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Computed Radiography:Computed Radiography:Acceptance TestingAcceptance Testing
and and Quality ControlQuality Control
J. Anthony Seibert, Ph.D.J. Anthony Seibert, Ph.D.University of California DavisUniversity of California Davis
Department of RadiologyDepartment of RadiologySacramento, CaliforniaSacramento, California
IntroductionIntroductionCR is the primary means to capture 2D CR is the primary means to capture 2D
images in a PACS environmentimages in a PACS environment
•• Acceptance testingAcceptance testing validates performancevalidates performance
•• Quality controlQuality control verifies optimal operationverifies optimal operation
Considerations:Considerations:•• Knowledge of CR attributes and operationKnowledge of CR attributes and operation•• Understanding the testsUnderstanding the tests•• Determining appropriate resultsDetermining appropriate results
Presentation OutlinePresentation Outline
Overview of CROverview of CRHow does it work? How does it work? What are the issues?What are the issues?
Quality control Quality control When ? When ? What? What? How often? How often?
Acceptance test proceduresAcceptance test proceduresWhat tests? Why? What tests? Why? How? How?
Computed Radiography (CR)Computed Radiography (CR)...is the generic term applied to an imaging system ...is the generic term applied to an imaging system
comprised of:comprised of:
Photostimulable Storage PhosphorPhotostimulable Storage Phosphorto acquire the xto acquire the x--ray projection imageray projection image
CR ReaderCR Readerto extract the electronic latent imageto extract the electronic latent image
Digital electronicsDigital electronicsto convert the signals to digital formto convert the signals to digital form
CR Image AcquisitionCR Image Acquisition
Phosphor platePhosphor plate
XX--rayraysystemsystem
1.1. XX--ray Exposureray Exposure
ImageImageScalingScaling
3.3.ImageImageRecordRecord
4.4.
PatientPatientComputedComputedRadiographRadiograph
5.5.unexposedunexposed
ImageImageReaderReader
2.2.
exposedexposed
Charge Charge collection collection
devicedevice
XX--ray converterray converterxx--rays rays →→ electronselectrons
Transmitted xTransmitted x--raysraysthrough patientthrough patient
Analog to DigitalConversion
Analog to DigitalAnalog to DigitalConversionConversion
1. Acquisition1. Acquisition
2. Display2. Display
3. Archiving3. Archiving
Digital Digital processingprocessing
Digital to AnalogConversion
Digital to AnalogDigital to AnalogConversionConversion
Digital PixelDigital PixelMatrixMatrix
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
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Film laser printerFilm laser printer
DICOMDICOM
PACS SoftPACS Soft--copy reviewcopy reviewCR CR -- QC WorkstationQC Workstation
CRCRReaderReader
CR NetworkingCR Networking
•• PACS and DICOMPACS and DICOM–– Digital Imaging Digital Imaging COmmunicationsCOmmunications in Medicinein Medicine–– Provides standard for modality interfaces, Provides standard for modality interfaces,
storage/retrieval, and printstorage/retrieval, and print
•• Modality Worklist Input (from RIS via HLModality Worklist Input (from RIS via HL--7)7)
•• Technologist QC WorkstationTechnologist QC Workstation–– Image manipulation and processingImage manipulation and processing–– Processed / Unprocessed imagesProcessed / Unprocessed images
•• DICOM image outputDICOM image output
Photostimulated LuminescencePhotostimulated LuminescenceConduction bandConduction band
Valence bandValence band
PSLPSL3.0 eV3.0 eV
t t EuEu
EuEu 2+2+EuEu 3+3+//4f 4f 77
8.3 eV8.3 eVLaser Laser
stimulationstimulation
2.0 eV2.0 eV
F/FF/F++
PSLC complexes (F centers) are created in PSLC complexes (F centers) are created in numbers proportional to incident xnumbers proportional to incident x--ray ray intensityintensity
ee--
t t tunnelingtunneling
t t recombinationrecombination
4f 4f 66 5d5d
phononphonon
CR: How does it work?CR: How does it work?
