position 2
– Contact mode (LFS, grid): 2, 4, 6, 8 cm phantom
Mag mode (SFS, no grid): 4 cm phantom
– Variation of target pixel values
≤ 10% of the mean target pixel value
AEC Function Performance
AEC Function Performance
2. Performance at different compensation levels
– 4 cm acrylic or BR-12
– Compensation levels:
Step -5 to Step +5
– Use average target count at
Step 0 as reference
– Compare target count at
other steps to the reference
Step -5
0.23 – 0.28
Step -4
Step -3
Step -2
Step -1
Step +1
Step +2
Step +3
Step +4
Step +5
0.36 – 0.44
0.50 – 0.61
0.63 – 0.77
0.77 – 0.94
1.04 – 1.27
1.17 – 1.43
1.31 – 1.60
1.44 – 1.76
1.58 – 1.93
Collimation Assessment
1. X-Ray Field to Light Field
2. X-Ray Field to Image Receptor
3. Compression Paddle to Image Receptor
Collimation Assessment
• One test for 24×29 cm imaging mode
• Three tests for 18×24 cm imaging modes
– Left imaging position
– Center imaging position
– Right imaging position
L
M
R
Collimation Assessment
Use “coin method” as described in ACR manual
Collimation Assessment
1. X-Ray Field to Light Field
– Measure deviations between the edges of the
light field (exterior edge of the coin) and the xray field at al four sides
– Sum of the magnitude of deviations on opposite
sides ≤ 2% of the SID
SID = 66 cm Æ 2% of the SID = 1.32 cm
Collimation Assessment
2. X-Ray Field to Image Receptor
– d1: measured on film
distance from the inner edge of the coin to the edge of the x-ray field
– d2: measured on digital image
distance from the inner edge of the coin to the edge of the detector
– (d1×1.06 ) - d2
– The x-ray field shall extend beyond the chest wall side of the image
receptor
– The x-ray field must NOT extend >2% of the SID at any of the four
sides of the image receptor
Collimation Assessment
3. Compression Paddle to Image Receptor
– Measure distance from the outer edge of the coin to
the edge of the image
– The anterior edge of the compression paddle must be
aligned just beyond the chest wall edge of the image
receptor, but ≤ 1% of the SID
Collimation Assessment
Collimation Assessment
Collimation Assessment
Evaluation of System Resolution
• Line pair phantom
• 4 cm acrylic block
• Line pair phantom placed
at 45º to the detector row
Evaluation of System Resolution
Limiting spatial resolution ≥ 7 c/mm (lp/mm)
Detector Ghosting (Optional)
1. Create ghosting effect
2. Quantify ghosting effect
Detector Ghosting (Optional)
1. Create ghosting effect
Ghosting area
Detector Ghosting (Optional)
2. Quantify ghosting effect
Ghosting area
Detector Ghosting (Optional)
2. Quantify ghosting effect
• | Ghosting factor | ≤ 0.3
ROI1 in background
without ghosting
ROI2 in Al filter
without ghosting
ROI3 in Al filter
with ghosting
Ghosting Factor =
meanregion2 - meanregion3
meanregion1 - meanregion2
Thank you!
Tao Wu
twu@hologic.com
Tel: 203-207-4574