Ct for Nuclear Medicine Technologists QC


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Ct for Nuclear Medicine Technologists QC

  1. 1. CT for Nuclear MedicineCT 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
  2. 2. CT Types in NuclearCT Types in Nuclear medicinemedicine NonNon –– diagnosticdiagnostic GE Infinia Hawkeye / Hawkeye 4GE Infinia Hawkeye / Hawkeye 4 Siemens Symbia TSiemens Symbia T Phillips/Other manufacturersPhillips/Other manufacturers -- None?None? PET/CTPET/CT –– None?None? Generally low mAsGenerally 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
  3. 3. CT typesCT types –– continued....continued.... DiagnosticDiagnostic GEGE –– None in SPECTNone in SPECT SiemensSiemens –– Symbia T2, T6, T16,Symbia T2, T6, T16, PETPET –– BiographBiograph Phillips Precedence (16 slice)Phillips Precedence (16 slice) PETPET –– GeminiGemini Full CT capabilities, kV, pitch, rotation speedFull CT capabilities, kV, pitch, rotation speed Typical mAsTypical mAs –– 100100--300 capable of 400+300 capable of 400+
  4. 4. NonNon ––Diagnostic CTDiagnostic CT Uses: Attenuation correction Registration/Localisation
  5. 5. Diagnostic Quality CTDiagnostic Quality CT Main Uses: Localisation Diagnosis Attenuation Correction
  6. 6. Quality AssuranceQuality Assurance Like gamma cameras QA is required forLike 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
  7. 7. GuidelinesGuidelines ForFor ‘‘diagnosticdiagnostic’’ CT machinesCT machines American College of Radiology (ACR)American College of Radiology (ACR) Frequency and type of testingFrequency and type of testing ImPACTImPACT –– UK CT Evaluation CentreUK CT Evaluation Centre Testing methodsTesting methods
  8. 8. When/Who?When/Who? Frequency determined by assessingFrequency determined by assessing importance and/or likelihood of changeimportance and/or likelihood of change PhysicistPhysicist Acceptance/commissioning at installationAcceptance/commissioning at installation AnnuallyAnnually Following some major hardware/software changesFollowing some major hardware/software changes TechnologistTechnologist DailyDaily Weekly/monthly/quarterlyWeekly/monthly/quarterly
  9. 9. What tests should be done?What tests should be done? SafetySafety shielding, signage, leakage, patient collision, emergency stopsshielding, signage, leakage, patient collision, emergency stops Image qualityImage quality Uniformity, CT number, Spatial resolution, imaged sliceUniformity, CT number, Spatial resolution, imaged slice thickness, contrast, noise, artifactsthickness, contrast, noise, artifacts Mechanical and light alignmentMechanical and light alignment Patient couch, lasersPatient couch, lasers DosimetryDosimetry CTDI, geometric efficiencyCTDI, geometric efficiency Display deviceDisplay device Ensures the display device is displaying info accuratelyEnsures the display device is displaying info accurately
  10. 10. HoweverHowever…….. Will the CT scan be used for diagnosticWill the CT scan be used for diagnostic purposes?purposes? What about nonWhat about non--diagnostic CT scanners?diagnostic CT scanners? Purpose of following sectionPurpose of following section Explain testsExplain tests Describe existing manufacturer basedDescribe existing manufacturer based guidelinesguidelines Make recommendationsMake recommendations
  11. 11. CT Number Accuracy and LinearityCT Number Accuracy and Linearity Routine daily/monthlyRoutine daily/monthly Accuracy of CT number for waterAccuracy of CT number for water Acceptance & AnnuallyAcceptance & Annually Accuracy and linearity of range of materialsAccuracy and linearity of range of materials TolerancesTolerances Air and water within 10UAir 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 1000 μμ(water)(water)
  12. 12. UniformityUniformity UniformityUniformity 5ROI5ROI’’s Sets Set Maximum diff betweenMaximum diff between mean CT number of themean CT number of the central and that ofcentral and that of peripheral regionsperipheral regions ToleranceTolerance -- Periphery HUPeriphery HU values +/values +/-- 15HU from15HU from central valuecentral value
  13. 13. 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, detectorctor 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 baseline20% from baseline 10% between slices10% between slices
  14. 14. CTDICTDI Valuable and sensitive measurementValuable and sensitive measurement Clear dose indicatorClear dose indicator Detect changes in tube output, beam collimation, focal spot, beDetect changes in tube output, beam collimation, focal spot, beamam filtrationfiltration Measured Annually by physicistMeasured Annually by physicist In air (CTDIIn air (CTDI100100)) In phantom (CTDIIn phantom (CTDIww))
