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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

  • JRC Ispra6 July 2011

    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))

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    ++++

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    -

    -

    -

    -E

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

    ====

    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

    (E)

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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 10-4240.1410Cement350.1110Water

    @ 400 keV

    2 10-132.910Iron40.3210Cement180.1710Water

    @ 100 keV%cm-1cm

    ThicknessMaterial

    400

    ( ) tE

    0

    eII =

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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)

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    ( )[ ] = 1Ramp 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 902 views

    All images courtesy of S. Matej, UPenn

  • JRC Ispra6 July 2011

    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

  • JRC Ispra6 July 2011

    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 n

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