John Rowlands

Sunnybrook Heath Sciences Centre

University of Toronto

Fluoroscopic Equipment Design:Fluoroscopic Equipment Design:

WhatWhat’’s Different with Flat Panel?s Different with Flat Panel?

Financial disclosure statementFinancial disclosure statement

• Researchsupportedby AnradCorp

• AnradCorp is a manufacturersof seleniumbased flat panelimagers

Concept of flat panel imagerConcept of flat panel imager Flat Panel Array DesignFlat Panel Array Design

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System ArchitectureSystem Architecture

A

B

TOSHIBA

Low VoltagePowerSupply Real Time

Image Processor

Acquisition Workstati on

DetectorX-RayGeneratorControl

Fiber Optic Links

TOSHIBA

X-ray tube

Automatic Exposure Control Automatic Exposure Control in fluoroscopyin fluoroscopy

Image Processing Chain

Flat PanelDetector

Real TimeImage

Processing

Real TimeData

Correction

X-ray andAcquisition

Control

Correction of:• Offset• Gain• Pixel defect• Horizontal noise

• Temporaland spatial filter

• Image Resizing•Gamma correction

AcquisitionWorkstation

andX-ray generator

CRT operation and CRT operation and characteristic curve of monitorcharacteristic curve of monitor-- Need for gamma correctionNeed for gamma correction

Offset and gain correctionsOffset and gain corrections

•• Dark fieldDark field –– offsetcorrectionoffset correction

Bright fieldBright field –– gain correctionsgain corrections

As acquiredimage

Enlarged“bad”region

GainandOffsetcorrectedwith

Bright field and DarkField imagesrespectively

Badlinesand pointsreplacedbyinterpolation

Gammaandsharpnesscorrectedimage

Distortion in an XRIIDistortion in an XRII

Pincushiondistortion

S-distortion

Complete XRII imaging systemComplete XRII imaging system Quantum accounting diagram Quantum accounting diagram for XRII video systemfor XRII video system

Flat panel detector typesFlat panel detector types

Indirect conversion Direct conversion(CsI) (a-Se)

Quantum accounting diagram Quantum accounting diagram for flat panel systemfor flat panel system

Intrinsic sources of blurring in Intrinsic sources of blurring in xx--ray imaging systemsray imaging systems Phosphor blurring sourcesPhosphor blurring sources

Photoconductor blurring sourcesPhotoconductor blurring sourcesComponents of MTF in an XRIIComponents of MTF in an XRII

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

electron lens

output screen

CsI inputscreenXRII

MT

F

spatial frequency (lp/mm)

Components of MTF in an Components of MTF in an XRII and flat panelXRII and flat panel

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

electron lens

output screen

CsI inputscreenXRII

MT

F

spatial frequency (lp/mm)

Flat panel

MTF of XRII and flat panel

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

(a)

Nyquist 1.6 lp/mm

XRII

CsI flat panel

MT

F

spatial frequency (lp/mm)

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

(b)

Nyquist 3.2 lp/mm

XRII zoom

XRIICsI flat panel

MT

F

spatial frequency (lp/mm)

Normalmode Zoomedmode

Principle of photolithographyPrinciple of photolithography Thin film transistor or TFTThin film transistor or TFT

(Courtesy of Dr. R. Weisfield,dpiX

127µm

TFT+Photodiode Pixel DesignTFT+Photodiode Pixel DesignArray Design RulesArray Design Rules

• Distancebetweenneighboringfeatures

• Width of control lines

• Thicknessof differentlayers

Fill Factor Fill Factor vsvs Pixel SizePixel Size

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250

Pixel Size (microns)

Ph

oto

dio

de

Fill

Fac

tor

Conservative Design Rules

Aggressive Design Rules

" Diode on Top " Design

Readout of a flat panel detector

Data Lines

-5 V

-5 V

ExternalElectronics

Switch Line 2

Switch Line 3

-5 V Switch Line 1

Data Lines

-5 V

-5 V

External Electronics

Switch Line 2

Switch Line 3

-5 V Switch Line 1+10 V Switch Line 1

Data Lines

-5 V

-5 V

ExternalElectronics

Switch Line 2

Switch Line 3

-5 V Switch Line 1+10 V Switch Line 1-5 V Switch Line 1

+10V Switch Line 2

Data Lines

-5 V

-5 V

External Electronics

Switch Line 2

Switch Line 3

-5 V Switch Line 1+10 V Switch Line 1-5 V Switch Line 1

+10 V Switch Line 2Switch Line 2-5 V

+10 V Switch Line 3

Data Lines

-5 V Switch Line 1

-5 V

ExternalElectronics

Switch Line 2

+10 V Switch Line 3-5 V Switch Line 3 Artifacts arising from inadequateArtifacts arising from inadequatecorrectionscorr ections

• Regionsof differentintensity

• Blurring

• Linecorrelatednoise

ImageCourtesy of Dr . UImageCourtesy of Dr . U NeitzelNeitzel, Philips, Philips Image Courtesy of Dr. UImageCourtesy of Dr . U NeitzelNeitzel, Philips, Philips

DQE of XRII andflat panelDQE of XRII andflat panel

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

(a)

XRII zoom

XRII

CsI flat panel

DQ

E

spatial frequency (lp/mm)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

(b)

CsI flat panel

XRII

DQ

E

input dose (nGy)

As a functionof spatialfrequency As a functionof doseto detector

CardiaccineCardiaccine

CsI flat panelCsI XRII/video

Advantages of flat panel imagersAdvantages of flat panel imagers

• High dynamic range

• Correctionsfor monitor nonlinearity

• Compactform factor

•Suitability for advancedapplications

Future developmentsFuture developments

• Not yet quantumnoiselimited at low exposures•Amplif ier per pixel•High conversionefficiencyphotoconductor•Avalanchegain

• Systemon glass