IncidentIncidentxx--rays rays
ee
Energy Band Energy Band BaFBrBaFBr
300300400400500500600600700700800800
Rela
tive
inte
nsity
Rela
tive
inte
nsity
0.00.0
0.50.5
1.01.0
λλ (nm)(nm)
Energy (eV)Energy (eV)33 442.52.5221.51.5
Stimulation and Emission SpectraStimulation and Emission Spectra
1.751.75
EmissionEmissionStimulationStimulation
DiodeDiode680 nm680 nm
BaFBr: EuBaFBr: Eu2+2+
OpticalOpticalBarrierBarrier
Photostimulated LuminescencePhotostimulated Luminescence
Incident Laser BeamIncident Laser Beam
PMTPMT
Protective LayerProtective Layer
Phosphor LayerPhosphor Layer
Base SupportBase Support
LightLightScatteringScattering
Laser Light SpreadLaser Light Spread
PhotostimulatedPhotostimulatedLuminescenceLuminescence
"Effective" readout diameter"Effective" readout diameter
ExposedExposedImagingImaging
PlatePlate
Light guideLight guidePSLPSLSignalSignal
CR: Latent Image ReadoutCR: Latent Image Readout
PMTPMT
Polygonal Polygonal MirrorMirror
LaserLaserSourceSource
Light channeling guideLight channeling guide
Output SignalOutput Signal
ReferenceReferencedetectordetector Cylindrical mirrorCylindrical mirror
ff--θθlenslens
ADCADC
Laser beam: Laser beam: Scan directionScan direction
Plate translation: Plate translation: SubSub--scan directionscan direction
To imageTo imageprocessorprocessor
ADCADC
x= 1279x= 1279y= 1333y= 1333z= 500z= 500
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
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Scan DirectionScan Direction
SubSub--scan Directionscan Direction
Laser beam deflectionLaser beam deflection
Plate translationPlate translation
Typical CR resolution:Typical CR resolution:35 x 43 cm 35 x 43 cm ---- 2.5 lp/mm (200 2.5 lp/mm (200 µµm)m)24 x 30 cm 24 x 30 cm ---- 3.3 lp/mm (150 3.3 lp/mm (150 µµm)m)18 x 24 cm 18 x 24 cm ---- 5.0 lp/mm (100 5.0 lp/mm (100 µµm)m)
Screen/film resolution:Screen/film resolution:77--10 lp/mm (80 10 lp/mm (80 µµm m -- 25 25 µµm)m)
Phosphor Plate CyclePhosphor Plate Cycle
PSP PSP
Base supportBase support
reusereuse
plate erasure:plate erasure:remove residualsremove residuals
light erasurelight erasure
plate exposure:plate exposure:create latent imagecreate latent image
xx--ray exposureray exposure
plate readout:plate readout:extract latent imageextract latent image
laser beam scanlaser beam scan
Computed RadiographyComputed Radiography
•• Acquisition, Display and Archive are Acquisition, Display and Archive are separateseparatefunctionsfunctions
•• Variable speed detectorVariable speed detector–– 20 to 2000 speed 20 to 2000 speed
•• Wide dynamic rangeWide dynamic range–– 0.01 to 100 mR0.01 to 100 mR
•• Image processing is a Image processing is a crucialcrucial requirement requirement
Exposure Latitude: Dynamic RangeExposure Latitude: Dynamic Range
FilmFilmFilm
100:1100:1100:1
Log relative exposureLog relative exposure
Sign
al o
utpu
tSi
gnal
out
put
10000:110000:110000:1
CRCRCR
Raw imageRaw image
•• Inherent subject Inherent subject contrast displayedcontrast displayed
•• Contrast inverted Contrast inverted (to screen(to screen--film)film)
•• PSL signal amplitude PSL signal amplitude log amplifiedlog amplified
Processing the ImageProcessing the Image
•• Image preImage pre--processingprocessing–– Find pertinent image information (histogram analysis)Find pertinent image information (histogram analysis)–– Scale data to an appropriate rangeScale data to an appropriate range
•• Contrast enhancementContrast enhancement–– Anatomy specific grayscale manipulationAnatomy specific grayscale manipulation
•• Spatial frequency enhancementSpatial frequency enhancement
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
44
Finding the Image LocationFinding the Image Location
•• Image recognition phaseImage recognition phase–– Collimation (Agfa)Collimation (Agfa)
–– EDR, automatic mode (Fuji)EDR, automatic mode (Fuji)
–– Segmentation (Kodak)Segmentation (Kodak)
•• Finding collimation borders and edgesFinding collimation borders and edges
Histogram analysisHistogram analysis
•• Frequency distribution of pixel values within a Frequency distribution of pixel values within a defined area in the imagedefined area in the image
•• Shape is anatomy specificShape is anatomy specific
•• Sets minimum and maximum “useful” pixel valuesSets minimum and maximum “useful” pixel values
Histogram:Histogram:frequency distribution of pixel values in an imagefrequency distribution of pixel values in an image
ValueValue
Freq
uenc
yFr
eque
ncy
Histogram DistributionHistogram Distribution
33
222222
2222
222222
444444
4444
4444
4444
444444
1111
1111
0000 11 22 33 44 55
224466881010121214141616
ValueValue
Freq
uenc
yFr
eque
ncy
Histogram DistributionHistogram Distribution
The shape is dependent on radiographic study, The shape is dependent on radiographic study, positioning and techniquepositioning and technique
AnatomyAnatomy
Freq
uenc
yFr
eque
ncy
Useful signalUseful signal
Collimated Collimated areaarea
Direct Direct xx--ray ray areaarea
Pixel valuePixel value
Histogram DistributionHistogram Distribution
Digital Digital valuevalue
Freq
uenc
y of
Fr
eque
ncy
of
Dig
ital N
umbe
rD
igita
l Num
ber
0.01mR0.01mR 0.1mR0.1mR 1mR1mR 10mR10mR 100mR100mR
511511
10231023
00Q1Q1
S1S1
Q2Q2
S2S2
Sensitivity (S)Sensitivity (S)2000020000 20002000 200200 2020 22
SSKK
Latitude (L)Latitude (L)
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
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Data conversionData conversionExposure into digital numberExposure into digital number
00 511511 102310231010331010--11 101000 101022101011
Exposure inputExposure input
Rel
ativ
e PS
LR
elat
ive
PSL
Raw Digital OutputRaw Digital Output
101011
1010--11
101000
101022
Input to output digital Input to output digital numbernumber
Input digital numberInput digital number200200 600600 1,0001,00000
200200
400400
600600
800800
1,0001,000
Out
put
digi
tal n
umbe
rO
utpu
t di
gita
l num
ber
Grayscale transformationGrayscale transformation
HistogramHistogram
Find the Find the signal signal
minmin maxmax
1.1. Scale toScale torange range
2.2. Create film Create film looklook--alikealike
3.3.
