8/1/2011
James A. Zagzebski, Ph.D.
Dept. of Medical Physics
University of Wisconsin, Madison, WI, USA
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How we do US QA in our institution
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Guidelines available from US facility accreditation bodies
(ACR; AIUM)
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Emphasis is given to safety, cleanliness, and very basic performance tests.
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Most common fault is transducer damage, element dropout.
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Issues related to image performance, such as spatial resolution, are not included in QA (except ACR breast).
• Traditional “parameters” such as distance measurements are believed by many to be unnecessary for “routine” testing. Included in some protocols, as demands and challenges increase.
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Steps to assure electrical and mechanical safety and sterility
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Transducer tests
 Image Uniformity
 Look for element dropout
 System sensitivity and/or penetration capability
 Do for 2 probes (?) ; we do all
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Photography and other hard copy recording
 Match PACs workstation and system monitor
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Verify measurement accuracy during program initiation
American Institute of Ultrasound in Medicine:
General US QC
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Drafted by physicists,
Sonographers and clinicians
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Outlines what to do
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Sonographers
 Physicists/engineers
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Limited information on methodology
Requires a phantom
 Phantom left to users
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See www.aium.org
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American Institute of Ultrasound in Medicine: General
Sonography (physicist, engineer)
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Cables OK, air filters clean, mechanical and electrical inspection
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Transducer Uniformity
 Phantom
 Electronic probe tester
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Sensitivity, Maximum depth of visualization into a phantom
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Distance measurement accuracy
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Target detection and imaging
 Focal targets such as simulated cysts or low contrast objects
 Choice of phantoms left to users
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Image display fidelity
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Minimum frequency: annual for physicists/engineer tests
 Transducer Inspection
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Delaminations
Frayed cables
Proper cleaning
 Console
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Air filters
Viewing monitor, keyboard clean
Lights, indicators
Wheels, wheel locks
Proper cleaning
8/1/2011
 Water-based gels
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Advantages:
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Speed of sound = 1540 m/s
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Attenuation proportional to frequency
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Backscatter
Disadvantages:
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Subject to desiccation (?)
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Must be kept in containers
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Requires scanning window
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Solid, non-water-based materials (urethane)
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Advantages:
 Not subject to desiccation
 No need for scanning window; possibility for soft, deformable scanning window
 Produce tissue-like backscatter
 Disadvantages:
 C= 1430-1450 m/s
 Attenuation not proportional to frequency (~f 1.6
)
 Surface easily damaged if not cleaned regularly to remove gels
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Considered by many as a good overall check of the integrity of the system
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FOV at 18 cm (or set to match the phantom)
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Output power (MI) at max
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Transmit focus at deepest settings
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Gains, TGC for visualization to the maximum distance possible
How far can you see the speckle pattern in the material?
8/1/2011
Objective Maximum Depth of Visualization
• Gibson, Dudley, Griffith, “A computerized Quality Control System for
Bmode Ultrasound,” Ultrasound Med Biol 27 :1697-1711, 2001.
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Shi, Al-Sadah, Mackie, Zagzebski, Signal to Noise Ratio Estimates on Ultrasound Depth of Penetration (abstract only), Medical Physics
30 : 11367, 2003.
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Gorny, Tradup, Bernatz, Stekel, and Hangiandreou , “Evaluation of an Automated Depth of Penetration Measurement ofr the Purpose of
23: S76, 2004.
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Compute mean pixel value vs depth for phantom (signal) and for noise only (noise)
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Depth where signal/noise = 1.5 =DOP
 Considered to be the most important and useful test!
 Ideally:
 No evidence of element dropout
 No vertical
„shadows‟
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Turn off spatial compounding, speckle reduction
Use 1 tx focus
Search for
“shadows” emanating from transducer
Common in new and old probes!
Checking uniformity for curvilinear transducers
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Solution 1: rock transducer from side to side
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Solution 2: Use a liquid TM material
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Solution 3: Use newer phantoms with special curved windows
8/1/2011
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Solution 1: rock transducer from side to side
Need Proper Technique to Detect Element Dropout
Transducer with severe element dropout scanned using compound imaging
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Need Proper Technique to Detect Element Dropout
Transducer with severe element dropout
Disable spatial compounding
Use single, shallow transmit focus
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Visualizing 1-2 element dropouts
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Use persistence; translate transducer.
8/1/2011
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Visualizing 1-2 element dropouts
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Record Image loops while translating the transducer;
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Compress a 100 frame loop into 1 image (averages speckle) - Project of the AAPM
1 image
Ultrasonix SonixTouch
Enables masking off individual elements
Elements 95 and 96 masked
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Visualizing 1-2 element dropouts
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Record Image loops while translating the transducer;
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Compress a 100 frame loop into 1 image (averages speckle)
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Computer analysis
Average image
Ultrasonix SonixTouch
Enables masking off individual elements
Elements 95 and 96 masked
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Gray Scale Photography, Workstation Fidelity
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Important for monitor on machine to be set up properly to view all echo levels available and entire gray bar pattern.
