routine ultrasound equipment tests for quality...

7/14/2010

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Routine Ultrasound Equipment Tests for

Quality Assurance

James A. Zagzebski, Ph.DJames A. Zagzebski, Ph.D..

Nick Rupert, M.S.Nick Rupert, M.S.

Ryan Ryan DeWallDeWall, M.S., M.S.

TomyTomy Varghese, Ph.D.Varghese, Ph.D.

Dept. Dept. of Medical of Medical PhysicsPhysics

University of Wisconsin, Madison, WI, USAUniversity of Wisconsin, Madison, WI, USA

Contents

•• Elements of a Routine Test Program Elements of a Routine Test Program

•• What system components are considered What system components are considered most important in routine testing?most important in routine testing?� Concentrate on transducers!

•• Steps to carry out tests on a regular basisSteps to carry out tests on a regular basis

•• Activity of Ultrasound Lab Accreditation Activity of Ultrasound Lab Accreditation GroupsGroups

•• Basic QA methodsBasic QA methods� Phantoms and tests

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Routine QA Program

•• Guidelines available from US facility Guidelines available from US facility

accreditation bodies (ACR; AIUM)accreditation bodies (ACR; AIUM)

•• Emphasis is given to safety, cleanliness, and Emphasis is given to safety, cleanliness, and

very basic performance tests.very basic performance tests.

•• Issues related to image performance, such as Issues related to image performance, such as

spatial resolution, are not spatial resolution, are not included (except included (except

ACR breast). ACR breast).

•• Traditional “parameters” such as distance Traditional “parameters” such as distance

measurements are believed by many to be measurements are believed by many to be

unnecessary. unnecessary. IncludediIncludedi n some protocols, but n some protocols, but

only briefly.only briefly.

Routine QA (ACR General US Program)

•• System sensitivity and/or penetration capabilitySystem sensitivity and/or penetration capability

� 1999: Do for 2 probes (?)

•• Image Uniformity Image Uniformity

� Look for element dropout

•• Photography and other hard copy recording Photography and other hard copy recording � 2010: workstation monitor display

•• Low contrast object Low contrast object detectabilitydetectability

•• Assurance of electrical and mechanical safety Assurance of electrical and mechanical safety and sterility and sterility

•• Verify measurement accuracy during program Verify measurement accuracy during program initiationinitiation

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American College of Radiology Requirements:

General Sonography

• ACR physics committee developing this standard based it

on measurements using a phantom.

� A phantom was selected (fall,1998) but turned out to be much

more costly than originally promised.

� Physics Committee chose to leave the choice of phantoms to the

user

� ACR staff published the following:

• “Using a phantom will be helpful in responding to questions

about low contrast detectability …. However, the use of a

phantom is optional at this time. Questions relating to

characteristics associated with system sensitivity and image

uniformity may be answered without the use of a phantom or

test object.”

American Institute of Ultrasound in Medicine:

General US QC

• 2008

• Originally called “QA in the

Clinic”

� Sonographers and clinicians

helped draft

• Outlines what to do

� Sonographers

� Physicists/engineers

• Limited information on

methodology

� Requires a phantom

� Phantom left to users

• See www.aium.org

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General US QC


General Sonography (physicist, engineer) • Transducer Uniformity

� Phantom

� Electronic probe tester

• Sensitivity, Maximum depth of visualization into a

phantom

• Distance measurement accuracy

• Target detection and imaging

� Focal targets such as simulated cysts or low contrast objects

� Choice of phantoms left to users

• Image display fidelity

• Cables OK, air filters clean, mechanical and electrical

inspection

• Minimum frequency

� Annual for physicists/engineer tests

� Program includes daily, weekly checks by sonographers

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Currently used materials:

�� WaterWater--based gelsbased gels

� Advantages:

�Speed of sound = 1540 m/s

�Attenuation proportional to frequency

�Backscatter

� Disadvantages:

�Subject to desiccation

�Must be kept in containers

�Requires scanning window

Currently used TM materials:

•• Solid, Solid, nonnon--waterwater--based based

materials (urethane)materials (urethane)

•• AdvantagesAdvantages::� Not subject to desiccation

� No need for scanning window

� Produce tissue-like backscatter

� Disadvantages:� C= 1430-1450 m/s

� Attenuation not proportional to frequency (~f1.6)

� Surface easily damaged if not cleaned regularly to remove gels

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Maximum Depth of Visualization

•• Considered by many as a good Considered by many as a good overall check of the overall check of the integrity integrity of of the systemthe system

•• FOV at 18 cm (or set to match FOV at 18 cm (or set to match the phantom)the phantom)

•• Output power (MI) at maxOutput power (MI) at max

•• Transmit focus at deepest Transmit focus at deepest settingssettings

•• Gains, TGC for visualization to Gains, TGC for visualization to the maximum distance the maximum distance possiblepossible

Maximum Depth of Visualization

How far can you see the speckle pattern in the material?

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Objective Maximum Depth of Visualization

•• Gibson, Dudley, Griffith, “A computerized Quality Control System for Gibson, Dudley, Griffith, “A computerized Quality Control System for

BB--mode Ultrasound,” mode Ultrasound,” Ultrasound Med Ultrasound Med BiolBiol 2727:1697:1697--1711, 2001.1711, 2001.

•• Shi, AlShi, Al--SadahSadah, Mackie, Zagzebski, Signal to Noise Ratio Estimates , Mackie, Zagzebski, Signal to Noise Ratio Estimates

on Ultrasound Depth of Penetration (abstract only), on Ultrasound Depth of Penetration (abstract only), Medical Physics Medical Physics

3030: 11367, 2003. : 11367, 2003.

•• GornyGorny, , TradupTradup, , BernatzBernatz, , StekelStekel, and , and HangiandreouHangiandreou, “Evaluation of , “Evaluation of

an Automated Depth of Penetration Measurement an Automated Depth of Penetration Measurement ofrofr the Purpose of the Purpose of

Ultrasonic Scanner Comparison”, (abstract only), J. Ultrasound Med Ultrasonic Scanner Comparison”, (abstract only), J. Ultrasound Med

23: S76, 2004. 23: S76, 2004.

•• Compute mean pixel value Compute mean pixel value vsvs depth for phantom (signal) and for depth for phantom (signal) and for

noise only (noisenoise only (noise))

•• Depth where signal/noise = 1.5 =DOPDepth where signal/noise = 1.5 =DOP

MPV’

SNR’-DOP tracks well Observer-DOP

0.0 0.2 0.4 0.6 0.8 1.0 1.2

7

8

9

10

11

12

13

14

15

16

Observer's DOP

DOP using SNR'= 1.5

Observers-DOP & SNR-DOP comparision (ATL C5-2)

Mechanical Index MI

De

pth

(cm

)

(Al-Sadah, UW-Madison)

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Routine QA: Image Uniformity

�� Considered to be Considered to be

the most the most imporimpor--

tanttant and useful and useful

test!test!

�� Ideally:Ideally:

� No evidence of

element dropout

� No vertical

‘shadows’

� No loss of

sensitivity near

edges

Uniformity

�� Turn off spatial Turn off spatial

compounding, compounding,

speckle reductionspeckle reduction

�� Use 1 Use 1 txtx focusfocus

�� Search for Search for

“shadows” “shadows”

emanating from emanating from

transducertransducer

�� Common in new Common in new

and old probes!and old probes!