Histogram: pediatric imageHistogram: pediatric image
0
200
400
600
800
0 400 600 800 1000 Digital value
Freq
uenc
y
to 8323to 9368
Useful image range for anatomyUseful image range for anatomy
200
PrePre--processed processed “raw” image“raw” image
Scaled and inverted:Scaled and inverted:“unprocessed” image“unprocessed” image
Data conversion for overexposureData conversion for overexposureExposure into digital numberExposure into digital number
ExposureExposureinputinput
Rel
ativ
e PS
LR
elat
ive
PSL
00 511511 10231023
Raw Digital OutputRaw Digital Output
(scaled and log amplified)(scaled and log amplified)
Reduce overall gain Reduce overall gain
1010331010--11 101000 101022101011
101011
1010--11
101000
101022
minmin maxmaxoverexposureoverexposure
Screen-Film
Underexposed Overexposed
Computed Radiography
Underexposed Overexposed
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
66
Data conversion for wide latitudeData conversion for wide latitudeExposure into digital numberExposure into digital number
Rel
ativ
e PS
LR
elat
ive
PSL
101011
1010--11
101000
101022
00 511511 10231023
Raw Digital OutputRaw Digital Output
(scaled and log amplified)(scaled and log amplified)
ExposureExposureinputinput 1010331010--11 101000 101022101011
Change gradientChange gradient(auto mode)(auto mode)
low kVplow kVp(wide range)(wide range)
minmin maxmax
ScreenScreen--FilmFilm80 kVp, 18 mAs80 kVp, 18 mAs 80 kVp, 64 mAs80 kVp, 64 mAs
CRCR80 kVp, 18 mAs80 kVp, 18 mAs
L=4, wide latitudeL=4, wide latitude400 speed screen 400 speed screen -- filmfilm
Contrast EnhancementContrast Enhancement
•• Optimize image contrast via Optimize image contrast via nonnon--linearlineartransformation curvestransformation curves
•• Unprocessed images display linear “subject contrast”Unprocessed images display linear “subject contrast”–– “Gradation processing” (Fuji)“Gradation processing” (Fuji)–– “Tone scaling” (Kodak)“Tone scaling” (Kodak)–– “MUSICA” (Agfa)“MUSICA” (Agfa)
LookLook--upup--table transformationtable transformation
Input digital numberInput digital number
Ou
tpu
t di
gita
l nu
mbe
rO
utp
ut
digi
tal n
um
ber
00 200200 400400 600600 800800 1,0001,00000
200200
400400
600600
800800
1,0001,000
AAEELLMM
Fuji SystemFuji SystemExample LUTsExample LUTs
GTGTGradient TypeGradient Type
RawRaw UnprocessedUnprocessed Contrast EnhancedContrast Enhanced
Spatial frequencySpatial frequency
Original MTFOriginal MTF
Resp
onse
Resp
onse
lowlow highhigh
Spatial Frequency ProcessingSpatial Frequency Processing
“Edge Enhancement”“Edge Enhancement”
Spatial frequencySpatial frequency
Solid: original responseSolid: original response
Dash: low pass filteredDash: low pass filtered
Resp
onse
Resp
onse
lowlow highhigh
Spatial frequencySpatial frequency
Original Original -- filteredfiltered
Difference:Difference:
lowlow highhigh
Spatial frequencySpatial frequency
SumSum
lowlow
Difference + OriginalDifference + Original
Edge Enhanced:Edge Enhanced:
highhigh
OriginalOriginal BlurredBlurred
DifferenceDifference Edge enhancedEdge enhanced
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
77
Anatomy LUT shape parametersFrequency enhancement
parameters
Fuji CR Parameter Settings
