design and performance characteristics of digital ... · • screen-film radiography – iq...

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Design and Performance Characteristics of Digital Radiographic Receptors

Design and Performance Characteristics Design and Performance Characteristics of Digital Radiographic Receptorsof Digital Radiographic Receptors

J. Anthony Seibert, Ph.D.University of California, Davis Medical Center

Sacramento, California

J. Anthony Seibert, Ph.D.J. Anthony Seibert, Ph.D.University of California, Davis Medical CenterUniversity of California, Davis Medical Center

Sacramento, CaliforniaSacramento, California

Learning ObjectivesLearning ObjectivesLearning Objectives

• Describe digital detector technologies for radiography and mammography

• Review functional attributes

• Compare detectors in terms of IQ and dose

• Summarize advantages/disadvantages

•• Describe digital detector technologies for Describe digital detector technologies for radiography and mammographyradiography and mammography

•• Review functional attributesReview functional attributes

•• Compare detectors in terms of IQ and doseCompare detectors in terms of IQ and dose

•• Summarize advantages/disadvantagesSummarize advantages/disadvantages

Presentation OutlinePresentation OutlinePresentation Outline

• Acquisition System Overview

• Digital Detector Attributes

• Digital Detector Technologies

• Factors affecting Image Quality & Dose

• Clinical Implementation and QC

•• Acquisition System OverviewAcquisition System Overview

•• Digital Detector AttributesDigital Detector Attributes

•• Digital Detector TechnologiesDigital Detector Technologies

•• Factors affecting Image Quality & DoseFactors affecting Image Quality & Dose

•• Clinical Implementation and QCClinical Implementation and QC

2

DetectorEfficiencyResolutionScatter grid

DQE

DetectorDetectorEfficiencyEfficiencyResolutionResolutionScatter gridScatter grid

DQEDQE

Image acquisition, display, & interpretationImage acquisition, display, & interpretationImage acquisition, display, & interpretation

X-rayskVpmAs

Tube filtrationCollimation

XX--raysrayskVpkVpmAsmAs

Tube filtrationTube filtrationCollimationCollimation

PatientSize

RestraintsExam typeESE, dose

PatientPatientSizeSize

RestraintsRestraintsExam typeExam typeESE, doseESE, dose

HumanRadiologistPhysician

ExperienceCondition

HumanHumanRadiologistRadiologistPhysicianPhysician

ExperienceExperienceConditionCondition

ComputerDigitization

PreprocessingPostprocessingConfiguration

ComputerComputerDigitizationDigitization

PreprocessingPreprocessingPostprocessingPostprocessingConfigurationConfiguration

PACSData deliveryData displayData storage

Workflow

PACSPACSData deliveryData deliveryData displayData displayData storageData storage

WorkflowWorkflow

Acquisition to Interpretation: Image QualityAcquisition to Interpretation: Image QualityAcquisition to Interpretation: Image Quality

• Image quality is an indicator of the relevance of information presented in the image to the task we seek to accomplish using the image

• Considered in terms of portrayal of – Normal anatomy– Depiction of potential pathology

• Not necessarily the “same” in all images

• A constraining factor is radiation dose

•• Image quality is an indicator of the relevance Image quality is an indicator of the relevance of information presented in the image to the of information presented in the image to the task we seek to accomplish using the imagetask we seek to accomplish using the image

•• Considered in terms of portrayal of Considered in terms of portrayal of –– Normal anatomyNormal anatomy–– Depiction of potential pathologyDepiction of potential pathology

•• Not necessarily the Not necessarily the ““samesame”” in all imagesin all images

•• A constraining factor is radiation doseA constraining factor is radiation dose

Image QualityImage QualityImage Quality

• Screen-film radiography– IQ “built in” to the characteristics of the film– Film is acquisition, display and archive medium– Dose is determined by screen-film speed

• Digital radiography– IQ dependent on Signal to Noise Ratio (SNR)– Separation of acquisition, display, and archive– Dose is variable and dependent on required SNR

•• ScreenScreen--film radiographyfilm radiography–– IQ IQ ““built inbuilt in”” to the characteristics of the filmto the characteristics of the film–– Film is acquisition, display and archive mediumFilm is acquisition, display and archive medium–– Dose is determined by screenDose is determined by screen--film speedfilm speed

•• Digital radiographyDigital radiography–– IQ dependent on Signal to Noise Ratio (SNR)IQ dependent on Signal to Noise Ratio (SNR)–– Separation of acquisition, display, and archiveSeparation of acquisition, display, and archive–– Dose is variable and dependent on required SNRDose is variable and dependent on required SNR

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Gray ScaleGray Scaleencoded on encoded on

filmfilm

Film processing: Film processing: light to optical densitylight to optical density

Log Relative ExposureLog Relative Exposure

Opt

ical

Den

sity

Opt

ical

Den

sity

Conventional screen/film detectorConventional screen/film detector

FilmFilm Intensifying Screens Intensifying Screens xx--rays rays →→ lightlight

Transmitted xTransmitted x--raysraysthrough patientthrough patient

1. Acquisition, Display, Archiving1. Acquisition, Display, Archiving

Digital XDigital X--ray Detectorray Detector

Transmitted xTransmitted x--raysraysthrough patientthrough patient

Charge Charge collection collection

devicedevice

XX--ray converterray converterxx--rays rays →→ electronselectrons

Analog to DigitalAnalog to DigitalConversionConversion

1. Acquisition1. Acquisition

2. Display2. Display

3. Archiving3. Archiving

Digital Digital processingprocessing

Digital to AnalogDigital to AnalogConversionConversion

Digital PixelDigital PixelMatrixMatrix

4

Exposure LatitudeExposure Latitude

Log relative exposureLog relative exposure

Sig

nal o

utpu

tS

igna

l out

put

10000:110000:1

DigitalDigital

Spatial ResolutionSpatial ResolutionAnalog versus DigitalAnalog versus Digital

MTF of pixel aperture (DEL)

00.10.20.30.40.50.60.70.80.9

1

0 1 2 3 4 5 6 7 8 9 10 11Frequency (lp/mm)

