Reconstruction Methods for Coplanar Translational ... · 8 Laminography & Reconstruction 8.3 Ewert et al. - June 2015 Radiological Methods 8 Coplanar Translational Laminography: Star

1Laminography & Reconstruction

Ewert et al. - June 20158.3 RadiologicalMethods 1

Reconstruction Methods for Coplanar TranslationalLaminography Applications

U. EWERT, K.-U. THIESSENHUSEN, A. DERESCH, C. BELLON, S. HOHENDORF, S. KOLKOORI, N. WROBEL, B. REDMER, M. TSCHAIKNER, BAM, Berlin

www.bam.de [email protected]

Digital Industrial Radiology and Computed Tomography (DIR 2015) 22-25 June 2015, Belgium, Ghent - www.ndt.net/app.DIR2015



Content- Different laminographic methods

- Coplanar translational laminographic techniques

- Reconstruction techniques

- Fast filtered shift average technique (also FBP)

- Algebraic reconstruction techniques (ART)

- Applications of coplanar translational laminography (CTL)

- Welding

- Security

- Concrete impact measurements

- Artifacts of coplanar translational laminography

- Cross artifacts

- Overshoot at edges

- New ART technique: „Next to Base Plane MART” for reduction of artifacts



Laminographic methods:

• Translational laminography

• Planar Tomography

• Swing laminography

• Limited view CT

• Rotational laminography

• Tomosynthesis with free trajectories

Laminographic TechniquesTomosynthesis - Describes

reconstruction algorithm from incomplete set of projections.

Laminography – Describes acquisition geometry.



• Shift of X-ray tube parallel to detector plane• Acquisition of projections• Reconstruction

Coplanar Translational Laminography

Detector

Manipulator

Test object



Coplanar Translational Laminography

A classic algorithm of Computed Laminography is the

fast „Shift Average Algorithm“

Each projection is shifted “digitally” and the backprojection is performed by averaging of the related projection elements.

Profiles after Average Reconstruction

Pro

ject

ion

num

ber

Spatial coordinate

Averaging



Co-Planar Translational Laminography„Filtered Shift Average Algorithm“ as used in our applications

The X-ray tube is shifted with constant speed and projections are taken in equidistant steps.

Consequently, at longer SDD more projections are acquired for improved SNR

The projections are weighted considering the nonlinear angle stepping from projection to projection and the variation of the beam length.

A directional high pass filter is applied to achieve a filtered backprojection.

The reconstruction is performed in parallel beam geometry for fast reconstruction via GPU

A cone beam correction after reconstruction is used for geometric correction.

Num

ber

of r

econ

stru

ctio

n la

yer

Position in reconstruction space



Translational Laminography: Artifacts

Cross artefakts

Limited View reconstruction (±45°) : No information from dead angle, high projection number

Artifacts Cross artifacts are almost the same for FBP and ART . Overshoots of intensities are similar for FBP and ART .

Filtered Shift Average Algorithm (FBP) vs. Algebraic Reconstruction Technique (ART)

Filtered Shift Average reconstructionVery fast

ART

Reconstruction ofsimulated data set,

± 45°, 500 projections

Overshot Reconstruction of 3 lead balls



Coplanar Translational Laminography: Star Artefacts

Filtered shift average reconstruction (FBP) and effect of dead angle

aRTist modeling of a star crack phantom in a weld (16 mm thickness)

Crack notches 150 x 0,2 x 1 mm³

All notches are visible Notches at 2°and 3°to reconstr uction direction are visible

with reduced contrast

Reconstruction angle ± 45°200 projections



New pipe scanner for in-service inspection of circumferential welds withoverview RT and cross section laminography

Applications: TomoWELD Pipe Scanner

X-ray tube

Manipulator: AREVA X-ray tube: rtw Detector: XCounter/Ajat

Photon counting DDA

360°rotation

15°tilted to pipe axis



Test of TomoWELD-Scanner in NPP at secondary circuit pipe, Block I

Field Test in a Nuclear Power Station

Mounting of scanner at pipe

Block I is not in use since 2011.

