CR / DR QC workshop
What are the vendors doing?
J. Anthony Seibert, Ph.D.
University of California, Davis
Medical Center
Sacramento, California
Definition: Quality Assurance
Quality Assurance
Are we operating
the devices
properly?
Quality Control
Medical
Maintenance
Scheduled
Unscheduled
Admin / Tech
services
Are the devices
operating
properly?
Are the devices
properly
supported?
Introduction
CR and DR are the primary means to
capture projection images in a PACS
environment
• Acceptance testing validates performance
and determines baseline values
• Quality control verifies optimal operation
CR/DR Workshop
Vendor representatives to present QC program
Phantoms? Software? Analysis?
Acceptance test procedures
What tests?
Why?
Quality control
When ? What?
How?
How often?
Ease of use?
1
Recommended Acceptance Tests
Recommended Acceptance Tests
• Physical Inspection–
Inspection–Inventory–
Inventory–PACS Interfaces
• Noise / LowLow-Contrast Response
• Imaging Plate Uniformity and Dark Noise (CR)
• Distortion
• Signal Response: Linearity and Slope
• Erasure Thoroughness (CR)
• Signal Response: Exposure calibration and
beam quality
• Artifact Analysis: Hardware/Software
• Laser Beam Function (CR)
• High Contrast Resolution
Acceptance test tools required
• Positioning and collimation robustness
• Image Throughput
7/10/98
Date:
7/10/98
Date:
Medical
Medical Physicist:
Physicist: Anthony
Anthony Seibert,
Seibert, Ph.D.
Ph.D.
Location:
Location:
System
System Identification:
Identification:
UCDMC,
UCDMC, ACC,
ACC, 33
CR
CR unit
unit 33
UC Davis Medical Center
CR
CR Reader
Reader and
and Screens
Screens
• Exposure meter/dosimeter
Inspection Results Summary
• Spatial resolution phantom
• Low contrast phantom
• Vendor QC phantom (periodic tests)
• SMPTE test pattern
• Anthropomorphic phantom
• Documentation log / spreadsheet / instructions
Acceptable
Acceptable
1.
1. Physical
Physical Inspection
Inspection -- Inventory
Inventory
2.
2. Imaging
Imaging Plate
Plate Uniformity
Uniformity and
and Dark
Dark Noise
Noise
3.
3. Signal
Signal Response:
Response: Linearity
Linearity and
and Slope
Slope
4.
Signal Response:
Response: Calibration
Calibration and
and Beam
Beam Quality
Quality
4. Signal
5.
5. Laser
Laser Beam
Beam Function
Function
6.
6. High-Contrast
High-Contrast Resolution
Resolution
7.
7. Noise/Low-Contrast
Noise/Low-Contrast Response
Response
8.
8. Distortion
Distortion
9.
9. Erasure
Erasure Thoroughness
Thoroughness
10.
10. Anti-Aliasing
Anti-Aliasing
11.
11. Positioning
Positioning and
and Collimation
Collimation Errors
Errors
12.
Throughput
12. Throughput
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes*
Yes*
Yes
Yes
Yes
Yes
Yes
Yes
Comments:
Comments:
2
Quality Control
Three levels of system performance quality control
1. Routine: Technologist level
- minimal radiation measurements (e.g., oneone-shot phantom)
2. Full inspection: Physicist level
- radiation measurements and nonnon-invasive adjustments
3. System adjustment: Vendor service level
Periodic Quality Control
• Daily (technologist(technologist-level tests)
– Inspect CR system and status.
– Interfaces: PACS broker, ID terminal, QC workstation
– Erase image receptors (if status unknown).
- initial configuration, hardware and software maintenance
- onon-line system verification / tests
Periodic Quality Control
• Weekly / Biweekly (technologist)
– Acquire QC phantom test images. Verify performance.
– Verify image quality on PACS, other monitors.
– Recommended maintenance by vendor (e.g., screen
cleaning (CR), flatflat-field acquisition (DR).
