state-of-the-art full field digital mammography – detector ...9light converted to analog signal...

StateState--ofof--thethe--Art Full Field Digital Art Full Field Digital Mammography Mammography –– Detector Technology Detector Technology used in FDA Approved FFDM Systems used in FDA Approved FFDM Systems

and Newly Emerging Detector Technologyand Newly Emerging Detector Technology

AAPM 2004 Annual MeetingAAPM 2004 Annual MeetingCE: Mammography Physics and Technology CE: Mammography Physics and Technology –– 8 8

Jerry A. Thomas, M.S., DABR, CHP, DABSNMAssistant Professor of Radiology

Department of Radiology and Radiological SciencesUniformed Services University

Bethesda, MD 20814

Image Quality AdvantagesImage Quality Advantages

FilmFilm--Screen vs. DigitalScreen vs. Digital

Film Screen DigitalHigher Spatial Resolution Higher Image Contrast

Higher DQE (SNR, Dose)

Contrast & Dynamic RangeContrast & Dynamic RangeScreen - Film Characteristic Curve

Screen - Film Characteristic Curve

Skin LineSkin Line

Average TissueAverage Tissue

Dense TissueDense Tissue

.

LowLow Med.Med. HighHighLog Relative ExposureLog Relative Exposure

VeryVeryLowLow

Opt

ical

Den

sity

Opt

ical

Den

sity

HighHigh

LowLowContrastContrast

Log Relative ExposureLog Relative ExposureLo

g Si

gnal

Log

Sign

al

Digital Detector Characteristic Curve

Digital Detector Characteristic Curve

3-4 x Improvement in Dynamic Range3-4 x Improvement in Dynamic Range

Spatial Resolution for MammographySpatial Resolution for Mammography

0

0.1

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1

1 2 3 4 5 6 7 8 9 10

GE PanelKodak Min-R

Con

tras

t tra

nsfe

r fun

ctio

n

Spatial Frequency (line pairs/mm)

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

• DQE of a detector

• Measures transfer of both signal and noise.

• DQE of a detector

• Measures transfer of both signal and noise.

DQE = DQE = SNR2 at detector outputSNR2 at detector outputSNR2 at detector inputSNR2 at detector input

SNR = signal-to-noise ratioSNR = signal-to-noise ratio

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

• Input SNR2 proportional to patient dose

• Noise is a limiting factor for detectability, image processing, and advanced applications

• Doubling DQE means:

• Same output SNR (“image quality”) at half the dose

• 40% improvement in SNR at same dose

• Input SNR2 proportional to patient dose

• Noise is a limiting factor for detectability, image processing, and advanced applications

• Doubling DQE means:

• Same output SNR (“image quality”) at half the dose

• 40% improvement in SNR at same dose

DQE ∝DQE ∝Image QualityImage QualityPatient DosePatient Dose

DQE and NoiseDQE and NoiseControl DQE & noise by:•increasing x-rays reaching detector

•efficient detection of x-rays

- efficient conversion to signal

- efficient scatter rejection

•efficient coupling between elements in

the detection chain

•Low electronic noise

Applications of Digital Applications of Digital MammographyMammography

• Large Field Systems– Diagnostic application– 20 x 30 Field-of-View– 2000 - 4000 pixels– 50 - 100 um pixel size

Approaches to Digital MammographyApproaches to Digital Mammography

•Scanning slot

•Large amorphous silicon arrays with CsI

•Direct conversion/selenium plates

•Photostimulated Luminescence

•Silicon microstrip detectors

FFDM SystemsFFDM SystemsTechnologyTechnology DetectorDetector Vendor

CRDual Sided Reading Fugi

Scanning Slot

CsI - CCD Fischer

Silicon Microstrip Sectra

Flat Panel a-Silicon Panel

CsI

AgfaSingle Sided Reading

Vendor

a-Selenium

GE

LoradSiemens

AgfaPlanmed

Indirect SensorsX-rays converted into light

Light converted to analog signal

Analog converted to digital signal

Noise Source(s)Conversion of x-rays to light/analog/digital signals

Detector dark current

Electronic noise

Examples:Film screen

CsI to CCD’s or photo-diodes (a-Si panels)

