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:Samantha.eustace@cancercare.mb.caSamantha.eustace@cancercare.mb.ca

Idris.elbakri@cancercare.mb.caIdris.elbakri@cancercare.mb.ca

Medical Physics Medical Physics CancerCareCancerCare ManitobaManitoba1 204 787 49101 204 787 4910