ACR MRI Accreditation: Medical Educational …...Physics - ACR MRI Accreditation Program 9 Must be able to resolve 0.8 mm holes vertically and horizontally. 12 cm FOV, 192 x 152 matrix

D.M.Reeve: AAPM 2009: Practical Medical Physics - ACR MRI Accreditation Program

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ACR MRI Accreditation: Medical ACR MRI Accreditation: Medical Physicist Role in the Application Physicist Role in the Application

ProcessProcessDonna M. Reeve, MS, DABR, DABMPDonna M. Reeve, MS, DABR, DABMP

Department of Imaging PhysicsDepartment of Imaging PhysicsUniversity of Texas M.D. Anderson Cancer CenterUniversity of Texas M.D. Anderson Cancer Center

•• Present an overview of the new modular ACR MRI Present an overview of the new modular ACR MRI Accreditation program as it applies to phantom image Accreditation program as it applies to phantom image acquisition for accreditation application.acquisition for accreditation application.

•• Discuss the role of the medical physicist in the application Discuss the role of the medical physicist in the application process.process.

•• Discuss phantom image quality failures, possible causes Discuss phantom image quality failures, possible causes and potential remedies.and potential remedies.

•• Provide advice for avoiding common pitfalls in the Provide advice for avoiding common pitfalls in the phantom image submission process.phantom image submission process.

Educational ObjectivesEducational Objectives

ACR MRI Accreditation ProgramACR MRI Accreditation Program•• Modular program launched October 20, 2008Modular program launched October 20, 2008•• 6 modules 6 modules (head, spine, body, MSK, MRA, cardiac)(head, spine, body, MSK, MRA, cardiac)

•• Allows accreditation of whole body, dedicated Allows accreditation of whole body, dedicated and certain specialty MRI systemsand certain specialty MRI systems

•• Added a second, small phantom for use in small Added a second, small phantom for use in small bore orthopedic MRI systemsbore orthopedic MRI systems

New Modular ProgramNew Modular Program

Whole bodyWhole bodyCardiacCardiac

HeadHeadSpineSpineMusculoskeletal (MSK)Musculoskeletal (MSK)BodyBodyMagnetic Resonance Magnetic Resonance Angiography (MRA)Angiography (MRA)CardiacCardiac

*Breast MR: to be included with Breast Imaging Accreditation programs(Mammography, Stereotactic Breast Biopsy, Breast Ultrasound)

Previous programs

ACR MRI Accreditation ProgramACR MRI Accreditation Program

•• Unit based facility accreditation program: Unit based facility accreditation program: ““For every For every unit must apply for unit must apply for all modules routinely performed on all modules routinely performed on that unitthat unit for a facility to be accredited.for a facility to be accredited.””

•• Allowances made for loaner units and Allowances made for loaner units and ““emergency use emergency use of magnetsof magnets””•• <10 exams in 30 day period, or<10 exams in 30 day period, or•• <50 exams in any 12 month period<50 exams in any 12 month period

•• MRI scanners dedicated to Interventional MRI and MRI scanners dedicated to Interventional MRI and Radiation Therapy treatment planning are exempt.Radiation Therapy treatment planning are exempt.

•• Additional guidance documentsAdditional guidance documents•• Guidance documents available Guidance documents available www.acr.orgwww.acr.org•• Online application processOnline application process•• Longer time period to acquire phantom and Longer time period to acquire phantom and

clinical images (+/clinical images (+/-- 1 month from phantom 1 month from phantom exam)exam)

ACR MRI Accreditation ProgramACR MRI Accreditation Program


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Guidance documentsGuidance documents

www.acr.org

ACR Technical Standards

Clinical images Clinical images –– guidance guidance documentsdocuments

Describes criteria ACR uses to evaluate clinical images submitted for each of the six modules:

Head BodySpine MRAMSK Cardiac

2004 ACR MRI Quality Control 2004 ACR MRI Quality Control ManualManual

Radiologist’s section

Technologist’s section

Medical Physicist’s section

In the process of being revised.

