An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014...
Transcript of An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014...
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MaxEnt 2014
An entropy model fordiffusion MRI
Pierre Marechal
UNIVERSITY DE TOULOUSE
Septembre 24, 2014
– p. 1/30
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Outline
• Diffusion MRI• Building a general entropy model• Partially infinite convex programming• Application to Diffusion MRI
– p. 2/30
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Outline
• Diffusion MRI• Building a general entropy model• Partially infinite convex programming• Application to Diffusion MRI
– p. 2/30
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What is dMRI ?A non-invasive imaging technique of the diffusion of
water in biological tissues, for the study of theconnectivity in the brain
– p. 3/30
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What is dMRI ?A non-invasive imaging technique of the diffusion of
water in biological tissues, for the study of theconnectivity in the brain
ProbabilityP of particle displacements in each voxelof the volume to be imaged within a given time
interval
– p. 3/30
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What is dMRI ?A non-invasive imaging technique of the diffusion of
water in biological tissues, for the study of theconnectivity in the brain
ProbabilityP of particle displacements in each voxelof the volume to be imaged within a given time
interval
dP (x) = p(x) dx
– p. 3/30
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Overview of the processStep 1 From MRI Fourier data
zj =
∫
R3
p(x)e−2iπ〈qj ,x〉 dx, j = 1, . . . ,m
reconstruct
• eitherdiffusion tensors, under the assumptionthatP is gaussian[DTI]
• or Orientation Diffusion Functions (ODF) viaprobability distributions
ψ(s) :=
∫
R
p(rs)r2 dr, s ∈ S2
– p. 4/30
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Overview of the processStep 1 From MRI Fourier data
zj =
∫
R3
p(x)e−2iπ〈qj ,x〉 dx, j = 1, . . . ,m
reconstruct
• eitherdiffusion tensors, under the assumptionthatP is gaussian[DTI]
• or Orientation Diffusion Functions (ODF) viaprobability distributions
ψ(s) :=
∫
R
p(rs)r2 dr, s ∈ S2
Step 2 Image fibers[fiber tracking]– p. 4/30
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Fiber tracking
Source: Human Connectome Project
http://www.humanconnectomeproject.org/gallery/– p. 5/30
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Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
– p. 6/30
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Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
P is assumed to be supported on a sphere
– p. 6/30
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Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
P is assumed to be supported on a sphere
Our aim is to write a flexible model:
– p. 6/30
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Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
P is assumed to be supported on a sphere
Our aim is to write a flexible model:
→ probabilityP supported inR3
– p. 6/30
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Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
P is assumed to be supported on a sphere
Our aim is to write a flexible model:
→ probabilityP supported inR3
→ possibility to account for moment constraints
– p. 6/30
![Page 15: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/15.jpg)
