phasecontrast xray imaging in two and three dimensions · slide: 1 phasecontrast xray imaging in...
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Slide: 1
Phasecontrast xray imagingin two and three dimensions
P. Cloetens Propagationbased phasecontrast imaging
the forward problem; Fresnel diffraction coherence conditions
The inverse problem phase retrieval methods holotomography
Recent developments Projection microscopy KBbased imaging
Slide: 2
Phase Contrast vs Absorption
Absorption
Sample Sample
PhaseSimple transmission
• Dream 2: Improve the Sensitivity Absorption contrast too low high spatial resolution
light materialssimilar attenuation
• Dream 1: Zero DoseIncrease the energyAbsorption contrast ↓ replaced by phase contrast
Slide: 3
Transmission through a sample
∆z
refractive index n = 1 δ + iβ
Transmission functionprojection of the refractive index distribution
uinc(x,y) u0(x,y) = T(x,y). uinc(x,y)z
xy
e ikmedium
z=e
i 2
n z=e
i 2
z. e
−i 2
z. e
−2
z
T(x,y) = A(x,y).eiϕ(x,y)
Phase
Amplitude
x , y =0−2 ∫x , y , z dz
A x , y =e−B x , y =e
−2∫ x , y , z dz
Slide: 4
Phase contrast vs Absorption
Gain of up to a few 1000 !
Hard XraysWater window
BeC
Al
FeAu
Energy (keV)
Slide: 5
Phase Sensitive Techniques
Phase Retardation
s∆−=∆ .2 δλπϕ∆s
Deflection⇔
Phase gradients∆α ~ µrad=−
2∂
∂ x
At zero distance:Intensity
⇒ all phase information is lost
I 0=∣u0∣2=I inc .exp −∫ dz
Slide: 6
Phase Contrast Imaging methods
Analyzerbased PCI
Gratingbased PCI
Propagationbased PCI
ID17Medical Imaging
BM05/ID19wavefront sensorCh David, F PfeifferT Weitkamp
ID19 / ID22NIEdge enhancementHolotomography
Slide: 7
edge detection versus holography (Fresnel diffraction)
each edge imaged independentlyno access to phase, only to border
access to phase, if recorded at ≠ D’sdefocused imageλ = 0.7 Å
50 µm
D = 0.15 m D = 3.1 m
towardsFraunhoferdiffraction
D≪a D≈a
Slide: 8
Simulation
Direct Space Reciprocal SpaceOBJECT
multiplication wave withtransmission function
convolutionT = eB eiϕ
PROPAGATION
diffraction integral multiplication FT wave withpropagator PD = exp(iπλDf2)
INTENSITY
autocorrelation
ü
IDcoh x,y( ) = u(x,y)
2
COHERENCE / DETECTORmultiplication FT intensity withdegree of coherencedetector transfer function
|µ12
(λDf)|R(f)
convolution intensity withprojected sourcePSF detector
Known Object ⇒ Image
Slide: 9
Simulation
λ = 0.52 ÅD = 0.4 m
Hole =dodecahedron seen
along the 2fold axis
2 4 6 µm
Simulations
Porosity in Quasicrystals
Known Object ⇒ Image
Slide: 10
Fresnel diffractionD
u0(x,y) uD(x,y)
For example at λ = 0.5Å (25 keV)a = 1 µm ⇒ D = 10 mma = 40 mm ⇒ D = 16 m
First Fresnel zone determines the sensed lengthscale Distance to be most sensitive to object with size a Dopt=
a2
2
In principle: complete object contributes to a point of the image In practice: only finite region: first Fresnel zone
radius r F= D
Slide: 11
Contrast Transfer Functions
Fourier Transforms of the intensity and phase are linearly related
phase contrast factor
ID(f) = δDirac(f) 2 cos(πλDf 2) . B(f) + 2 sin(πλDf 2) . ϕ(f)
2
1
0
1
2
0 0.5 1 1.5 2 2.5
amplitudephase
contrastfactor
frequency
valid in case of a slowly varying phase, weak absorptionamplitude contrast factor
Slide: 12
Variable period
2 µm
period 720 nm≈
period 610 nm≈
Contrast depends strongly on period or spatial frequency
period 530 nm≈
Object invisible !