Medical Physicist/MR ScientistMedical Physicist/MR Scientist

Medical Physicist:Medical Physicist:Board Certification in radiological physics or diagnostic radiolBoard Certification in radiological physics or diagnostic radiological ogical

physics (recommended) physics (recommended) Ref:Ref: ACR Accreditation Program Requirements, 2009ACR Accreditation Program Requirements, 2009

Board Certification in appropriate Board Certification in appropriate subfield(ssubfield(s) by the American Board of ) by the American Board of Radiology (ABR), the Canadian College of Physics in Medicine, orRadiology (ABR), the Canadian College of Physics in Medicine, or for for MRI, by the American Board of Medical Physics (ABMP) in magneticMRI, by the American Board of Medical Physics (ABMP) in magneticresonance imaging physics.resonance imaging physics.

Ref: ACR Technical Standard for Diagnostic Medical Physics Ref: ACR Technical Standard for Diagnostic Medical Physics Performance Monitoring of MRI Equipment, 2006Performance Monitoring of MRI Equipment, 2006

Medical Physicist/MR ScientistMedical Physicist/MR Scientist

MR Scientist:MR Scientist:A qualified MR Scientist is an individual who has obtained a A qualified MR Scientist is an individual who has obtained a graduate degree in a physical science involving nuclear MR graduate degree in a physical science involving nuclear MR or MRI. Should have 3 years documented experience in a or MRI. Should have 3 years documented experience in a clinical MRI environment.clinical MRI environment.

Refs: ACR Accreditation Program Requirements, 2009;Refs: ACR Accreditation Program Requirements, 2009;ACR Technical Standard for Diagnostic Medical Physics ACR Technical Standard for Diagnostic Medical Physics Performance Monitoring of MRI Equipment, 2006Performance Monitoring of MRI Equipment, 2006

Medical Physicist / MR Scientist roleMedical Physicist / MR Scientist role

•• Member of team: supervising physician, MRI Member of team: supervising physician, MRI technologist; involved in the accreditation process.technologist; involved in the accreditation process.

•• Acquires or assists in acquisition of phantom imagesAcquires or assists in acquisition of phantom images•• Performs phantom image evaluation to assess image Performs phantom image evaluation to assess image

quality and determine if images will pass ACR.quality and determine if images will pass ACR.•• Evaluates spatial and temporal resolution of Evaluates spatial and temporal resolution of

submitted clinical imagessubmitted clinical images


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• Scanner purchase specifications and MRI system siting

• Acceptance testing and scanner testing after installation and after major upgrade or repair**

•• Annual medical physicist performance evaluationAnnual medical physicist performance evaluation**•• Establishment and oversight of equipment QC & Establishment and oversight of equipment QC &

performance monitoringperformance monitoring**

• Protocol development and optimization

Medical Physicist / MR Scientist roleMedical Physicist / MR Scientist role

*topics covered by next two speakers

ACR MR Accreditation PhantomsACR MR Accreditation PhantomsManufacturer: J.M Specialty Parts

San Diego, CA

$1050 “large phantom” $780 “small phantom”

Guidance for Phantom testsGuidance for Phantom tests Guidance for Phantom testsGuidance for Phantom tests

ACR (large) Phantom AnalysisACR (large) Phantom Analysis#1

#5

#7 #8

#9 #10 #11

#1) Slice thickness and position, geometric accuracy, high contrast resolution#5) Geometric accuracy

#7) Percent image uniformity, ghosting#8-11) Low contrast object detectability, and slice position (in #11)

Slide courtesy of E.F. Jackson, PhD

ACR (small)ACR (small)PhantomPhantomAnalysis Analysis

Sag localizer) Geometric accuracy

#1) Slice thickness and position, geometric accuracy, high contrast resolution

#3) Geometric accuracy#5) PIU, ghosting#6-7) LCD

From “Phantom Test Guidance for Small MRI Phantom for the ACR MRI Accreditation Program”

1 sag 20 mm slice

7 axial 5mm slicesw/ 3mm gap

FOV 12 cm192 x 152 matrix


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ACR Accreditation: PreparationACR Accreditation: Preparation

•• Service engineer check system prior to acquiring Service engineer check system prior to acquiring phantom & clinical images.phantom & clinical images.

•• Physicist acquire and evaluate phantom images in Physicist acquire and evaluate phantom images in advance of starting accreditation process.advance of starting accreditation process.