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Set up during acceptance testing
Take steps to avoid the “meat hook” effect (mark or inscribe contrast and brightness controls)
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Workstation monitors and/or hardcopy devices should be matched to the machine monitor.
AAPM,August, 2011
Check hardcopy, workstation displays.
Are all gray bar transitions visible?
8/1/2011
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Available on some scanners
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0% to 100% gray bar pattern
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Squares for detecting geometric distortion
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Are all gray transitions visible?
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After seeing the test result, the sonographer mentioned that images being sent for accreditation tended to be washed out, cysts seemed to be filled in.
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Sonographers were
“over-gaining” the machine to compensate for the poor monitor performance.
Pacs
Workstation
Logiq 9
Monitor
(simulation)
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Distance Measurement Accuracy: Vertical
 Actual 2.5
 Measure 2.46
 error 1.5%
 Acceptable
Distance Measurement Accuracy: Horizontal
 Actual 1.0
 Measure 1.01
 error <1%
 Acceptable
8/1/2011
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Distance Measurement
Accuracy tests
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Necessary?
(“Scanner is a transducer tied to a computer.”)
May be important for specific uses
• Images reregistered from 3-D data sets
• Workstation measurements
• Radiation seed implants
Acquisition Plane
(Normal 2-D view)
Reconstructed Elevational Plane
4-year Experience with a clinical ultrasound quality control program Hangiandreou et al, Mayo Clinic, Rochester, Minnesota,
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About 50 scanners (47-55 over the 4 year period; most Siemens and a few Philips)
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About 300 transducers (267-322 over the 4 year period)
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Quarterly assessments of:
 Depth of penetration
 Distance measurement accuracy
 Transducer uniformity (element dropout)
 Mechanical integrity
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8/1/2011
4-year Experience with a clinical ultrasound quality control program,
(Ultrasound Med Biol 37, 1350-1357, 2011)
Hangiandreou et al, Mayo Clinic, Rochester, MN
Minnesota, USA
Evaluation
Method
# of detected
“failures”
% of detected
“failures”
47 25.1
Mechanical
Integrity
Image uniformity
Distance
Accuracy
DOP
(penetration)
124
0
3
66.3
0.0
1.6
Clinical
Problems
TOTAL
13
187
7.0
100.
4-year Experience with a clinical ultrasound quality control program,
(Ultrasound Med Biol 37, 1350-1357, 2011)
Hangiandreou et al, Mayo Clinic, Rochester, MN , USA
Evaluation
Method
Mechanical
Integrity
Image uniformity
Distance
Accuracy
DOP
(penetration)
Clinical
Problems
TOTAL
# of detected
“failures”
47
124
0
3
13
187
% of detected
“failures”
25.1
Recommendation
Quarterly
66.3
0.0
1.6
7.0
100.
Quarterly
Annually
Annually, (if done with software)
Sonographer‟s daily inspections
Image of a phantom is useful for qualitative comparisons!
(DOP or Distance Measureent)
Conventional Spatial Compounding
Images obtained during routine Breast QC testing, 3/2010
Conventional Spatial Compounding
Images obtained 1 month later, after a software change;
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 Use Stored Presets
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Sonographers can set up
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FOV
Focus
Gain
Compound off, etc
Generate a backup
 updates often wipe out old presets
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Setting up, maintaining an equipment QA program is straight forward
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The ACR listed procedures are a useful, basic QA program
 Directed by physicist or lab personnel
 Integrated effort including lab and technical staff
 Requires a Phantom
 Closely correlates with AIUM list of factors needing to be tested
• Transducer uniformity is a frequent fault in today‟s scanning machines. I recommend testing ALL transducers.
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Computational methods can be developed for objective tests
8/1/2011
• Goodsitt et al, “Real-time B-mode ultrasound quality control test procedures”, Medical Physics 1998; 25:1385-1406.
• J Zagzebski, “US quality assurance with phantoms.” In Categorical
Course in Diagnostic Radiology Physics: CT and US Cross-Sectional
Imaging, Edited by L. Goldman and B. Fowlkes, 2000, Oak Brook, IL:
Radiological Society of North America, pp. 159-170.
• J Zagzebski and J Kofler, “Ultrasound Equipment Quality Assurance,” in Quality Management in the Imaging Sciences, ed. By J Papp, 2002,
St. Louis, Mosby, pp. 207-215.
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QA Manual for Gray Scale Ultrasound Scanners, 1995, American
Institute of Ultrasound in Medicine, Laurel, MA.
• D Groth et al, “Cathode ray tube quality control and acceptance program: initial results for clinical PACS displays, Radiographics
2001, 21: 719.
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Hangiandreou, Stekel, Tradup, Gorny, and King, Four-Year experience with a clinical ultrasound quality control program, UMB
2011, 37: 1350-57.
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