Mod

ulat

ion

1000 µm

200 µm

100 µm

DetectorDetectorElement,Element,

““DELDEL””SamplingSamplingPitchPitch

FilmFilm

100:1100:1

Digital DetectorsDigital DetectorsDigital Detectors

• Separation of acquisition, display and archive

• Digital acquisition is not contrast limited– Image processing

• Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) impacts “image quality”

• Detector DQE determines the exposure required to achieve a required SNR

•• Separation of acquisition, display and archiveSeparation of acquisition, display and archive

•• Digital acquisition is Digital acquisition is not contrast limitednot contrast limited–– Image processingImage processing

•• Signal to Noise Ratio (SNR) and Contrast to Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) impacts Noise Ratio (CNR) impacts ““image qualityimage quality””

•• Detector DQE determines the exposure required Detector DQE determines the exposure required to achieve a required SNRto achieve a required SNR

Digital DetectorsDigital DetectorsDigital Detectors

• Sampling and quantization (new noise sources)

• Detector pre-processing (correct imperfections)

• Image post-processing (enhance image contrast)

•• Sampling and quantization (new noise sources)Sampling and quantization (new noise sources)

•• Detector preDetector pre--processing (correct imperfections)processing (correct imperfections)

•• Image postImage post--processing (enhance image contrast)processing (enhance image contrast)

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Digital Detector TechnologiesDigital Detector TechnologiesDigital Detector Technologies

• Photostimulable Storage Phosphor (PSP or CR)

• Charge Coupled Device (CCD)

• Complementary MetalOxide Semiconductor (CMOS)

• Thin-Film-Transistor array (TFT)

• Photon counters (not discussed)

•• Photostimulable Storage Phosphor (PSP or CR)Photostimulable Storage Phosphor (PSP or CR)

•• Charge Coupled Device (CCD)Charge Coupled Device (CCD)

•• Complementary Complementary MetalOxideMetalOxide Semiconductor (CMOS)Semiconductor (CMOS)

•• ThinThin--FilmFilm--Transistor array (TFT) Transistor array (TFT)

•• Photon counters (not discussed)Photon counters (not discussed)

Computed Radiography (CR)Computed Radiography (CR)Computed Radiography (CR)...is the generic term applied to an imaging system

comprised of:

Photostimulable Storage Phosphorto acquire the x-ray projection image

CR Readerto extract the electronic latent image

Digital electronicsto convert the signals to digital form

...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

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CR DetectorCR DetectorCR Detector

• Photostimulable Storage Phosphor (PSP)• Direct replacement for S/F; positioning flexibility•• Photostimulable Storage Phosphor (PSP)Photostimulable Storage Phosphor (PSP)•• Direct replacement for S/F; positioning flexibilityDirect replacement for S/F; positioning flexibility

Phosphor PlatePhosphor PlatePhosphor Plate Cassette HolderCassette HolderCassette Holder

CR Image AcquisitionCR Image AcquisitionCR Image Acquisition

Phosphor platePhosphor plate

XX--rayraysystemsystem

1.1. XX--ray Exposureray Exposure

ImageImageScalingScaling

3.3.ImageImageRecordRecord

4.4.

PatientPatientComputedComputed

RadiographRadiograph5.5.

unexposedunexposed

ImageImageReaderReader

2.2.

exposedexposed

Display / ArchiveDisplay / Archive

Laser film printerLaser film printer

DICOM / PACSDICOM / PACS

Image AcquisitionImage Acquisition

Latent image producedLatent image produced

CRCRReaderReader

Latent Latent image image

extractedextracted

CR QC CR QC WorkstationWorkstationPatient information

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Photostimulated LuminescencePhotostimulated LuminescenceConduction bandConduction band

Valence bandValence band

PSLPSL3.0 eV3.0 eV

ττ 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 PSLC complexes (F centers) are created in numbers proportional to created in numbers proportional to incident xincident x--ray intensityray intensity

ee--

ττ tunnelingtunneling

τ τ recombinationrecombination

4f 4f 66 5d5d

phononphonon

CR: How does it work?CR: How does it work?

IncidentIncidentxx--rays rays

ee

Energy Energy Band BaFBrBand BaFBr

300300400400500500600600700700800800

Rel

ativ

e in

tens

ityR

elat

ive

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 Incident Laser BeamBeam

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

8

CR: Latent Image ReadoutCR: Latent Image Readout

PMTPMT

Polygonal Polygonal MirrorMirror

LaserLaserSourceSource

Light channeling guideLight channeling guide

Output SignalOutput Signal

ReferenceReferencedetectordetector Cylindrical mirrorCylindrical mirrorff--θθ

lenslens

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

Scan DirectionScan Direction

SubSub--scan Directionscan Direction

Laser beam deflectionLaser beam deflection

Plate translationPlate translation

TypicalTypical CR resolution: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 residual signalremove residual signal

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

9

CR InnovationsCR InnovationsCR Innovations

• High-speed line scan systems (<10 sec)

• Dual-side readout capabilities (increase DQE)

• Structured phosphors

• Mammography applications ????

• Low cost table-top CR readers

•• HighHigh--speed line scan systems (<10 sec)speed line scan systems (<10 sec)

•• DualDual--side readout capabilities (increase DQE)side readout capabilities (increase DQE)

•• Structured phosphorsStructured phosphors

•• Mammography applications ????Mammography applications ????

•• Low cost tableLow cost table--top CR readerstop CR readers

5 sec scan

Laser LineSource

ShapingLens

Linear CCDArray

LensArray

Line excitation PSL

Sub-scanDirection

CR CR ““lineline--scanscan””

Side View

Linear Laser Source

Light Collection Lens

Linear CCDArray

Stationary IP

Charge Coupled Device: CCDCharge Coupled Device: CCDCharge Coupled Device: CCD

• X-rays on scintillator• Light collection: optical or fiberoptical• Emitted light to CCD photo-sensor • Electronic charge created on silicon• Charge transfer moves packets• Charge to voltage conversion & amplification

•• XX--rays on scintillatorrays on scintillator•• Light collection: optical or Light collection: optical or fiberopticalfiberoptical•• Emitted light to CCD photoEmitted light to CCD photo--sensor sensor •• Electronic charge created on siliconElectronic charge created on silicon•• Charge transfer moves packetsCharge transfer moves packets•• Charge to voltage conversion & amplificationCharge to voltage conversion & amplification