•• Identify and correct scanner and coil problems.Identify and correct scanner and coil problems.•• ReRe--acquire phantom images and evaluate to ensure acquire phantom images and evaluate to ensure

images meet ACR limits.images meet ACR limits.

Phantom image quality problemsPhantom image quality problems•• CausesCauses•• Potential remedies available to the Potential remedies available to the

Medical Physicist Medical Physicist

Common pitfalls Common pitfalls –– phantom imagesphantom images

Phantom positionPhantom positionScan 3Scan 3--plane localizer prior to acquiring sagittal plane localizer prior to acquiring sagittal series to optimize phantom positionseries to optimize phantom position•• Axial rotationAxial rotation•• Sagittal tiltSagittal tilt•• Coronal alignmentCoronal alignment

Poor phantom positioning (off Poor phantom positioning (off isocenterisocenter))Geometric accuracy (gradient nonGeometric accuracy (gradient non--linearity, Blinearity, B00inhomogeneity)inhomogeneity)

•• Low contrast detectability (LCD), high contrast resolutionLow contrast detectability (LCD), high contrast resolution•• Phantom not centered in coil: Phantom not centered in coil:

•• PIU (nonPIU (non--uniform RF)uniform RF)

Large phantom Large phantom -- Slice PositionSlice Position

Slice 1 Slice 11

Criteria:<5mm

Small phantom Small phantom -- Slice PositionSlice Position

Slice 1

Criteria:<5mm

Phantom positionPhantom position

Off Off isocenterisocenter 100 mm inferior100 mm inferiorIsocenterIsocenter


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Phantom positionPhantom position

Off Off isocenterisocenter 100 mm superior100 mm superiorIsocenterIsocenter

Important to position phantom at center of boreImportant to position phantom at center of boreOffOff--isocenterisocenter: potential for distortion due to gradient non: potential for distortion due to gradient non--linearity and field inhomogeneitylinearity and field inhomogeneity

Phantom position:Phantom position:small bore orthopedic systemssmall bore orthopedic systems

Common pitfalls Common pitfalls –– clinical imagesclinical images•• Poor image quality on Site T1 and Site T2 series due to Poor image quality on Site T1 and Site T2 series due to

incorrect slice positions. incorrect slice positions.

Solution:Solution:•• Scan 3Scan 3--plane localizer to optimize phantom positionplane localizer to optimize phantom position•• Slices must intersect correct areas of the phantom. Slices must intersect correct areas of the phantom.

•• Large phantom: 5mm thick / 5mm gap Large phantom: 5mm thick / 5mm gap image spacing 10mmimage spacing 10mm•• Small phantom: 5mm thick / 3mm gap Small phantom: 5mm thick / 3mm gap image spacing 8mmimage spacing 8mm

Reference:Reference: “Site Scanning Instructions for use of the MR Phantom for the MRI Accreditation Program”, www.acr.org

Low contrast Low contrast detectabilitydetectability

Factors that impact LCD score:Factors that impact LCD score:•• Field strengthField strength•• Slice position accuracySlice position accuracy•• Phantom position off Phantom position off isocenterisocenter•• Coil, coil connection, whether coil is working Coil, coil connection, whether coil is working

properly (passes QC test)properly (passes QC test)

Large phantom Large phantom ––Low Contrast Detectability (LCD)Low Contrast Detectability (LCD)

Slice 8: 1.4%

Slice 9: 2.5%

Slice 10: 3.6%

Slice 11: 5.1%

Criteria:

≤1.5T - at least 9 spokes (total)

3T - at least 37 spokes (total)

Small phantom Small phantom ––Low Contrast Detectability (LCD)Low Contrast Detectability (LCD)

Slice 6: 3.6%

Slice 7: 5.1%

Criteria:

at least 9 spokes (total)

Slice 7


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Low field systemsLow field systems

Lower SNRLower SNRChallenge: to pass low contrast detection test Challenge: to pass low contrast detection test Clinical protocols modified to increase SNRClinical protocols modified to increase SNR

Increase number of averages (impacts scan time)Increase number of averages (impacts scan time)Narrow bandwidth (impacts chemical shift, geometric Narrow bandwidth (impacts chemical shift, geometric distortion)distortion)Use of higher SNR pulse sequences Use of higher SNR pulse sequences

Phantom alignment and slice position in LCD Phantom alignment and slice position in LCD sections is importantsections is important 0.2T0.2T

