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Principles of industrial Principles of industrial digital radiographydigital radiography

XDRS handsXDRS hands--on sessionon session

JRCJRC--Ispra, July 6, 2011Ispra, July 6, 2011

Operational Issues in Radioactive Waste Operational Issues in Radioactive Waste Management and Nuclear DecommissioningManagement and Nuclear Decommissioning

3rd3rd International Summer SchoolInternational Summer School

JRC Ispra6 July 2011

1. X1. X--RAY BASICSRAY BASICSa.a. XX--ray physics & equipmentray physics & equipmentb.b. Image formation (contrast & signal)Image formation (contrast & signal)c.c. Imaging geometryImaging geometry

2. DIGITAL RADIOGRAPHY2. DIGITAL RADIOGRAPHYa.a. Digital imagesDigital imagesb.b. XDRS digital imagesXDRS digital imagesc.c. CalibrationCalibrationd.d. Scatter reductionScatter reduction

3. PRINCIPLES OF TOMOGRAPHIC RECONSTRUCTION3. PRINCIPLES OF TOMOGRAPHIC RECONSTRUCTIONa.a. Analytical methods (iterative methods not treated)Analytical methods (iterative methods not treated)

SummarySummary


XX--ray nature and generationray nature and generation

XX--rays are photons (electromagnetic radiation)rays are photons (electromagnetic radiation)They are generated by:They are generated by:•• Fluorescence (characteristics XFluorescence (characteristics X--rays)rays)•• Braking radiation (Braking radiation (BremsstrahlungBremsstrahlung))

-

++++

-

-

-

-

-E


XX--ray nature and generationray nature and generation

XX--rays tubes are used to generate Xrays tubes are used to generate X--rays in a controlled rays in a controlled manner. The user can select:manner. The user can select:•• The voltageThe voltage•• The currentThe current•• FilteringFiltering

Voltage

Cu

rren

t

XDRS max parameters:XDRS max parameters:•• 450 kV450 kV•• 20 20 mAmA

http://labspace.open.ac.uk/mod/resource/view.php?id=361885


XX--ray attenuation (I)ray attenuation (I)XX--rays are attenuated in any material depending on:rays are attenuated in any material depending on:•• The The energyenergy of the X raysof the X rays•• TheThe

oo thicknessthicknessoo density density oo compositioncomposition

of the of the materialmaterial

( )0

7.10

cm10 cm

g1 g

cm17.0

0tE

0 I 18.0eIeIeII3

2

==== −−

ρμ−

t

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1 10 100 1000

keV

Atte

nuat

ion

coef

ficie

nt (1

/cm

)

Water

Iron

Cement

I0

ρ

μ(E)ρ


XX--ray detectorsray detectors

XDRS is based on an axial line of 384 CdWOXDRS is based on an axial line of 384 CdWO44 crystalscrystalsCrystals emit light when hit by XCrystals emit light when hit by X--raysraysCdWOCdWO44 dimensions are 9 x 3 x 6 mm (width, height, depth)dimensions are 9 x 3 x 6 mm (width, height, depth)Each crystal is associated to (read out by) a Si photodiodeEach crystal is associated to (read out by) a Si photodiodePhotodiode converts crystal light into an electric signalPhotodiode converts crystal light into an electric signal

38

4 d

etec

tors

6 mm

9 mm

3 mm


XX--ray image formationray image formation

Detectors count more or fewer XDetectors count more or fewer X--rays depending on the rays depending on the attenuation met on the path from tube to detectorattenuation met on the path from tube to detectorCounts are associated to a color and displayedCounts are associated to a color and displayed

Detector array

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1 10 100 1000

keV

Atte

nuat

ion

coef

ficie

nt (1

/cm

)

Water

Iron

Cement


Imaging geometry: Imaging geometry: planar radiographyplanar radiography

The drum is scanned sideways to obtain a planar radiographyThe drum is scanned sideways to obtain a planar radiographyXDRS images have 384 x 200 pixels (200 is adjustable).XDRS images have 384 x 200 pixels (200 is adjustable).

Det

ecto

r ar

ray

Det

ecto

r ar

ray

Det

ecto

r ar

ray


1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1 10 100 1000

keV

Atte

nuat

ion

coef

ficie

nt (1

/cm

)

Water

Iron

Cement

XX--ray settings: voltageray settings: voltage

Iron 0.7310

Transmission

6 10-4

240.1410Cement350.1110Water

@ 400 keV

2 10-132.910Iron40.3210Cement180.1710Water

@ 100 keV%cm-1cm

μρThicknessMaterial

400

( ) tE

0

eII ρμ−=

Changing the voltage:Changing the voltage:•• Changes penetration (higher voltage, more penetration)Changes penetration (higher voltage, more penetration)•• Changes contrast between materialsChanges contrast between materials


Cu

rren

tXX--ray settings: currentray settings: current

Increasing the current of the XIncreasing the current of the X--ray tube increases the number of ray tube increases the number of photons collected and thus decreases image noise.photons collected and thus decreases image noise.