Purpose of this workD.C. ALEXANDER, Maximum entropy sphericaldeconvolution for diffusion MRI, InformationProcessing in Medical Imaging, 19:76-87, 2005
P is assumed to be supported on a sphere
Our aim is to write a flexible model:
→ probabilityP supported inR3
→ possibility to account for moment constraints
→ use of more general entropies
– p. 6/30
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Outline
• Diffusion MRI• Building a general entropy model• Partially infinite convex programming• Application to Diffusion MRI
– p. 7/30
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Fourier data
zj =
∫
R3
e−2iπ〈qj ,x〉 dP (x), j = 1, . . . ,m
– p. 8/30
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Fourier data
zj =
∫
R3
e−2iπ〈qj ,x〉 dP (x), j = 1, . . . ,m
yj =
∫
R3
γj(x) dP (x), j = 1, . . . , 2m
with
γj(x) =
cos(2π〈q[(j+1)/2],x〉
)if j is even,
sin(2π〈q[(j+1)/2],x〉
)if j is odd
– p. 8/30
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Fourier data
zj =
∫
R3
e−2iπ〈qj ,x〉 dP (x), j = 1, . . . ,m
yj =
∫
R3
γj(x) dP (x), j = 1, . . . , 2m
with
γj(x) =
cos(2π〈q[(j+1)/2],x〉
)if j is even,
sin(2π〈q[(j+1)/2],x〉
)if j is odd
y = EP [γ] with γ(x) :=(γ1(x), . . . , γ2m(x)
)⊤
– p. 8/30
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Fourier data
zj =
∫
R3
e−2iπ〈qj ,x〉 dP (x), j = 1, . . . ,m
yj =
∫
R3
γj(x) dP (x), j = 1, . . . , 2m
with
γj(x) =
cos(2π〈q[(j+1)/2],x〉
)if j is even,
sin(2π〈q[(j+1)/2],x〉
)if j is odd
y = EP [γ] with γ(x) :=(γ1(x), . . . , γ2m(x)
)⊤
Normalization:1 = EP [1] =
∫
R3
dP (x)
– p. 8/30
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Optional moment constraints
From a physical viewpoint, it seems reasonable toassume in addition that the random variablex is
centered or almost centered
– p. 9/30
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Optional moment constraints
From a physical viewpoint, it seems reasonable toassume in addition that the random variablex is
centered or almost centered
EP [x] =
∫
R3
x dP (x) = 0
– p. 9/30
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Entropy model∣∣∣∣∣
Minimize K (P‖ν)
s.t. (1,y) = EP [(1,γ)]
– p. 10/30
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Entropy model∣∣∣∣∣
Minimize K (P‖ν)
s.t. (1,y) = EP [(1,γ)]
K (P‖ν) :=
∫
u(x) lnu(x) dν(x) if P ≺≺ ν
∞ otherwise
– p. 10/30
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Entropy model∣∣∣∣∣
Minimize K (P‖ν)
s.t. (1,y) = EP [(1,γ)]
K (P‖ν) :=
∫
u(x) lnu(x) dν(x) if P ≺≺ ν
∞ otherwise
u :=dP
dν(Radon-Nikodym derivative)
– p. 10/30
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Rewriting Fourier data
(1,y) = EP [(1,γ)]
– p. 11/30
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Rewriting Fourier data
(1,y) = EP [(1,γ)] = A◦u
– p. 11/30
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Rewriting Fourier data
(1,y) = EP [(1,γ)] = A◦u
Notation:
Au = EP [γ] =
∫
R3
γ(x)u(x) dν(x)
Iu = EP [1] =
∫
R3
u(x) dν(x)
Mu = EP [x] =
∫
R3
xu(x) dν(x)
– p. 11/30
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Rewriting Fourier data
(1,y) = EP [(1,γ)] = A◦u
Notation:
Au = EP [γ] =
∫
R3
γ(x)u(x) dν(x)
Iu = EP [1] =
∫
R3
u(x) dν(x)
Mu = EP [x] =
∫
R3
xu(x) dν(x)
A◦u = (Iu,Au)
– p. 11/30
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An equivalent formulation
(P)
∣∣∣∣∣∣∣∣
Minimize Hν(u) :=
∫
h(u(x)
)dν(x)
s.t. u ∈ L1ν(R
3)
1 = Iu, y = Au
– p. 12/30
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An equivalent formulation
(P)
∣∣∣∣∣∣∣∣
Minimize Hν(u) :=
∫
h(u(x)
)dν(x)
s.t. u ∈ L1ν(R
3)
1 = Iu, y = Au
h(t) :=
t ln t si t > 0
0 si t = 0
∞ si t < 0
– p. 12/30