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Difficulties with Uniformity

•• Coupling to a flat surface phantom scanning window with Coupling to a flat surface phantom scanning window with

curvilinear transducerscurvilinear transducers


•• Coupling to a flat surface Coupling to a flat surface phantom scanning window phantom scanning window with with


•• Solution 1: rock transducer from side to sideSolution 1: rock transducer from side to side

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•• SolutsideSolutside to sideto side




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•• Solution 2: Use a liquid TM materialSolution 2: Use a liquid TM material


•• Coupling to a flat surface with curvilinear transducersCoupling to a flat surface with curvilinear transducers

•• Solution 2: Use a liquid TM material (pseudo liquid TM Solution 2: Use a liquid TM material (pseudo liquid TM

slurry; Madsen et al.)slurry; Madsen et al.)

Sensitivity

0

0.2

0.4

0.6

0.8

1

1 11 21 31 41 51 61 71 81 91 101 111 121

Elements

Volts p-p

Electronic Probe test

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•• Solution 3: Use a phantom having concave windows Solution 3: Use a phantom having concave windows

((GoodsittGoodsitt et al)et al)


•• Visualizing 1Visualizing 1--2 element dropouts2 element dropouts

•• Use persistence; translate transducer.Use persistence; translate transducer.

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•• Use persistence; Use persistence; translate transducer.translate transducer.



•• Record Image loops while translating the transducer;Record Image loops while translating the transducer;

•• Compress a 100 frame loop into 1 image (averages Compress a 100 frame loop into 1 image (averages

speckle)speckle)

Ultrasonix SonixTouch

Enables masking off individual elements

Elements 95 and 96 masked

1 image

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•• Record Image loops while translating the transducer;Record Image loops while translating the transducer;

•• Compress a 100 frame loop into 1 image (averages Compress a 100 frame loop into 1 image (averages

speckle)speckle)

Ultrasonix SonixTouch

Enables masking off individual elements

Elements 95 and 96 masked

Average image



•• Use persistence; translate transducer Use persistence; translate transducer

•• Use Record Image loops while translating the transducer; Use Record Image loops while translating the transducer;

compress a 100 frame loop into 1 image (averages compress a 100 frame loop into 1 image (averages

speckle)speckle)

•• Phased array transducer performance Phased array transducer performance

� Need electronic probe tester

� Transducer test modes on the ultrasound instrument are possible;

manufacturers need to be encouraged to provide these

•• Future 2Future 2--D probes, probes that do part of the beam D probes, probes that do part of the beam

forming within the probe housingforming within the probe housing

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Gray Scale Photography, Workstation

Fidelity

•• Important for monitor on machine Important for monitor on machine to be set up properly to view all to be set up properly to view all echo levels available and entire echo levels available and entire gray bar pattern.gray bar pattern.� Set up during acceptance testing

� Take steps to avoid the “meat hook” effect (mark or inscribe contrast and brightness controls)

•• Workstation monitors and/or Workstation monitors and/or hardcopy devices should be hardcopy devices should be matched to the machine monitor. matched to the machine monitor.

AAPM, July, 2010

Check hardcopy, workstation displays.

Are all gray bar transitions visible?

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SMPTE Test Pattern

•• Available on most Available on most

scanners scanners

•• 0% to 100% gray 0% to 100% gray

bar patternbar pattern

•• Squares for Squares for

detecting geometric detecting geometric

distortiondistortion

•• Are all gray Are all gray

transitions visible?transitions visible?

Distance Measurement Accuracy: Vertical

�� Actual 2.5Actual 2.5

�� Measure 2.46Measure 2.46

�� error 1.5%error 1.5%

�� AcceptableAcceptable

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Distance Measurement Accuracy: Horizontal

�� Actual 1.0Actual 1.0

�� Measure 1.01Measure 1.01

�� error <1%error <1%

�� AcceptableAcceptable

Routine QA (ACR General US Program)

•• Distance Measurement Accuracy tests as neededDistance Measurement Accuracy tests as needed

� 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

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ACR Recommended QC for Breast US