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CCD Charge CollectionCCD Charge CollectionCCD Charge Collection

TransparentTransparentpolysiliconpolysilicon

““gategate”” electrodeelectrode

Silicon dioxideSilicon dioxide

Silicon substrateSilicon substratePhotoPhoto--generatedgeneratedelectronselectrons

--VVoo --VVoo+V+Voo

PotentialPotentialWellWell

PotentialPotentialBarrierBarrier

PotentialPotentialBarrierBarrier

Light photonsLight photons

ee--

ee--ee--ee--ee--ee--ee--

ee--ee-- ee--

ee-- ee--

CCD charge transferCCD charge transferCCD charge transfer

• Voltage potential of gate electrode pushes electrons towards collection amplifiers

• 24 volts bias for good transfer efficiency• Larger pixel dimension has inefficient transfer• Pixel dimensions:

– 8, 10, 15, 20 micron

• Form factor of CCD array very small

•• Voltage potential of gate electrode pushes Voltage potential of gate electrode pushes electrons towards collection amplifierselectrons towards collection amplifiers

•• 24 volts bias for good transfer efficiency24 volts bias for good transfer efficiency•• Larger pixel dimension has inefficient transferLarger pixel dimension has inefficient transfer•• Pixel dimensions:Pixel dimensions:

–– 8, 10, 15, 20 micron8, 10, 15, 20 micron

•• Form factor of CCD array very smallForm factor of CCD array very small

Light emission & Optical couplingLight emission & Optical couplingLight emission & Optical coupling

Lens

Scintillator

CCDCCDDetectorDetector

Large loss of light!!!

Demagnification >10:1

Optical coupling inefficiencyOptical coupling inefficiency

XX--raysrays

LightLight

11

CCD detectorCCD detectorCCD detector• Silicon chip with photosensitive layer•• Silicon chip with photosensitive layerSilicon chip with photosensitive layer

35 cm x 43 cm 2.5 cm

2.5

cm

Optical de-magnificationLens efficiency?

Secondary Quantum Sink

High fill factor ~ 100 %Good light conversion

efficiency (~85%)

5 cm

5 cm

Larger CCD Larger CCD arraysarrays

ScintillatorScintillator

CCD acquisition and readoutCCD acquisition and readoutCCD acquisition and readout

Pixel

Silicondioxide

Electrode

CCD

HorizontalReadout Register

Masking

ParallelParallelclocksclocks

Serial clocksSerial clocks

Serial RegisterSerial Register

CMOSComplementary Metal Oxide Semiconductor

CMOSCMOSComplementary Metal Oxide SemiconductorComplementary Metal Oxide Semiconductor

• “RAM” with photodiode converter

• Random access readout

• Low voltage operation (5V)

• ? NOISE ……

• Large FOV detector available (tiled CMOS)

• High sampling resolution possible

•• ““RAMRAM”” with photodiode converterwith photodiode converter

•• Random access readoutRandom access readout

•• Low voltage operation (5V)Low voltage operation (5V)

•• ? NOISE ? NOISE …………

•• Large FOV detector available (tiled CMOS)Large FOV detector available (tiled CMOS)

•• High sampling resolution possibleHigh sampling resolution possible

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CMOS detector on a chipCMOS detector on a chip

LATC

HES

CO

UN

TER

DEC

OD

ER

RO

W D

RIV

ERS

COLUMN SIGNAL CONDITIONING

DECODER

COUNTER

LATCHES

TIMINGAND

CONTROL

PIXEL ARRAY

CLKRUN

DEFAULTLOAD

ADDRESSDATA

+5V

VS_OUT

VR_OUT

READ

FRAME

“Tiled” matrix array of CMOS in large FOV

Available:

Array of tiled CMOS sensorsArray of tiled CMOS sensorsArray of tiled CMOS sensors

XraysXrays

ScintillatorScintillator

Fiberoptic plateFiberoptic plate

MicrolensMicrolens opticsoptics

CMOS sensorsCMOS sensors

Controller electronicsController electronics

7000x7000 element array, 177000x7000 element array, 17”” x 17x 17”” FOV for one implementationFOV for one implementation

DeadZone

Amorphous SiliconAmorphous SiliconTFT TFT active matrixactive matrix arrayarray

ThinThin--Film Film Transistor Transistor

Storage Storage CapacitorCapacitor

Charge Charge Collector Collector ElectrodeElectrode

G1G1

G2G2

G3G3

Gate Gate switchesswitches

D2D2D1D1 D3D3

Data linesData linesCR2CR2 CR3CR3CR1CR1

Charge Charge Amplifiers Amplifiers

Analog to Analog to Digital Digital ConvertersConverters

Amplifiers – Signal out

Active Area

13

Amorphous SiliconAmorphous SiliconTFT TFT active matrixactive matrix arrayarray

G1G1

G2G2

G3G3

Expose to xExpose to x--raysrays

Store the chargeStore the charge

Active ReadoutActive ReadoutActivate gatesActivate gatesAmplify chargeAmplify charge

Convert to DigitalConvert to Digital

Amplifiers – Signal out

Indirect detector:Indirect detector:aa--SiSi TFT/ CsI phosphorTFT/ CsI phosphor

GGSS DD

Adjacent gate lineAdjacent gate lineTFTTFTStorage capacitorStorage capacitorPhotodiodePhotodiode

SourceSourceGateGateDrainDrain

Structured XStructured X--ray ray phosphor (CsI)phosphor (CsI)

XX--rayray

LightLight

++

ChargeCharge

XX--rays to light to electrons to electronic signalrays to light to electrons to electronic signal

Direct detector:Direct detector:aa--Se / TFT arraySe / TFT array

Top electrodeTop electrodeDielectric layerDielectric layerSelenium photoconductorSelenium photoconductor

Charge collection electrode Charge collection electrode (pixel size)(pixel size)ThinThin--FilmFilm--TransistorTransistorStorage capacitorStorage capacitorGlass substrateGlass substrate

High High voltagevoltage

Incident xIncident x--raysrays

+- ++ ++ ++

++

--

-- --

----

--

++

--

--++

Stored chargeStored charge

XX--rays to electrons to electronic signalrays to electrons to electronic signal

++ ++++ ++

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Image acquisition and displayImage acquisition and displayImage acquisition and display

Uncorrected Uncorrected ““RawRaw””

AcquisitionAcquisition

Corrected Corrected ““RawRaw””

PrePre--processingprocessing

““For displayFor display””enhancedenhanced

PostPost--processingprocessing

ImageImagecomparisonscomparisons

DisplayDisplay

XX--ray systemray system-- SpectrumSpectrum-- DetectorDetector

Dead pixelsDead pixelsColumn/line defectsColumn/line defectsShading/flatShading/flat--fieldingfieldingSignal amplificationSignal amplification

Enhancement:Enhancement:-- EqualizationEqualization

-- Contrast/Detail Contrast/Detail

Hard/Soft CopyHard/Soft CopyPerceptual linearizationPerceptual linearizationVOI LUT VOI LUT ---- DICOM GSDFDICOM GSDF

Hanging / ViewingHanging / Viewing

OutsideOutsideimagesimages

??