  15. 15. ResolutionResolution SubjectiveSubjective Visual interpretation ofVisual interpretation of test patterntest pattern Objective/QuantitativeObjective/Quantitative Calculation of ModularCalculation of Modular Transfer Function (MTF)Transfer Function (MTF)
  16. 16. MTFMTF Input Object Output Object MTF Recorded valuesRecorded values -- 50% MTF 10% MTF and 2% MTF50% MTF 10% MTF and 2% MTF
  17. 17. Resolution continuedResolution continued…….. In practice however we imageIn practice however we image an aluminum bead or wirean aluminum bead or wire Produces a Point/Line SpreadProduces a Point/Line Spread Function (analogous to countFunction (analogous to count profile)profile)
  18. 18. Contrast ResolutionContrast Resolution Ability to see low contrast objects Depends on spatial resolution and noise (and other factors e.g kV)
  19. 19. Slice ThicknessSlice Thickness Slice thickness = height x tanθ If θ = 450 Slice thickness = height Typical tolerance ~ 0.5mm θ
  20. 20. Presence of artifactsPresence of artifacts CuppingCupping -- Beam hardeningBeam hardening CircularCircular –– ReconstructionReconstruction issuesissues Photon StarvationPhoton Starvation
  21. 21. 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
  22. 22. Sagittal and CoronalSagittal and Coronal LightmarkersLightmarkers Light markers should mark the horizontal and vertical centers of the phantom When scanned the middle ofWhen scanned the middle of the phantom is determinedthe phantom is determined Result= deviation fromResult= deviation from horizontal and vertical middle ofhorizontal and vertical middle of image to middle of the phantomimage to middle of the phantom Tolerance =2mmTolerance =2mm
  23. 23. Movement AccuracyMovement Accuracy Is position indicatorIs position indicator accurate?accurate? Checked using a rulerChecked using a ruler Does the couch moveDoes the couch move accurately?accurately? Checked by imaging phantomChecked by imaging phantom with positional markerswith positional markers
  24. 24. Display DeviceDisplay Device AAPM Guidelines DICOM Calibrated Luminosity Linearity Low contrast resolution Spatial resolution Routine QA - SMPTE Pattern In SPECT/CT requirement depends on use of CT images Monitors used for reporting diagnostic CT images
  25. 25. XX--ray to NM Imageray to NM Image RegistrationRegistration XX--ray to NM Imageray to NM Image RegistrationRegistration FrequencyFrequency -- quarterlyquarterly Calc distance between CT andCalc distance between CT and NM images in x,y and z axesNM images in x,y and z axes Hawkeye alignment phantomHawkeye alignment phantom 6x10ml ~156x10ml ~15 -- 40MBq each40MBq each Same solutionSame solution No bubblesNo bubbles
  26. 26. XX--ray to NM Image registrationray to NM Image registration continuedcontinued…… Measurement of countMeasurement of count rate to determinerate to determine time/projection (manual)time/projection (manual) Scout imageScout image SPECT/CT acquisitionSPECT/CT acquisition ProcessingProcessing –– calculationcalculation of given distancesof given distances TolerancesTolerances xx (mm)(mm) yy (mm)(mm) zz (mm)(mm) Hawkeye 1Hawkeye 1 33 33 55 Hawkeye 4Hawkeye 4 33 33 33
  27. 27. 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)
  28. 28. PhantomsPhantoms Siemens 1.Water phantom 2 slice thickness phantom 3.Wire phantom (resolution) (4. low contrast) GE 1. Slice alignment, spatial resolution, CT scale, slice thickness 2. Low contrast resolution 3. Water phantom
  29. 29. Daily QCDaily QC Warm upWarm up –– few slicesfew slices at low kVat low kV Calibrations (GE)Calibrations (GE) –– AirAir Table CalibrationTable Calibration QC TestsQC Tests GEGE SiemensSiemens ImageImage uniformityuniformity CT value ofCT value of water (HU)water (HU) Pixel noisePixel noise Tube voltageTube voltage
  30. 30. Monthly/Quarterly QCMonthly/Quarterly QC Limited 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
  31. 31. Our RecommendationsOur Recommendations Amount depends somewhat on CT type and use:Amount depends somewhat on CT type and use: Non diagnostic equipment/useNon diagnostic equipment/use DailyDaily UniformityUniformity QuarterlyQuarterly XrayXray to NM registrationto NM registration AnnuallyAnnually Physics testing relevant to usePhysics testing relevant to use Diagnostic capability/useDiagnostic capability/use DailyDaily Uniformity, noise, crudeUniformity, noise, crude xrayxray--NM image registrationNM image registration MonthlyMonthly Image Quality using manufacturers phantomImage Quality using manufacturers phantom AnnualAnnual Physics full range of testsPhysics full range of tests
  32. 32. Thank you!Thank you! Contacts:Contacts: Samantha.eustace@cancercare.mb.caSamantha.eustace@cancercare.mb.ca Idris.elbakri@cancercare.mb.caIdris.elbakri@cancercare.mb.ca Medical PhysicsMedical Physics CancerCareCancerCare ManitobaManitoba 1 204 787 49101 204 787 4910