QC ProtocolsQC ProtocolsGamma Camera &Gamma Camera &

SPECT SystemsSPECT Systems

James R Halama, PhDJames R Halama, PhD

Loyola University Medical CenterLoyola University Medical Center

Maywood, ILMaywood, IL

OutlineOutline

1.1. Gamma Camera ImagingGamma Camera Imaginga.a. Brief overview of Gamma Camera OperationBrief overview of Gamma Camera Operation

b.b. Brief overview of Camera CalibrationsBrief overview of Camera Calibrations

2.2. SPECT Phantom ImagingSPECT Phantom Imaginga.a. Acquisition & ReconstructionAcquisition & Reconstruction

b.b. EvaluationEvaluation

c.c. ACR & ICANL Accreditation RequirementsACR & ICANL Accreditation Requirements

3.3. Final RecommendationsFinal Recommendations

Gamma Camera Imaging ofRadioactive Sources in Patients

Three major Components:

1. Collimator –channels the

-rays and localizes thesource in the patient

2. NaI(Tl) Crystal (single ormulti-crystal) over width ofpatient stops the -rays.

3. Array of PMT’s –localizes

-ray interaction in crystal

Collimator

PMTPMT

NaI Crystal

Localize -ray Hit in Crystal byPosition Weighed Sum of PMT Pulses

Figure 4Figure 4--22

P2P1 P3 P4 P5 P6 P7 P8

p1

p2

p3

p4

p5

p6

p7

p8

r1

r2

r3

r4

r5

r6

r7

r8

X

p1r1+ p2r2+… + p7r7+ p8r8

p1+p2+… +p7+p8X =

X+

SummingAmplifier

pi - PMTi pulse

ri - positional weightNaI crystal

Components of Gamma CameraSpatial Resolution

nn IntrinsicIntrinsic ResolutionResolution––Ability ofAbility ofthethe NaI(NaI(TlTl) crystal and PMT) crystal and PMTcombination to localizecombination to localize --rayrayinteractions in the crystal.interactions in the crystal.

nn CollimatorCollimator ResolutionResolution––Ability ofAbility ofthe collimator to localize thethe collimator to localize the --ray source in the patient.ray source in the patient.

nn ExtrinsicExtrinsic ResolutionResolution––OverallOverallresolution combining collimatorresolution combining collimatorand intrinsic factors. Totaland intrinsic factors. Totalresolution is quadratic sum ofresolution is quadratic sum ofthe twothe two componetscomponets..

PMTPMT

NaI Crystal

Collimator Resolution

FWHMC

d

L

t

c

f

c

(l+f+c)d

l

d –hole diameterl –hole lengtht –septal thickness of leadf –collimator to sourcedistancec –collimator to crystalcenter

distance

Collimator Ratio –Resolving power of collimator

Source to CrystalDistance

l

Available CollimatorsCollimator

TypeHole

Diameter(mm)

HoleLength(mm)

FWHMat 0 cm(mm)**

FWHMat 10 cm(mm)**

FWHMat 20 cm(mm)**

Sensitivity(CPM/ Ci)

Low Energy AllPurpose (LEAPor GAP)

1.43 23.6 4.4 9.1 15.3 360 (99mTc)

Low EnergyHigh Resolution

1.11 23.6 4.2 7.5 12.3 230 (99mTc)

Low EnergyUltra-HighResolution

1.08 35.6 4.2 5.9 8.6 100 (99mTc)

Medium Energy 3.02 40.6 5.6 12.1 19.7 288 (67Ga)

High Energy 4.32 62.8 6.6 13.8 22.0 176 (131I)

Ultra-HighEnergy

3.4 75.0 6.0 10.4 ~20.0 60 (18F)

** Siemens Orbiter Gamma Camera System with intrinsic resolution of 3.9 mm FWHM

Gamma Camera Quality ControlGamma Camera Quality Control

nn Basic Planar QC ProceduresBasic Planar QC Procedures

Intrinsic Spatial ResolutionMeasurement

GammaCamera

99mTc Point Source(400 –800 uCi)

4-Quad Bar Phantom

4-Quadrant barphantom replacesthe collimator –The image is theshadow of the leadbars on the crystal.

GammaCamera

4-QuadrantBar Phantom

Collimator

Extrinsic Spatial ResolutionMeasurement

Planar FloodSource

(10 mCi 99mTc or57Co)

Planar Sheet Sources

57Co Shhet Source –T1/2

270 days; 122 keV ; 10-15 mCi at time ofpurchase.

99mTc Sheet Source(water filled) –T1/2 6hrs.; 140 keV ; 10-15mCi at time of filling.