Signal to Noise Ratio (SNR)Signal to Noise Ratio (SNR)Signal to Noise Ratio (SNR)

• Determines detectability of an object

• The signal is derived from the x-ray quanta

• The noise is from a variety of sources:– X-ray quantum statistics– Electronic noise– Fixed pattern noise– Sampling noise (aliasing)– Anatomical noise

• System pre and post processing are crucial

•• Determines detectability of an objectDetermines detectability of an object

•• The signal is derived from the xThe signal is derived from the x--ray quantaray quanta

•• The noise is from a variety of sources:The noise is from a variety of sources:–– XX--ray quantum statisticsray quantum statistics–– Electronic noiseElectronic noise–– Fixed pattern noiseFixed pattern noise–– Sampling noise (aliasing)Sampling noise (aliasing)–– Anatomical noiseAnatomical noise

•• System pre and post processing are crucialSystem pre and post processing are crucial

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Pre-ProcessingPrePre--ProcessingProcessing

• Detector / x-ray system flaws– Pixel defects– Sensitivity variations– Offset gain variations

• Wide detector dynamic range– Identify image location– Scale image data– Optimize quantization levels for “post-processing”

•• Detector / xDetector / x--ray system flawsray system flaws–– Pixel defectsPixel defects–– Sensitivity variationsSensitivity variations–– Offset gain variationsOffset gain variations

•• Wide detector dynamic rangeWide detector dynamic range–– Identify image locationIdentify image location–– Scale image dataScale image data–– Optimize quantization levels for Optimize quantization levels for ““postpost--processingprocessing””

Two major steps correct and adjust for: Two major steps correct and adjust for: Two major steps correct and adjust for:

Preprocessing, Step 1: correct flawsPreprocessing, Step 1: correct flawsPreprocessing, Step 1: correct flaws

• Detector origin– stationary patterns (structured), fixed-point noise– thickness non-uniformities – drop-outs, dead pixels, dead columns– dark current variation

• Equipment origin– heel effect– stationary patterns/artifacts (e.g., tube filter, grid)

•• Detector originDetector origin–– stationary patterns (structured), fixedstationary patterns (structured), fixed--point noisepoint noise–– thickness nonthickness non--uniformities uniformities –– dropdrop--outs, dead pixels, dead columnsouts, dead pixels, dead columns–– dark current variationdark current variation

•• Equipment originEquipment origin–– heel effectheel effect–– stationary patterns/artifacts (e.g., tube filter, grid)stationary patterns/artifacts (e.g., tube filter, grid)

Pre-processing schemesPrePre--processing schemesprocessing schemes

• 1-D shading correction– Computed Radiography (CR)– Linear CCD

• 2-D flat-field correction– Area CCD, CMOS – TFT arrays

•• 11--DD shadingshading correctioncorrection–– Computed Radiography (CR)Computed Radiography (CR)–– Linear CCDLinear CCD

•• 22--DD flatflat--fieldfield correctioncorrection–– Area CCD, CMOS Area CCD, CMOS –– TFT arraysTFT arrays

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n 1, i ; O(x) - I(x) (x)I iiO ==

Shading correction techniques: 1Shading correction techniques: 1--D dataD data

(x)I

I Sh(x)

O

xO=

( ) x)Sh O(x) - I(x) C(x) (×=

Apply offset correction to uniform exposures, n averages:Apply offset correction to uniform exposures, n averages:

Create normalized shading correction array:Create normalized shading correction array:

Implement shading correction (line by line):Implement shading correction (line by line):

1-D shading correction11--D shading correctionD shading correction

ResponseResponse

Low noise, inverted, normalized correction traceLow noise, inverted, normalized correction trace


Corrected responseCorrected response

Scan DirectionScan Direction

2-D flat-field correction22--D flatD flat--field correctionfield correction

• Non-functioning components:– Dead pixels in columns and/or rows

• Intensity variations:– Uneven phosphor coating– Optical coupling (vignetting, barrel distortion)– Converter sensitivity

• Variation in offset and gain of sub-panels

• Variation in black-level correction

•• NonNon--functioning components:functioning components:–– Dead pixels in columns and/or rowsDead pixels in columns and/or rows

•• Intensity variations:Intensity variations:–– Uneven phosphor coatingUneven phosphor coating–– Optical coupling (vignetting, barrel distortion)Optical coupling (vignetting, barrel distortion)–– Converter sensitivityConverter sensitivity

•• Variation in offset and gain of subVariation in offset and gain of sub--panelspanels

•• Variation in blackVariation in black--level correctionlevel correction

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Uncorrected flat-panel imageUncorrected flatUncorrected flat--panel imagepanel image

+ , + , --column defectscolumn defects

row defectsrow defects

pixel defectspixel defects

SubSub--panel offset gain variationpanel offset gain variation

BackgroundBackgroundsignalsignal

n 1, i ; y)O(x, - y)I(x, y)(x,I iiO ==

FlatFlat--field techniques: 2D imagefield techniques: 2D image(fixed detector)(fixed detector)

y)(x,I I

y)FF(x,O

O=

( ) y)x,FF y)O(x, - y)I(x, y)C(x, (×=

Apply offset and average of <n> uniform exposures:Apply offset and average of <n> uniform exposures:

Create normalized flatCreate normalized flat--field correction matrix:field correction matrix:

Implement flatImplement flat--field correction on acquired image:field correction on acquired image:

2-D Flat-field correction22--D FlatD Flat--field correctionfield correction

Raw, RawRaw, Raw

Background variationsBackground variationsColumn, line defectsColumn, line defects““DelDel”” dropoutsdropouts

Correction Correction ““maskmask””

Avg, inverted backgroundAvg, inverted backgroundColumn, line, pixel repairColumn, line, pixel repairNormalized valuesNormalized values

RawRaw

PrePre--processed imageprocessed imageImage pixel value to Image pixel value to exposure relationship?exposure relationship?