Decreasing linewidthIncreasing spatial frequency
Slide: 13
Spatial Coherence
Hard Xray / neutron sources are ~ incoherent
Wave is partially coherent when the source is small and far
source object detector
s αblurring= z2.α= z2/z1.s
z1 z2
szl
2.
21
cohλ
αλ ==
Feature size a (1/f)Dopt=
a2
2|µ12(λDf)|
lcoh > a / 2
Transverse coherence length
Slide: 14
Temporal Coherence Incoherent sum of intensity for different wavelengths Approximation:
second coherence envelope transfer function ID(f) = δDirac(f) + sinc(∆λDf 2/2) . 2 sin(πλ
0Df 2) . ϕ(f)
2
1.5
1
0.5
0
0.5
1
1.5
2
0 2 4 6 8 10
=0
=0.05
2
1.5
1
0.5
0
0.5
1
1.5
2
0 2 4 6 8 10
Slide: 15
Edge Detection
Essentially edge enhancementWeak defocusing (and weak contrast!)
Radiography (2D)
Tomography (3D)
Detection of cracksholesreinforcing fibres, particles
absorption term refraction termLaplacian refractive index
aD <<λ
absorption image phase term2D Laplacian phase
I D x , y ≈ I 0 x , y . [1− D2
xyx , y]
o x , y , z ≈ x , y , z − D .xyzx , y , z
Slide: 17
Insect Anatomy
Virtual slices through heads of tiny staphylinid beetles
100 µm
O. Betz (Univ. Tuebingen), U. Wegst, D. Weide et al, J. Microscopy, 227, 51 (2007)
Slide: 18
Phase Retrieval
How to retrieve the phase and amplitude in the object plane?
Phase in image plane is lost
Image(s) ⇒ Object ???Inverse Problem
Slide: 19
Phase retrieval and holography
ID f = ∣∣2D
* e−iD f 2
f e iD f 2
*− f NonLin.
e iD f 2
ID f ≠0 = * f e i 2D f 2
* − f Backpropagation
FT object FT conjugate object
e iD1
f 2
I 1 f ≠0 = * f e i2D
1f 2
*− f
⋮
e iDN
f 2
IN f ≠0 = * f ei 2D
Nf 2
*− f
Multiple distances to avoid twin image problem
Consider weak object
kinc κ.kinc
k T x =x ⟨x ⟩=0with
Slide: 20
Phase Retrieval in practice
Flemish School: D. Van Dyck, P. Cloetens, JP GuigayTransfer Function Approach / Focus variation
D1 D2 Dn
Series of images recorded at different distances
Each distance is most sensitive to a specific range of spatial frequencies
Australian School: K. Nugent, T. Gureyev, D. PaganinTIE (transport of intensity) ∂ I
∂ z=−
2∇ I ∇
Slide: 21
Phase Retrieval: multiple distances
• nonabsorbing foam• 4 images recorded• E = 18 keV D
D = 0.21 m D = 0.51 m D = 0.90 mD = 0.03 m
50 µm
Dvariable
K=∑m∣I m
exp f −I m
calc[ f ]∣2
Least squares minimization of cost functional
Slide: 22
Holotomography
3D distribution of δ or the electrondensityimproved resolutionstraightforward interpretation
processing
2) tomography: repeated for ≈ 1000 angular positions
PS foam
1) phase retrieval with images at different distances
Phase mapD
P.Cloetens et al., Appl. Phys. Lett. 75, 2912 (1999)
Slide: 23
Phase retrieval: transfer function approach
)sin( 2Dfπλ“transfer function”
Noniterative (fast!)