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An equivalent formulation
(P)
∣∣∣∣∣∣∣∣
Minimize Hν(u) :=
∫
h(u(x)
)dν(x)
s.t. u ∈ L1ν(R
3)
1 = Iu, y = Au
h(t) :=
t ln t si t > 0
0 si t = 0
∞ si t < 0
Minimizing Hν(u) corresponds to the desire tointroduceas little prior information as possible. The
reference measure may be chosen as anisotropicgaussian measure, the one we would have in an
isotropic medium with no fiber– p. 12/30
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Relaxation
(P )
∣∣∣∣∣∣∣∣∣
Minimize Hν(u)
s.t. u ∈ L1ν(R
3)
1 = Iu, y = Au
– p. 13/30
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Relaxation
(Pα)
∣∣∣∣∣∣∣∣∣
Minimize Hν(u)+1
2α‖y −Au‖2
s.t. u ∈ L1ν(R
3)
1 = Iu
– p. 13/30
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Relaxation
(Pα)
∣∣∣∣∣∣∣∣∣
Minimize Hν(u)+1
2α‖y −Au‖2
s.t. u ∈ L1ν(R
3)
1 = Iu
(Pα)
∣∣∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(R
3)
1 = Iu
– p. 13/30
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Relaxation
(Pα)
∣∣∣∣∣∣∣∣∣
Minimize Hν(u)+1
2α‖y −Au‖2
s.t. u ∈ L1ν(R
3)
1 = Iu
(Pα)
∣∣∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(R
3)
1 = Iu
g(η) := −1
2α‖y − η‖2
– p. 13/30
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Relaxation
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(R
3), 1 = Iu
– p. 14/30
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Relaxation
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g(Au)+δ(Iu|{1})
s.t. u ∈ L1ν(R
3)
– p. 14/30
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Relaxation
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g(Au)+δ(Iu|{1})
s.t. u ∈ L1ν(R
3)
δ(x|S) =
{0 if x ∈ S
∞ otherwise
– p. 14/30
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Relaxation
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g(Au)+δ(Iu|{1})
s.t. u ∈ L1ν(R
3)
δ(x|S) =
{0 if x ∈ S
∞ otherwise
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
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Relaxation
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g(Au)+δ(Iu|{1})
s.t. u ∈ L1ν(R
3)
δ(x|S) =
{0 if x ∈ S
∞ otherwise
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
g◦(η◦,η) = g(η) − δ(η◦|{1})
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Outline
• Diffusion MRI• Building a general entropy model• Partially infinite convex programming• Application to Diffusion MRI
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Duality (main issues)
(1) Write the dual problem of(Pα)
(2) Study the constraint qualification conditions
(3) Establish theprimal-dualrelationship
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Fenchel dualityTheorem A
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex• H⋆ : L⋆ → (−∞,∞] its convex conjugate
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex• H⋆ : L⋆ → (−∞,∞] its convex conjugate• g : Rd → [−∞,∞) proper concave
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex• H⋆ : L⋆ → (−∞,∞] its convex conjugate• g : Rd → [−∞,∞) proper concave• g⋆ : Rd → [−∞,∞) its concave conjugate
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex• H⋆ : L⋆ → (−∞,∞] its convex conjugate• g : Rd → [−∞,∞) proper concave• g⋆ : Rd → [−∞,∞) its concave conjugate
Assumeri(A domH) ∩ ri(dom g) 6= ∅. Then
η := infp∈L
{H(p)− g(Ap)
}= max
λ∈Rd
{g⋆(λ)−H⋆(A⋆λ)
}
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Fenchel dualityTheorem A• L,L⋆ vector spaces, paired by〈·, ·〉• A : L→ R
d linear• A⋆ : Rd → L⋆ its (formal) adjoint• H : L→ (−∞,∞] proper convex• H⋆ : L⋆ → (−∞,∞] its convex conjugate• g : Rd → [−∞,∞) proper concave• g⋆ : Rd → [−∞,∞) its concave conjugate
