Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

3D TeraHertz Tomography

B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3

J-P. Caumes,2 and E. Abraham1

1LOMA, Université de Bordeaux / CNRS2ALPhANOV, Centre Technologique Optique et Lasers, Université de Bordeaux

3LaBRI, Université de Bordeaux / CNRS351 cours de la Libération

33405 talence Cedex, France

Journées Problèmes Inverses - IMS - IMB - LaBRI - Avril 2011

1/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Outline

Introduction about TeraHertz Tomography

THz Imagery and properties of THz radiations,

Reminder about tomographic principles,

Two acquisition systems.

TeraHertz Tomography : first results

Reminder about usual tomographic reconstruction methods,

Result comparisons (reconstruction method, the projection number, materialcharacteristics),

Acquisition limitations (CW and TDS).

Applications and Perspectives

Inspection of opaque objects (composed of teflon, foam, metal, ...),

Archeology : imaging of potteries.

Investigated acquisition optimizations and reconstruction models.

2/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

THz Imagery : Principles

Properties

THz region between microwave (100GHz) and infrared (10THz),

Wavelength between 30µm and 3mm,

Contrary to X-Ray THz radiation is non ionizing and low-energy (1 and 40meV ).

Two Principles

Passive Imagery : capture of THz natural emission object : security systems,Active Imagery : source focalized on the object + detector measuring variation :

spectroscopy : to determine the composition of an object,3D Laser scan : to acquire the external surface of the object,

3/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

THz Imagery : Principles

Known limitations

T-Ray propagation can not be correctly described by a geometrical ray line,

Diffraction or scattering effects blur or deform the acquired signal,

Complex objects signal analysis are complicated by multiple reflections andrefractions of THz radiations.

Signal advantages for THz Imagery

The signal can go through particular matter :

Transmission process,

THz Imagery (applications in Archeology),

Investigations in THz Tomography.

4/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Reminder about tomographic principles

Definition

Imagery technique to reconstruct the volume of an object from a set of non invasivemeasures acquired from the exterior of the object.

Modeled in continuous domain by the Radon Transform [Radon 1919]

Acquisition proccess : to get the projections (direct transform),

Reconstruction process : inverse Radon transform or Fourier space reconstruction.

5/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Reminder about tomographic principles : Acquisition

(a) (b)

Figure: (a) Projection line defined by an angle θ and a module ρ. Its value corresponds to theray attenuation going through matter (data modeled by the function f (x, y)) along the blueline. (b) Data given by only one projection does not allow the reconstruction of f .

Direct Radon Transform

Rθ(ρ) =∫ ∞−∞

∫ ∞−∞

f (x , y)δ(ρ− x cos θ − y sin θ)dxdy (1)

6/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Reminder about tomographic principles : Reconstruction

(a) (b)

Figure: (a) Acquisition following several angles. (b) Intersection of data contained on theprojection set allows a better recovering of the original domain f .

Retroprojection (Inverse Radon Transform)

f (x , y) =∫ π

0

∫ ∞−∞Rθ(ρ)δ(ρ− x cos θ − y sin θ)dρdθ (2)

7/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Two THz acquisition systems : Pulsed THz Acquisition

Properties

Pulse source used in spectrocopy,

Non destructive and contactless imaging,

Transparent to amorphous materials, plastic, tissues, paper, wood, ...

Strong interaction with polar molecules (H2O for instance),

Acquisition system

8/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Two THz acquisition systems : Pulsed THz Data analysis

Acquisition data

Amplitude, Temporal response (delay), Spectral response.

Create sinograms from all available data.

Ampl.

Delay

9/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Continuous Wave THz Tomography : Acquisition

Acquisition System

A continuous signal with a wavelength around 1mm is emitted by a diode Gunn.

The signal is focalized on the objet (translation XZ - rotation Y),

Signal attenuation is measured by a infrared thermal sensor.

Differences Between pulsed and CW Acquisitions

Pulsed Acquisition Continuous WaveAcq.

Frequency 1 femtosecond (1to 10THz (each80MHz)

A continuous milli-metre wave (0.1 to0.4THz)

Type Transmission Transmission and Re-flexion

Scan Area 100 × 100mm2 100 × 100mm2Resolution(diffractionlimited)

10µm to 300µm 1 to 3mm

Measures Temporal (Am-plitude) / Delay(Phase) / Spectral

Delay

Acquisition(Nθ = 18,1002)

between 2 and 3 days 3 hours

Object Pro-perties

very low-density andlow-thickness objects

less sensitive to thedensity and thicknessof acquired objects

10/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

TeraHertz Tomography : Reconstructions

State of Art

Investigated at the origin by Physician Labs (Fergusson [2004]),

Coupled with Spectroscopy analysis and 3D laser scan (object surface),

A method becames a standard : BFP,

A main goal : reduce the acquisition time (i.e. projection number).