Slice 11 Slice 11 –– Low Contrast Detection section of large Low Contrast Detection section of large ACR MRI phantom (ACR T1 series)ACR MRI phantom (ACR T1 series)

1.5T1.5T

SNR vs. Field strengthSNR vs. Field strength

LCD score sensitiveto slice position

1.5T1.5TSlice 8 Slice 8 –– Low Contrast Detection section of large Low Contrast Detection section of large

ACR MRI phantom (8 channel array, ACR T1 series, SCIC)ACR MRI phantom (8 channel array, ACR T1 series, SCIC)

3.0T3.0T

SNR vs. Field strength SNR vs. Field strength Geometric accuracyGeometric accuracy

Factors that impact geometric accuracy:Factors that impact geometric accuracy:•• Phantom position off Phantom position off isocenterisocenter•• Gradient nonGradient non--linearity, Blinearity, B00 field inhomogeneityfield inhomogeneity•• Gradient nonGradient non--linearity correctionlinearity correction

•• Gradient correction application is a user choice on some, Gradient correction application is a user choice on some, but not all scannersbut not all scanners

•• Receive bandwidthReceive bandwidth

Large phantom Large phantom -- Geometric AccuracyGeometric Accuracy

Slice 1 Slice 5Sag Loc

Criteria: 148 ± 2 mmCriteria: 190 ± 2 mm

Small phantom Small phantom -- Geometric AccuracyGeometric Accuracy

Slice 1 Slice 3 Sag Loc

Criteria: 100 ± 2 mm


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Correction ONCorrection ON

ACR T1 series, Slice 5 ACR T1 series, Slice 5 –– large ACR MRI phantomlarge ACR MRI phantom

Correction OFFCorrection OFF

Gradient nonlinearity correction Gradient nonlinearity correction

IsocenterIsocenter IsocenterIsocenter

196 mm190 mm

+/+/-- 4 kHz = 31.25 Hz/pixel4 kHz = 31.25 Hz/pixel

ACR Sag T1 ACR Sag T1 –– large ACR MRI phantomlarge ACR MRI phantom

+/+/-- 16 kHz = 122.1 Hz/pixel16 kHz = 122.1 Hz/pixel

Receive bandwidth: geometric accuracyReceive bandwidth: geometric accuracy

frequency

ACR Axial T1 ACR Axial T1 –– large ACR MRI phantomlarge ACR MRI phantom

Receive bandwidth: geometric accuracyReceive bandwidth: geometric accuracy

frequency

+/+/-- 4 kHz = 31.25 Hz/pixel4 kHz = 31.25 Hz/pixel +/+/-- 16 kHz = 122.1 Hz/pixel16 kHz = 122.1 Hz/pixel +/+/-- 4 kHz4 kHz

ACR Axial T1 ACR Axial T1 –– large ACR MRI phantomlarge ACR MRI phantom

+/+/-- 16 kHz16 kHz

Receive bandwidth: chemical shift Receive bandwidth: chemical shift

UniformityUniformity

Factors that impact PIU score:Factors that impact PIU score:•• Dielectric effect at 3T Dielectric effect at 3T •• Use of 8 channel phased array coilsUse of 8 channel phased array coils•• Phantom position inside coilPhantom position inside coil•• Gradient nonGradient non--linearity, Blinearity, B00 field inhomogeneity; field inhomogeneity;

geometric distortion correctiongeometric distortion correction

Both phantoms Both phantoms --Percent Image UniformityPercent Image Uniformity

1.5T: Criteria: PIU≥ 87.5%PIU=[1-(max-min)/(max+min)] • 1003.0T: Criteria: PIU≥ 82 %


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3T3T

Decreased uniformity: Decreased uniformity: Reduced Reduced

RF penetration with RF penetration with increasing frequencyincreasing frequency

Apply Surface Coil Apply Surface Coil Intensity Intensity

CorrectionCorrection

1.5T1.5T

Impacts Uniformity measurement

3 Tesla systems 3 Tesla systems –– Dielectric effectDielectric effect

MRI Devices 8 channel HR Brain array: Images acquired from individual channels

Composite image

Phased array coilsPhased array coils•• Small coil elements improve SNRSmall coil elements improve SNR•• Multiple elements for anatomical coverageMultiple elements for anatomical coverage•• Independent receivers Independent receivers –– enables parallel imagingenables parallel imaging

8 channel head coils8 channel head coils

““If your facility uses an eight channel head If your facility uses an eight channel head coil, it is necessary to perform all phantom coil, it is necessary to perform all phantom scans using the scans using the surface coil intensity surface coil intensity correctioncorrection option.option.””