Assumeri(A domH) ∩ ri(dom g) 6= ∅. Then
η := infp∈L
{H(p)−g(Ap)
}= max
λ∈Rd
{g⋆(λ) −H⋆(A⋆λ)︸ ︷︷ ︸
D(λ)
}
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Primal dual relationshipTheorem B
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Primal dual relationshipTheorem B With the notation and assumptions ofthe previous theorem, assume that
(⋆) ri dom g⋆ ∩ ri dom(H⋆ ◦ A⋆) 6= ∅
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Primal dual relationshipTheorem B With the notation and assumptions ofthe previous theorem, assume that
(⋆) ri dom g⋆ ∩ ri dom(H⋆ ◦ A⋆) 6= ∅
and that
(a) H⋆⋆ = H andg⋆⋆ = g
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Primal dual relationshipTheorem B With the notation and assumptions ofthe previous theorem, assume that
(⋆) ri dom g⋆ ∩ ri dom(H⋆ ◦ A⋆) 6= ∅
and that
(a) H⋆⋆ = H andg⋆⋆ = g
(b) there existλ, a dual solution, andu in ∂H⋆(A⋆λ)such thatH⋆ ◦ A⋆ hasAu as gradient atλ
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Primal dual relationshipTheorem B With the notation and assumptions ofthe previous theorem, assume that
(⋆) ri dom g⋆ ∩ ri dom(H⋆ ◦ A⋆) 6= ∅
and that
(a) H⋆⋆ = H andg⋆⋆ = g
(b) there existλ, a dual solution, andu in ∂H⋆(A⋆λ)such thatH⋆ ◦ A⋆ hasAu as gradient atλ
Thenu is a primal solution
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Back to our entropy problem
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
g◦(η◦,η) = g(η) − δ(η◦|{1})
– p. 19/30
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Back to our entropy problem
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
g◦(η◦,η) = g(η) − δ(η◦|{1})
The previous framework may be a powerful toolprovided it is possible to compute the conjugate
functionsH⋆ν and(g◦)⋆
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Back to our entropy problem
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
g◦(η◦,η) = g(η) − δ(η◦|{1})
The previous framework may be a powerful toolprovided it is possible to compute the conjugate
functionsH⋆ν and(g◦)⋆
(g◦)⋆(λ◦,λ) = λ◦ + g⋆(λ) = λ◦ + 〈λ,y〉 −α
2‖λ‖2
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Back to our entropy problem
(Pα)
∣∣∣∣∣
Minimize Hν(u) − g◦(A◦u)
s.t. u ∈ L1ν(R
3)
g◦(η◦,η) = g(η) − δ(η◦|{1})
The previous framework may be a powerful toolprovided it is possible to compute the conjugate
functionsH⋆ν and(g◦)⋆
(g◦)⋆(λ◦,λ) = λ◦ + g⋆(λ) = λ◦ + 〈λ,y〉 −α
2‖λ‖2
The computation ofH⋆ν is more tricky: it involves
conjugacy through the integral sign
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Conjugacy through the integralPaired spaces
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space• ν positive andσ-finite
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space• ν positive andσ-finite• L,Λ are 2 spaces of measurable functions
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space• ν positive andσ-finite• L,Λ are 2 spaces of measurable functions• Assume:∀f ∈ L, ∀ϕ ∈ Λ, fϕ ∈ L1(X)
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space• ν positive andσ-finite• L,Λ are 2 spaces of measurable functions• Assume:∀f ∈ L, ∀ϕ ∈ Λ, fϕ ∈ L1(X)
(f, ϕ) 7→ 〈f, ϕ〉 :=
∫
X
f(x)ϕ(x) dν(x)
– p. 20/30
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Conjugacy through the integralPaired spaces
• (X,A , ν) complete measure space• ν positive andσ-finite• L,Λ are 2 spaces of measurable functions• Assume:∀f ∈ L, ∀ϕ ∈ Λ, fϕ ∈ L1(X)
(f, ϕ) 7→ 〈f, ϕ〉 :=
∫
X
f(x)ϕ(x) dν(x)
Example The case whereL = L1ν andΛ = L∞
