MULTI-MODE TFM IMAGING WITH ARTEFACT FILTERING USING CIVA UT FORWARD MODELS

Transcription

1 MUI-MODE FM IMAGING WIH AREFAC FIERING USING CIVA U FORWARD MODES Ekaterina IAKOVEVA Sylvain CHAION hilippe BREDIF Steve MAHAU CEA-IS, Saclay

2 OUINE 1. Imaging algorithm otal Focusing Method (FM) 1.1. Full Matrix Capture Acquisition 1.2. FM post-processing 1.3. Multi-mode FM 1.4. Fusion of FM images 2. Imaging artefacts: analysis tools and filtering 2.1. Echo ransformation Method (EM) 2.2. Filtering of artifacts in corner echoes reconstructions 3. Conclusions & perspectives

3 FU MARIX CAURE ACQUISIION otal Focusing Method N successive shots (N : nb of elements) One shot: 1 transmitting element All elements receiving ransmit Receive Acquisition N elements N N elementary signals S ij (t) S 11 (t) Flaws S 12 (t) S 13 (t) NB : Other acquisition modes allow to perform array imaging with less data : lane wave imaging Sparse Matrix Capture S NN (t)

4 FM OS-ROCESSING otal Focusing Method ost-processing A posteriori synthetic focusing by coherent summation of all the received S ij (t) signals for all points of the region of interest Acquisition N elements N N elementary signals S ij (t) Elt n j Elt n i A 11 () S 11 (t) ij () x Region FM Of Interest Image (ROI) A 12 () A 13 () S 12 (t) S 13 (t) Algorithm: Computation of all times of flight ij () for all pairs of transmit and receive elements (i;j) Summation of NxN amplitudes A ij () = S ij [t = ij ()] at each image point A NN () S NN (t)

5 MUI-MODE FM otal Focusing Method Objective: Imaging of extended defects of complex geometry using several propagation modes (direct or over skip imaging) and several types of waves (). Commonly used reconstruction modes: Direct mode Corner echo mode Indirect mode x Rx x Rx x Rx or 4 possible paths : 8 possible corner echoes : 16 possible paths :,,,,,,,,,,... Other possible reconstruction modes: x Rx x RX or

6 MUI-MODE FM otal Focusing Method Example of multi-mode FM reconstruction on planar geometry. Simulation of the FMC acquisition with 3 notches at different locations /orientations 3 Regions Of Interest FMC simulation inear array 2 MHz 42 elts : longitudinal wave : transverse wave Direct echo: ip diffraction Corner echo Indirect echo : Specular reflexion provide : Full image of the notch ip diffraction Multi-mode FM complementary indications!

7 FUSION OF FM IMAGES otal Focusing Method Fusion of data allows a simultaneous use of FM images Sum of FM images Observation of complementary indications (tip diffraction + corner echo) Characterization: - lanar defect - Height and orientation can be known

8 IMAGING ARIFACS : ANAYSIS OOS AND FIERING Multi-mode FM reconstruction on planar geometry with full ROI FMC Simulation O45, 1Mhz, 32 elts Backwall echo? ip diffraction Direct echo d Full image ROI Breaking notch? Corner echo Direct echo d?? Corner echo d roblem: Some FM images contain the indications without physical meaning (imaging artifacts) : Risk of misinterpretation o fully exploit potential of multi-mode, development of analysis and filtering tools of imaging artifacts are needed

9 IMAGING ARIFACS : ANAYSIS OOS AND FIERING Origin of the most commonly seen artifacts: For each given pair of x/rx element, one given echo may be associated to different reconstruction paths. FM post-processing of one elementary signal: Signal S ij (t) Direct echo d R j R Backwall echo j E i E i Direct echo d * he paths E i R j and E i * R j have identical time of flight Amplitude at the reconstruction points and * related to the backwall echo detected in direct mode d

10 IMAGING ARIFACS : ANAYSIS OOS AND FIERING Origin of the most commonly seen artifacts: For each given pair of x/rx element, one given echo may be associated to different reconstruction paths. FM post-processing of all acquired data: Direct mode d Direct mode d Backwall echo Artifact induced by backwall echo detected in mode d Flaw and/or geometry echoes detected in some reconstruction mode can induce the artifacts in other reconstruction mode when there is a coincidence of time of flight. Objective: rovide tools needed to predict the artifacts associated with different indications in reconstruction mode d (flaw echo, backwall echo) in other reconstruction modes (d, d, ).

