Download - Ct for Nuclear Medicine Technologists QC
CT for Nuclear Medicine CT for Nuclear Medicine Technologists: Technologists:
Use and Quality ControlUse and Quality Control
Samantha Eustace (nee Russell)Samantha Eustace (nee Russell)Imaging PhysicistImaging Physicist
CancerCare ManitobaCancerCare Manitoba
CT Types in Nuclear CT Types in Nuclear medicinemedicine
Non Non –– diagnosticdiagnosticGE Infinia Hawkeye / Hawkeye 4GE Infinia Hawkeye / Hawkeye 4Siemens Symbia TSiemens Symbia TPhillips/Other manufacturers Phillips/Other manufacturers -- None?None?PET/CT PET/CT –– None?None?
Generally low mAs Generally low mAs (GE 1 (GE 1 -- 2.5, Siemens ~132.5, Siemens ~13--17)17)
Limited parameter variations i.e. kV, pitch, Limited parameter variations i.e. kV, pitch, rotation speedrotation speed
CT types CT types –– continued....continued....
DiagnosticDiagnosticGE GE –– None in SPECTNone in SPECTSiemens Siemens –– Symbia T2, T6, T16,Symbia T2, T6, T16,
PET PET –– Biograph Biograph
Phillips Precedence (16 slice)Phillips Precedence (16 slice)PET PET –– Gemini Gemini
Full CT capabilities, kV, pitch, rotation speedFull CT capabilities, kV, pitch, rotation speedTypical mAs Typical mAs –– 100100--300 capable of 400+300 capable of 400+
Non Non ––Diagnostic CTDiagnostic CTUses: Attenuation correction Registration/Localisation
Diagnostic Quality CTDiagnostic Quality CTMain Uses: Localisation Diagnosis Attenuation Correction
Quality AssuranceQuality Assurance
Like gamma cameras QA is required for Like gamma cameras QA is required for CT machines to ensure:CT machines to ensure:
Adequate functionalityAdequate functionality
Consistent performanceConsistent performance
Safety and radiation protectionSafety and radiation protection
GuidelinesGuidelines
For For ‘‘diagnosticdiagnostic’’ CT machinesCT machines
American College of Radiology (ACR)American College of Radiology (ACR)Frequency and type of testingFrequency and type of testing
ImPACT ImPACT –– UK CT Evaluation CentreUK CT Evaluation CentreTesting methodsTesting methods
When/Who?When/Who?
Frequency determined by assessing Frequency determined by assessing importance and/or likelihood of changeimportance and/or likelihood of change
PhysicistPhysicistAcceptance/commissioning at installationAcceptance/commissioning at installationAnnually Annually Following some major hardware/software changesFollowing some major hardware/software changes
TechnologistTechnologistDailyDailyWeekly/monthly/quarterlyWeekly/monthly/quarterly
What tests should be done?What tests should be done?Safety Safety
shielding, signage, leakage, patient collision, emergency stopsshielding, signage, leakage, patient collision, emergency stops
Image qualityImage qualityUniformity, CT number, Spatial resolution, imaged slice Uniformity, CT number, Spatial resolution, imaged slice thickness, contrast, noise, artifactsthickness, contrast, noise, artifacts
Mechanical and light alignment Mechanical and light alignment Patient couch, lasersPatient couch, lasers
Dosimetry Dosimetry CTDI, geometric efficiencyCTDI, geometric efficiency
Display deviceDisplay deviceEnsures the display device is displaying info accuratelyEnsures the display device is displaying info accurately
HoweverHowever……..
Will the CT scan be used for diagnostic Will the CT scan be used for diagnostic purposes?purposes?
What about nonWhat about non--diagnostic CT scanners?diagnostic CT scanners?
Purpose of following section Purpose of following section Explain tests Explain tests Describe existing manufacturer based Describe existing manufacturer based guidelinesguidelinesMake recommendations Make recommendations
CT Number Accuracy and LinearityCT Number Accuracy and Linearity
Routine daily/monthlyRoutine daily/monthlyAccuracy of CT number for waterAccuracy of CT number for water
Acceptance & AnnuallyAcceptance & AnnuallyAccuracy and linearity of range of materialsAccuracy and linearity of range of materials
TolerancesTolerancesAir and water within 10U Air and water within 10U and within 5% of baselineand within 5% of baseline
CT number = CT number = μμ(object) (object) –– μμ(water)(water) x 1000x 1000μμ(water)(water)
UniformityUniformity
UniformityUniformity5ROI5ROI’’s Sets SetMaximum diff between Maximum diff between mean CT number of the mean CT number of the central and that of central and that of peripheral regionsperipheral regionsTolerance Tolerance -- Periphery HU Periphery HU values +/values +/-- 15HU from 15HU from central valuecentral value
Image NoiseImage Noise
Influenced by:Influenced by:Tube output, beam width, focal spot size, beam, filtration, deteTube output, beam width, focal spot size, beam, filtration, detector ctor calibration and sensitivity, image reconstruction filterscalibration and sensitivity, image reconstruction filters
Testing: Testing: 2 scans (several for baseline) 2 scans (several for baseline) Noise = Noise = S.d of CT no.s (in ROI)S.d of CT no.s (in ROI)
CT scale factorCT scale factor
Tolerances:Tolerances:20% from baseline 20% from baseline 10% between slices10% between slices
CTDICTDIValuable and sensitive measurement Valuable and sensitive measurement
Clear dose indicatorClear dose indicatorDetect changes in tube output, beam collimation, focal spot, beDetect changes in tube output, beam collimation, focal spot, beam am
filtrationfiltration
Measured Annually by physicistMeasured Annually by physicistIn air (CTDIIn air (CTDI100100))In phantom (CTDIIn phantom (CTDIww))
ResolutionResolution
SubjectiveSubjectiveVisual interpretation of Visual interpretation of test patterntest pattern
Objective/QuantitativeObjective/QuantitativeCalculation of Modular Calculation of Modular Transfer Function (MTF)Transfer Function (MTF)
MTFMTFInput Object
Output Object
MTF
Recorded values Recorded values -- 50% MTF 10% MTF and 2% MTF50% MTF 10% MTF and 2% MTF
Resolution continuedResolution continued……..