Anatomical regionAnatomical region GAGA GTGT GCGC GSGS RNRN RTRT REREGeneral chest (LAT)General chest (LAT) 1.01.0 BB 1.61.6 --0.20.2 4.04.0 RR 0.20.2General chest (PA)General chest (PA) 0.60.6 DD 1.61.6 --0.50.5 4.04.0 RR 0.20.2Port Chest GRIDPort Chest GRID 0.80.8 FF 1.81.8 --0.050.05 4.04.0 TT 0.20.2Port Chest NO GRIDPort Chest NO GRID 1.01.0 DD 1.61.6 --0.150.15 4.04.0 RR 0.50.5PedsPeds chest NICU/PICUchest NICU/PICU 1.11.1 DD 1.61.6 --0.20.2 3.03.0 RR 0.50.5FingerFinger 0.90.9 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5WristWrist 0.80.8 OO 0.60.6 0.20.2 5.05.0 TT 0.50.5ForearmForearm 0.80.8 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5Plaster cast (arm)Plaster cast (arm) 0.80.8 OO 0.60.6 0.40.4 5.05.0 TT 0.50.5Elbow*Elbow* 0.80.8 OO 0.60.6 0.40.4 7.07.0 TT 1.01.0Upper Ribs*Upper Ribs* 0.80.8 OO 1.61.6 0.00.0 5.05.0 RR 1.01.0Pelvis*Pelvis* 0.90.9 OO 0.60.6 0.20.2 6.06.0 TT 1.01.0Pelvis portablePelvis portable 0.90.9 OO 0.60.6 0.20.2 4.04.0 TT 0.50.5TibTib/Fib/Fib 0.90.9 NN 0.60.6 0.250.25 5.05.0 FF 0.50.5FootFoot 0.80.8 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5Foot*Foot* 1.21.2 NN 0.60.6 --0.050.05 7.07.0 TT 0.50.5OsOs CalcisCalcis 0.80.8 OO 0.60.6 0.40.4 5.05.0 FF 1.01.0Foot castFoot cast 0.80.8 OO 0.60.6 0.50.5 5.05.0 FF 0.50.5CC--spine spine 1.11.1 FF 0.60.6 0.50.5 5.05.0 PP 0.50.5TT--spinespine 0.80.8 FF 1.81.8 --0.050.05 4.04.0 TT 0.20.2SwimmersSwimmers 1.21.2 JJ 0.90.9 0.30.3 5.05.0 TT 0.50.5Lumbar spineLumbar spine 1.01.0 NN 0.90.9 0.40.4 5.05.0 TT 1.01.0Breast specimenBreast specimen 2.52.5 DD 0.60.6 0.350.35 9.09.0 PP 1.01.0
Acceptance Test / QC considerationsAcceptance Test / QC considerations
•• Image acquisitionImage acquisition
•• ElectroElectro--Mechanical readoutMechanical readout
•• Image processingImage processing
•• PACS / RIS interfacesPACS / RIS interfaces
•• Image handlingImage handling
Recommended Acceptance TestsRecommended Acceptance Tests
•• Physical InspectionPhysical Inspection––InventoryInventory––PACS Interfaces PACS Interfaces
•• Imaging Plate Uniformity and Dark NoiseImaging Plate Uniformity and Dark Noise
•• Signal Response: Linearity and SlopeSignal Response: Linearity and Slope
•• Signal Response: Exposure calibration and Signal Response: Exposure calibration and beam qualitybeam quality
•• Laser Beam Function Laser Beam Function
•• High Contrast ResolutionHigh Contrast Resolution
Recommended Acceptance TestsRecommended Acceptance Tests
•• Noise / LowNoise / Low--Contrast ResponseContrast Response
•• DistortionDistortion
•• Erasure ThoroughnessErasure Thoroughness
•• Artifact Analysis: Hardware/Software Artifact Analysis: Hardware/Software
•• Positioning and collimation robustnessPositioning and collimation robustness
•• Imaging Plate ThroughputImaging Plate Throughput
Acceptance test tools requiredAcceptance test tools required
•• Exposure meter/dosimeterExposure meter/dosimeter
•• Spatial resolution phantomSpatial resolution phantom
•• Low contrast phantomLow contrast phantom
•• Vendor QC phantom (periodic tests)Vendor QC phantom (periodic tests)
•• SMPTE test patternSMPTE test pattern
•• Anthropomorphic phantomAnthropomorphic phantom
•• Documentation log / spreadsheet / instructionsDocumentation log / spreadsheet / instructions
CR: Spatial ResolutionCR: Spatial Resolution
•• Phosphor plate sizes: impact on resolutionPhosphor plate sizes: impact on resolution
35x43 (14x17)35x43 (14x17)
0.2 mm pixels0.2 mm pixels
24x30 (10x12)24x30 (10x12)
0.14 mm pixels0.14 mm pixels 0.1 mm pixels0.1 mm pixels
18x24 (8x10)18x24 (8x10)
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
88