⇒ Optimizationof the choice of distances
1/N∑m sin2 Dm f 2
4 distances
Linear least squaresI m f =2sin Dm f 2
f
f =∑m sin Dm f 2
I m f
∑m2 sin2
Dm f 2
Slide: 24
Phase retrieval: regularization
Remains illposed for low spatial frequencies Requires regularization:
e.g. limit the energy of the solution
K=∑m∣I m
exp f −I m
calc[ f ]∣2∣ f ∣2
Model error Regularization error
f =∑m sin Dm f 2
. I m f
∑m2sin2Dm f 2
⇓
Slide: 25
Phase Tomography of Arabidopsis seeds
3D structure of Arabidopsis seeds in their native state wet sample, no preparation no staining, no fixation, no cutting, no cryocooling
Holotomographic approachContrast proportional to the electron density4 distances, 800 anglesE = 21 keV
P Cloetens, R Mache, M Schlenker, S LerbsMache, PNAS (2006) 103, 14626
Slide: 26
Phase Tomography of Arabidopsis seeds
Holotomographic approachFour distancesE = 21 keV
Seed of Arabidopsis
30 µm
Tomographic Slices
CotyledonP Cloetens, R Mache, M Schlenker, S LerbsMache, PNAS (2006) 103, 14626
Slide: 27
Phase Tomography of Arabidopsis seeds
Seed of Arabidopsis
protoderm
organites(protein stocks)
tegumenintercellular spaces
10 µm
Tomographic Slice
5 µm
Slide: 28
Phase Tomography of Arabidopsis seeds
threedimensional network of intercellular air space
gas exchange during germinationand/orrapid water uptake during imbibition
Role?
Seed of Arabidopsis
P Cloetens, R Mache, M Schlenker, S LerbsMache, PNAS (2006) 103, 14626
Slide: 29
Phase retrieval: mixed approach (absorption case)
Transfer function approach is robust, optimized solutionbut it is only valid for weak absorption
Transport of Intensity Equation (TIE) is 'exact' (∆D → 0)but contrast is not optimized, less robust
Merge and extend validity of both methods
Leads to a 'moderately iterative' solution (35 iterations)valid for slowly varying objects
I D f =I D=0
f 2sin D f 2FT {I 0} f cosD f 2
D2
FT {∇∇ I 0} f
Perturbation termTransfer function like
JP Guigay, M Langer, R Boistel, P Cloetens, Opt. Lett., 32, 1617 (2007)
Tafforeau P., Kaminskyj S.Tafforeau P., Kaminskyj S.
Absorption
D = 6 mm
Oldest terrestrial fossil plant from Rhynie (Scotland)
100 µm
Tafforeau P., Kaminskyj S.Tafforeau P., Kaminskyj S.
Phase contrast
D = 100 mm
Oldest terrestrial fossil plant from Rhynie (Scotland)
100 µm
Tafforeau P., Kaminskyj S.Tafforeau P., Kaminskyj S.
Phase contrast
D = 300 mm
Oldest terrestrial fossil plant from Rhynie (Scotland)
100 µm
Tafforeau P., Kaminskyj S.Tafforeau P., Kaminskyj S.
Holotomographic reconstruction
Oldest terrestrial fossil plant from Rhynie (Scotland)
100 µm
Slide: 34
Phase retrieval: regularization using a prior estimate
Can the absorption provide the low spatial frequencies? Prior estimate (cf homogeneous object – phase/attenuation duality)
f =∑m
sin Dm f 2 . I m f
prior f
∑m2 sin2
Dm f 2
prior
f =−
B f
⇓
Use this as a prior estimate (different from a constraint)K=∑m
∣I mexp
f −I mcalc
[ f ]∣2∣ f −prior
f ∣2
Model error Regularization error
M Langer, P Cloetens. F Peyrin, submitted to IEEE TIP
Slide: 35
Phase retrieval: automatic parameter selection
How to determine the regularization parameter ε ? Automatic using Lcurve method !