ν is aclassical example for which the above pairing iswell-defined
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Conjugacy through the integral
Definition A spaceL of A -measurable functions issaid to bedecomposableif it contains all functions ofthe form
1Af0 + 1ACf
whereA ∈ A is such thatν(A) <∞, f0 is ameasurable function such thatf0(A) is bounded andfis any function inL
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Conjugacy through the integral
Definition A spaceL of A -measurable functions issaid to bedecomposableif it contains all functions ofthe form
1Af0 + 1ACf
whereA ∈ A is such thatν(A) <∞, f0 is ameasurable function such thatf0(A) is bounded andfis any function inL
Example TheLp-spaces are decomposable (foreveryp ∈ [1,∞])
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Conjugacy through the integralTheorem 1 [Rockafellar]
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Conjugacy through the integralTheorem 1 [Rockafellar]
• (X,A , ν) a complete measure space
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Conjugacy through the integralTheorem 1 [Rockafellar]
• (X,A , ν) a complete measure space• ν positive andσ-finite
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Conjugacy through the integralTheorem 1 [Rockafellar]
• (X,A , ν) a complete measure space• ν positive andσ-finite• h : R×X → (−∞,∞] measurable, withh(·, x)
l.s.c. for everyx
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Conjugacy through the integralTheorem 1 [Rockafellar]
• (X,A , ν) a complete measure space• ν positive andσ-finite• h : R×X → (−∞,∞] measurable, withh(·, x)
l.s.c. for everyx
Then, the conjugate integrandh⋆, defined byh⋆(·, x) = [h(·, x)]⋆, is a measurable integrand
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Conjugacy through the integralTheorem 1 [Rockafellar]
• (X,A , ν) a complete measure space• ν positive andσ-finite• h : R×X → (−∞,∞] measurable, withh(·, x)
l.s.c. for everyx
Then, the conjugate integrandh⋆, defined byh⋆(·, x) = [h(·, x)]⋆, is a measurable integrand
Corollary For every measurable functionϕ, thefunctionx 7→ h⋆(ϕ(x), x) is measurable and theintegral ∫
h⋆(ϕ(x), x) dν(x)
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Conjugacy through the integral
Theorem 2 [Rockafellar]
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Conjugacy through the integral
Theorem 2 [Rockafellar]LetL,Λ be spaces of measurable functions, paired by
(f, ϕ) 7→ 〈f, ϕ〉 :=
∫
X
f(x)ϕ(x) dν(x)
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Conjugacy through the integral
Theorem 2 [Rockafellar]LetL,Λ be spaces of measurable functions, paired by
(f, ϕ) 7→ 〈f, ϕ〉 :=
∫
X
f(x)ϕ(x) dν(x)
With the notation and assumptions of the previoustheorem, assume thatL is decomposable, and that{f ∈ L|H(f) ∈ R} 6= ∅. ThenH⋆ is given onΛ by
H⋆(ϕ) =
∫
h⋆(ϕ(x), x) dν(x)
– p. 23/30
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Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
– p. 24/30
![Page 82: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/82.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem
– p. 24/30
![Page 83: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/83.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅
– p. 24/30
![Page 84: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/84.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅• g⋆⋆ = g
– p. 24/30
![Page 85: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/85.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅• g⋆⋆ = g
• h(·, x) convex l.s.c.