High Contrast (Spatial) ResolutionHigh Contrast (Spatial) Resolution18 x 24 cm18 x 24 cm 35 x 43 cm35 x 43 cm MTF Curves MTF Curves
00 22 44 66 88 101000
0.20.2
0.40.4
0.60.6
0.80.8
11
Spatial Frequency (lp/mm)Spatial Frequency (lp/mm)
MTF
MTF
Standard CRStandard CR
Hi Hi res res CRCR
ScreenScreen--filmfilm
SampledSampled MTF:MTF:Standard CRStandard CR2K x 2K matrix2K x 2K matrix35 x 43 cm35 x 43 cm
SubscanSubscanScanScan
PrePre--sampledsampledMTFMTF
XX--ray Absorption Efficiencyray Absorption Efficiency
00 2020 4040 6060 8080 100100 120120 14014000
0.20.2
0.40.4
0.60.6
0.80.8
11
Energy (keV)Energy (keV)
Phot
on a
bsor
ptio
n fra
ctio
nPh
oton
abs
orpt
ion
fract
ion
GdGd22OO22S, 120 mg/cmS, 120 mg/cm22
BaFBr, 50 mg/cm²BaFBr, 50 mg/cm²
BaFBr, 100 mg/cm²BaFBr, 100 mg/cm²
Low Contrast Response: Leeds TOLow Contrast Response: Leeds TO--1616
0.5 mR0.5 mR3.5 mR3.5 mR 70 kVp70 kVp
10 mAs10 mAs 20 mAs20 mAs
UniformityUniformity
498498 508508
490490
497497 505505
537537
487487544544
513513
480480
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
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Radiation Dose for CRRadiation Dose for CR
•• Variable Speed DetectorVariable Speed Detector
•• Optimal doseOptimal dose (UC Davis)(UC Davis)–– Adult chest image: Adult chest image: S=200S=200--300300–– Neonates/pediatrics: Neonates/pediatrics: S=400S=400--600600–– Extremities:Extremities: S= 75S= 75--100100
–– Lower detection efficiency, luminance and readout noiseLower detection efficiency, luminance and readout noise
•• AntiAnti--scatter grids neededscatter grids needed
Sensitivity number, SSensitivity number, S
•• Estimate of the incident exposure on the IPEstimate of the incident exposure on the IP
•• Comparable to screenComparable to screen--film “speed”film “speed”
•• Amplification required to map median value of Amplification required to map median value of histogram to 511 (0 to 1023 grayscale)histogram to 511 (0 to 1023 grayscale)
•• Dependent on histogram shape Dependent on histogram shape andand examination examination selectedselected
Date: 7/10/98 Location: UCDMC, ACC, 3 Medical Physicist: Anthony Seibert, Ph.D. System Identification: CR unit 3
UC Davis Medical CenterCR Reader and Screens
Signal Response: Calibration and Beam Quality
Note: Use mAs values to provide an approximate exposure of 1 mR to the IP.
Menu = TEST Exposure ConditionsIP Type: ST 14x17 SubMenu = Ave 2.0 Focal spot Time delay SID (cm) SMD (cm)
IP SN: L = 2, EDR = semi 1.2 mm ~2 min 140 130
kVp DependencykVp Filtration mAs mR-meter mR-IP S S (1mR) OD NA60 1 Al/0.5 Cu 15.00 1.06 0.91 121.00 110.59 1.41 NA80 1 Al/0.5 Cu 4.5 1.06 0.91 108.00 98.71 1.38 NA115 1 Al/0.5 Cu 1.13 1.14 0.98 115.00 113.04 1.45 NA
Maximum Difference: 14.33 0.07 NAFiltration Dependency
kVp Filtration mAs mR-m eter mR-IP S S (1mR) OD NA80 none 0.50 0.96 0.83 187.00 154.79 1.40 NA80 1 Al/0.5 Cu 4.50 1.06 0.91 108.00 98.71 1.38 NA80 1Al/2.5Cu 60.00 0.99 0.85 124.00 105.85 1.40 NA
Maximum Difference: 56.08 0.02 NA
0.00
20.00
40.00
60.00
80.00
100.00
120.00
50 70 90 110 130kVp
Resp
onse
S (1mR)
0.0020.0040.0060.0080.00
100.00120.00140.00160.00180.00
none 1 Al/0.5 Cu 1Al/2.5CuFiltration
Res
pons
e
S (1mR)
Date: 7/10/98 Location: UCDMC, ACC, 3 Medical Physicist: Anthony Seibert, Ph.D. System Identification: CR unit 3
UC Davis Medical CenterCR Reader and Screens
Signal Response: Calibration and Beam Quality
Note: Use mAs values to provide an approximate exposure of 1 mR to the IP.