Block II will be operated until 2022 latest.

www.enbw.com/kernkraft



Evaluation in three views permits the evaluation by different standards

KTA 3211.4 in service inspectionISO 5817 cross section evaluationDIN 25435-7: 2015 RT-practice

Inner surface t = 16 mm

Slag inclusion

Undercut

Digital radiograph

Indications permissible andin agreement with indications found after manufacturing

Field Test in a Nuclear Power StationTest of TomoWELD-Scanner in NPP at secondary circuit pipe, Block I

Slag inclusion

Slag inclusion

Length 1.6 mm

Slag inclusion

depth

width

Outer surface



Co-Planar Translational Laminography

Applications for Large Objects

Laminography withHigh Energy X-raY Technology

Scanning DDA or LDAScanning source

PhiS PhiO

Source Object Detector

PhiD Laminographic Focussing with DDA Scan



Aviation Security (Project SiLuFra) High‐energy X‐ray imaging

of air freight containers

Matrix

detector

Air freight container

X‐ray source (7.5 MV)

Container content

•Computer screen•Electronic printer•Steel pipe•Automobile parts•Simulated dangerous objects

High‐resolution (400µm) X‐ray imaging

Detection of complex patterns of materials

Flexible rotation of source and detector

Matrix detector

X‐raysource

Detector

tower

Source tower

Rotary table



Region of interest (R1) Region of interest (R2) Region of interest (R3)

DARC alarm (insufficient penetration) bottle filled with dangerous material

R1

R2

R3

pattern of simulated IED mock-up

Mobile High-Energy X-ray Imaging of Air Freight Containers

CTL withScanning DDA



Concrete Impact Sample with 2 Layers of Steel Reinforcement, 1.5 x 1,5 m² , 7.5 MV

HEXY-Tech and laminogrphy offirst enforcement layer in the concrete blockand orthogonal views.Measured with scanning DDA.

Front view

Side view

Cross view

Cro

ss v

iew



Coplanar Translational Laminography: Artefacts

Fast filtered Shift Average method (modified FBP) vs.

Simultaneous-Algebraic Reconstruction Technique (S-ART)

Cracks in a concrete block after impact 1.5 x 1.5 x 0,3 m³

Fast filtered Shift Average method

Simultaneous-Algebraic Reconstruction Technique

Horizontal steel reinforcement visible, but without depth information,Better visibility of volumetric indications and better CNR

Horizontal steel reinforcement missing

Reconstruction angle ± 8°



Translational Laminography: Artifacts

Reduction of artifacts by „next to base plane“ multiplicative S-ART

S-ARTNew:NBP – MART

Limited View reconstruction (±45°) : No information from dead angle, high projection number

Artifacts Artifact reduction by multiplicative S-ART next to base plane . Prior condition: Do not allow that indication intensities cross the base plane1st Reconstruction result cannot provide values below base plane2nd Reconstruction result cannot provide values above base plane Combination of both reconstructions if required.



„Next-to-Baseplane“ Multiplikative ART

Measurement and preprocessing of projections

Initial assumption,e.g. unfilteredbackprojection

Calculate projections

Iteratedreconstruction

matrix

Correction bycomparison with measured data

Result

Forward projection

Multiplicative; consider base plane, no change of sign in projection

Logarithmization, subtract base plane

),,( iyxQ

),,( iyxP

shyxQabs

shyxPabsyxK

i

ii )],,([

)],,([),,(

shyxQabs

shyxK

ii )],,([),,(

Correction term at same sign of P und Q

Correction if different signs will be permitted



NBP-MART

NBP – next to base plane MART

Special reconstruction for objects with low amount of indications as e.g. welds.

An indication size is selected which is extracted with a modified Median high-pass.

The NBP-MART can be overlaid onto the FBP reconstruction for better visualization.

Shift average reconstruction

Combination of NBP-MART for the short scaled fraction with an FBP

NBP-MART



- Laminography is used if CT is not applicable.

- The fast shift average reconstruction and ART-based reconstruction have proven to be successful techniques for measurements with high number of projections and limited view conditions (e.g. ± 45°).

- ART-based reconstructions provide acceptable reconstruction results if a limited number of projections is used, but fine cracks may be missed.

- Both construction techniques generate cross artefacts and edge overshoots..

- The new ART-technique, „next to base plane-MART“, was developed and tested to reduce cross artefacts and overshoots.

- A base plane is calculated by a Median based high pass filter.

- The NBP-MART iteration is controlled in a way that the sign of a structure indication will be maintained in relation to the base plane.

- Coplanar translational laminography was successfully tested for evaluation of

- Welded cross sections,

- Complex cargo structures and

- Large concrete impact samples.

Summary



End

[email protected]

z

x

zz

x

z

xx

z

FBP ART NBP - MART

Acknowledgement:We thank A. Rogge, F. Hille and M. Grunwaldfor concrete samples and interesting discussions.

Reconstruction Methods for Coplanar Translational ... · 8 Laminography & Reconstruction 8.3 Ewert et al. - June 2015 Radiological Methods 8 Coplanar Translational Laminography: Star

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