Reference:Reference: “ACR MRI Accreditation Program Testing Instructions”, rev 1-13-2009, www.acr.org

1.5T Quad head coil1.5T Quad head coil

ACR T1 series, Slice 7 ACR T1 series, Slice 7 –– Uniform section of large Uniform section of large ACR MRI phantomACR MRI phantom

1.5T 8 channel array1.5T 8 channel array

Uniformity vs. Coil Uniformity vs. Coil

1.5T 8 channel array1.5T 8 channel arraySCIC appliedSCIC applied

High contrast resolutionHigh contrast resolution

Factors that impact resolution score:Factors that impact resolution score:•• Excessive phantom rotation Excessive phantom rotation •• Excessive ghosting due to motion or vibrationExcessive ghosting due to motion or vibration

•• Ensure that coil is stableEnsure that coil is stable•• Immobilize phantom in coilImmobilize phantom in coil

•• Excessive low pass filtrationExcessive low pass filtration•• Filter application and degree of filtration is a user choice Filter application and degree of filtration is a user choice

on some, but not all scannerson some, but not all scanners

Large phantom Large phantom ––High Contrast Spatial ResolutionHigh Contrast Spatial Resolution

Must be able to resolve 1.0 mmholes vertically and horizontally.

25 cm FOV, 256 x 256 matrixPixels: 0.98 mm x 0.98 mm

1.1mm 1.0mm 0.9 mm


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Must be able to resolve 0.8 mmholes vertically and

horizontally.

12 cm FOV, 192 x 152 matrixPixels: 0.63 mm x 0.79 mm

0.9 mm 0.8 mm 0.7 mm

Small phantom Small phantom ––High Contrast Spatial ResolutionHigh Contrast Spatial Resolution FILTER ONFILTER ON

ACR T1 series, Slice 5 ACR T1 series, Slice 5 –– large ACR MRI phantomlarge ACR MRI phantom

FILTER OFFFILTER OFF

Low pass filter Low pass filter

Reduces truncation artifactsReduces truncation artifactsMay impact high contrast May impact high contrast resolution scoreresolution score

Prominent truncation artifactsProminent truncation artifacts

Common pitfalls Common pitfalls –– phantom imagesphantom images•• ACR Sagittal T1 image ACR Sagittal T1 image ““localizerlocalizer”” not included on CDnot included on CD•• CD not readable by the reviewerCD not readable by the reviewer•• Not uncompressed DICOM formatNot uncompressed DICOM format•• Embedded viewer Embedded viewer –– ACR reviewer unable to evaluate ACR reviewer unable to evaluate

DICOM imagesDICOM images

Solution:Solution:•• Review images on Review images on PC(sPC(s) separate from PACS and MRI ) separate from PACS and MRI

systems using (systems using (OsirisOsiris and/or Kand/or K--PACS) before submitting PACS) before submitting to ACR.to ACR.

•• Verify correct series and scan parameters Verify correct series and scan parameters -- view DICOM view DICOM header information.header information.

SummarySummary•• Presented a brief overview of the new modular ACR MRI Presented a brief overview of the new modular ACR MRI

Accreditation program. Accreditation program.

•• Medical physicist involvement in the application process is Medical physicist involvement in the application process is important as part of the accreditation team. important as part of the accreditation team.

•• Discussed phantom image quality problems, possible causes Discussed phantom image quality problems, possible causes and potential remedies, with focus on solutions available to and potential remedies, with focus on solutions available to the physicist.the physicist.

•• Provided advice for avoiding common pitfalls in the phantom Provided advice for avoiding common pitfalls in the phantom image submission process.image submission process.

Documents

ACR MRI Accreditation: Medical Educational …...Physics - ACR MRI Accreditation Program 9 Must be able to resolve 0.8 mm holes vertically and horizontally. 12 cm FOV, 192 x 152 matrix