Menu = TEST Exposure ConditionsIP Type: ST 14x17 SubMenu = Ave 2.0 Focal spot Time delay SID (cm) SMD (cm)
IP SN: L = 2, EDR = semi 1.2 mm ~2 min 140 130
kVp DependencykVp Filtration mAs mR-meter mR-IP S S (1mR) OD NA60 1 Al/0.5 Cu 15.00 1.06 0.91 121.00 110.59 1.41 NA80 1 Al/0.5 Cu 4.5 1.06 0.91 108.00 98.71 1.38 NA115 1 Al/0.5 Cu 1.13 1.14 0.98 115.00 113.04 1.45 NA
Maximum Difference: 14.33 0.07 NAFiltration Dependency
kVp Filtration mAs mR-m eter mR-IP S S (1mR) OD NA80 none 0.50 0.96 0.83 187.00 154.79 1.40 NA80 1 Al/0.5 Cu 4.50 1.06 0.91 108.00 98.71 1.38 NA80 1Al/2.5Cu 60.00 0.99 0.85 124.00 105.85 1.40 NA
Maximum Difference: 56.08 0.02 NA
0.00
20.00
40.00
60.00
80.00
100.00
120.00
50 70 90 110 130kVp
Resp
onse
S (1mR)
0.0020.0040.0060.0080.00
100.00120.00140.00160.00180.00
none 1 Al/0.5 Cu 1Al/2.5CuFiltration
Res
pons
e
S (1mR)
Guidelines for QC based on ExposureGuidelines for QC based on Exposure
•• >1000>1000 <0.2 mR<0.2 mR
•• 600 600 –– 10001000 0.30.3--0.2 mR0.2 mR
•• 300 300 -- 600600 1.01.0--0.3 mR0.3 mR
•• 150 150 -- 300300 1.31.3--1.0 mR1.0 mR
•• 75 75 --150150 1.31.3--2.7 mR2.7 mR
•• 50 50 -- 7474 4.04.0--2.7 mR2.7 mR
•• <50<50 >4.0 mR>4.0 mR
•• Underexposed: repeatUnderexposed: repeat
•• Underexposed: QC exceptionUnderexposed: QC exception
•• Underexposed: QC reviewUnderexposed: QC review
•• Acceptable rangeAcceptable range
•• Overexposed: QC reviewOverexposed: QC review
•• Overexposed: QC exceptionOverexposed: QC exception
•• Overexposed: repeatOverexposed: repeat
Sensitivity numberSensitivity number IndicationIndication
Sensitivity number, SSensitivity number, S
•• Imaging plate (HR vs. ST) differencesImaging plate (HR vs. ST) differences
•• Examination specific histogram shapesExamination specific histogram shapes–– S number varies with examination type S number varies with examination type
•• EDR mode effectsEDR mode effects–– Automatic (determines S1 and S2 values on histogram)Automatic (determines S1 and S2 values on histogram)–– SemiSemi--automatic (average value within ROI)automatic (average value within ROI)–– Fixed (system acts like screenFixed (system acts like screen--film detector)film detector)
•• XX--ray beam spectrum effectsray beam spectrum effects–– S number varies with beam hardness (calibration required)S number varies with beam hardness (calibration required)
What S value is appropriate?What S value is appropriate?
•• Determined by examination Determined by examination UCDMC targetsUCDMC targets–– Adult exams (CXR, abdomen, etc) Adult exams (CXR, abdomen, etc) 150 150 –– 300300–– Extremities Extremities (ST plates) (ST plates) 75 75 –– 150150–– PediatricsPediatrics 300 300 –– 600600
•• CR’sCR’s variable speed should be used to advantagevariable speed should be used to advantage
•• Anatomical information can be lost with too high or too Anatomical information can be lost with too high or too low exposurelow exposure
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
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Adult portable chest calculated exposuresAdult portable chest calculated exposuresFirst half, 1994, 4572 examsFirst half, 1994, 4572 exams
Incident ExposureIncident ExposureLowLow HighHigh
500
500
400
400
300
300
200
200
100
100
<50
<50
00
100100
200200
300300
400400
500500
600600
System speed (S #)System speed (S #)
#ex
ams
#ex
ams
38.3% 53.9% 7.8%38.3% 53.9% 7.8%
Target Target exposure exposure rangerange
Q1Q1
Q2Q2Q3Q3
Q4Q4
Adult portable chest calculated exposuresAdult portable chest calculated exposuresSecond half, 1994, 4661 examsSecond half, 1994, 4661 exams
23.1% 73.5% 3.4%23.1% 73.5% 3.4%
Target Target exposure exposure rangerange
Incident ExposureIncident ExposureLowLow HighHigh
500
500
400
400
300
300
200
200
100
100
<50
<50
00
100100
200200
300300
400400
500500
600600
System speed (S #)System speed (S #)
#ex
ams
#ex
ams
April 1 April 1 -- 17, 199617, 1996Adult Portable ChestAdult Portable Chest
002020404060608080
100100120120140140160160180180
>1000
>1000
600
600--6
9969
9
500
500--5
4954
9
400
400--4
4944
9
350
350--3
7437
4
300
300--3
2432
4
250
250--2
7427
4
200
200--2
2422
4
150
150--1
7417
4
100
100--1
2412
4
5050--7
474
Sensitivity numberSensitivity number
Num
ber
of e
xam
inat
ions
Num
ber
of e
xam
inat
ions
Grid techniqueGrid techniquewithout a gridwithout a grid
April 1 - 17, 1996April 1 April 1 -- 17, 199617, 1996
Adult Portable ChestAdult Portable ChestAdult Portable Chest
000202020404040606060808080
100100100120120120140140140160160160180180180
