lorad ffdm qc procedures for medical physicist...– select a computer-generated flat-field image...
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Lorad FFDM QC Procedures for Medical Physicist
Tao Wu, Ph.D.Hologic, Inc.
Lorad Selenia FFDM
Tests Following Lorad QC Manual
• 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 LoginMedical Physicist
username: phys password: phys
Detector Warm-UpAfter 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 LoginUsername:AndreaPassword: 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• 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 EvaluationEvaluation 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 monitorWindow width = 500, Level = 350
Artifact Evaluation
Artifact Evaluation
Artifact EvaluationEvaluation 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• 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: filter, kVp, mAs all automatically determined Auto-kV: filter manually selected
kVp and mAs automatically determined Auto-Time: filter and kVp manual selected
mAs automatically determined
• AEC Method- Filter and kVp are determined by breast thickness (in Auto-Filter and Auto-kV modes)- A pre-exposure is used to determine mAs
• AEC positionsAuto-AEC (The densest tissue gets enough exposure) Seven manual positions (marked on compression paddle)
AEC Function Performance1. Performance at different thickness and
imaging modes 2. Performance at different compensation
levels
AEC Function Performance1. 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 Performance2. 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 – 0.28Step -4 0.36 – 0.44Step -3 0.50 – 0.61Step -2 0.63 – 0.77Step -1 0.77 – 0.94Step +1 1.04 – 1.27Step +2 1.17 – 1.43Step +3 1.31 – 1.60Step +4 1.44 – 1.76Step +5 1.58 – 1.93
Collimation Assessment1. X-Ray Field to Light Field2. X-Ray Field to Image Receptor3. 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 RM
Collimation AssessmentUse “coin method” as described in ACR manual
Collimation Assessment1. X-Ray Field to Light Field
– Measure deviations between the edges of the light field (exterior edge of the coin) and the x-ray field at al four sides
– Sum of the magnitude of deviations on opposite sides ≤ 2% of the SID SID = 66 cm 2% of the SID = 1.32 cm
Collimation Assessment2. X-Ray Field to Image Receptor
– d1: measured on filmdistance from the inner edge of the coin to the edge of the x-ray field
– d2: measured on digital imagedistance 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 Assessment3. 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 effect2. 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
ROI1 in background without ghosting
ROI2 in Al filter without ghosting
ROI3 in Al filter with ghosting
• | Ghosting factor | ≤ 0.3
Ghosting Factor =
meanregion2 - meanregion3
meanregion1 - meanregion2