Measure Spatial Linearity withPLES Phantom

Images of PLES (parallel line equal spacing)phantom with 99mTc source

Deviation fromstraight line ofless than 1.0mmfor UFOV.

Measure Linearity with 4-Quadrant Bar Phantom

Note wavey/curve-linear appearanceof lead barsthroughout theimage.

Measuring Intrinsic Uniformity

GammaCamera

Point Source400-800 uCi

5 UFOVDiameterdistance

5-15 Million Counts1-3 min.

Edge Packing(higher sensitivity)

at edge

Statistical Variation:• 3 Mcts. ~ 1600 ct/cm2 (+ 2.5%)• 15 Mcts. ~ 4800 ct/cm2 (+ 1.4%)

No Collimator

Flood Image

Measuring Extrinsic Uniformity

GammaCamera

Collimator

Planar SheetSource

10-15 mCi of57Co or 99mTc

5-15 Million Counts3-15 min.

Edge Packingshielded by

collimator ring.

Gamma Camera CalibrationsGamma Camera Calibrations

1.1. PMT GainsPMT Gains

2.2. EnergyEnergy

3.3. LinearityLinearity

4.4. UniformityUniformity

FirstPMT Gain

By FSE

PMT & Energy CalibrationsPMT & Energy Calibrations

SecondEnergy

CorrectionBy FSE

Linearity & UniformityLinearity & UniformityCalibrationsCalibrations

ThirdLinearity

CorrectionBy FSE

FourthUniformityCorrectionBy Tech.

Quality Control PracticesQuality Control Practices1. Photopeak –Daily ensure isotope energy level centered over

photopeak.2. Uniformity - Flood images of 5-15 million counts each day of

use, before imaging begins.a) Extrinsic flood image is preferred and tests heavily used

collimators.b) Intrinsic flood image to test detector only, especially at

the periphery of the FOV. Acquired at least one perweek.

3. Resolution - Intrinsic (preferred) or extrinsic images of 5-10million counts of four-quadrant bar phantom once per week.

4. Linearity - Intrinsic (preferred) or extrinsic images of 5-10million counts with PLES or four-quadrant bar phantomonce per week.

5. Uniformity Correction Matrix –Corrects residual non-uniformities. Flood images of 100 Mcts once per month foreach isotope used.

QuantitateQuantitate Daily FloodsDaily Floods

Plot IU for UFOV or CFOV daily

PrePre--Assigned Action LevelsAssigned Action LevelsI. Good – no further evaluation neededII. Marginal – repeat flood once; if still marginal next day/week contact Physicist

or supervisor to determine status; a re-calibration may be necessary.III. Unacceptable – repeat flood once; if still unacceptable contact Physicist or

supervisor to determine status; a re-calibration may be necessary

Gamma Camera Intrinsic Uniformity – IUin UFOV

Extrinsic Uniformity – IUin UFOV

VertexI – below 3.5II – 3.5 – 5.0III – above 5.0

I –below 5.0II – 5.0 – 6.0III – above 6.0

Forte II – below 3.5II – 3.5 – 5.0III – above 5.0

I – below 5.0II – 5.0 – 6.0III – above 6.0

Forte III – below 3.5II – 3.5 – 5.0III – above 5.0

I – below 5.0II – 5.0 – 6.0III – above 6.0

Forte III

Irregradless of IU, if a single tube is visible in the flood image, contact Physicist or supervisor todetermine status.

Intrinsic and/or Extrinsic Floods?Intrinsic and/or Extrinsic Floods?

Det 2 –Co-57

Det 2 - Tc-99m

Det 1 –Co-57

Det 1 –Tc-99m

Routine Bar Pattern ImagesRoutine Bar Pattern Images ––Why?Why?

3.5 mm

2.5 mm 2.0 mm

3.0 mm

3.5 mm

2.5 mm

2.0 mm

3.0 mm

90 Deg. Rotation

Intrinsic and/or Extrinsic Bars?Intrinsic and/or Extrinsic Bars?

Co-57Extrinsic

3.5 mm

2.5 mm

2.0 mm

3.0 mm

Tc-99mIntrinsic

3.5 mm

2.5 mm

2.0 mm

3.0 mm

Intrinsic BarsIntrinsic Bars ––Better Assess X/YBetter Assess X/YResolutionResolution

Tc-99m

3.5 mm

2.5 mm2.0 mm

3.0 mm

3.5 mm

2.5 mm

2.0 mm

3.0 mm

Intrinsic BarsIntrinsic Bars ––Better AssessBetter AssessLinearityLinearity

Note –wavy barswrapped around

PMT’s

Rotating Gamma Camera SPECTRotating Gamma Camera SPECT

SPECT AcquisitionWhole Body Planar Bone Bone SPECT

• 256x1024 image• 20 min.• 2.3 million counts

• 120 128x128images

• 3o step & shootrotation over360o

• 30sec/image/head

• 32 min. totalacq.