– p. 24/30
![Page 86: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/86.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅• g⋆⋆ = g
• h(·, x) convex l.s.c.• h⋆(·, x) ∈ C 1(R) for almost allx
– p. 24/30
![Page 87: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/87.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅• g⋆⋆ = g
• h(·, x) convex l.s.c.• h⋆(·, x) ∈ C 1(R) for almost allx• ∃λ ∈ int domD, dual optimal, such that
u(x) := (h⋆)′(A⋆λ(x), x
)∈ L1
ν(X)
– p. 24/30
![Page 88: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/88.jpg)
Primal solution∣∣∣∣∣∣
Minimize Hν(u) − g(Au)
s.t. u ∈ L1ν(X)
withHν(u) =
∫
h(u(x), x
)dν(x)
Theorem Assume:
• riA domHν ∩ ri dom g 6= ∅• g⋆⋆ = g
• h(·, x) convex l.s.c.• h⋆(·, x) ∈ C 1(R) for almost allx• ∃λ ∈ int domD, dual optimal, such that
u(x) := (h⋆)′(A⋆λ(x), x
)∈ L1
ν(X)
Thenu is a primal solution– p. 24/30
![Page 89: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/89.jpg)
Back to our entropy problem
Hν(u) =
∫
h(u(x)
)dν(x)
with
h(t) :=
t ln t si t > 0
0 si t = 0
∞ si t < 0
– p. 25/30
![Page 90: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/90.jpg)
Back to our entropy problem
Hν(u) =
∫
h(u(x)
)dν(x)
with
h(t) :=
t ln t si t > 0
0 si t = 0
∞ si t < 0
h⋆(τ) = exp(τ − 1)
– p. 25/30
![Page 91: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/91.jpg)
Back to our entropy problem
Hν(u) =
∫
h(u(x)
)dν(x)
with
h(t) :=
t ln t si t > 0
0 si t = 0
∞ si t < 0
h⋆(τ) = exp(τ − 1)
SinceL1ν(R
3) is decomposable,
H⋆ν (ϕ) =
∫
R3
exp(ϕ(x) − 1) dν(x), ϕ ∈ L∞ν (R3)
– p. 25/30
![Page 92: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/92.jpg)
The dual problem
(Dα)
∣∣∣∣∣
Maximize D(λ◦,λ)
s.t. (λ◦,λ) ∈ R1+2m
– p. 26/30
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The dual problem
(Dα)
∣∣∣∣∣
Maximize D(λ◦,λ)
s.t. (λ◦,λ) ∈ R1+2m
D(λ◦,λ) = (g◦)⋆(λ◦,λ) − (H⋆ν ◦A
⋆◦)(λ◦,λ)
– p. 26/30
![Page 94: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/94.jpg)
The dual problem
(Dα)
∣∣∣∣∣
Maximize D(λ◦,λ)
s.t. (λ◦,λ) ∈ R1+2m
D(λ◦,λ) = (g◦)⋆(λ◦,λ) − (H⋆ν ◦A
⋆◦)(λ◦,λ)
= λ◦ + 〈λ,y〉 −α
2‖λ‖2
−
∫
exp(A
⋆◦(λ◦,λ)(x)
︸ ︷︷ ︸
λ◦+〈λ,γ(x)〉
− 1)dν(x)
– p. 26/30
![Page 95: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/95.jpg)
The dual problem
(Dα)
∣∣∣∣∣
Maximize D(λ◦,λ)
s.t. (λ◦,λ) ∈ R1+2m
D(λ◦,λ) = (g◦)⋆(λ◦,λ) − (H⋆ν ◦A
⋆◦)(λ◦,λ)
= λ◦ + 〈λ,y〉 −α
2‖λ‖2
−
∫
exp(A
⋆◦(λ◦,λ)(x)
︸ ︷︷ ︸
λ◦+〈λ,γ(x)〉
− 1)dν(x)
= λ◦ + 〈λ,y〉 −α
2‖λ‖2
−exp(λ◦ − 1)
∫
exp〈λ,γ(x)〉 dν(x)
– p. 26/30
![Page 96: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/96.jpg)
Optimality system
• D is concave, with effective domainR1+2m
– p. 27/30
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Optimality system
• D is concave, with effective domainR1+2m
• D ∈ C 1R
1+2m
– p. 27/30
![Page 98: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/98.jpg)
Optimality system
• D is concave, with effective domainR1+2m
• D ∈ C 1R
