qa in digital mammography: local activities and remote control h. bosmans et al
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QA in digital mammography: local activities and remote control
H. Bosmans et al.
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Belgium, 1996
• Role of radiographers in QC minimal• Enthusiasm of radiologists for QC: minimal• No physicists working in X-ray imaging
• EC-guided screening made the difference
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Recall film-screen-mammography…
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Constancy in film-screen mammography
• AEC: long term reproducibility• AEC: object thickness and tube voltage
compensation• sensitometry: base and fog• sensitometry: speed• Sensitometry: Contrast & Gradient• Imge quality: artefacts• Image quality: spatial resolution, reference ROI• Image quality: threshold contrast visibility
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Centrally supervised performance tests
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Centrally supervised performance tests
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Digital imaging: 10th birthday• It is another world, with other challenges• We stayed with centrally supervised QC
– Long term reproducibility– Detector homogeneity– Uncorrected defective DELs (DR)– Uncorrected defective DELs (DR)– Display & printer: Geometrical distortion (CRT)– Display & printer: Contrast visibility– Display & printer: Displaying artefacts
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Data from DICOM header & global scoreFrom 2 ‘FOR PROCESSING’ flood images:
• DICOM header is scrutinized for kV, mAs, anode/filter, detector temperature, detector ID, thickness & compr force, MGD, detector calibration date, …
• Follow up in time
• Comparison between DICOM headers possible
• Limiting values set
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Screenshot of our platform
Automated constancy check in digital mammography: implementation and first results of a multi-center study J. Jacobs , K. Lemmens , F. Shannoun , G. Marchal and H. Bosmans, RSNA 2007
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Centrally supervised performance tests
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Data from DICOM header & global score
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Data from the images
From 2 ‘FOR PROCESSIING’ flood images:In homogenous segment:• Noise power spectrum (1D, radial or 2D NPS)
In reference ROI:• Pixel value, SNR, st dev, variance
Global image analysis:• Thumbnail images of PV, SNR and variance; color coded if
%-value• Automatic artefact detection & pixel value copying
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Example: Siemens system
» Mean PV; SNR; Std. Dev.» calculate values from small
ROIs
2 mm * 100 µm 20 x 20px (GE DR) * 70 µm 28 x 28px (Siemens DR, Hologic DR) * 50 µm 40 x 40px (Fuji CR, Agfa CR)
Mean PV; SNR; Std. Dev.; Variance; Min PV; Max PV;
Median PV; Kurtosis; Skewness THUMBNAILS
Data from the images
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Data from the images
Type 1DR: find out the service technician came along
Type 1
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Scanning system (Philips Microdose) : normal situation
Type 2
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Type 2
GE system: normal situation, be happy
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Type 2
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Type 2
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• CR system: Scan line artefact
Mean pixel value SNR Deviation SNR
Type 3
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Type 3
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Type 3
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CR: inhomogeneities
Type 4
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Type 4
Agfa DM1000 DR
Type 4
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Latest example: artefact in the Ag filter
• Acquisition with 4cm of PMMA
• Acquisition with 7cm of PMMA, using Ag filter
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DR: calibration too quickly after a patient scan (ghost)
Type 5
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• A suboptimal start….
Type 5
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DR: Ghost artefact & small field used at calibration
Type 5
Type 5
Calibration phantom artefactCalibration needs 4 x rotation / flipping of phantom
Type 5
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Type 5: latest example
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Suggestions for improved mammo DQC
• CR: include all CR cassettes systematically in the DQC procedure• CR: Enforce completely filled in DICOM headers• CR&DR: Include all clinically used anode/filter combinations in
the DQC procedure• CR&DR: Work with NPS data, using averaging• Apply big data analysis techniques• Include QC (quality and dose) of the clinical image• Extra analysis of local variance ‘variations’Unchanged:2 homogenous acquisitions each day, with phantom rotated over 180° !!!!
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Daily QC could help prioritize the work!
(IWDM 2010, K. Michielsen) Hypothesis:“systems that show little or no deviation during DQC show basically unchanged results in the half-yearly quality control”• For 50 systems of 6 vendors (CR and DR)• 129 events: 2 half yearly tests and DQC• 74 events: 2 half yearly tests and DQC and same CDMAM
phantom• Data: the mean glandular dose (MGD) and signal-
difference to noise ratio (SDNR) for 2, 3, 4, 5, 6 and 7 cm of PMMA and small aluminum disk of 0.2 mm;
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• Declared unchanged if both SDNR & MGD did not change by more than 10%
• A system was declared as unchanged between two half-yearly QC tests if the contrast threshold did not increase by more than 15%.
• The DQC results were declared as ‘unchanged’ between these two points if the following criteria were met: – no change in anode/filter combination, – a maximum change of the average nominal kVp of 1.0, – less than 5% change in SNR, – less than 10% change in mAs– no change of detector ID.
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Part 2
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Daily QC of monitors
• Obligation• To be done with a variable pattern
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MoniQA - pattern
J. Jacobs, J Kotre, … , Med Phys. 2007 Jul;34(7):2744-58
Luminance checkGeometric check
Resolution check
General artefacts
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• It can all be poor.. Yet we don’t see deviations in half yearly test. Is it a reading test for operators?
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Results from data analysis
1. Barco MDMG 5121 (N=89) 10. Eizo GS510 (N=108)
2. Barco MDMG 5221 (N=2) 11. Eizo GS520 (N=64)
3. Barco MDMG 5212 (N=1) 12. Eizo GS521 (N= 52)
4. Barco MDNG 5121 (N=164) 13. Eizo GX530 (N=2)
5. Barco MDNG 6121 (N=66) 14. Eizo GX1030 (N=3)
6. Barco MFGD 5421 (N=38) 15. Eizo G51-BLS (N=64)
7. Barco MFGD 5620 (N=6) 16. GE (N=2)
8. Barco MFGD 5621 (N=100) 17. Siemens SMD (N=62)
9. Barco E-5620 (N=6)
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• Mean score of all monitors:
Dag van de week Gemiddelde score Standaard deviatie Maandag 97.37 6.979 Dinsdag 97.02 8.511
Woensdag 97.16 7.527 Donderdag 97.24 7.527
Vrijdag 97.27 7.023 Weekend 97.87 4.032
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• Half yearly tests and daily QC tests are hardly correlating. ρ(652) = 0.107, p < 0.01.
• These tests may be testing other aspects of the imaging chain.
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Suggestions for improved monitor DQC
Make a very simple daily QC testKeep present test on weekly basis
– Not acceptable in euref protocol– Therefore not acceptable for application in
Belgium
Conclusion
It is possible to organize qualityQuality control is not necessarily very time consuming !
Acknowledgement
• The Leuven QA team & all our students• The Leuven mammography and LUCK• J Jacobs, Qaelum NV (www.qaelum.com)• The OPTIMAM project• The EUREF team