ProcessedProcessed

Contrast, resolution Contrast, resolution enhancement; proprietaryenhancement; proprietaryprocessingprocessing


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Preprocessing, Step 2: find / scale imagePreprocessing, Step 2: find / scale imagePreprocessing, Step 2: find / scale imageDetermine CollimationDetermine Collimation

CollimationCollimationBorderBorderShift and SubtractShift and Subtract

Create / analyze Histogram DistributionCreate / analyze Histogram DistributionCreate / analyze Histogram 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

Data conversionData conversionExposure into digital numberExposure into digital number

200200 600600 1,0001,00000

200200

400400

600600

800800

1,0001,000

Raw Input digital numberRaw Input digital number

Out

put d

igita

l num

ber

Out

put d

igita

l num

ber

Grayscale transformationGrayscale transformationInput to output digital numberInput to output digital number

1010331010--11 101000 101022101011

Exposure inputExposure input

Rel

ativ

e P

SL

Rel

ativ

e P

SL

101011

1010--11

101000

101022

00 511511 10231023Raw Digital OutputRaw Digital Output

HistogramHistogramminmin maxmax

Find the Find the signal signal

1.1. Scale toScale torange range

2.2. Create film Create film looklook--alikealike

3.3.

19

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 ““rawraw”” imageimage

Scaled and inverted:Scaled and inverted:““For ProcessingFor Processing”” imageimage

Data conversion for overexposureData conversion for overexposureExposure into digital numberExposure into digital number

ExposureExposureinputinput

Rel

ativ

e P

SL

Rel

ativ

e P

SL

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

20

Screen – Film

Digital

Identical exposure

Data conversion for wide latitudeData conversion for wide latitudeExposure into digital number: less kV dependenceExposure into digital number: less kV dependence

Rel

ativ

e P

SL

Rel

ativ

e P

SL

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(broad histogram)(broad histogram)

minmin maxmax

Contrast EnhancementContrast EnhancementContrast Enhancement

• Optimize image contrast via non-lineartransformation curves

• Unprocessed images: “subject contrast”

• Proprietary processing:– “Gradation processing” (Fuji)– “Tone scaling” (Kodak)– “MUSICA” (Agfa)– …….. And others by the various manufacturers

•• Optimize image contrast via Optimize image contrast via nonnon--linearlineartransformation curvestransformation curves

•• Unprocessed images: Unprocessed images: ““subject contrastsubject contrast””

•• Proprietary processing:Proprietary processing:–– ““Gradation processingGradation processing”” (Fuji)(Fuji)–– ““Tone scalingTone scaling”” (Kodak)(Kodak)–– ““MUSICAMUSICA”” (Agfa)(Agfa)–– ………….. And others by the various manufacturers.. And others by the various manufacturers

21

Look-up-table transformationLookLook--upup--table transformationtable transformation

Input digital numberInput digital number

Out

put d

igita

l num

ber

Out

put d

igita

l num

ber

00 200200 400400 600600 800800 1,0001,00000

200200

400400

600600

800800

1,0001,000

AAEELLMM

Fuji SystemExample LUTsFuji SystemFuji SystemExample LUTsExample LUTs

RawRaw UnprocessedUnprocessedContrast Contrast EnhancedEnhanced

““For processingFor processing””CADCAD

VOI LUTVOI LUT

““For presentationFor presentation””ProprietaryProprietary

Limited variabilityLimited variability

““PrePre--processedprocessed””No scalingNo scalingNo flatfieldNo flatfield

Types of image output:Types of image output:Types of image output:

VOI LUT: a more flexible approachVOI LUT: a more flexible approachVOI LUT: a more flexible approach

• Value Of Interest Look-Up-Table (DICOM)• Adjustment of contrast, brightness with non-linear

LUT adjustment• Provides for manipulation of raw data

(“For Processing” images)• Universal support (modalities, PACS) not available• Future universal image processing workstation?

•• Value Of Interest LookValue Of Interest Look--UpUp--Table (DICOM)Table (DICOM)•• Adjustment of contrast, brightness with nonAdjustment of contrast, brightness with non--linear linear

LUT adjustmentLUT adjustment•• Provides for manipulation of raw data Provides for manipulation of raw data

((““For ProcessingFor Processing”” images)images)•• Universal support (modalities,Universal support (modalities, PACS) not availablePACS) not available•• Future universal image processing workstation?Future universal image processing workstation?

22

DICOM VOI LUTDICOM VOI LUTDICOM VOI LUT• Configure CR/DX modality to send specific VOI LUT

– Eliminates “burned-in” LUT and potential information loss

• PACS must be able to use and vary VOI LUT

•• Configure CR/DX modality to send specific VOI LUTConfigure CR/DX modality to send specific VOI LUT–– Eliminates Eliminates ““burnedburned--inin”” LUT and potential information lossLUT and potential information loss

•• PACS must be able to use and vary VOI LUT PACS must be able to use and vary VOI LUT

Raw image histogram valuesRaw image histogram values P P -- valuesvalues

40954095

00

Adjustable VOI LUT

Adapted from Mike Flynn presentationAdapted from Mike Flynn presentation

Spatial Frequency ProcessingSpatial Frequency ProcessingSpatial Frequency Processing

“Edge Enhancement”““Edge EnhancementEdge Enhancement””

OriginalOriginal BlurredBlurred

DifferenceDifference Edge enhancedEdge enhancedSpatial frequencySpatial frequency