Follow curve log(regularization error) vs log(model error) Use point of maximum curvature
M Langer, P Cloetens. F Peyrin, submitted to IEEE TIP
Slide: 36
Phase retrieval: prior estimate
Prior estimate from absorption and automatic parameter selectionWithout prior estimate With prior estimate
Slide: 37
The NanoImaging Project
Projection Microscopy PXMStructureDose efficient, fastPhase contrast
Fluorescence mapping XFMMicroanalysisSlowTrace elementsPhase contrast
Slide: 38
Projection Microscopy (PXM)
objectz1 z2 detector
equivalent toD
+
Plane wave illumination Magnification
Limit casesz1 >> z2
D = z2 ; M = 1z1 << z2
D = z1 ; M = z2/z1
Prop. by D Van Dyck, J Spence
M=z1z2
z1D=z1 . z2
z1z2
Slide: 39
Projection Microscopy
D = 225 mmM = 17
D = 175 mmM = 22
D = 125 mmM = 31
E = 20.5 keVExposure time = 1 s (16bunch)
≤ 50 ms (ID22NI)
Towards focus
D = 45 mmM = 87
10 µmNeuron cells
No Xray optics behind the sampleDose efficient
Slide: 40
D = 175 mmD = 125 mmD = 75 mmD = 45 mmD = 225 mm
Projection Microscopy: Phase Retrieval
5distances
10 µm
Rel. Phase MapMass ⇒ Quantitative Fluorescence Neuron cell
Slide: 41
0.49 mm
z1 = 93 mm; voxel = 0.24 µm
260 µm
z1 = 49 mm; voxel = 125 nm
200 µm
z1 = 38 mm; voxel = 97 nm
175 µm
z1 = 33 mm; voxel = 85 nm
1 mm
z1 = 200 mm; voxel = 0.5 µm
Zoom Tomography
Keep sample preparationstraightforwardNot too destructiveSample size >> field of viewE = 17 keV1801 projections; 0.1s/proj
Slide: 42
Zoom Tomography
R Mokso, P Cloetens, E Maire, W Ludwig, JY Buffière, APL, 2007, 90, 144104
Inside φ = 1 mm sample → local tomography!E = 20.5 keVXray magnification ~ 80 (voxel size = 90 nm)
Al / Si alloytomographic slice
75 µm
SiPoreAl5FeSi
Slide: 43
Nano XRF of a Siemens star
E = 17.5 keV600 x 600 pixels30 ms / point50 nm step (zap)3 hoursDetector limited
30 µm
Slide: 44
Fresnel diffraction of a Siemens star
E = 17.5 keV500 ms exposurez1: 133 → 7 mm 'Pixel' : 250 → 13 nm
Slide: 46
Some references
• E. Hecht, Optics, 3th ed. (AddisonWesley, 1998).• M. Born and E. Wolf, Principle of Optics, 6th ed. (Pergamon Press, Oxford, New York,
1980).• J.W. Goodman, Introduction to Fourier optics, 2nd ed. (McgrawHill, 1988).• D. Paganin, Coherent Xray Optics (Oxford University Press, USA, 2006).
• P. Cloetens, R. Barrett, J. Baruchel, J.P. Guigay and M. Schlenker, J. Phys. D: Appl. Phys. 29, 133 (1996).
• K.A. Nugent, T.E. Gureyev, D.F. Cookson, D. Paganin, Z. Barnea, Phys. Rev. Lett. 77, 2961 (1996).
• P. Cloetens, M. PateyronSalomé, J.Y. Buffière, G.Peix, J. Baruchel, F. Peyrin and M. Schlenker, J.Appl. Phys. 81, 9 (1997).
• P. Cloetens, W. Ludwig, J. Baruchel, D. Van Dyck, J. Van Landuyt, J.P. Guigay, and M. Schlenker, Appl. Phys. Lett. 75, 2912 (1999).
• S. Zabler, P. Cloetens, J.P. Guigay, J. Baruchel, M. Schlenker, Rev. Sci. Instrum. 76, 073705 (2005).