DoseDose--Efficiency for Digital Mammography SensorsEfficiency for Digital Mammography Sensors

Indirect SensorsDirect Sensors

X-rays converted to analog signal

Analog converted to digital signal

Noise Source(s)Conversion of x-rays to analog/digital

signal

Detector dark current

Electronic noise

Example:a-Selenium


Indirect SensorsDirect Sensors

Direct Photon Counting SensorsX-rays detected/counted individually

Noise Source(s)Eliminated by using thresholding

Example:Silicon microstrip


SCANNING MOTION OF DETECTORSCANNING MOTION OF DETECTOR

Fischer Imaging Corporation

Fischer ImagingSenoScan FFDM SystemFischer ImagingSenoScan FFDM System

Requirements of the Phosphor for Requirements of the Phosphor for Scanning Slit DetectorScanning Slit Detector

• High DQE - detector quantum efficiency

• Fast rise time

• Short persistence (low afterglow)

• Low radiation memory

Composition of Composition of

SenoscanSenoscan® Detector® Detector

Cesium Iodide

221 mm

Fiber Optic

Plate

4 CCD’s

10 mm

Fischer Slot Scan FFDMFischer Slot Scan FFDMDetector:

• 1.0cm x 22 cm (scans 30 cm)

• 4 CCD chips (each 405 x 2048 pixels)

• 27 Micron pixel at CCD

• Use 2 x 2 electronic averaging

• 54 x 54 micron pixels

• Matrix 4096 x 5600

• 60 micron dead zone between CCD’s

Fischer Slot Scan FFDMFischer Slot Scan FFDM

Scintillator:•CsI

•0.150 mm thick

•85% absorption at 20 kev


Scan time:

•5 sec total scan

•200 mA

•200 ms exposure to tissue (40mAs)

•1200 mAs

•22 x 30cm image area (standard)

Fisher Slot Scan FFDMFisher Slot Scan FFDM

X-ray Tube:• 4 inch Tungsten-Rhenium target• 7 degree target angle• 4 cm spacing • Axis perpendicular to scan• Use 32 – 34 KVp ( SNR Contrast)• Collimate to 1.2 cm width


•High Resolution mode

- ½ field length and

width (11x15)

- ½ scan velocity

- 400 ms tissue exposure (80mAs)

- 27 x 27 micron pixels

- same matrix and scan time

- double dose

Velocity Vector

Column Vector4 3 2 1

Charge Transfer

Transfer

GateTime Delay IntegrationTime Delay Integration

SR CCD

Time Delay IntegrationTime Delay Integration

Accuracy dependent upon:

•Synchronism of detector motion and charge transfer rates

•Alignment of detector motion vector and pixel matrix

•Efficiency of charge transfer between pixels

Fischer System MTFFischer System MTF

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11.1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Slot 27 u PixelSlot 54 u Pixel

Frequency (cycles/mm)

MTF

a-Silicon Array with CsIa-Silicon Array with CsI

Glass SubstrateGlass Substrate

AmorphousSilicon ArrayAmorphousSilicon ArrayContact FingersContact Fingers

Scintillator(CsI)

Scintillator(CsI)