MTF: original responseMTF: original response

Res

pons

eR

espo

nse

lowlow highhigh

Spatial frequencySpatial frequency

Solid: original responseSolid: original response

Dash: low pass filteredDash: low pass filtered

Res

pons

eR

espo

nse

lowlow highhigh


Original Original -- filteredfiltered

Difference:Difference:

lowlow highhigh


SumSum

lowlow

Difference + OriginalDifference + Original

Edge Enhanced:Edge Enhanced:

highhigh

NonNon--linear linear weightingweighting




““Multi frequencyMulti frequency””enhanced imageenhanced image

Optimize subOptimize sub--band weightingband weighting

Multi-band Frequency ProcessingMultiMulti--band Frequency Processingband Frequency Processing

23

Standard ProcessingStandard Processing MultiMulti--frequency Processingfrequency Processing

Compliments of Keith Strauss, Boston Compliments of Keith Strauss, Boston ChildrensChildrens HospitalHospital

SNR and CNR (dSNR)SNR and CNR (SNR and CNR (dSNRdSNR))

• SNR: Average value / Std Dev of background

• CNR: ∆ Attenuation / Std Dev of background

– Contrast: tissue differences, tissue/bone differences

– Subject contrast: X-ray energy

• Detection: CNR of 3 to 5 – Size (diameter); image processing

•• SNR: Average value / Std Dev of backgroundSNR: Average value / Std Dev of background

•• CNR: CNR: ∆∆ Attenuation / Std Dev of backgroundAttenuation / Std Dev of background

–– Contrast: tissue differences, tissue/bone differencesContrast: tissue differences, tissue/bone differences

–– Subject contrast: XSubject contrast: X--ray energyray energy

•• Detection: CNR of 3 to 5 Detection: CNR of 3 to 5 –– Size (diameter); image processingSize (diameter); image processing

SNR and CNRSNR and CNRSNR and CNR

BackgroundBackground420.3 420.3 ±±3.33.3

ObjectObject411.8 411.8 ±±3.33.3

420.3SNR = = 127.43.3

420.3 - 411.8CNR = = 2.63.3

24

Noise SourcesNoise SourcesNoise Sources• Incomplete x-ray absorption: η• Secondary quantum noise: quantum sink

– # secondary quanta ≤ incident q

• Spatial gain variation (flat-field)• Aliasing (insufficient sampling)• Swank Factor

– Different x-ray photons produce variable signal

• Lubberts Effect– Different x-ray photons produce variable PSF’s

• Additive system noise– Electronic, quantization, shot, etc.

•• Incomplete xIncomplete x--ray absorption: ray absorption: ηη•• Secondary quantum noise: quantum sinkSecondary quantum noise: quantum sink

–– # secondary quanta # secondary quanta ≤≤ incident incident qq

•• Spatial gain variation (flatSpatial gain variation (flat--field)field)•• Aliasing (insufficient sampling)Aliasing (insufficient sampling)•• Swank Factor Swank Factor

–– Different xDifferent x--ray photons produce variable signalray photons produce variable signal

•• LubbertsLubberts EffectEffect–– Different xDifferent x--ray photons produce variable ray photons produce variable PSFPSF’’ss

•• Additive system noiseAdditive system noise–– Electronic, quantization, shot, etc.Electronic, quantization, shot, etc.

Visual Detection of ObjectVisual Detection of ObjectVisual Detection of Object

• SNR (CNR) is x-ray quanta dependent• Detection is determined by CNR and object size

• k = SNR × d × C

C = contrastd = diameterk = 3 to 5 for detection

•• SNR (CNR) is xSNR (CNR) is x--ray quanta dependentray quanta dependent•• Detection is determined by CNR and object sizeDetection is determined by CNR and object size

•• k = SNR k = SNR ×× d d ×× CC

C = contrastC = contrastd = diameterd = diameterk = 3 to 5 for detectionk = 3 to 5 for detection

Low Contrast Response: Leeds TO-16Low Contrast Response: Leeds TOLow Contrast Response: Leeds TO--1616

0.5 mR0.5 mR0.5 mR3.5 mR3.5 mR3.5 mR 70 kVp70 kVp70 kVp

25

What determines necessary dose?What determines What determines necessarynecessary dose?dose?

• Patient thickness

• X-ray technique; GRID or NO GRID

• Detector absorption AND conversion efficiency

• Detector electronic and stationary noise

• Detector Detective Quantum Efficiency (DQE)

• Required SNR / CNR of examination

• Pre and post processing algorithms

• Display and viewing conditions

•• Patient thicknessPatient thickness

•• XX--ray technique; GRID or NO GRIDray technique; GRID or NO GRID

•• Detector absorption Detector absorption AND AND conversion efficiencyconversion efficiency

•• Detector electronic and stationary noiseDetector electronic and stationary noise

•• Detector Detective Quantum Efficiency (DQE)Detector Detective Quantum Efficiency (DQE)

•• Required SNR / CNR of examinationRequired SNR / CNR of examination

•• Pre and post processing algorithmsPre and post processing algorithms

•• Display and viewing conditionsDisplay and viewing conditions

0102030405060708090

100

10 20 30 40 50 60 70 80 90 100 110 120 130 140

Energy (keV)

% A

bsor

ptio

n Fr

actio

n

CsI: 175 mg/cm2

Gd2O2S: 120 mg/cm2

BaFBr: 100 mg/cm2

X-ray absorption Efficiency: CsI, BaFBr, Gd2O2S

Detective Quantum Efficiency (DQE)Detective Quantum Efficiency (DQE)Detective Quantum Efficiency (DQE)

• A measure of the information transfer efficiency of a detector system

• Dependent on:– Absorption efficiency– Conversion efficiency– Spatial resolution (MTF)– Conversion noise– Electronic noise– Detector non-uniformities / pattern noise

•• A measure of the A measure of the information transfer information transfer efficiency efficiency of a detector systemof a detector system

•• Dependent on:Dependent on:–– Absorption efficiencyAbsorption efficiency–– Conversion efficiencyConversion efficiency–– Spatial resolution (MTF)Spatial resolution (MTF)–– Conversion noiseConversion noise–– Electronic noiseElectronic noise–– Detector nonDetector non--uniformities / pattern noiseuniformities / pattern noise