• 60,000cts/image

Reconstructed Bone SPECT ImagesReconstructed Bone SPECT Images

Each line across the imagecorresponds to onetransaxial slice in thetomographic volume.

• 4 mm slice thickness for 128matrix over 50 cm field-of-view.

FPB vs. Iterative Reconstructions

Iterative - OSEM FBP

Gamma Camera SPECT QCGamma Camera SPECT QC

nn Uniformity CorrectionsUniformity Corrections

nn COR CorrectionsCOR Corrections

nn SPECT Phantom ImagingSPECT Phantom Imaging

Concentric rings of alternating high and lowcount densities appear in the transaxial imagesdue to insufficient gamma camera uniformity.

Bullseye Ring ArtifactBullseye Ring Artifact

Uniformity CorrectionUniformity Correction

Acquire High CountFlood Image

Generate FloodCorrection Matrix

30-100 million count flood images,10 times daily flood requirements

Uniformity Correction is aUniformity Correction is aCalibrationCalibration

•Uniformity correction applied

to all patient images

•Both planar and SPECT

imaging

Intrinsic Uniformity CalibrationIntrinsic Uniformity Calibration

1.1. Performed for TcPerformed for Tc--99m and/or other99m and/or other

isotope used clinicallyisotope used clinically

2.2. Precise point sourcePrecise point source

3.3. Low background and scatter freeLow background and scatter free

4.4. Correct count rateCorrect count rate

5.5. Correct total countsCorrect total counts

6.6. FOLLOW THE MANUALFOLLOW THE MANUAL

Fractured Point Sources?Fractured Point Sources?

• Isotope in 0.1 - 0.2 ml in hub ofsyringe or in end of the needle cap.

• Requires exchange of needle.

• Do not mishandle and fracturesource.

Can this be used?Can this be used?

Acquired at 100 Kcps

Intrinsic Uniformity Correction –May Mask Underlying Problems!

Detector with intrinsic linearity problems

Extrinsic Uniformity CalibrationExtrinsic Uniformity Calibration

1.1. Ideally the bestIdeally the best -- Corrects for bothCorrects for both

collimator and intrinsic detectorcollimator and intrinsic detector

2.2. Requires planar flood sourceRequires planar flood source

3.3. Ideally TcIdeally Tc--99m, Co99m, Co--57 is only a surrogate57 is only a surrogate

4.4. Required for each collimatorRequired for each collimator

5.5. FOLLOW THE MANUALFOLLOW THE MANUAL

Extrinsic Uniformity Correction –May Mask Collimator Problems!

Damaged collimator with crushed lead septa

Extrinsic or Intrinsic Correction?

Co-57 Extrinsic

Tc-99m Intrinsic

SPECT Center-of-Rotation

The center ofthe gamma

camera in allacquired

images must beknown

SPECTSPECTCOR Acquisition is a CalibrationCOR Acquisition is a Calibration

1.1. Used to correct patient imagesUsed to correct patient images

2.2. Extrinsic calibration for both 180 and 90 degreeExtrinsic calibration for both 180 and 90 degreedetector separationsdetector separations

3.3. Must follow manufacturer recommendationsMust follow manufacturer recommendationsregarding number and placement of sourcesregarding number and placement of sources

4.4. Sources must have sufficient activitySources must have sufficient activity

5.5. Completed monthly, or per manufacturerCompleted monthly, or per manufacturerspecificationsspecifications

Jaszczak Phantom:Cold Rods: 12.7, 11.1, 9.5, 7.9, 6.4, 4.8 mmCold Spheres: 31.8, 25.4, 19.1, 15.9, 12.7, 9.5 mm

SPECT Phantom ImagingSPECT Phantom Imaging

ACR SPECT PhantomPlanar Extrinsic Spatial Resolution

Planar Images 500 K

5000 K

1. Determine smallest rod sections visible2. Compare count rates –for multiple detectors, must

be within 5% of one another (remember to decaycorrect for Tc-99m)

1. Acquire SPECT phantom studies with 2-3 times

counts obtained clinically (24 million for ACR).

2. Reconstruct at highest resolution filter. Use FBP

for ACR.

SPECT Phantom Imaging ProtocolSPECT Phantom Imaging Protocol

• Look for bullseyeartifacts. If present,new intrinsiccorrection floodmust be acquired.

• Spatial resolution –number of rodsections observed.

• Contrast –numberof spheresobserved.

ReconstructedReconstructedSPECT PhantomSPECT Phantom

ImagesImages

180 Degree Orbit SPECT180 Degree Orbit SPECT

SPECT PhantomAcquisitions for dualhead SPECT system offixed heads and 180degree acquisition only.