Contact LeadsFor Read-Out

Electronics

Contact LeadsFor Read-Out

Electronics

ScintillatorScintillator

a-Si Arraya-Si Array

Opticlad ReflectorOpticlad Reflector

Glass SubstrateGlass Substrate

Graphite CoverGraphite Cover

Epoxy SealEpoxy Seal

CsI a-Silicon ArrayCsI a-Silicon Array

ReflectorReflector

10µ needle width10µ needle width

Light photonsguided via CsI needle structure

Light photonsguided via CsI needle structure

X-Ray PhotonsX-Ray Photons

Scintillator & ReflectorScintillator & Reflector

300

to 4

00 µ

C

sI30

0 to

400

µ

CsI

Scintillator

Photo D/TFT

preamp preamp preamp preamp

preamp preamp preamp preamp

TFTPhoto D

Driv

ers

Flat Panel-Light SensorFlat Panel-Light Sensor

FETFET

data linedata line

scan linescan line

PitchPitch

Fill Factor =Fill Factor =Sensitive AreaPitch x Pitch

Sensitive AreaPitch x Pitch

Very High Fill Factor

Very High Fill Factor

Pitc

hPi

tch

Flat Panel-Light SensorFlat Panel-Light Sensor

• Operation - single element– FET is turned on --diode is

charged– FET is turned off – X-rays exposure creates

electron-hole pairs in diode causing it to partially discharge

– FET is turned on--diode is re-charged--amount of charge needed is measured

• Operation - single element– FET is turned on --diode is

charged– FET is turned off – X-rays exposure creates

electron-hole pairs in diode causing it to partially discharge

– FET is turned on--diode is re-charged--amount of charge needed is measured

scan electronics(DRIVERS)

scan electronics(DRIVERS)

scan linescan line

data linedata line

readout electronics

(DATA COLLECTION)

readout electronics

(DATA COLLECTION)

VbiasVbias

FETFET

PhotodiodePhotodiode

GE Senographe 2000DGE Senographe 2000D

a-Selenium Technologya-Selenium TechnologyPhotonsPhotons

SeleniumSelenium

Amorphous Silicon PanelAmorphous Silicon Panel

Digital DataDigital Data

Electrons

Read Out ElectronicsRead Out Electronics

Electrons

X-rays

a-Se

Top electrode(A)

++

_

_

Field effect transistor channel

Si02Gate(A1)

Glass substrate Pixel electrode (B)

GroundStorage Capacitor Cij

V

High Efficiency of aHigh Efficiency of a--SeSe••Selenium provides almost 100% charge collection efficiency due tSelenium provides almost 100% charge collection efficiency due to o electrostatic field effects in the photoconductorelectrostatic field effects in the photoconductor

•Almost complete absorption of the x-rays is achieved within ~200µm layers

••Selenium allows high fill factor for small pixel size required iSelenium allows high fill factor for small pixel size required in n mammographymammography

--------- - - - - - - - -- - - --

-

Pixel electrodes

trapped

image

charge

-HV top bias electrode

a-Se+

Blocking layer

M U L T I P L E X E R Digitizer computer

S C

A N

N I

N G

C O

N T

R O

LGate line (i+1)

Gate line (i)

Gate line (i-1)

Storage capacitor

Thin film transistor

Pixel electrode (B)

(j-1) (j) (j+1)

i,j-1 i,j i,j+1

Data (source) lines

a-Se Flat Panel Detector

Detective Quantum Efficiency vs. ExposureLazzari,et.al SPIE 2003

MTF of aMTF of a--Se detectorSe detector

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Frequency, lp/mm

MTF

aa--Selenium DetectorSelenium Detector

•Hologic/Lorad product approved: 24x29cm

* 70 micron pixel size

•Siemens (OEM detector from Anrad)

•Agfa (OEM detector/unit from Hologic/Lorad)

•Instrumentarium evaluating 17 x 24 prototype

* 85 micron pixel size

•Planmed (OEM detector from Anrad)

*Same detector specifications as Instrumentarium

Amorphous-Selenium DetectorAmorphous-Selenium Detector

Detector images to chest wall edgeDetector images to chest wall edge

SeleniaSelenia

HTC grid retracts

Small foot print

5 cm at chest wall

SiemensSiemensTaylored solutions for different needsTaylored solutions for different needs

Dedicated

LowVolume

HighVolume

Non-Dedicated

syngo

FFDM CR(syngo-based &

workflow-optimized)

FFDM CR(multi-organ)

FFDM FD(aSe detector)

syngo

Agfa Digital Mammography UnitAgfa Digital Mammography Unit

Plus Agfa workstation with

Musica Image Processing Software.