Maximum Depth of

visualization

Semiannually Service eng./physicist

Vertical and horiz

measurement accuracy

Semiannually Service eng./physicist

Hardcopy Recording Semiannually Service eng./physicist

Uniformity Semiannually Service eng./physicist

Elec-mechanical condition Semiannually Service eng./physicist

Anechoic void perception Semiannually Service eng./physicist

Ring down Semiannually Service eng./physicist

Lateral Resolution Semiannually Service eng./physicist

QC Checklist Semiannually Service eng./physicist

Adherence to infection

control procedures

After each biopsy Sonographer

Clean transducers After each biopsy Sonographer

Vertical and horiz

measurement accuracy

Quarterly Sonographer

Grey-scale photography Quarterly Sonographer

Dead Zone?

�� No suitable targets for No suitable targets for

dead zone testing, dead zone testing,

even in phantoms even in phantoms

that advertise that advertise

deadzonedeadzone tragetstragets!!

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Anechoic Sphere Imaging, a better choice

Anechoic Sphere Imaging

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Image of a phantom is useful for qualitative

comparisons!

Images obtained during routine Breast QC testing, 3/2010

Conventional Spatial Compounding

Image of a phantom is useful!

Images obtained 1 month later, after a software change;

Conventional Spatial Compounding

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Routine QA: Cleanliness, safety

�� Transducer InspectionTransducer Inspection� Delaminations� Frayed cables� Proper cleaning

�� ConsoleConsole� Air filters� Viewing monitor, keyboard clean� Lights, indicators� Wheels, wheel locks� Proper cleaning

Summary

•• Setting up, maintaining an equipment QA program is Setting up, maintaining an equipment QA program is straight forwardstraight forward

•• The ACR listed procedures are a useful, basic QA The ACR listed procedures are a useful, basic QA programprogram

� Directed by physicist or lab personnel

� Integrated effort including lab and technical staff

� Requires a Phantom

� Closely correlates with AIUM list of factors to test

•• Transducer uniformity is a frequent fault in today’s Transducer uniformity is a frequent fault in today’s scanning machinesscanning machines

•• Computational methods can be developed for Computational methods can be developed for objective testsobjective tests

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References

•• Goodsitt et al, “RealGoodsitt et al, “Real--time Btime B--mode ultrasound quality control test mode ultrasound quality control test procedures”, Medical Physics 1998; 25:1385procedures”, Medical Physics 1998; 25:1385--1406.1406.

•• J Zagzebski, “US quality assurance with phantoms.” In Categorical J Zagzebski, “US quality assurance with phantoms.” In Categorical Course in Diagnostic Radiology Physics: CT and US CrossCourse in Diagnostic Radiology Physics: CT and US Cross--Sectional Sectional Imaging, Edited by L. Goldman and B. Fowlkes, 2000, Oak Brook, IL: Imaging, Edited by L. Goldman and B. Fowlkes, 2000, Oak Brook, IL: Radiological Society of North America, pp. 159Radiological Society of North America, pp. 159--170. 170.

•• J Zagzebski and J Kofler, “Ultrasound Equipment Quality Assurance,” J Zagzebski and J Kofler, “Ultrasound Equipment Quality Assurance,” in Quality Management in the Imaging Sciences, ed. By J Papp, 2002, in Quality Management in the Imaging Sciences, ed. By J Papp, 2002, St. Louis, Mosby, pp. 207St. Louis, Mosby, pp. 207--215.215.

•• QA Manual for Gray Scale Ultrasound Scanners, 1995, American QA Manual for Gray Scale Ultrasound Scanners, 1995, American Institute of Ultrasound in Medicine, Laurel, MA.Institute of Ultrasound in Medicine, Laurel, MA.

•• D Groth et al, “Cathode ray tube quality control and acceptance D Groth et al, “Cathode ray tube quality control and acceptance program: initial results for clinical PACS displays, Radiographics program: initial results for clinical PACS displays, Radiographics 2001, 21: 719.2001, 21: 719.

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