11 ECHO RANSFORMAION MEHOD (EM) Imaging artifacts Echo ransformation Method - analysis tool of indications present in FM images. Algorithm : Step 1 : For a FM image obtained with one reconstruction mode, selection of ROI containing an echo whose origin is identified. Step 2 : Extraction of time of flight data associated with each point of ROI. Step 3 : FM post-processing with another reconstruction mode only using the time of flight data selected in step 2. Step 4 (filtering): FM post-processing with another reconstruction mode without using the time of flight data selected in step 2. Mode d ransformation of ROI in reconstruction mode d Full data Mode d ROI Artifact induced by backwall echo detected in direct mode d (can be shown using EM) ransformation Mode d with filtering Comparison Filtering Artifact induced by backwall echo detected in direct mode d

12 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Example of corner echo reconstruction on planar geometry: Corner echo d Breaking notch Artefact induced by backwall echo (can be shown by EM) Objective: Filtering of imaging artifacts induced by backwall echo from FM corner echoes reconstructions. Method 1: Filtering using echo transformation method (EM). Method 2 : Filtering of the backwall echoes from the acquired data. Method 3 : Filtering of paths without physical meaning by applying an angle criterion (parametric and weighting filters).

13 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 1: Echo transformation (EM) Application of EM on a planar component: Direct echo d ROI Corner echo d Filtered corner echo d Step 1: Selection of ROI containing the backwall echo Step 2: ransformation of selected ROI in corner echo mode Step 3: Filtering Corner echo d without filtering Corner echo d with filtering Breaking notch Artifact induced by backwall echo Suppression of artifacts due to backwall echo Inconvenience : Starting with area containing an echo whose origin is identified (not always possible).

14 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 2 : Filtering of the backwall echoes from the acquired data rinciple: Geometry of the inspected component must be known for FM corner echo reconstruction. Elimination of backwall echoes from the acquired data (using simulation tools for example). erform a FM corner echo reconstruction from a filtered data. Application on a planar component: Corner echo d without filtering Corner echo d with filtering Artifact induced by backwall echo Inconvenience : Simulation of the backwall echoes. Suppression of artifacts due to backwall echo

15 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : arametric filter rinciple: Filtering of paths without physical meaning by applying an angle criterion. Elimination of paths for angles (θ) between incident and reflected direction > maximum aperture θ max. Corner echo reconstruction without physical meaning: transmit receive θ Elimination of paths for θ θ max where θ max is an arbitrary value

16 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : arametric filter rinciple: Filtering of paths without physical meaning by applying an angle criterion. Elimination of paths for angles (θ) between incident and reflected direction > maximum aperture θ max. Application of parametric filter on a planar component: Corner echo d without filtering Corner echo d with filtering: Elimination of paths for θ > 130 Suppression of artifacts due to backwall echo Elimination of paths for θ > 150 Inconvenience : - Useful paths can be eliminated. - Setting the value of θ max.

17 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : Weighting filter rinciple: Filtering of paths without physical meaning by applying an angle criterion. Elimination of paths for angles (θ) between incident and reflected direction by introducing the function f ( ) f ( ) : f ( ) cos 1 cos( ( / 2 ) 2 2 ) 1 f ( ) 0 si si 0 For each image point, the FM corner echo image is formed as: I( ) M N i 1 j 1 f ij ( ) S ij ( t ij ( ))

18 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : Weighting filter rinciple: Filtering of paths without physical meaning by applying an angle criterion. Elimination of paths for angles (θ) between incident and reflected 2 direction by introducing the function f ( ) f ( ) cos / 2 Application of weighting filter on a planar component: Without filtering: With filtering: Corner echo d Corner echo d Corner echo d Corner echo d Advantage: not need to set the value of θ max

19 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : Weighting filter Application of weighting filter on a weld root profile: simulated data FMC acquisition inear array 4 MHz, 24 elts Breaking notch Region of interest Direct echo d Without filtering: Corner echo d With filtering: Corner echo d Backwall echo Artifact induced by backwall echo Artifacts induced by backwall echoes are removed Risks of misinterpretation significantly reduced Suppression of artifacts due to backwall echo Corner echo

20 Imaging artifacts FIERING OF ARIFACS IN CORNER ECHO MODE Method 3 : Weighting filter Application of weighting filter on weld root profile: experimental data FMC acquisition inear array 4 MHz, 24 elts Region of interest Without filtering: Corner echo d Corner echo d Corner echo Breaking notch Artifacts induced by backwall echo With filtering: Corner echo d Corner echo d Corner echo Artifacts induced by backwall echoes are removed Risks of misinterpretation significantly reduced Suppression of artifacts due to backwall echo

21 CONCUSIONS & ERSECIVES Multi mode FM reconstructions provide complementary indications Fusion of data allows a combined use of multi-mode FM images. But possible risks of misinterpretation induced by reconstruction artifacts. New analysis & filtering tools based on CIVA U forward models are developed. he new methods are valid for 2D & 3D multi-mode FM imaging. Corner echo 3D view Slice XY erspectives: Slice YZ Development of new processing techniques to enhance multi-mode FM imaging. Development of flaw characterization tools based on FM images.