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