Instrumentarium Detector SpecificationsInstrumentarium Detector Specifications

• Detector size:– 174 x 239 mm

– Larger size will be available in the future

• Pixel size– 85µm

• Matrix size:– 2048 x 2816

• Image size:– 11Mb

CR TechnologyCR Technology

Protective LayerProtective LayerPhoto-stimuable phosphor layerPhoto-stimuable phosphor layer

SupportSupport

Fuji Fuji MammoMammo CRCR

•Pixel size 50 micron

•Use dual sided reading to DQE

•Imaging Plate has thicker phosphor layer

•Results in 40 - 50% increase in NEQ (DQE)

•Post processing enhances image

(e.g. filtering to recognize and enhance calcifications)

Photo-detector

Trans-

Parent

support

Phosphor

layer

Protective

layer

mirror

emission

Laser beam

Imaging plate

Optical

guide

Optical guide Photo-detector

Image 1

Image 2

Image 1’

Image 2’

Addition

Image

Addition

Spatial Filter; 1-t

Spatial Filter; t

Front side

Back side

t;addition ratio

Addition Image = (1-t) x Image1 + t x Image2

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

0.5c/mm

1.0c/mm

1.5c/mm

2.0c/mm

2.5c/mm

3.0c/mm

0.0F

1.0

0.0F

0.9

0.2F

0.8

0.3F

0.7

0.4F

0.6

0.5F

0.5

0.6F

0.4

0.7F

0.3

0.8F

0.2

0.9F

0.1

1.0F

0.0

Addition Ratio (front back)

NEQ

Back

Side

image

Front

Side

image

Dependency of NEQ on

Addition Ratio at Each

Spatial Frequency

The maximum image quality with this new

method may be obtained when optimal addition ratio is simultaneously

used for each frequency.

t

1-t

1.0R

espo

nse

0Spatial Frequency

FujiCR MammographyReader

FujiCR MammographyReader

Fuji Clearview ReaderFuji Clearview Reader

• Four cassette stacker

• Processes 20 screening exams/hour (or 100 CR plates/hour)

• Multi-objective Frequency Processing (MFP) (enhances dense/peripheral tissue)

• Pattern Enhancement Processing for Mammography (PEM) (enhances calcifications)

Agfa CR Mammography Cassette/PlateAgfa CR Mammography Cassette/Plate

Agfa Mammography CR PlateAgfa Mammography CR Plate

100 micron pixel size

Agfa CR Plate ReaderAgfa CR Plate Reader

Sectra MicroDoseTM MammographySectra MicroDoseTM Mammography

• Equal or better image quality using only 1/5 of the

radiation dose compared to modern film-screen

systems

• One patient every 4-5 minutes

• A digital solution that support the entire workflow

from examination to a documented diagnose

Detector Technology - Conversion stepsDetector Technology - Conversion steps

CsI+aSi flat panel aSe flat panel Photon Counting

Scintillator amplification

A/D - ConverterAnalogue signal

Digital signal

Light

Capacitor charge storage

X-ray Photon

Analogue signal

aSe X-ray into electrons

A/D - Converter

Digital signal

Electrons

Capacitor charge storage

X-ray Photon

MicroDose Detector

X-ray Photon

12345Digital signal

5 (00000000000101)

Digital Mammography UnitDigital Mammography Unit

Analogue Digital

Digital DetectorFilm Cassette

What Decides the DQE on System Level?What Decides the DQE on System Level?