>1000
>1000
>1000
600-
699
600
600--6
9969
9
500-
549
500
500--5
4954
9
400-
449
400
400--4
4944
9
350-
374
350
350--3
7437
4
300-
324
300
300--3
2432
4
250-
274
250
250--2
7427
4
200-
224
200
200--2
2422
4
150-
174
150
150--1
7417
4
100-
124
100
100--1
2412
4
50-7
45050
--7474
Sensitivity numberSensitivity numberSensitivity number
Num
ber
of e
xam
inat
ions
Num
ber
of e
xam
inat
ions
Num
ber
of e
xam
inat
ions
“Exposure Creep”“Exposure Creep”“Exposure Creep”
Grid techniquewithout a gridGrid techniqueGrid techniquewithout a gridwithout a grid
Total # repeats = 1043 from Total # repeats = 1043 from Willis, RSNA 1996Willis, RSNA 1996
Positioning46%
Overexposure12%
Underexposure10%
Reprinting9%
Motion6%
Wrong exam5%
Other12% Repeated Repeated
Examinations with CRExaminations with CR
Radiation Dose for CRRadiation Dose for CR
•• Variable Speed DetectorVariable Speed Detector
•• Optimal doseOptimal dose for typical adult chest image is 2X higherfor typical adult chest image is 2X higherthan 400 speed screen/filmthan 400 speed screen/film
–– Lower absorption efficiencyLower absorption efficiency
–– Quantum and electronic noiseQuantum and electronic noise
–– Readout inefficiencies of latent imageReadout inefficiencies of latent image
•• AntiAnti--scatter grids necessary for most proceduresscatter grids necessary for most procedures
AEC adjustment proceduresAEC adjustment procedures•• A 200A 200--speed equivalent exposure is desirablespeed equivalent exposure is desirable
•• Empirically determine AEC setting(s) with simple uniform Empirically determine AEC setting(s) with simple uniform phantomsphantoms
•• UCDMC technique: use “fixed” mode (S=200) and sensitivity test UCDMC technique: use “fixed” mode (S=200) and sensitivity test menu; adjust AEC response according to changes in film optical menu; adjust AEC response according to changes in film optical densitydensity
•• Verify settings with semiVerify settings with semi--auto modeauto mode
•• Verify patient exposure “S” number; recheck oftenVerify patient exposure “S” number; recheck often
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
1111
Date: 7/10/98 Location: UCDMC, ACC, 3 Medical Physicist: Anthony Seibert, Ph.D. System Identification: CR unit 3
UC Davis Medical CenterCR Reader and Screens
Inspection Results Summary
Acceptab le1. Physical Inspection - Inventory Yes2. Imaging Plate Uniformity and Dark Noise Yes3. Signal Response: Linearity and Slope Yes4. Signal Response: Calibration and Beam Quality Yes5. Laser Beam Function Yes6. High-Contrast Resolution Yes7. Noise/Low-Contrast Response Yes8. Distortion Yes9. Erasure Thoroughness Yes*
10. Anti-Aliasing Yes11. Positioning and Collimation Errors Yes12. Throughput Yes
Comments:
Date: 7/10/98 Location: UCDMC, ACC, 3 Medical Physicist: Anthony Seibert, Ph.D. System Identification: CR unit 3
UC Davis Medical CenterCR Reader and Screens
Inspection Results Summary
Acceptab le1. Physical Inspection - Inventory Yes2. Imaging Plate Uniformity and Dark Noise Yes3. Signal Response: Linearity and Slope Yes4. Signal Response: Calibration and Beam Quality Yes5. Laser Beam Function Yes6. High-Contrast Resolution Yes7. Noise/Low-Contrast Response Yes8. Distortion Yes9. Erasure Thoroughness Yes*
10. Anti-Aliasing Yes11. Positioning and Collimation Errors Yes12. Throughput Yes
Comments:
•• FilmFilm--based performance measurements based performance measurements
•• Digital image analysis tools and evaluation methods Digital image analysis tools and evaluation methods not readily availablenot readily available
•• Low contrast resolution measurementsLow contrast resolution measurements
•• Lack of a standardized QC phantomLack of a standardized QC phantom
Problem areasProblem areas
Quality ControlQuality Control
Three levels of system performance quality controlThree levels of system performance quality control
1. Routine: Technologist level1. Routine: Technologist level-- no radiation measurementsno radiation measurements
2. Full inspection: Physicist level 2. Full inspection: Physicist level -- radiation measurements and nonradiation measurements and non--invasive adjustmentsinvasive adjustments
3. System adjustment: Vendor service level3. System adjustment: Vendor service level-- hardware and software maintenancehardware and software maintenance
Periodic Quality ControlPeriodic Quality Control
•• Daily (technologist)Daily (technologist)
–– Inspect CR system and status.Inspect CR system and status.