Currenthttp://www.mghradrounds.org/index.php?src=gendocs&link=2008_february


XX--ray imaging: resolutionray imaging: resolution

To improve To improve transaxialtransaxial resolution, the detectors can be resolution, the detectors can be collimated with lead platescollimated with lead platesImproved resolution comes at a cost in noise because fewer Improved resolution comes at a cost in noise because fewer photons are collected (e.g. increase current to compensate)photons are collected (e.g. increase current to compensate)


XX--ray imaging: scatter reductionray imaging: scatter reduction

Scattered photons contribute an unwanted background to Scattered photons contribute an unwanted background to the image and cause a loss of contrastthe image and cause a loss of contrastScatter can be reduced by collimating Scatter can be reduced by collimating the beam, the detectors or boththe beam, the detectors or both


XX--ray imaging: calibrationray imaging: calibration

Not all detectors have the same response:Not all detectors have the same response:•• Intrinsically different efficiencyIntrinsically different efficiency•• Different geometric efficiencyDifferent geometric efficiency

For this reason detectors are calibrated for:For this reason detectors are calibrated for:•• Dark current: Dark current: ddii

•• Efficiency: Efficiency: eeii

i

iii e

d - data Rawtmeasuremen Corrected =

Detector array2 4 3 3 2 1 2 4

85 92 98 99 97 97 91 84

di

ei


Imaging geometry: Imaging geometry: tomographytomography

Data for Data for tomographictomographic reconstruction are obtained by reconstruction are obtained by rotatingrotatingthe object and repeating the lateral the object and repeating the lateral scanscan..Rotation: 360Rotation: 360°° with 10 arc seconds repeatabilitywith 10 arc seconds repeatabilityLateral scan: 762 mm span with 10Lateral scan: 762 mm span with 10--um repeatabilityum repeatability

Det

ecto

r ar

ray


Tomography:Tomography:image reconstruction (I)image reconstruction (I)

Projection data are Projection data are backprojectedbackprojected

4 views

8 views

projection 0°

proj

ectio

n 90°

180 views

2 views

projection 0°

proj

ectio

n 90°

All images courtesy of S. Matej, UPenn


( )[ ] =•ℑℑ− 1

Ramp filter

Tomography:Tomography:image reconstruction (II)image reconstruction (II)

Projection data are filtered (multiplication Projection data are filtered (multiplication with ramp filter and inversewith ramp filter and inverse--Fourier Fourier transformed) and then transformed) and then backprojectedbackprojected

4 views

8 views

projection 0°

proj

ectio

n 90°

180 views

Filtered projection 0°

Filte

red

proj

ectio

n 90°2 views

All images courtesy of S. Matej, UPenn


Ramp filter

Tomography:Tomography:image reconstruction (III)image reconstruction (III)

A ramp filter works well in absence or with low noiseA ramp filter works well in absence or with low noiseIn real data noise is always presentIn real data noise is always present

•• A cutA cut--off frequency is introduced to reduce noiseoff frequency is introduced to reduce noise

A sharp cutA sharp cut--off causes ringing artifactsoff causes ringing artifactsApodizationApodization functions are used to reduce ringingfunctions are used to reduce ringing

•• HammingHamming•• HannHann•• CosineCosine•• …… and many, many othersand many, many others

Ramp filter with cut-off

Ramp filter apodized


Summary: 3 takeSummary: 3 take--away ideasaway ideas

XX--ray imaging essentially measures electron densityray imaging essentially measures electron density•• It does not measure emitted radiation nor identify isotopesIt does not measure emitted radiation nor identify isotopes

Current changes image noiseCurrent changes image noiseVoltage changes contrast and noise:Voltage changes contrast and noise:•• High voltage: good penetration, poor contrast (material High voltage: good penetration, poor contrast (material

discrimination) in light materials discrimination) in light materials •• Low voltage: poor penetration, better contrast in light materialLow voltage: poor penetration, better contrast in light materials s

Download - Principles of industrial digital radiography2011.radioactivewastemanagement.org/download/10a - ACCORSI.pdf · Principles of industrial digital radiography XDRS hands-on session JRC-Ispra,

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