In practice however we image In practice however we image an aluminum bead or wirean aluminum bead or wire
Produces a Point/Line Spread Produces a Point/Line Spread Function (analogous to count Function (analogous to count profile)profile)
Contrast ResolutionContrast ResolutionAbility to see low contrast objects
Depends on spatial resolution and noise
(and other factors e.g kV)
Slice ThicknessSlice Thickness
Slice thickness = height x tanθ
If θ = 450 Slice thickness = height
Typical tolerance ~ 0.5mm
θ
Presence of artifactsPresence of artifactsCupping Cupping -- Beam hardeningBeam hardening
Circular Circular –– Reconstruction Reconstruction issuesissues
Photon StarvationPhoton Starvation
Axial Light marker positionAxial Light marker position
Scan plane
=
light plane
Scan plane after light
marker
Scan plane before light
marker
Correct by feeding table in or out in 1mm increments
Tolerance =+/- 2mm
Assesses difference between light marker position and the scanning plane
Slice thickness test object– 2 radio-opaque strips within
Perspex phantom
Reference marking ‘etched’
onto phantom surface
Sagittal and Coronal Sagittal and Coronal LightmarkersLightmarkers
Light markers should mark the horizontal and vertical centers of the phantom
When scanned the middle of When scanned the middle of the phantom is determinedthe phantom is determined
Result= deviation from Result= deviation from horizontal and vertical middle of horizontal and vertical middle of image to middle of the phantomimage to middle of the phantom
Tolerance =2mmTolerance =2mm
Movement AccuracyMovement Accuracy
Is position indicator Is position indicator accurate? accurate? Checked using a rulerChecked using a ruler
Does the couch move Does the couch move accurately?accurately?Checked by imaging phantom Checked by imaging phantom with positional markerswith positional markers
Display DeviceDisplay Device
AAPM Guidelines
DICOM CalibratedLuminosityLinearityLow contrast resolutionSpatial resolution
Routine QA - SMPTE Pattern
In SPECT/CT requirement depends on use of CT images
Monitors used for reporting diagnostic CT images
XX--ray to NM Image ray to NM Image RegistrationRegistration
XX--ray to NM Image ray to NM Image RegistrationRegistrationFrequency Frequency -- quarterlyquarterlyCalc distance between CT and Calc distance between CT and NM images in x,y and z axesNM images in x,y and z axesHawkeye alignment phantomHawkeye alignment phantom
6x10ml ~15 6x10ml ~15 -- 40MBq each40MBq eachSame solutionSame solutionNo bubblesNo bubbles
XX--ray to NM Image registration ray to NM Image registration continuedcontinued……
Measurement of count Measurement of count rate to determine rate to determine time/projection (manual)time/projection (manual)Scout image Scout image SPECT/CT acquisitionSPECT/CT acquisitionProcessing Processing –– calculation calculation of given distancesof given distancesTolerances Tolerances
x x (mm)(mm)
y y (mm)(mm)
z z (mm)(mm)
Hawkeye 1Hawkeye 1 33 33 55
Hawkeye 4Hawkeye 4 33 33 33
Existing QA for SPECT/CTExisting QA for SPECT/CT
What is currently happening?What is currently happening?
(Based on GE and Siemens)(Based on GE and Siemens)
PhantomsPhantoms
Siemens1.Water phantom
2 slice thickness phantom3.Wire phantom (resolution)
(4. low contrast)
GE1. Slice alignment, spatial resolution,
CT scale, slice thickness2. Low contrast resolution
3. Water phantom
Daily QC Daily QC
Warm up Warm up –– few slices few slices at low kVat low kVCalibrations (GE) Calibrations (GE) –– Air Air
Table CalibrationTable CalibrationQC TestsQC Tests
GEGE SiemensSiemens
Image Image uniformityuniformity
CT value of CT value of water (HU)water (HU)
Pixel noisePixel noise
Tube voltageTube voltage
Monthly/Quarterly QCMonthly/Quarterly QCLimited Information
Siemens Ability to conduct monthly testing
Spatial resolution, Phantom position, Light marker position, Slice thickness,
Homogeneity, Pixel noise, Contrast resolution, CTDI air, Table positioning
GE (Hawkeye only)Quarterly
Xray-NM image registration
Our RecommendationsOur RecommendationsAmount depends somewhat on CT type and use:Amount depends somewhat on CT type and use:
Non diagnostic equipment/useNon diagnostic equipment/useDaily Daily UniformityUniformityQuarterly Quarterly XrayXray to NM registration to NM registration Annually Annually Physics testing relevant to usePhysics testing relevant to use
Diagnostic capability/useDiagnostic capability/useDaily Daily Uniformity, noise, crude Uniformity, noise, crude xrayxray--NM image registrationNM image registrationMonthlyMonthly Image Quality using manufacturers phantomImage Quality using manufacturers phantomAnnualAnnual Physics full range of testsPhysics full range of tests
Thank you!Thank you!
Contacts:Contacts:[email protected]@cancercare.mb.ca
[email protected]@cancercare.mb.ca
Medical Physics Medical Physics CancerCareCancerCare ManitobaManitoba1 204 787 49101 204 787 4910