–– Interfaces: PACS broker, ID terminal, QC workstationInterfaces: PACS broker, ID terminal, QC workstation
–– Erase image receptors (if status unknown).Erase image receptors (if status unknown).
Periodic Quality ControlPeriodic Quality Control
•• Weekly / Biweekly (technologist)Weekly / Biweekly (technologist)
–– Calibrate review workstation monitors (SMPTE).Calibrate review workstation monitors (SMPTE).
–– Acquire QC phantom test images. Verify performance.Acquire QC phantom test images. Verify performance.
–– Check filters / vents and clean as necessary.Check filters / vents and clean as necessary.
–– Clean screens with recommended agents.Clean screens with recommended agents.
Periodic Quality ControlPeriodic Quality Control
•• Quarterly (Technologist)Quarterly (Technologist)
–– Inspect cassettes. Clean with recommended agents.Inspect cassettes. Clean with recommended agents.
–– Review image retake rate and exposure trends. Review image retake rate and exposure trends.
–– Update QC log. Review outUpdate QC log. Review out--ofof--tolerance issues.tolerance issues.
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.
1212
Periodic Quality ControlPeriodic Quality Control
•• Annually (Physicist)Annually (Physicist)
–– Perform linearity / sensitivity / uniformity testsPerform linearity / sensitivity / uniformity tests
–– Inspect / evaluate image qualityInspect / evaluate image quality
–– ReRe--establish baseline values (Acceptance Tests)establish baseline values (Acceptance Tests)
–– Review retakes, exposures, service records.Review retakes, exposures, service records.
What is needed?What is needed?
•• Computer friendly phantomsComputer friendly phantoms
•• Objective quantitative analysis methodsObjective quantitative analysis methods
•• System performance tracking and database logsSystem performance tracking and database logs
•• Exposure monitoring tools and database trackingExposure monitoring tools and database tracking
FujiFuji
Single exposure, qualitative Single exposure, qualitative and quantitativeand quantitative
AgfaAgfa
Step wedge (signal, signal to Step wedge (signal, signal to noise and linearity response tests)noise and linearity response tests)
Diagonal bar Diagonal bar (laser jitter test)(laser jitter test)
Notches Notches ((geometricgeometricaccuracyaccuracytests)tests)
Line pair Line pair phantoms phantoms (contrast (contrast transfer tests)transfer tests)
Open area (scan Open area (scan uniformity test)uniformity test)
LumisysLumisys Home builtHome built
Lead attenuatorLead attenuator(dynamic range)(dynamic range)
Copper step wedgeCopper step wedge(dynamic range, linearity, SNR)(dynamic range, linearity, SNR)
Edge for Edge for Presampled Presampled
MTFMTF
ResolutionResolutionBar PatternBar Pattern(qualitative)(qualitative)
FiducialFiducial MarkersMarkers(distance accuracy)(distance accuracy)
40 line/cm grid40 line/cm grid(visual aliasing)(visual aliasing)
Additional Information / HelpAdditional Information / Help
•• AAPM Task Group #10 document:AAPM Task Group #10 document:•• Email: Email: jaseibertjaseibert@@ucdavisucdavis..eduedu
•• Dr. Dr. Ehsan Samei Ehsan Samei spreadsheets spreadsheets –– http://http://deckarddeckard.mc.duke..mc.duke.eduedu/~/~sameisamei/downloads /downloads
•• Vendor efforts for QC phantom development and Vendor efforts for QC phantom development and analysisanalysis
SummarySummary
•• CR is the mainstay for direct digital acquisition of CR is the mainstay for direct digital acquisition of projection radiographsprojection radiographs
•• CR acceptance testing and QC are essential for CR acceptance testing and QC are essential for optimal operationoptimal operation
•• A A TEAMTEAM approach is necessaryapproach is necessary–– Technologists, Radiologists, Physicists, Technologists, Radiologists, Physicists, –– Clinical Engineering, Information System GroupClinical Engineering, Information System Group
Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.