Investigation about others methods

Comparison analysis of the results obtained from BFP, SART and OSEM :

Quality loss according to the number of projections (measured by SSIM),

Precision comparison between the three methods (measured by PSF).

11/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

TeraHertz Tomography : Reminder about usual methods

Backprojection of Filtered Projections

I (i, j) =Nθ−1∑iθ=0

Nρ2∑

ρ=−Nρ2

Wθ(iθ )(ρ)∆(ρ − jcosθ(iθ ) − isinθ(iθ )) (3)

with :

θ(iθ ) = iθπNθ

,

Wθ (ρ) =

Nρ2∑

ν=−Nρ2

|ν|

Nρ2∑

ρs =−Nρ2

Rθ (ρs )e−i2πρsν

ei2πρν (BFP).

Iterative methods (SART - OSEM)

Iterative update of each pixel using all or a part of (sub-iterations) the projection setuntil convergence.

I (i, j)k+1 = I (i, j)k

Nθ−1∑iθ=0

Nρ−1∑iρ=0

pk(θ, ρ, i, j)Rθ (ρ)

Rkθ

(ρ)

Nθ−1∑iθ=0

Nρ−1∑iρ=0

pk(θ, ρ, i, j)

(4)

12/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

TeraHertz Tomography : Precision (PSF) results

(a) (b)

Figure: Sinograms of two metallic bars (12mm diameter)separated by 50mm, with a projection number Nθ = 72. (a)Ideal theoretical acquisition. (b) Acquisition using themillimeter wave tomographic scanner with the 110GHzsource.

(a) (b) (c) (d)

Figure: Cross sections of two metallic bars (12mm diameter)separated by 50mm.(a) Ideal theoretical imagereconstruction from 3(a). (b) BFP reconstruction from 3(b).(c) SART reconstruction from 3(b). (d) OSEMreconstruction from 3(b).

Figure: Intensity profiles along thehorizontal line intercepting the center of bothmetallic bars.

13/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

TeraHertz Tomography : Quality (SSIM) results

Nθ = 12 Nθ = 18 Nθ = 24 Nθ = 36 Nθ = 72(a)

(b)

(c)

Figure: Manufactured sample reconstructions using sinograms with12, 18, 24, 36, 72 projections and the BFP (a), SART (b) andOSEM (c) methods.

(a) (b)

Figure: (a) Photograph of original object :parallelepiped black foam (41 × 49) mm2 with 2holes, diameter 15mm (1 hole with air and 1hole containing a Teflon cylinder with a 6mmcylindrical air hole inside). (b) Sinogram withNθ = 72 projections (lines) and Nρ = 128samples per projection (columns).

Figure: Manufactured sample SSIM parameter asa function of the projection number and thereconstruction method.

14/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

TeraHertz Tomography : Quality results according to material characteristics

Phantoms reconstructed from CW acquisitions

Acquisition of phantoms made of Foam or Teflon, with hole or metallic bars,

18 projections sized around 100× 100.

Foam (n0 = 1.05)Cyl./Hole Cube/Hole Cube/Metal

BFP

SART

EM

Contours are well reconstructed (buthypersignal − > refraction losses),

Inner hole is visible,

Metallic bar − > hypersignal.

Teflon (n0 = 1.55)Cube/Hole Cube/Metal Cyl./Metal

Refractions are more important,

Inner hole is visible in the cube buthypersignal,

Matter coherence is lost.

15/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Limitations of the Acquisition system

Acquisition Limitations

Acquisition limitations depend on physicaland optical properties :

Absorption (by polar molecules),Refraction Losses.

TDS Refraction Losses CW Refraction Losses

Hypersignal and Interfaces

Hypersignal at interfaces due to the signal losses,

Hypersignal at contours in reconstructed images,

Non uniform signal loss near the interfaces.

16/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Applications

3D Internal Inspection ofindustrial materials

Archeology (volume inspection)

17/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Applications : Video samples

Matriochka

Figure: Matriochka

Volume

Figure: Urne Volume

OrthoSlice

Figure: Orthoslice

Surface

Figure: Surface

18/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First Results

Applications and Perspectives

Conclusion and Perspective

Conclusion

Pulsed or Continuous THz allows 3D-Tomography of opaque objects but :

Refraction losses makes it difficult in TDS to identify the amplitude and timedelay,

Non uniform losses around the interfaces.

Perspectives

Replace sensor/detector by 2D camera :to increase the acquisition time (but with the risk of ghosts),to get a subset of refracted signal and extract a priori object properties for thereconstruction.

Improve the spatial resolution (using super-resolution),

Develop specific reconstruction methods based on a non-linear / discontinuousattenuation to take into account the refraction losses.

19/19 B. Recur,3 A. Younus,1 S. Salort,2 P. Mounaix,1 B. Chassagne,2 P. Desbarats,3 J-P. Caumes,2 and E. Abraham13D TeraHertz Tomography

Introduction about TeraHertz TomographyTeraHertz Tomography : First ResultsApplications and Perspectives