Date post: | 22-Dec-2015 |
Category: |
Documents |
Upload: | brianna-scott |
View: | 224 times |
Download: | 0 times |
1iMinds-Vision Lab, University of Antwerp, Antwerp, Belgium.2Delft Center for Systems and Control, Delft University of Technology, Delft, The Netherlands.
Gabriel Ramos-Llordén1, Hilde Segers1, Willem J. Palenstijn1,Arnold J. den Dekker1,2 and Jan Sijbers1
Partial discreteness: a new type of prior knowledge for MRI reconstruction
…
12
3Bayes' theorem
1 2 3
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Some regions are approximately constant in intensity
Partial discrete images: piece-wise constant part + texture part
Partial discreteness as a prior for ill-posed reconstruction problems
IntroductionBreast implant Dental MRI FLAIR sequences Angiography
1/12
1 2 3 4
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Partial discreteness model
𝜌1
𝜌2
𝟏𝒜1
𝟏𝒜2
𝒙𝒜
Σ+¿+¿+¿
𝑒𝑖𝚽
𝒜=¿𝑘∈ {1,2 }𝒜𝑘𝑐𝑎𝑟𝑑 (𝒜𝑘 )≫0
Variant intensity class
Phase
2/12
5
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Partial discreteness model
𝜌1
𝜌2
𝟏𝒜1
𝟏𝒜2
𝒙𝒜
Σ+¿+¿+¿
𝑒𝑖𝚽
Variant intensity class
Phase
3/12
𝒜=¿𝑘∈ {1,2 }𝒜𝑘𝑐𝑎𝑟𝑑 (𝒜𝑘 )≫0
6
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Penalized iterative reconstruction
4/12
Discreteness error
iteratively estimated partial discrete imagespatially-variant weight diagonal matrix
k-space data
Fourier matrix
image Regularization parameter
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Bayesian segmentation operator
…
¿ 𝒙(𝑡 )∨¿
K-Gaussian mixture model fitting [Caballero J., MICCAI 2014]
13
2
A posteriori probability maps
Bayes' theorem
Past characterization
1 23
5/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Bayesian segmentation operator
…
¿ 𝒙(𝑡 )∨¿
13
2 Temporal regularization
Past characterization
𝒙𝑝𝑟𝑜𝑏=�̂�1𝑝1(𝑡 )+ �̂�2𝑝2
(𝑡 )+𝑝3(𝑡 )∘∨𝒙 (𝑡 )∨¿
𝑝1(𝑡 ) 𝑝3
(𝑡 ) 𝑝2(𝑡 )
�̂�1
�̂�2
5/12
1 23
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Bayesian segmentation operator
𝒙𝑝𝑟𝑜𝑏
Otsu thresholding
𝒜1
𝒜2 𝒜
𝒙𝒜 =𝟏𝒜 ∘ 𝒙𝑝𝑟𝑜𝑏
Estimated partially discrete image
6/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Weights determine where the discreteness error is considered
Bayesian segmentation operator‖𝑾 (𝑡 ) (𝒙−𝒗 (𝑡 ) )‖❑Discreteness error: with
𝑝1(𝑡 ) 𝑝2
(𝑡 ) 𝑝3(𝑡 )
7/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
• Simulations with breast implant and angiography data
• Single coil radial k-space sampling with varying number of spokes,
• Smoothly varying phase added
• Comparison against Conjugate Gradient (CG) with smoothness prior and Total Variation (TV) [Gai.J. et al. (Impatient Toolbox), ISMRM 2012]
Experiments
𝑁 𝑠𝑝𝑜𝑘𝑒𝑠
𝑘𝑥
𝑘𝑦
8/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Results
(a) CG + smoothness (b) CG + TV (c) Proposed
SNR=100
Recovered images and implant contour detection
Breast implant experiment
SNR=100,
9/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Results Breast implant experiment: segmentation metrics
10/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Results Angiography experiment
(a)Original (b)CG + smoothness (c)CG+TV (d)Proposed
SNR=100,
11/12
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Conclusions
12/12
Partial discreteness prior More detailed reconstructed images
Segmentation benefits from partial discreteness
Thanks for your attention!
Contact: http://visielab.uantwerpen.be/people/gabriel-ramos-llorden
Partial discreteness: a new type of prior knowledge for MRI reconstruction3417
Image references1. Radiopedia.org2. http://www.drbicuspid.com/3. www.reviewofoptometry.com4. https://www.healthcare.siemens.com/5. https://www.healthcare.siemens.com/magnetic-resonance-imaging/
options-and-upgrades/clinical-applications/advanced-angio6. M Maijers, PhD Thesis