DQE on System Level• Detector technology

– Noise in the electronics and the detector

– Absorption efficiency in the detector

– Energy Weighting - How the information in the photons are transferred to the image as a function of their energy

• Scattered radiation– Reduction of scattered radiation

• X-ray spectrum– The spectrum of the X-ray beam

Detector Technology - Photon CountingDetector Technology - Photon Counting

Silicon Silicon microstripmicrostrip detectorsdetectors

•Silicon p+n junction

•Reverse bias

•Edge-on exposure

•3 mm deep – 95% absorption to 20 kev

•Counts individual photons

-digitized upon detection

-suppresses noise

Silicon Silicon microstripmicrostrip detectordetector

•Dead volume layer on top

•Detector several cm long

•Detection rate 5 x 106 x-rays /sec/pixel

•Slit-scanning, 5 sec. scan time

•Very low dose

Detector Technology - Photon Counting

Detector Technology - Photon CountingDetector Technology - Photon Counting

Photon Counting - No Electronic NoisePhoton Counting - No Electronic Noise

Energy

X-ray photon

1 2 3

Threshold

Lowest Photon Energy

TimeElectronic Noise

Scattered Radiation – Scanning TechnologyScattered Radiation – Scanning Technology

Scattered Radiation - Scanning TechnologyScattered Radiation - Scanning Technology

X-ray photonsScanning technology with

slit detector

• 97% reduction

• High SNR

• Minimal dose

What decides the DQE on System level?What decides the DQE on System level?Generally

• Absorption efficiency in the detector

• How the information in the photons are transferred to the image as a

• Noise in the electronics and the detector

Sectra MDM

No noise

More than 90% absorption

Every X-ray photon is processed individually

function of their energy

• Reduction of scattered radiation

• The quality of the X-ray beam

Scattered radiation is reduced by 97%The beam quality from the Tungsten anode is optimal for the MicroDose detector

Digital Detector - FactsDigital Detector - Facts

• Photon counter– Counts every photon

• Superb image quality– 50 µm pixels (0.05 mm), 10 lp/mm – Image matrix 4800 x 5200 pixels– 14 bits contrast resolution– Large dynamic range– Excellent DQE

• Dose - efficient• Large FOV, 24 x 26 cm

Digital Mammography image

DQE on System Level - ComparisonDQE on System Level - Comparison

Picture of review station - #10Picture of review station - #10

Benefits of Digital MammographyBenefits of Digital Mammography• Reduced radiation dose• Post-acquisition image processing• Rapid image display• Improved imaging of dense breasts• Improved sensitivity and specificity• Simplified archival, retrieval, and transmission• Potential for computer-aided diagnosis• Potential for telemammography

Digital DetectorAdvanced ApplicationsDigital DetectorAdvanced Applications

• Computer-Aided Detection• Tele-Radiology• Tomosynthesis• Dual-Energy Subtraction• Digital Subtraction Angiography• Stereo / Computer Aided Localization

• Computer-Aided Detection• Tele-Radiology• Tomosynthesis• Dual-Energy Subtraction• Digital Subtraction Angiography• Stereo / Computer Aided Localization

Comparison of ACR Comparison of ACR Phantom ScoresPhantom Scores

0

1

2

3

4

5

6

Fibers CalcsObjects

Mass

Digital SystemFilm System

ConclusionsConclusions

• Digital mammography has numerous potential advantages over film screen imaging

• Full field systems approved, more expected

• Present unique challenges to assess

– trade-offs of technologies

– performance assessment

– QC/QA procedures

AcknowledgementsThanks for input from:AcknowledgementsAcknowledgementsThanks for input from:

• Agfa Gaevert• Instrumentarium Imaging• Fischer Imaging• Fujifilm Medical Systems• GE Medical Systems• Hologic/LORAD• MTMI• Planmed• Sectra Imtec AB• Siemens Medical Solutions

THANK YOUTHANK YOU

state-of-the-art full field digital mammography – detector ...9light converted to analog signal...

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