Uniformity Problems!Uniformity Problems!

Phantom Reconstruction no ACPhantom Reconstruction no AC

Phantom Reconstruction & ACPhantom Reconstruction & AC

ACR SPECT Phantom Formatting

Summing of Slices

Uniformity(3 slices)

Resolution(12 slices)

Contrast(2 slices)

NonNon--Aligned Detectors in XAligned Detectors in X

Sinogram

NonNon--Aligned Detectors in YAligned Detectors in Y

Linogram

ACR QC GuidelinesACR QC Guidelines ––TechnologistTechnologist1. Intrinsic or System Uniformity - each day of use

2. Intrinsic or System Spatial Resolution - weekly

3. Center-of-Rotation or Multiple Detector Registration

Calibration/Test for SPECT Systems - monthly

4. High-Count Floods For Uniformity Correction for SPECT

Systems - frequency as recommended by a qualified medical

physicist

5. Overall System Performance for SPECT Systems –quarterly

SPECT Phantom; Tc-99m must be done at least semiannually;

other radionuclides may be tested on alternate quarters.ACR Nuclear Medicine/PET Accreditation Program Requirements 3/28/2008

ACR QC GuidelinesACR QC Guidelines ––Annual TestsAnnual Tests

ACR Nuclear Medicine/PET Accreditation Program Requirements 3/28/2008

1. Intrinsic Uniformity

2. Intrinsic or System Spatial Resolution

3. System Uniformity - check all collimators

4. Sensitivity - verify that count rate per unit activity is satisfactory

5. Energy Resolution

6. Count Rate Parameters

7. Overall System Performance for SPECT Systems –SPECTPhantom

8. Formatter/Video Display

9. System Interlocks

ICANL QC GuidelinesICANL QC Guidelines

1. Energy peaking - Daily prior to use; documentation notrequired)

2. Intrinsic or extrinsic uniformity - Daily prior to use;(approximately 2-5 million counts)

3. Resolution and linearity –Weekly bar phantoms

4. Uniformity calibration - Monthly or per manufacturer’srecommendations

5. Center of rotation (SPECT) - Monthly

6. Collimator integrity - Annually

7. Preventive maintenance - Every 6 months

The ICANL Standards for Nuclear Cardiology, Nuclear Medicine and PET Accreditation, 2007

Recommended QC GuidelinesRecommended QC Guidelines --TechnologistTechnologist

1.1. Energy peakingEnergy peaking -- Daily prior to useDaily prior to use

2.2. Intrinsic or extrinsic uniformityIntrinsic or extrinsic uniformity -- Daily prior to use; (4Daily prior to use; (4--1010million counts)million counts)

3.3. Uniformity CalibrationUniformity Calibration -- Monthly, or per manufacturer’sMonthly, or per manufacturer’srecommendations:recommendations:

a.a. IntrinsicIntrinsic ––YesYes

b.b. ExtrinsicExtrinsic ––only when necessaryonly when necessary

4.4. Intrinsic uniformity, resolution and linearity QCIntrinsic uniformity, resolution and linearity QC ––QuarterlyQuarterly

5.5. SPECT Center of rotationSPECT Center of rotation ––Monthly, or per manufacturer’sMonthly, or per manufacturer’srecommendationsrecommendations

6.6. SPECT PhantomSPECT Phantom (quarterly)(quarterly)

7.7. Preventive maintenancePreventive maintenance ––semisemi--annual by FSEannual by FSE

RecommendedRecommended ––SPECT Phantom ImagingSPECT Phantom Imaging

1.1. Assesses intrinsic and collimator uniformity,Assesses intrinsic and collimator uniformity,

altogether. If only Tcaltogether. If only Tc--99m intrinsic uniformity99m intrinsic uniformity

correction is applied and not ring artifactscorrection is applied and not ring artifacts ––nono

collimator flood correction is needed.collimator flood correction is needed.

2.2. Assesses sensitivity differences in detectorsAssesses sensitivity differences in detectors

3.3. Assesses adequacy of COR corrections observedAssesses adequacy of COR corrections observed

inin sinogramsinogram andand linogramlinogram

4.4. Assesses overall SPECT resolution and contrastAssesses overall SPECT resolution and contrast

RecommendedRecommended ––QC Guidelines AnnuallyQC Guidelines Annually

1. Intrinsic uniformity, spatial resolution, & linearity

2. System uniformity - check all collimators

3. Sensitivity - verify that count rate per unit activity per detector issatisfactory

4. Detector energy resolution

5. Count rate parameters

6. Overall SPECT performance –SPECT Phantom and possiblyfor additional isotope

7. Formatter/Video display & system interlocks