2 2out2in N

SNR MTF( )DQE( ) =SNR NPS ( )

fff q

=×

2 2out2in N

SNR MTF( )DQE( ) =SNR NPS ( )

fff q

=×

26

“Pre-sampled” MTF““PrePre--sampledsampled”” MTFMTF

aa--Selenium: 0.13 mmSelenium: 0.13 mm

ScreenScreen--filmfilm

CsICsI--TFT: 0.20 mmTFT: 0.20 mm

CR: 0.10 mmCR: 0.10 mm0.00.0

0.10.1

0.20.2

0.30.3

0.40.4

0.50.5

0.60.6

0.70.7

0.80.8

0.90.9

1.01.0

0.00.0 0.50.5 1.51.5 2.52.5 3.53.5 4.54.51.01.0 2.02.0 3.03.0 4.04.0 5.05.0Frequency (lp/mm)Frequency (lp/mm)

Mod

ulat

ion

Mod

ulat

ion

CR: 0.05 mmCR: 0.05 mm

Noise Power SpectrumNoise Power SpectrumNoise Power Spectrum

• Noise transfer characteristics of detector

• Analyze sub-images, Fourier Transform, average – (IEC 62220-1 standard, AAPM Task Group on NPS)

• Output is the noise power estimate as a function of spatial frequency, NPS(f) in 2 dimensions

•• Noise transfer characteristics of detectorNoise transfer characteristics of detector

•• Analyze subAnalyze sub--images, Fourier Transform, average images, Fourier Transform, average –– (IEC 62220(IEC 62220--1 standard, AAPM Task Group on NPS)1 standard, AAPM Task Group on NPS)

•• Output is the noise power estimate as a function Output is the noise power estimate as a function of spatial frequency, of spatial frequency, NPS(NPS(ff) in 2 dimensions ) in 2 dimensions

CR Image NPSCR Image NPSScan directionScan direction

DQ

E(

f )

Spatial Frequency (cycles/mm)0.0 0.5 1.0 1.5 2.0 2.5

0.0

0.2

0.4

0.6

0.8CsI - TFT

Screen-film

CR Conventional

a-Se - TFT

CR “dual-side”

Detective Quantum Efficiency, Radiography

CCD

27

ScreenScreen--FilmFilm

aSiaSi/CsI Flat/CsI Flat--PanelPanel

CRCR

125 kVp125 kVp2 mAs2 mAs

MDACC: Chris Shaw, et alMDACC: Chris Shaw, et al

FlatFlat--field prefield pre--processingprocessing

Low contrastLow contrastresolutionresolution

Image quality depends on more than Image quality depends on more than quantum mottle!quantum mottle!

FlatFlat--field, absorption efficiency, scatter field, absorption efficiency, scatter ……

Shading, Flat-Field correctionShading, FlatShading, Flat--Field correctionField correction• Reduce structured noise

• Eliminate variable background

• Increase DQE( f )

•• Reduce structured noiseReduce structured noise

•• Eliminate variable backgroundEliminate variable background

•• Increase DQE( Increase DQE( f f ))

00.10.20.30.40.5

0 2 4 6 8 10

f (mm-1)

DQ

E(f) Flatfield

Raw

Digital Radiography: Radiation ExposureDigital Radiography: Radiation ExposureDigital Radiography: Radiation Exposure

• CR and DR tolerate poor radiographic technique

• Dose is dependent on DQE and “required” SNR

• Dose is roughly proportional to inverse of DQE

•• CR and DR tolerate poor radiographic techniqueCR and DR tolerate poor radiographic technique

•• Dose is dependent on DQE and Dose is dependent on DQE and ““requiredrequired”” SNRSNR

•• Dose is roughly proportional to inverse of DQEDose is roughly proportional to inverse of DQE

28

Exposure issuesExposure issuesExposure issues

• Incident exposure can be “hidden”

• Low exposures have excessive image noise

• High exposures lead to saturation signal loss

• Technique complacency, instead of “just enough”

• Feedback is necessary!! – S number, Exposure Index, LgM, f-number, other?

•• Incident exposure can be Incident exposure can be ““hiddenhidden””

•• Low exposures have excessive image noiseLow exposures have excessive image noise

•• High exposures lead to saturation signal lossHigh exposures lead to saturation signal loss

•• Technique complacency, instead of Technique complacency, instead of ““just enoughjust enough””

•• Feedback is necessary!! Feedback is necessary!! –– S number, Exposure Index, S number, Exposure Index, LgMLgM, f, f--number, other?number, other?

DigitalDigitalFilmFilm--screenscreen(400 speed)(400 speed)

0.01 0.1 1 10 1001

10

100

1,000

10,000

Exposure, mR

Rel

ativ

e in

tens

ity

Film

Opt

ical

Den

sity

0

1

2

3

4

20000 2000 200 20 2 Sensitivity (S)

UnderexposedUnderexposed

OverexposedOverexposed

Correctly exposedCorrectly exposed

Characteristic Curve:Response of screen/film vs. digital detectors

UselessUseless

UselessUseless5

How do manufacturers indicate estimated exposure?

How do manufacturers indicate How do manufacturers indicate estimated exposure?estimated exposure?

• Fuji: “S” – sensitivity number• S ≅ 200 / Exposure (mR)

• Kodak: “Exposure Index” – EI• EI ≅ 1000 × log (Exposure [mR] ) + 2000

• Agfa: “lg M” – relative exposure database

• IDC: “f-number” – provides analogy to camera speed• +1 = 2x exposure; +2 = 4x exposure

• DR: most systems currently do not have a feedback signal… but use phototiming (AEC)

•• Fuji: Fuji: ““SS”” –– sensitivity numbersensitivity number•• S S ≅≅ 200 / Exposure (mR)200 / Exposure (mR)

•• Kodak: Kodak: ““Exposure IndexExposure Index”” –– EIEI•• EI EI ≅≅ 1000 1000 ×× log (Exposure [mR] ) + 2000 log (Exposure [mR] ) + 2000

•• Agfa: Agfa: ““lglg MM”” –– relative exposure databaserelative exposure database

•• IDC: IDC: ““ff--numbernumber”” –– provides analogy to camera speedprovides analogy to camera speed•• +1 = 2x exposure; +2 = 4x exposure+1 = 2x exposure; +2 = 4x exposure

•• DR: most systems currently do not have a feedback DR: most systems currently do not have a feedback signalsignal…… but use phototiming (AEC)but use phototiming (AEC)