1+2m
Dual optimality reads
0 = 1 − exp(λ◦ − 1)
∫
R3
exp〈λ,γ(x)〉 dν(x)
0 = y − αλ − exp(λ◦ − 1)
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)
– p. 27/30
![Page 99: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/99.jpg)
Optimality system
• D is concave, with effective domainR1+2m
• D ∈ C 1R
1+2m
Dual optimality reads
0 = 1 − exp(λ◦ − 1)
∫
R3
exp〈λ,γ(x)〉 dν(x)
0 = y − αλ − exp(λ◦ − 1)
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)
– p. 27/30
![Page 100: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/100.jpg)
Optimality system
• D is concave, with effective domainR1+2m
• D ∈ C 1R
1+2m
Dual optimality reads
0 = 1 − exp(λ◦ − 1)
∫
R3
exp〈λ,γ(x)〉 dν(x)
0 = y − αλ − exp(λ◦ − 1)
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)
which reduces to
0 = y − αλ −
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)∫
R3
exp〈λ,γ(x)〉 dν(x)
– p. 27/30
![Page 101: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/101.jpg)
Optimality systemObserve that
0 = y − αλ −
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)∫
R3
exp〈λ,γ(x)〉 dν(x)
– p. 28/30
![Page 102: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/102.jpg)
Optimality systemObserve that
0 = y − αλ −
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)∫
R3
exp〈λ,γ(x)〉 dν(x)
is also the optimality system of
(Dα)
∣∣∣∣∣∣
Maximize 〈λ,y〉 −α
2‖λ‖2 − ln
∫
exp〈λ,γ(x)〉 dν(x)
s.t. λ ∈ R2m
– p. 28/30
![Page 103: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/103.jpg)
Optimality systemObserve that
0 = y − αλ −
∫
R3
γ(x) exp〈λ,γ(x)〉 dν(x)∫
R3
exp〈λ,γ(x)〉 dν(x)
is also the optimality system of
(Dα)
∣∣∣∣∣∣
Maximize 〈λ,y〉 −α
2‖λ‖2 − ln
∫
exp〈λ,γ(x)〉 dν(x)
s.t. λ ∈ R2m
Proposition The function
D(λ) := 〈λ,y〉 − α2‖λ‖2 − ln
∫exp〈λ,γ(x)〉 dν(x) is concave
and smooth (onR2m)
– p. 28/30
![Page 104: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/104.jpg)
Algorithm• MaximzeD(λ) → λ
– p. 29/30
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Algorithm• MaximzeD(λ) → λ
• Compute
exp(λ◦ − 1) =
(∫
exp〈λ,γ(x)〉 dν(x)
)−1
– p. 29/30
![Page 106: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/106.jpg)
Algorithm• MaximzeD(λ) → λ
• Compute
exp(λ◦ − 1) =
(∫
exp〈λ,γ(x)〉 dν(x)
)−1
• Compute ODF from
u(x) = exp(λ◦ − 1) exp〈λ,γ(x)〉
– p. 29/30
![Page 107: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/107.jpg)
Algorithm• MaximzeD(λ) → λ
• Compute
exp(λ◦ − 1) =
(∫
exp〈λ,γ(x)〉 dν(x)
)−1
• Compute ODF from
u(x) = exp(λ◦ − 1) exp〈λ,γ(x)〉
The optimalu is searched for in a smooth manifold ofdimension2m in L1
ν(R3)
– p. 29/30
![Page 108: An entropy model for diffusion MRI - Freedjafari.free.fr/MaxEnt2014/slides/23_slides.pdfMaxEnt 2014 An entropy model for diffusion MRI Pierre Marechal´ UNIVERSITY DE TOULOUSE Septembre](https://reader033.fdocuments.in/reader033/viewer/2022060309/5f0a59697e708231d42b35a6/html5/thumbnails/108.jpg)
Thank you for your attention !
– p. 30/30