Periodic Quality Control
• Quarterly (Technologist)
– Inspect system (e.g., CR plates, DR functions)
– Review image retake rate and exposure trends.
– Update QC log. Review outout-ofof-tolerance issues.
3
Periodic Quality Control
• Annually (Physicist)
– Perform linearity / sensitivity / uniformity tests
– Inspect / evaluate image quality
– ReRe-establish baseline values (Acceptance Tests)
– Review retakes, exposures, service records.
CR: Medical Physicist issues
• Radiation exposure estimates
– Exposure index: “S” number vs. “EI”
EI” vs. “LgM”
LgM”
• Image processing optimization
– Vendor specific details
– Grid vs. no grid
• Modality worklist; DICOM / PACS issues
• Frequent training and inin-services
– Technologists and Radiologists
Quality Control Issues
• Signal to Noise Ratio
What is needed?
• Computer friendly phantoms
• Acquisition, display, storage processes
• Sampling by detector, image, display
• Quantization errors
• FlatFlat-field corrections
• Distance measurements; aspect ratio
• Objective quantitative analysis methods
• System performance tracking and database logs
• Exposure monitoring tools and database tracking
• Image processing
4
Fuji
What are the vendors doing?
Agfa
Single exposure,
qualitative and
quantitative
Lumisys / Kodak
Horizontal lines (vertical
geometric accuracy test)
Line pair phantoms
(contrast transfer tests)
0.5, 1.0 and 2.0 lp/mm patterns
(contrast transfer test)
DMISTY digital phantom for mammography
Diagonal bar
(laser jitter test)
Open area (scan
uniformity test)
Step wedge
Notches
(geometric
accuracy
tests)
Vertical lines
(horizontal geometric
accuracy test)
(Dynamic
Range)
Diagonal line
(laser jitter test)
Step wedge (signal,
signal to noise and
linearity response tests)
NPS
uniformity
Low contrast
resolution
Reference area
(contrast transfer test)
Detail objects
Chest wall accuracy
5
Example QC test phantom (UC Davis)
40 line/cm grid
(visual aliasing)
Fiducial Markers
(locators and distance accuracy)
Lead attenuator
(dynamic range)
Resolution
Bar Pattern
(qualitative)
Acquisition geometry
QC phantom with CR imaging plate
Copper step wedge
(dynamic range, linearity, SNR)
Brass stock with
sharp edgeedge-on exit side
(presampled MTF)
Images were acquired on an 18x24 cm detector at 80 kVp and 2 mAs at 180 cm (approx 2 mR incident)
Raw Image
Distance accuracy
and aspect ratio
measurements
583 / 1.1
203 / 9.6
ROIs - Step wedge
Open field
Beam stop
For L=4, S=200
Exposure (mR) = exp(0.009 x PV - 4.6)
where PV is the pixel value
Ave ra ge Digita l Num be r
Step wedge response
500
450
400
350
300
250
200
0
1
2
3
4
5
6
7
8
Step Number (0.25 mm Cu / Step)
9
10
11
581 / 1/0
268 / 8.9
273 / 10.0
279 / 10.5
288 / 10.3
302 / 8.9
323 / 7.1
349 / 6.0
382 / 4.2
425 / 2.7
484 / 1.4
583 / 1.2
583 / 1.0
234 / 5.0
585 / 1.0
Avg / Std Dev
6
Horizontal MTF results
MTF analysis
windows
MTF horizontal
MTF vertical
Summary
• A TEAM
approach is necessary
– Technologists, Radiologists, Physicists, Info Systems,
clinical engineers, AND VENDORS
• The system is only as good as the weakest link
– Display monitors, image processing issues, other…
other…..
Additional Information / Help
• AAPM Task Group #10 document:
– Request via email
• CR10v5.doc
• email: jaseibert@ucdavis.edu
• Dr. Ehsan Samei spreadsheets
– http://deckard.mc.duke.edu/~samei/downloads
http://deckard.mc.duke.edu/~samei/downloads
• Vendor efforts for QC phantom development and analysis
7