29

CR vs DR and dose efficiencyCR CR vsvs DR and dose efficiencyDR and dose efficiency

• CR ~ 2X more exposure than a 400 speed film ~200 equivalent speed

• DR DQE(0) values vary substantially (20 - 80%)

• Dose efficiency related to DQE for given SNR

• Slot-scan systems most efficient

•• CR ~ 2X more exposure than a 400 speed film CR ~ 2X more exposure than a 400 speed film ~200 ~200 equivalent equivalent speedspeed

•• DR DQE(0) values vary substantially (20 DR DQE(0) values vary substantially (20 -- 80%)80%)

•• Dose efficiency related to DQE for given SNRDose efficiency related to DQE for given SNR

•• SlotSlot--scan systems most efficientscan systems most efficient












• Modality interface: DICOM & HL-7– PACS, RIS connections, Modality Worklist

• Image Size & Storage considerations• 8 - 32 Mbytes Uncompressed

– 10 - 12 Pixels/mm– Up to 4000 x 4000 x 2 Bytes

• 3 - 13 Mbytes: ~2.5:1 Lossless Compression

• Network Transmission• 100 Mbit/sec minimum

•• Modality interface: DICOM & HLModality interface: DICOM & HL--77–– PACS, RIS connections, PACS, RIS connections, Modality WorklistModality Worklist

•• Image Size & Storage considerationsImage Size & Storage considerations•• 8 8 -- 32 Mbytes Uncompressed32 Mbytes Uncompressed

–– 10 10 -- 12 Pixels/mm12 Pixels/mm–– Up to 4000 x 4000 x 2 BytesUp to 4000 x 4000 x 2 Bytes

•• 3 3 -- 13 Mbytes: ~2.5:1 Lossless Compression13 Mbytes: ~2.5:1 Lossless Compression

•• Network TransmissionNetwork Transmission•• 100 100 MbitMbit/sec minimum/sec minimum

CR/DR implementationCR/DR implementationCR/DR implementation

30


• Uniformity for CR/DR images and Display

– Acceptance Testing• Measurement of Performance• Correction of Substandard Performance

– Calibration of CR/DR Response (presentation state)

– Calibration of Monitors• Maximum brightness• Look-up-Tables, DICOM GSDF, Part 14

– Periodic Quality Control • Evaluation of resolution, contrast, artifacts• Monitor technologist performance, exposure indices

•• Uniformity for CR/DR images Uniformity for CR/DR images and and DisplayDisplay

–– Acceptance TestingAcceptance Testing•• Measurement of PerformanceMeasurement of Performance•• Correction of Substandard PerformanceCorrection of Substandard Performance

–– Calibration of CR/DR Response (presentation state)Calibration of CR/DR Response (presentation state)

–– Calibration of MonitorsCalibration of Monitors•• Maximum brightnessMaximum brightness•• LookLook--upup--Tables, DICOM GSDF, Part 14Tables, DICOM GSDF, Part 14

–– Periodic Quality Control Periodic Quality Control •• Evaluation of resolution, contrast, artifactsEvaluation of resolution, contrast, artifacts•• Monitor technologist performance, exposure indicesMonitor technologist performance, exposure indices


• Image Processing optimization– Establish Contrast Scale– Balance Edge Enhancement with perceived noise– Multi-frequency Enhancement parameter

adjustments– Determine DC offset (brightness) for display

monitors

• Provide processing “looks” to Radiologists

• Verify image display conditions– Soft copy and hard copy

•• Image Processing optimizationImage Processing optimization–– Establish Contrast ScaleEstablish Contrast Scale–– Balance Edge Enhancement with perceived noiseBalance Edge Enhancement with perceived noise–– MultiMulti--frequency Enhancement parameter frequency Enhancement parameter

adjustmentsadjustments–– Determine DC offset (brightness) for display Determine DC offset (brightness) for display

monitorsmonitors

•• Provide processing Provide processing ““lookslooks”” to Radiologiststo Radiologists

•• Verify image display conditionsVerify image display conditions–– Soft copy and hard copySoft copy and hard copy

What is emerging as the lead technology?What is emerging as the lead technology?What is emerging as the lead technology?Attribute CR DR CCD

Positioning flexibility **** ** **

Replacement for S/F **** ** **

DQE / dose efficiency ** *** **

Patient throughput * *** **

X-ray system integration ** **** ****

PACS integration ** **** ****

Cost per pat. throughput *** ** ***

Technologist ease of use * *** ***

31

Digital Radiography ConsiderationsDigital Radiography ConsiderationsDigital Radiography Considerations

• Replacement of S/F, aging CR

• High throughput, ambulatory imaging

• Advanced image acquisition and processing– Digital tomosynthesis and CT– Dual energy radiography– Replacement of image intensifiers

• Low dose screening devices with CAD – Lung cancer screening with dual energy– Quantitative bone density analysis?

•• Replacement of S/F, aging CR Replacement of S/F, aging CR

•• High throughput, ambulatory imagingHigh throughput, ambulatory imaging

•• Advanced image acquisition and processingAdvanced image acquisition and processing–– Digital tomosynthesis and CTDigital tomosynthesis and CT–– Dual energy radiographyDual energy radiography–– Replacement of image intensifiersReplacement of image intensifiers

•• Low dose screening devices with CAD Low dose screening devices with CAD –– Lung cancer screening with dual energyLung cancer screening with dual energy–– Quantitative bone density analysis?Quantitative bone density analysis?

ConclusionsConclusions

•• CR is the most CR is the most flexibleflexible and costand cost--effectiveeffective technologytechnology

•• DirectDirect digital radiographic devices have advantages in digital radiographic devices have advantages in efficiency and throughput efficiency and throughput

•• The distinction between CR and DR is blurringThe distinction between CR and DR is blurring–– Portable versus integrated; active versus passivePortable versus integrated; active versus passive–– ““CassetteCassette”” versus versus ““CassettelessCassetteless””

•• All technologies are becoming faster, better, cheaperAll technologies are becoming faster, better, cheaper

•• The digital solution is best accomplished as a The digital solution is best accomplished as a complementary mix of technologiescomplementary mix of technologies

design and performance characteristics of digital ... · • screen-film radiography – iq...

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